Tag Archives: HPA

You must run a filter between your compressor and your airgun

If you are into precharged pneumatic (PCP) airguns and have bought a compressor – you need to also make sure you have a good inline filter. The reason is pretty simple, any compressor sucks in everything that is in the air including dust and moisture. You may not have stopped and though about it, but there are also impurities the are bonded to the water as well – sulfurs, acids, minerals, etc. You really need to filter the air before you pump it into your airgun or air cylinder.

If you are wondering why this is critical it is because your airguns use precise maching and a ton of O-rings. You don’t want contaminants to be introduced that cause premature wear or corrision of the aluminum surfaces. The cleaner your air supply is, all things being equal, the more reliable your airgun will be and the less maintenance required. Please note I am not saying this will make your o-rings and what not last forever – all airguns will require maintenance at some point and the most common need is to go though and replace the seals. Clean air will help them last longer than dirty air is all I am saying.

“But isn’t the oil & water separator in my air compressor enough?” is often asked and the answer is a resounding “No, it is not”. High pressure air is hot and as it expands and cools, condensation forms and this continues after the separator. Yes, the separator is better than nothing but it is not sufficient. What you need is a long filter made up of multiple elements.

Buying a Filter

First off, and I can’t stress this enough, you need a filter with a working pressure equal to or greater than your compressor. A high-pressure air (HPA) compressor has working pressures between 4-5,000 PSI these days so your filter must as well and they are specialized – these are not shop air compressors working at 150-250 PSI. One of those would explode.

Second, you need a long filter. When you go to Amazon or other sites you will notice there are short stubby filters that are 1.5-2.0″ long. I sometimes use them from the tank to the gun but I would not recommend them as the filter immediately after the compressor. They are better than nothing but they are too short and usually just have mesh or foam filter elements inside – no dessicant or carbon.

The ones I would recommend are 11.8″ (300mm) long and outside diameter of 1.9″ (50mm) at least. These filters tend to use replaceable cartridges that contain a mesh for particulants, a dessicant for drying the air and a carbon section for neutralizing chemicals that remain.

Air enters at the dessicant end (the white section) and moves towards the black carbon and out the end. There are mesh wafers at the ends and between the dessicant and carbon to trap particulants. The end caps of the filter unscrew and this cartridge can be pushed out and replaced with a new one as it becomes more and more discolored. If airflow stops or you notice fill times taking longer and longer, a plugged filter cartridge is your most likely culprit.
This is my GX CS4 compressor and I am using the factory airline and its 8mm quick connect female fitting to connect to the filter’s male plug. The filter I am currently using and really like is sold on Amazon by “FASTTOBUY”. It’s very well made and you can buy additional filter cartridges. The brass colored nut you see on the surface of the left side’s end cap is the burst disc. A burst disc is designed to break first and let air leak vs. allowing the filter to exceed its safe operating pressure. From the filter, there is a Manloney brand air hose with an 8mm plug on one end and an extended length female fitting on the other.

If you read the captions, I really like my 300mmx50mm FASTTOBUY filter. It’s long enough for a fair amount of drying and cleaning to happen but also ins’t completely unwieldy either as I need to move my compressor around. I have toyed with running two filters in series as a first stage and a second stage and may try that some day but for now, I just run the one.


I can supply clean dry air to my PCP airguns at home with this set up. The FASTOBUY unit works and the fittings they used have worked with what I have so far. They also provide some spare parts including another filter cartridge.

Do you have to go with the one I am recommending? No, of course not. Just look for a long one that gets good reviews and you can get spare filter cartridges for.

What I am telliing you very directly is NOT to fill your airguns right off the air hose direct from the compressor. You need a filter to get rid of water and other contaminants before you fill your airgun or air cylinder.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

The CS4 Grease Pot – How to add grease to your compressor and refill the pot

The GX CS4 is a very cool compressor and one of the two ways it gets the long run time is through staying properly greased. (The other is through the use of fluid coolant that I covered in a blog post about setting up and testing the unit). After 4-6 hours of compressing air with your GX CS4, you are supposed to given the top grease pot knob one full turn. How does that work and how does one refill it?

Adding Grease Every 4-6 Hours

It’s simple, turn the top knob one full turn to introduce grease. You may be wondering why I even bothered adding a blog post. The reason is that when I turned the knob there was so much resistance that I thought the pot was empty – it wasn’t. What I want you to see is why there is resistance:

To add grease, you turn the top knob with the arrows one full turn clockwise. The problem was that mine stopped right around 3/4ths of the way around. I thought maybe it had been shipped without the grease pot being filled.
To remove the grease pot simply turn the lower portion of the pot counter-clockwise and it will unscrew. It then lifts out.
Well, it was definitely full. I can honestly say I have never seen a grease with this color and texture. Note the black thing down in the very bottom of the pot.
It’s a simple mechanism. You turn the pot counter-clockwise to cause the plunger to move to the top so you can fill it. Or, you turn it clockwise, the plunger comes down and it pushes grease in … or at least it should.
There was a black disc down in the pot / the chamber the pot threads into depending on how you want to describe it.
I fished the black disc out using a finger, wiped it off and there was a very small hole in the middle. The black disc is a flow limiter! Now I understand why there was resistance! What this tells us is that you can only turn the screw so much and the limiter will cause resistance. So, turn the top screw until it stops and run the compressor. You can turn the screw on the pot the rest of the way as the grease goes into the mechanism but do not introduce more than one full turn worth of grease.

Refilling the Pot

Well, I had really made a mess playing around with the grease pot and lost most of the grease in the process. I asked the Amazon seller, Ankul, what I should use and he told me to go with a general food grade grease. I asked if silicone would work because that seemed to be the composition of most, if not all, food grade greases on Amazon and he said “yes”. Based on that, I ordered a tube of the below Haynes Silicone Grease off Amazon due to it’s good reviews. The important part for you to bear in mind is to go with food grade and I assume this is to protect the seals or something.

This Haynes grease has very good reviews on Amazon so I went with it.
I turned the knob counter clockwise and screwed the plunger all the way to the top of the pot and then topped off the pot with the silicone grease and screwed the pot back into the compressor.
Once it was installed, I gave the top knob a turn, ran the pump for a minute and then turned it the rest of the way.


In hindsight, it is very straight forward but I didn’t expect the flow limiter to stop the knob from turning and I didn’t know what grease to use to refill the pot so it seemed like good info to share.

I hope this helps you out.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

A Peek Inside the GX CS4 Compressor

Okay, I used my GX CS4 compressor to top of my 6.8L tank the other day and ran it for about 30 minutes or so to top off the tank at 300 bar. As you may have guessed, I’m a tinkerer and am always curious how things work. So, I looked at the CS4, it looked at me and I removed the case.

It’s really easy to do – I removed the little sheet black metal screws that run around the edges of the red sheet metal cover, removed the coolant tank cover, unfurled the power cord wrapped on the spool and the cover just comes straight off.

Here are some photos:

The first thing that struck me was how cleanly it is laid out. The blue lines are the coolant lines – they are that color because the GL48 70/30 mix I am using is blue. It sure makes them stand out – you can see the water intake at the bottom of the fluid reservoir in the middle. The silver hard line is the high pressure air running from the top of the compressor over to the aluminum manifold block that has the pressure gauge assembly and the male foster fitting. Note how all of the machining is well done. Care was taken with the design, machining and assembly of this unit to look like this.
Another angle looking towards the rear of the unit. You can clearly see the cooling lines – if someone needed to trouble shoot a fluid leak, it would be very easy to do.
This is a view from the other side. The grease by the grease pot is my fault. I had removed the pot to look at it and made a bit of a mess. It wiped right off.
Looking towards the front of the unit – those are the switches for the pump to the top left and the mast switch in the middle. You also get a pretty good look at the electric motor.


The design is well executed – everything is neatly assembled and the pump continues to work great. There are probably over 5-6 run time hours on it so far.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Setting Up & Testing the GX CS4 PCP 400 Bar/5,800 PSI Air Compressor

In the last post I discussed purchasing a new GX CS4 compressor and showed you some photos of it out of the box. In this post, I want to give you some recommendations on setting the unit up and testing it. There are definitely details around the CS4 that you need to know and it is critical you don’t just take it out of the box and try to start using it.

Read the Instruction Pamphlet

There should be a small pamphlet in with the CS 4. Take a minute and read the instructions for use. Afterwards read the following.

Distilled Water or Antifreeze for Cooling?

So the pump gets its really long duty cycle in no small part due to the liquid cooling system. Liquid is a far, far more efficient conductor of heat than air is. You see, water is much more dense than air and depending on the article you read it is 9 to 13 times more efficient at carrying away heat – maybe even more.

In the automotive world, to lower the freezing point and raise the boiling point, various chemicals have been discovered and are often referred to generically as “antifreeze”. You look deeper though and there are tons of variations for different manufacturers and different specifications.

GX said to use either distilled water or a PH-neutral antifreeze. Well, I wasn’t sure how hot the pump would get so I was worried about using distilled water. The benefits of distilled water is that it is cheap and it is PH neutral being neither acidic nor alkaline so it’s not going to cause excessive corrosion. On the other hand, it can freeze or boil like any other water plus there aren’t any corrosion inhibitors or pump lubricating agents.

I was very keen to use an antifreeze for longer like plus I was worried about boiling. I didn’t plan to keep the pump outside so freezing wasn’t a worry. The problem began when I tried to find “PH-neutral” antifreeze. I could not find any antifreeze with a true PH of 7. I turns out that you will be hard pressed to find it – I found cutting fluids (coolants for doing metal cutting) with a PH of 7, brake like antifreeze that had a PH of 7 — it was almost pure methanol, but not a thermal transfer fluid that I could buy in small quantities (like 1-2 gallons).

The more digging I did the more I realized that I could use an automotive antifreeze but needed to find one with a relatively low PH (7-9) and also that contained corrosion inhibitors and was aluminum and plastics & hose friendly. To make a long story short, this led me to Valvoline’s Zerex G48 coolant and I opted for a 70/30 mix of coolant to distilled water. My local Napa autoparts store was able to order in a gallon jug with same day in store delivery. It’s a fortune to mail order but only $14-17/gallon at a store.

Do not add it to the unit yet! You will need to test and flush the cooling system first

I thought I had it all figured out. I had premixed a 500ml 70/30 solution. That means 350ml was G48 and 150 was distilled water. I’ll explain why this didn’t work out the way I had hoped further down.

Powering It Up

Before you get to far, plug the AC-to-DC adapter in the wall. You should hear the cooling fan turn on — it definitely needs it so if you don’t hear the can make sure there is AC power through the power cord to the adapter. There isn’t an on-off switch – the unit should turn on as soon as you plug it in.

Put a multimeter on the power supply terminals and you should see around 13 volts. My CS3 power supply is 13.16 volts and the CS4’s power supply which is the same model just newer measures 13.06 volts.

Make sure the CS4’s switches are off before you connect the compressor to the power supply.

Flushing the Liquid Cooling System

The nut with viewing glass that covers the water tank should just be on hand tight. If you must, use a wrench to remove it but just put it on hand tight when you re-install it going forward. The system is not pressurized – you can take the cap off while it is operating.

For some reason my CS4 shipped with a little bit of water in it – maybe from testing at the factory and there was also some kind of brownish sediment on the bottom of the “water tank”.

This is what I saw when I removed the cover to the water tank. It should be shiny silver so you can see there is some kind of brownish sediment.

The liquid had no smell and felt like water – I have to guess it was water so I just dumped it out. I then refilled the tank with clean distilled water and swirled it around. I did this four times until the water stayed nice and clean.

For testing and flushing the system, just use distilled water. It’s cheap and doesn’t make a huge mess if there is a problem or something spills. Been there, done that – use water – trust me. By the way, purified water may not be distilled – the purified water might just be filtered. Distilled water uses a process that not only purifies the water but has the minerals removed as well. You don’t want minerals to leave a scaly buildup so use distilled.

The fluid return is near the top and you fill the water or antifreeze to the bottom of it.

I then turned the unit on and watched the water – nothing happened. There is a water pump – the intake is in the center bottom of the tank and the return is on the side about 3/4ths of the way up – there was no water moving. Oh man … I started to get really worried that maybe the water had frozen and snapped the pump but everything was dry when I took it out of the box … but …. stuff happens.

The water intake is at the bottom. Now this is where I got nervous – notice there is no water movement. I knew from the diagram that there was a pump. I could hear the unit’s fan running but there was no way to hear or feel if the pump was. I started to wonder if the pump didn’t have power, had cracked or something else.

I started to take the case’s screws off to look inside. At one point, I leaned the unit part way over to get to a bottom screw and heard the familiar “glug glug glug” sound of water running into a void that previously had air in it. That was a very, very welcome sound because it dawned on me that the little water pump had lost its prime.

I looked at the water tank and the water level had definitely gone down. I turned on the pump’s main switch and the pump started moving the water! Lesson learned there – prime the pump.

This is what it looks like when the pump is working. The sediment blew out of the lines too so then I realized I needed to flush the system again. I did this a number of times until the water was clear.

The next thing was that brown sediment was entering the tank as the lines blew out in the unit. I then dumped out the water and flushed the lines three more times until everything looked clear. Each time I would wiggle the compressor around leaning it slightly from side to side and front to back until the pump would prime. You fill the water tank to the bottom of the return line. This gives room for the coolant to expand and it also gives you a visual cue if the pump is working.

Now this told me something – there would be more water in the unit than just what was visible in the tank. In the instruction pamphlet they say you need to add 500ml of liquid to the unit. The unit came with some amount of water in it and each time when I drained the unit, I was only adding back in about 130 ml of water each time – I was using a 1000ml graduated cylinder for all of this. So, 500-130=370ml of trapped water in the system. Hmmm…. this was throwing my planned antifreeze ratios all off. 500ml of fluid at a 70/30 ratio would mean 350ml of antifreeze and 150ml of distilled water. I was going to be off and you need enough water in an antifreeze for the chemicals to move around properly.

In general, 100% pure antifreeze concentrate is a bad idea – there is a ratio you need to follow either based on the temperature range you need or what the vehicle manufacturer recommends. With G48, most vehicle makers recommend a 50/50 mix and there is actually a premixed formula with a typical PH of 8.1 (the range is 8-9). I was going for 70/30 to have as low of a PH as possible (pure G48 has a PH between 7.1-7.3) and to maximize corrosion protection.

After dumping the final batch of distilled water out of the unit, I could only put in just over 130ml. This cylinder had 500ml of the 70/30 mix before pouring.

Well, the trapped water was throwing a wrench in my plans because I had already mixed the 70/30 not realizing I would have a bunch of extra water in the jacked and lines. Rather than drive myself nuts, I decided to go ahead and test the unit by draining out whatever water I could my tilting/moving the machine around while it was upside down and then refill with 70/30. After testing I will drain the tank get the antifreeze ratio closer to 70%.

I was not able to collect the final PH at this time. My test strips are absolutely useless with the dark blue of the G48 fluid. A friend has a calibrated digital tester that we will use some time in the future.

As I was writing this blog post, I was talking to my friend John, who is a master mechanic and has forgotten more than I will ever know, and told him about this. He didn’t even have to think about it – he said “pull a vacuum through the inlet or return and drain the system”. Duh. He was spot on – I sure hadn’t thought about doing that.

I used a MityVac MV-6830 brake line bleeder to suck all of the liquid out through the inlet. I put 70/30 in the tank and used a right angle adapter to pull all of the fluid that way. I then refilled the tank with 70/30 and pulled just enough vacuum to the point I saw fluid entering the hose and stopped – I did that last part to pull fluid into the pump.

The Mityvac MV6830 connects to an airline and uses the venturi-effect to create a vacuum. There are several lines that come with the kit – a straight siphon line that is shown above and a right angle rubber fitting for brake line fittings. Guess what? The .26-.27 outer diameter siphon line fits the inlet perfectly and I could suck all of the fluid out of the lines. I then used the right angle fitting to draw G48 through the outlet line.
The 0.26-0.27 siphon line fits the inlet perfectly.
The right angle fitting can be pushed against the return outlet to suck fluid through. It’s a bit of a challenge and takes two hands. One to hold the adapter and a finger from the other hand to apply pressure so the fitting seals enough against the return. Note, the fluid level in the tank goes down fast.

I then turned on the master switch so the fan and water pump would start. Nice clean 70/30 G48 was coming out. I slowly added more mix to the tank until I got to the bottom of the return line. I had to top it off just a tad maybe 2-3x as fluid filled little pockets. I let the unit run for another five minutes and when the fluid level stayed the same, I put the cap back on – done. It helps to have smart friends.

Here’s my lessons learned that I want to share when it comes to the cooling system:

1. Flush the cooling system out using distilled water and then use a vacuum bleeder or siphon tool to more fully drain the system. I put put about 250-350ml of fluid to fill the system in the end. The important thing is to fill the tank to the bottom of the return.

2. If you don’t see the fluid moving, you most likely need to prime the pump either by moving the CS4 around to work fluid down into the pump or draw it into it using a vacuum bleeder.

3. Test the cooling system with water – not antifreeze or you will make a mess plus water is cheaper.

4. While you can use distilled water, I would recommend Zerex G48 at either 70/30 or 50/50. I went with 70/30 that I had to mix from the concentrate.

Testing the CS4

Now that the critical coolant discussion has been addressed and you have filled the unit accordingly, let’s switch gears and start actually testing the unit. After every test, drain the unit using the bleed valve. I will bring this up again later but do not attempt to start the compressor with pressure already in the line.

There will be some very high pressures involved. If a fitting does not want to come off, STOP. Many times a quick release collar will not move or a threaded fitting turn because the line is pressurized. Always make sure the line is depressurized before you work on it, remove a fitting, etc.

Each bold heading below is a test I would recommend that you perform and if it fails, stop and contact the Amazon seller – Ankul. I am not a representative – just a user. With that said, here are the tests:

  • Make sure the fluid pump is running

Before you start pressurizing the system, again, turn on the master red switch but not the pump. You should see the coolant circulating, If you do not, try moving the unit around to get the pump to prime

  • Turn the compressor on with nothing attached

With the airline off and just the male foster fitting exposed with nothing on it, turn on the pump by pushing the top silver button. You should hear the pump start and feel air blowing out from the end of of the foster fitting rhythmically – there is a piston so the air will come out as the piston pushes upwards – it is not a continuous flow. You should not hear any awful grinding noises or banging sounds. Slight squeaks as things start to lubricate and wear in are possible – you are listening for “OMG – what the hell is that?” sounds.

Let it run for a minute or two and if no scary sounds start then shut off the compressor.

  • Test with the supplied pressure hose only

To test high pressure air systems, always pressurize incrementally starting with the smallest thing first and work your way up to larger and larger volumes. In this case, start with just the air hose attached.

This is our first real test of the compressor under pressure plus we get to check the hose assembly. With that said, connect the air line and insert the test plug in the end. Make sure the plug is fully seated. Also, make sure the drain valve / pressure relief valve is closed – this is the black knob on the front of the unit. Clockwise closes the valve – it screws closed basically.

Set the limit switch / stop switch on the top to 300 bar. Put the secondary switch at 310/320 bar. I put my second switch just before 400bar but in hindsight, I would tell you to put it around 310/320.

Turn on the compressor by pushing the silver button. You should see the pressure build very quickly – the manual says it should reach the target 300 bar pressure in 38 seconds. I think mine was a bit faster than that.

The supplied pressure hose will fill quickly for testing and will only hold a small volume of air so if something fails it will be less of a problem

Now, don’t do a thing. Watch the pressure gauge. It should just sit there – if it is going down there is a leak. The most likely culprit is the drain valve isn’t fully closed. Wait until it leaks all the way down or open the bleed valve to speed things up. You don’t need to go crazy tightening the valve knob as you are liable to hurt something but it should be firmly closed. Make sure it is snug and try again. 90+% of the time that fixes the issue.

If it still leaks drain the system, remove the test plug and look in the female foster fitting – is the rubber o-ring still down in there? Same goes for the other end of the hose that plugs into the machine. It could be missing. So, if it is, insert an o-ring and try again. If the o-rings are there, sometimes just removing and reseating a quick connect fitting/plug can solve the issue. Make sure the bleed valve is closed and try again. If it will not build pressure, contact Ankul on Amazon.

So the first limit switch at the 9 o’clock position was set to 300. The black needle is the actual pressure. Notice that the unit stops just short of the indicated pressure. The second limit switch which is the failsafe was set at about 390. In hindsight I would tell you to set that second switch just a tad higher than the first one. If I wanted the first switch to be at 300 then I would set the second one close to it at 310/320. You can’t put them right on top of each other.

Soapy water in a spray bottle can help you find where the leak is at. Do not run your hands right against the fittings or you risk air getting injected into your body and that is very bad.

By the way, I let mine sit for about 3-5 minutes before I decide. Usually a leak is really obvious in the first minute – the first few seconds even. Either it will not build pressure at all or it leaks down fast.

Bleed off any residual pressure. Opening the bleed valve also allows any trapped moisture to blow out of the drain line also. I doubt you will see it with this short of a test but you will sooner or later so don’t worry. It’s supposed to do that.

  • Test with the filter installed

Assuming the pressure line passes testing, it’s time to up the volume game and pressurize the air line and whatever external filter you want to run. I am using a big 300mm long filter with a 50mm outside diameter sold by FastToBuy on Amazon. Yes, the CS4 has an internal filter – but I really want the air to be dry.

First, make sure the system is depressurized by opening the bleed valve. Then plug your filter into the air hose and this time put the test plug on the end of the filter. All of your fittings should fit together very nicely. If you find something doesn’t want to go together, stop. Buy a replacement fitting, I like Air Venturi brand but any reputable brand will do. I’ve had Chinese no-name filters, hoses and other items with out of spec fittings that will not go together. Last month, I had a brand name fitting whip off a Hatsan Jet II and hit me in the glasses so hard that the polycarbonate lens was gouged and my glasses were flattened against my face on one side – I had tried to push the fittings together and they didn’t mate properly. Moral of the story – fitting should go together easily without forcing.

Once the assembly is together, the bleed valve is closed, set the pressure limit switches to 300 and 310 bar then turn on the compressor. It may take it a minute or two for enough pressure to build up to show on the pump’s pressure gauge. It may take a few more minutes depending on how big the filter is before it reaches 300 bar. As before – stop and watch the pressure gauge, it should hold steady and not leak down. If it does, then check the bleed valve, o-rings, etc.

Testing the big inline filter. It is very nicely made and comes with a spare filter cartridge.

The absolute most common source of leaks is at the fittings – worn or missing o-rings or one fitting not really sealing well against another and you then need to decide which fitting to replace. Soapy water in a spray bottle can help you find where the leak is at. Do not run your hands right against the fittings or you risk air getting injected into your body and that is very bad. Notice the repeat on that safety comment.

If everything passes, open the bleed valve to dump the air in the filter and line.

  • Time to Fill The Tank

Part of my push for the new CS4 was to also fill my new 6.8L 4500 PSI Airmarksman tank. I really wanted to go with a new Omni or Patriot (US made Omnis) but the 6.8L model is hard to find so I went with Airmarksman because I really wanted two gauges – one with line pressure and the other with tank pressure. Standard single gauge units just show you line pressure.

It’s nice, the Air Marksman’s air hose attaches via a quick connect. I can go right from a female foster fitting on an airline right into the tank – no more little male-to-male quick connect fittings that are easy to lose.

I also bought a really nice 3′ long Manloney air hose extension to go from the new filter to the tank. In general, I am not a fan of hanging a filter right on a fitting because you create a long lever arm that is too easy to snag and break. Instead, I prefer a hose to the filter and then a hose from the filter into the tank.

You know what this means right? I tested the Manloney hose extension by inserting the test plug, and doing everything we’ve talked about previously.

Tested the Manloney hose extension and everything was good.

I then bled the air off and let the unit’s cooling system run until the exhaust temperature was the same as surrounding surfaces because it was time to get real. Filling the tank from empty to 300 bar would take at least 2.5 hours and I wanted to record times, pressures, temperatures and and decibel readings along the way.

Filling the tank. Note – do not put the power supply in front of the exhaust fan. I noticed it was getting quite warm and moved it to the side a while after this photo was taken.
This is the pressure gauge on the tank. It read higher than the compressor so I followed it for safety’s sake. In other words, I did not want to exceed the rated 310 bar on the bottle – I actually only went to 300 bar – but if I had followed the gauge on the pump I would have gone higher. Which gauge was right / more accurate? No idea but I will always play it safe to not avoid a stated safety limit. By the way, the thank has another gauge on the back and they both agreed with one another.
This table shows you what I noted during testing. I just did the fill one time.

I couldn’t just sit next to the compressor and tank for the 3:22 minutes the test was running. I set the shut off on the pump to 300 bar but what I found was the needle you are moving around to shut off the pump is not precise. For example, I wanted 300 bar but what I got was 257 bar of 3,725 PSI. I then ran the unit another 10 or 15 minutes to take it up to 300 bar even and then moved the limit switch / shut off needle slowly backward until it stopped. Now the first switch is set where I want it. The second need is just behind it by about 10-20 bar.

The temperature management is remarkable. I was using a very good Fluke infrared thermometer to measure the exhaust fan area’s temperature and once it got up to about 100 degrees it pretty much stayed there once the unit warmed up. The noted coolant temperatures were collected by me removing the lid of the water tank and using the Fluke infrared thermometer to get a reading.

Speaking of temperature – this ran far cooler than I thought it would. I actually thought the fluid would get hotter and risk boiling. I still like using antifreeze for the corrosion protection and lubrication of the pump but boiling is not a concern and I don’t foresee it ever being some place where it could freeze but I guess lowering the freezing point is a good idea just in case.

In terms of sound, the unit turned on with just the fan and coolant pump running is 71DB according my BAFX 3608 decibel meter. The sound level with the compressor running was in the 82-84DB range about 8-10 inches from the side of the unit – not bad at all. I thought it might get louder as the pressure increased but it didn’t.

Last comment – the unit ran for well over 3 hours and thirty minutes – probably more like 4-4.5 with all of the testing. There were no funny sounds, no unexplained leakages, etc. That amount of running gave me a real good impression of the unit. After all of that running, I did turn the grease pot one rotation.

Special Note: DO NOT Start or Re-start The Compressor Under Load!

GX stated in multiple places to not try and start the pump with the system pressurized. I imagine it puts too much strain on the electric motor and other parts to get spinning. When I did the top off fill mentioned above, I closed the tank’s valve and opened the bleed valve on the compressor to depressurize the line. Unsurprisingly, maybe a teaspoon or two of water came out as well. I then closed the bleed valve, started the compressor and after it came back up to speed only then did I re-open the tank valve and put the system back under load.

By the way, I am not surprised by this at all. With shop air systems, part of the pressure limit switch is to also open a bleed off valve to depressurize the pump. It’s fairly common for these switches and valves to wear out. If the air doesn’t bleed off then a breaker may trip given the increased load. So, giving the CS4 a chance to start without a load and come up to speed first makes sense to me.


I was really impressed by the smaller CS3 model that I have used since November 2020. I bought this new CS4 model because I had such a good experience in fact and now that I have run the CS4 over four hours, I’m pretty happy. The CS4 will fill the niche in the GX line-up for a medium-duty machine for 6.8 Liter and smaller bottles. The CS3 will continue to be sold for people filling 1.5L or smaller cylinders.

Wrapping up – I really like the unit so far and will definitely post updates as time goes on.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

The Next Generation GX CS4 PCP Air Compressor Is Amazing!

Life is a funny thing – I grew up with firearms. Yeah, my dad had these two old pump action Daisy airguns that were fun to shoot tin cans with but starting at a pretty early age I liked things that went “bang”! Sometime in the early 2000s, I got back into airguns to deal with pests. I started hearing about a class of airguns called “pre-charged pneumatics” (PCPs) that used 3,000 PSI high pressure air cylinders somewhere on the rifle to propel the pellet. They were reported to be accurate, reliable and capable of rapid repeating fire through through the use of a manually operated bolt and a magazine.

I thought that sounded so neat – especially the rapid follow up shots. What stopped me from buying one was that they had to be refilled from a SCUBA tank that was filled at a diving shop. Well, I eventually found out there were specialized hand pumps and you didn’t need to spend a fortune on a tank and hassles with going to the dive shop. I bought a Hill Mk.4 hand pump along with a .22 Hatsan Gladius Long that I used for a few years.

Along the way, I found out that high pressure air compressors were falling in price. Those things used to be well past a $1,000, large, noisy, heavy and there was just no way I could swing one. In the fall of 2020 while surfing around on Amazon, a very affordable high pressure air compressor was doing really well. It was affordable, getting great reviews, portable and I didn’t have to mess with all kinds of oils and ice water cooling baths. It was the CS3 air compressor from GX. I bought one for $529.99 on November 23, 2022 – Amazon is cool in that I can search order history and pull up dates that I would have forgotten otherwise.

I wrote a post about buying it and also one about setting it up and testing it. I almost always used the CS3 to top off a really nice little Omni 18 cubic foot tank that I would then use to fill my growing number of PCP airguns. It really worked well – the tank was really convenient to pull out and top off an airgun and I would only occasionally need to bring out the CS3. Sure, I could have filled the airguns directly from the CS3 but I wanted to keep things simple.

Fast forward to January 2023 – I bought a .30 Umarex Gauntlet with a big cylinder and was planning to get one or two other high air consumption PCP rifles in 2023 so I started thinking about how to feed them. It was a total coincidence that GX unveiled their next generation CS4 compressor on Amazon. There were just a few four or five reviews at the time and I decided to gamble on the new pump and bought it on January 29, 2023. I took the leap because I had such a positive experience with the CS3 and I knew I could return it to Amazon if it turned out to be a problem child. [Yes, I bought this so you are getting my honest observations.]

On January 31, 2023 the Amazon driver brought be a big heavy cardboard box with the CS4 and I started getting my stuff together to do some testing plus a time slot to fill a big 6.8L carbon fiber tank from empty to 300bar which would take 2-3 hours I figured.

Now, I’m going to tell you something – it is slick. It is really, really slick. I’m telling you this so you take the time to read more in this post plus one about setting it up and testing it.

What is the CS4?

The CS4 is an additional pump offering from GX for people wanting to fill larger cylinders than the CS3. It also reflects design advancements to the CS3 unit – here are the features that really caught my eye:

Working Pressure
(Mfg supplied)
30MPa/300 bar (4,351 PSI)40MPa/400 bar (5,801 PSI) – 33% more pressure
Air volume
(Mfg supplied)
7 liters/minute (0.247 cubic feet/min)11 liters/min (0.388 cubic feet/min) – 57% more air volume output
Suggested Maximum Air Cylinder Size2.5 Liters6.8 Liters
CoolingAir with fansCoolant with radiator and fan
(Mfg supplied)
12V 250 Watts12V 350 Watts – 40% more watts
Duty Cycle (Mfg supplied)30 minutes working and 20 minutes cooling5 hours continuously working. Manual says to let it run for 1-2 minutes after pumping is complete – 10x longer duty cycle.
Sound Level (Mfg supplied)75db70db
Pump lubricationNot needed (until it slows down – mine hasn’t so far)Has a grease pot to add grease every 4-6 hours of run time
Limit switchSimple rotary dial limit switchProtected twin pin design where you can set both the limit and failsafe limit
Hose19.6″ permanently attached hose19.6 hose that is removable via a quick connect foster fitting
Weight (my digital scale)19.4 pounds29 pounds with antifreeze – 55% heavier
Dimensions (me with a tape measure)5-3/8″ wide (about 5-7/8″ wide including the wire spool on the side) x
9-1/2″ deep (10-1/4″ if you include the release valve) x
10-1/2 high at the top of the case (about 11-1/2 overall if you include the handle)
6″wide case (6-1/2″ wide with the wire spool) x
11-78 deep (12-3/4 if you include the release valve) x
12-1/2″ at the top of the case (about 13-1/2 at either the top of the grease pot or the folded handle) – about 62% larger overall

For me, the really long duty cycle is what I was looking for. The 57% increase in air output is a welcome enhancement to have over the CS3. Since I would fill my guns from my tank, I was never in a rush. Now that I have 6.8L tank, the fills will probably be less often but a lot more volume will be needed so it’s good to get that increase.

The increase in air pressure is overkill right now – there aren’t affordable 400 bar working pressure tanks as of yet – they are out there for specialty applications but are in the $1,500-2500 range. I’m sure the price will come down over time but most carbon fiber air tanks that PCP shooters are using are in the 300-310 bar working pressure range. If you see 400 bar, read the ad again because they may be talking about the test pressure and not the working pressure – you fill to the working pressure only – never to the test limit.

To be clear, the CS4 is not replacing the CS3. They have added the CS4 to fill larger tanks faster. They identify the 6.8 liter tanks as being the target max size for the CS4 and for me the duty cycle is the more important number. You can fill anything you want as long as you don’t bake the pump.

With the CS3 for example, the 20 minute duty cycle is what limits a convenient tank size. If I needed to fill my Omni 100 cu in (1.64 liter) tank from empty – I would let it run for 20 minutes and then I would stop the pump but let the fan run until it cooled down to room temp. I’d then close the cylinder valve, bleed the air out of the line, start the air pump again and as it came up to speed I would open the cylinder’s valve again. It took a while but it worked just fine. I tried to always be mindful of the duty cycle and give the unit a chance too cool down before I either shut it off or resume – I’m sure that’s one reason I’ve had zero problems with the CS3 since I bought it.

A five hour duty cycle with the CS4 is pretty amazing. I’ll tell you more about it when we get into the setup and testing.

Out of the Box Pictures

Let’s take a look here:

The CS4 was well packed. Amazon’s delivery group sometimes smashes delicate packaging so I was glad to see the unit was well protected in a plastic bag with styrofoam holding and protecting everything inside of the box.
They are using the same 12 volt 46.2 amp power supply. This allows you to either power the pump with a car/truck battery or use this power supply to charge at home. You can see the removable air hose under it still sitting in the styrofoam.
This is really nice. With the CS3, the air hose is bolted to the unit and gets in the way at times. With the CS4, there is a standard Foster quick connect. Notice the thought put into the hardline portion on the left side of those – this is the end that plugs into the pump and the metal line bends at an angle thus avoiding collapsing or weakening a flexible airline. It’s a well thought out change.
Starting from the top back – the silver cylinder is the grease pot that you use every 4-6 hours to introduce grease into the cylinder. The brass fitting is the safety burst disc. A burst disc plays an important safety role – it will blow out before an extreme pressure situation could cause a catastrophic failure of the pump. The clear circle has the pressure gauge and the two limit switches you can set. On the left is the power wire spool. The silver nozzle sticking out is the male foster fitting that the quick connect air hose goes to. On front side (colored black) – top right are the on/off switches for the pump itself. The red master switch turns the unit on and both the fan and coolant pump begin working. The black knob is the pressure release / bleed valve. Behind the circular slots sits the CS4’s radiator that has a fan cooling it – the antifreeze/distilled water flows through it to cool off.
The pressure gauge and limit switches surprised me. I went to rotate the switches by turning the silver knob and immediately felt a weird springy resistance. On the CS3 I always checked the pressure because if you bumped the knob the pressure limit changed. Well, now move the top silver “finger” around and push down to turn either limit switch. It’s less prone to being bumped and you have two limits – not just one. It’s not absolutely goof proof but I think it is a good next step from a safety perspective.
With high pressure systems, play it safe. My tank gauge vs. the pump’s gauge don’t match so I go with the higher of the two pressures. It’s called “conservativism” – go with the most conservative or safe number given the situation – don’t base your fill on the low-reading gauge, go with the one that says there is more air pressure just to be safe. In my shop’s air system I probably have a dozen pressure gauges and they all read slightly differently – I guess it is just the nature of the beast unless you want to spend a mint on calibrated accurate gauges.
On the back of the unit are vertical slots and when you look in you can see the cooling fins of the first stage cylinder liner.
The larger CS4 is on the left and the CS3 is on the right. The CS4 is intended for filling up to 6.8L bottles and the CS3 is targeted for smaller bottles and/or airguns. Note: GX makes two versions of the CS3 now – one with the external 12 volt power supply like I have as well as one that just plugs directly into the wall and does not have a 12 volt supply.
CS3 on the left vs the CS4 on the right.
One last comparison photo – the CS3 is on the left, the CS4 is on the right and the dogs’ water bowl is in the back 🙂 See how the air hose just dangles on the CS3? Being able to remove it completely from the CS4 really cleans things up plus opens the door for future hoses should you need them.

Here are Amazon links where you can read more about the units and/or buy them:


The CS4 compressor is a great new product offering from GX. In the next blog post I will walk you through setting the unit up and then testing. I’ve already done all of this so I’m telling you right now the CS4 is a solid unit. In the next post I’ll explain why I am so impressed along with what I did to set up and test it.

6/12/23 Update: Fixed the wording about being conservative. Thanks KG!

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Buying an Omega 18 Cubic Foot High Pressure Air Cylinder and Filling It With My New GX CS3 Compressor

In my last post, I described how I set up and test my brand new GX CS3 compressor. The next step I wanted to do with it was to charge my Omega 18 cubic foot air cylinder. As easy as the GX CS3 is to use, I still wanted a small high-pressure air (HPA) cylinder to use to top off my airguns vs. needing to haul the compressor out every time.

So, why did I pick an Omega HPA cylinder?

I actually have a prime reason – safety. Back when I started SCUBA diving back in the early 1980s, 3,000 PSI 80 cubic foot air tanks were the rage. One of the things they drilled into us during our classes was that this much air pressure needed to be respected. You made sure your tanks were taken care, properly inspected every 5 years via a process known as ‘hydro testing” and you even loaded them in your care secured the valve forward because if the valve broke off then the main body of the tank would take off like a rocket as the air escaped and you didn’t want it coming forward towards you!

At any rate, I had safety top of mind when I started reading on HPA cylinders. Folks, there are cheap virtually generic tanks out there that I would not trust. As I visited the various PCP airgun vendors, I would note what brands of HPA cylinders they would carry and Omega was a brand that I saw repeatedly.

I’m not saying Omega is the only brand to look at by the way – it’s brand I decided on when I looked at price, reviews, and availability. The pandemic has thrown off supplies of just about everything these days.

Omega is a brand you ought to consider because they are owned by the Korean firm Inocom who has done a lot of R&D of carbon fiber HPA cylinders for fire and rescue, medical, SCUBA diving and even PCP airguns — which is what we are talking about today. Inocom produces over 150,000 cylinders a years that conform to a bunch of different standards and my point is that they know their stuff.

In the US, you can find Omega Air Cylinders at a number of different vendors including Airguns of Arizona, Talon Air, and many other places. I bought my particular 18 cubic foot tank from Airguns of Airzona (AofA) because they had them in stock — the relatively small 18 cubic foot tanks can be hard to track down.

Airguns of Airzona Video

AofA took the time to assemble a video review of the Omega tanks. There are a number of sizes and you can spend quite a bit before you know it.

But what about those cheap generic tanks on Amazon and eBay?

I’m not a fan of taking unnecessary risks when it comes to high pressure air. That is a ton of pressure to gamble with. I would much rather spend the money and buy a tank made by a reputable vendor. I suppose you could always a cheap tank to a dive shop that can do hydro testing and have them check it but why go to the extra work and expense?

Out of the box

The Omega arrived just a few days after I ordered it from Airguns of Arizona and boy did it look nice. I’ve always liked the look of real carbon fiber and the tank looked awesome. It also comes with the meter long no-kink hose that also converts from the air tank fitting to a 1/8″ BSPP threaded end that comes with a foster fitting already installed.

The carbon fiber work is visually stunning. Wow.

It comes with a really nice oil filled pressure gauge that tells you the pressure in the line – not the tank. If you want to know the pressure in the tank, you would need to put a dead-head, or test fitting, into the quick release foster fitting in the hose and pressurize the line.

Inside the red circle in the photo is the pressure relief button that depressurizes the line when pressed.

Protecting Your Investment – Get a Bag

As cool as carbon fiber is, I would recommend protecting it from getting cut or gouged with a bag. I bought a Workpro 16″ tool bag off Amazon and the tank fits great. I did add old gun case foam to the bottom of the bag for some added protection.

I have the tank pulled part way out for the photo. It fits with the fill line installed, no problem. You can see the pluckable foam that I put in the bottom. The bag also gives me room for spare fittings – they are in that small grey pouch you see.

Filling the Tank – Remember Your Compressor’s Duty Cycle

Okay, first off, bear in mind that your compressor likely has a duty cycle. In other words, it was designed to run for a certain number of minutes and then be allowed to cool down for another amount of minutes. For my GX CS3, the duty cycle is to run for up to 30 minutes and then be allowed to cool for 20 with the cooling fan running.

To connect the GX CS3 to the tank, I used an Air Venturi foster fitting male-to-male adapter plug. This fitting will allow you to connect the female foster fitting on the compressor to the female foster fitting of the tank.

This is an Air Venturi brand male-to-male Foster fitting adapter.
The male-to-make Foster fitting adapter allows us to easily join the two airlines together via their quick detach fittings.

So what do we do first? Test the lines

Assuming you tested your pump and know that it holds air, we need to next test the fitting and airline from the compressor to the tank. You do this by keeping the tank’s air valve closed and then pressurizing the airline only in steps.

I found out immediately that air was leaking where the airline connected with the tank and used a wrench to snug the fitting down. Note, do not use your hand to look for high-pressure air leaks – use soapy water and look for bubbles.

During testing, I found that air was leaking out of this fitting. Some people say you can install this fitting by hand and it will seal. Due to carpal tunnel, I probably do not have the strength of many and I did use a wrench on the flat sections of the fitting to snug it up and everything sealed beautifully.

So, I pressurized the lined to 1,000 PSI after I fixed the above and watched the pressure gauge for a few minutes. It held. I then opened the bleed valve on pump and let the air out.

I repeated the above going to 2,000, then 3,000, then 4,000 and finally 4,500 pounds. In all cases the line held pressure after the initial tightening down of the air fitting to the tank.

Filling the tank itself

By now I was feeling comfortable with the compressor. I decided to run the compressor in 25 minute cycles to see how far it would get and how warm the exhaust air would get.

At 25 minutes, the tank had reached 2,200 PSI. I could hear the pump was making a different sound as it was operating under load but nothing scary like metal on metal grinding. I turned off the pump but let the cooling fan keep running for 20 minutes.

I restarted the pump and in another 25 minutes, the tank air pressure increased to 4,100 pounds. I used a Fluke IR thermometer to measure the exhaust vent and it was at 116F degrees (for reference, the floor measured 67F next to it. I measured temperature at a few other places too out of curiosity: Top of the case was 105.8F. Neck of the cylinder was 92F, the male-to-male coupling was 76F and the top of the power supply case was 86F. Nothing alarming in short.

I let the unit sit and cool for 20 minutes. The exhaust vent had cooled to 91F. Almost 3 minutes and 24 seconds after restarting the tank reached about 4,500 PSI and the compressor automatically shut off.

I watched the air pressure for a few minutes and it held. That was a good sign.

Interestingly, when I bled the line about a teaspoon of water came out of the pump. The GX CS3 does come with an internal water and oil separator. I do plan to add filters both to the pump and the tank just to be sure – I am real nit picky about having clean air – it comes from my plastics business. At any rate, I will report more on the filters later.


The Omega tank worked without a hitch and I am very happy. I filled my Hatsan Gladius Long from the tank and boy was that easy. My old Hill Mk.4 hand pump has served me well and is now a back up just in case but now that I have a compressor and tank, my life just got a whole bunch easier.

I did need to put a Foster fitting on my Hatsan fill probe. This has made the probe very portable as I can now put it on the tank, the compressor or the Hill hand pump. One recommendation is to stick with the same brand of Foster fittings – this is an Air Venturi female 1/8″ BSPP adapter to male foster plug.

I hope you found this post useful.

2/2/2021 Update: The tank is working great. It is incredibly convenient to have this tank around to top off airguns. I used to dread breaking out the hand air pump and now it’s just a matter of a few second and the gun is full again. The GX3 compressor has proven itself to be a great addition also.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Setting Up And Testing The GX CS3 PCP Air Compressor

As I mentioned in my last post, IU ordered my GX CS3 air compressor off Amazon and it arrived in great shape. The next day, I reread the very terse instructions in the manual and decided I better follow some basic test procedures because you don’t want surprises with high pressure air (HPA) systems – think small explosion when they do. My intent was to bring the unit up in stages.

Current Version Does Not Require Additional Water or Grease

Unlike other pumps, you do not need to add water or oil/grease to this pump. You take it out of the box and run it. I even contacted the seller just to confirm because they still include the old instruction guide that says to add grease and the Amazon listing says you do not need to do so anymore. In short, it’s ready to go out of box.

Take the time to read the very brief owner’s guide/instructions. If the Amazon listing still says you do not need grease and there is no grease supplied, that part of the guide is outdated. You can still see what they say about testing, their exploded parts diagram, etc.

Set up and Testing

Here’s what I did and would recommend to a new owner:

1. Make sure the AC power adapter’s input voltage switch is set accordingly.

If you are in the US, the switch should be on 110V. You only need to do this once.

Do not plug it into the AC power yet. You need to connect the pump first.

2. Connect the pump’s power cables to the adapter.

First, I connected the power clamps to the AC adapter and then plugged the AC adapter into the wall. I debated testing the power to see if I was getting 12-13 volts but decided to just run with it. Note, there is no power switch on the adapter so connect the clamps from the pump to the compressor and then plug the power adapter into the wall.

Important: Connect the pump’s power leads to the AC adapter first before you plug it in. Also, mke absolutely sure the red power line is clamped to the red “+” terminal and the black line is to the white “-” terminal. Do not reverse the polarities.
The power cord to the wall plugs into the bottom receptacles. The red clamp from the pump plugs to the red “+” and the black cord plugs to the white “-“.

You can see the lower AC cord socket. This is your normal office plug so you have tons of cord options if you need to replace the cord down the road. There are also lots of AC adapters on the market with a very similar set up – just make sure they output 13V and and least 46.2 amps to support the compressor.

So your setup should look something like the above at this point.

With the power adapter plugged into the wall, the cooling fan on top should start right away and that is how you know it is running. If it does not, use a test meter to check the AC power cord for 110-120 volts. If the cord is good then see if you have 12-13 volts at the terminals. You will need to contact the vendor as the fan is critical for cooling even if you do have power. If there is no output power then the vendor needs to replace the power adapter.

If the fan is running, let’s go to the next step.

3. Testing the pump and line

Set up really is that easy. At this point, it was time to turn on the pump and pressure test the line. To do this, the maker supplies a test Foster plug that goes into to supplied female Foster fitting.

The test plug, sometimes called a dead head plug or dead head fitting is to the left. The female Foster fitting that is pre-installed on the pump’s airline is to the right. Pulling that silver collar back from the end will release whatever is inserted into the coupling.

Note, my test plug came already installed in the end of those. In general, I like the idea of keeping the test plug inserted when the pump is not in use to help keep the fitting clean.

Two things, the quick connect fittings on HPA lines, tanks and guns is known as “Foster” fittings and you have the make plugs and female couplers with a locking ring you slide back to release the male plug. They are a really handy means to switch between filling different things – tanks, guns, certain types of fill probes, etc. Just make sure you get fittings that are rated for the pressure you need. For example, I’ll be filling tanks up to 4,500 PSI so my fittings are all rated for 5,000 PSI.

If you mix fittings between vendors, there’s a risk of a leak due to tolerances stacking the wrong way. In other words, vendor X and vendor Y might have slightly different allowances during machining and when you combine them, there is enough of a gap for air to leak out. With this in mind, I try to stick with Air Venturi brand fittings and if I have a problem, I swap out the fitting in question with one from that brand and I keep spares on hand just in case. Note, they can also wear out from repeated use as well – another good reason to have a few spares.

This is my Hatsan fill probe with an Air Venturi foster fitting on it. Note, the pipe thread on these fittings and air lines is 1/8″ BSPP – British Standard Parallel Pipe. It is not NPT. Use quality pipe tape or a Dowty washer to seal the threads. Here, I am using quality pipe tape.

My Testing Procedure

I am paranoid. If something is going to break, I want it to happen with the lowest air pressure and volume of air behind it that I can get. Right now, we need to test the pump itself, the air line and fittings that came with tank.

WARNING: Never run your hand over a charged high pressure air line and fittings in search of leaks. You run the risk of injecting high pressure air into your blood and having an embolism. Either spray soapy water on the suspect and look for bubbles or even dip the area in soapy water.
Please note that the gauge has a dial indicator you move around to the air pressure limit you want the pump to stop at. You can move this dial around by turning the silver knob at top. Here, my pump is set to turn off at 4,500 PSI. You would set your’s at the limit whatever you plan to fill. Note how the indicator has both PSI and bar settings. If your airgun has a limit of 200 bar, you would set it to 200 bar for example. You will likely find some difference between what the pump says the pressure is vs. your tank or airgun by the way. For safety, stick with whichever value is lower. If you set the pump to 200 bar and your airgun reports it is past 200 bar then stop the pump and bleed some air off. Adjust your dial so you do not exceed the maximum pressure of the device you are filling. When in doubt, play it safe.

Here is what I did to test my pump and fittings and if you are not comfortable with any of it, please do not do it (safety first):

  1. Ensure the test fitting is installed in the end of the Foster fitting of the pump’s air line.
  2. Set the air pressure limit on top to 1,000 pounds.
  3. Flip the toggle switch as the base of the pump to On.
  4. Push the start button on the front of the pump. If it does not turn on, double check the power connections. You should also hear the relatively loud cooling fan turn on in the pump at the same time. If it will not turn on or you don’t hear the cooling fan once it does, you will need to contact your vendor. My fan turned on when I pushed the silver start button on the unit.
  5. The pump should start and in a few seconds pressurize the line to 1,000 PSI. If not, then contact the vendor.
  6. By the way, the pump better shut off at the assigned 1,000 PSI limit. If not then this is a serious safety concern and you should contact the vendor.
  7. With the pump off and the line charged, watch the pressure gauge for 30-60 seconds. If the pressure falls then that means there is a leak somewhere and you should contact the vendor. If it stays steady, go to the next step. If you want to wait for longer, you certainly can.
  8. Open the bleed valve and release the air pressure. Water from condensation may come out the drain tube on the side and that is fine. It may, it may not.
  9. Next, turn the dial up to 2,000 PSI and repeat the above test. We are increasing the pressure in steps testing the unit. You do not need to go higher than you plan to use the unit — stop where you want. For me, I am going up to 4,500 PSI for my carbon fiber tank so I drained and filled the line several times.
  10. Also, none of these incremental tests should take more than 10-15 seconds to complete.
  11. Do it again at 3,000 PSI.
  12. Do it again at 4,000 PSI.
  13. Do it one last time at 4,500 PSI.

I’m happy to say that my new pump system passed all the tests!

If you run into any problems with the above, contact the vendor. You do not want to void your warranty or get hurt so don’t go taking things apart – talk to the vendor first. I can’t stress that enough. HPA systems require knowledge to service safely and you will probably be far better off exchanging for a whole new pump vs. taking things apart.

That translucent tube is where condensation will blow out from when you open the bleed off valve.

Duty Cycle

Please note that this compressor has a duty cycle that you must keep in mind. It is designed to run for up to 30 minutes straight and then it needs to cool for 20 minutes. Leave the unit powered on so the fan can help cool it off. So, if you have a big tank to fill, keep this in mind. You can fill it but do so in however many steps you need to honor this duty cycle.

Video Of It Running

I’m going to put this video both here and in the introductory blog post. Today, I recorded a quick video as I topped off my tank today – January 7, 2022. It ran for about 20 minutes as I took that tank from about 3,000 to 4,500 PSI.

When done, I let the unit’s fan run for about 10 minutes until the air coming out was cool again. Since the unit is air cooled, give it time for the fan to do just that. I also bled off the unit to replace air pressure and get rid of any condensation.

Note the odd double filter rig I am running in the video – that’s just because the double-male Foster fitting will not seat all the way in the big filter’s female fitting. I need to replace it with an Air Venturi brand fitting some day when I have time.

Safety comment: Never try to force fittings apart after a fill. Most likely there is high pressure air that needs to be bled out of the lines. With that big inline filter, the output side from it to the tank stays under pressure so I need to bleed down both the compressor and tank sides before I can safely disconnect the various fittings. Just remember to think things through carefully before you force a fitting off – high pressure air dangerous.


Hopefully your system passed the tests and you are now ready to fill your tank or device. If you had problems, be sure to reach out to the vendor and ask questions. I found them both helpful and responsive.

In my next post I will extend testing to include setting up and filling my 4,500 PSI Omega 18 cubic foot tank.

I hope you found this post useful.

2/2/2021 Update: The compressor is still working great. No problems at all!

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Finally, An Affordable And Reliable 4500 PSI Air Compressor For PCP Airguns! The GX CS3

Folks, I think Pre-Charged Pneumatic (PCP) airguns are awesome. They have an onboard high-pressure cylinder that holds enough air to shoot a certain number of rounds before needing to be recharged. After years of having your basic pneumatic and spring-piston air rifles, I bought my first PCP, a Hatsan Gladius Long in .22, back in May of 2017 and a Hill Mk IV hand pump. In this post I want to recap what your options are and then talk about move into the world of having my own compressor.

You Have Three Options To Fill PCP Airguns

To fill a PCP airgun, you have three options: own a hand pump, have an air cylinder or own a compressor. For almost three and a half years, I’ve used a Hill Mk IV hand pump to top off the Gladius and it has worked well. These pumps are like an old fashioned bike tire pump on serious steroids as they can enable you to fill a cylinder with thousands of pounds of air pressure. By the way, the secret to longevity with a hand pump is to keep the shaft lubricated to protect the O-rings with silicone grease and to not overheat parts if you are doing a lot of pumping.

The second option is to have an air tank that you would take to your local dive shop and have them fill it to 3,000 to 4,500 pounds. You would then use this to top off your airgun until it too was low and you’d go back to the dive shop to get the tank refilled. We do have a dive shop in the area but this never appealed to me because I didn’t shoot enough to need a tank vs. the hand pump. I also figured that I could use the hand pump any time day or night as needed. You can only refill an air tank if the dive shop is open or you own your own compressor.

Now, this brings us to the third option and that is to own a high pressure air (HPA) compressor. These are not what you get for a garage and air tools – those only go to 175-200 pounds. With PCP airguns, you are talking 3,000-4,500 PSI depending on the rating of the tank or airgun you are filling. What stopped many people for years was that these HPA compressors were a fortune and then crossed below $1,000 a few years ago and now you can see inexpensive units from China that are below $400 but they require water cooling, lubrication, and don’t always get good reviews (some do though).

In many cases, you get what you pay for. The decent HPA compressors start at $800 and go up from there. In 2019, I ran across an HPA compressor on Amazon that I had not heard about before – the manufacturer was Ankul and the model was the FX CS3 compressor. The price was around $500 and it was getting good reviews. At the time, I didn’t really need it so I added it to be “Save For Later” list in Amazon just in case.

Maybe 3-4 times since then, I would open up the listing and read the reviews. You know what? The reviews stayed solid over time. Ankul released an updated model that was air cooled – no more water to deal with – and it was self-lubricated and didn’t need the user to add oil or grease. What’s more, the reviews stayed positive – it scores a 4.6 out of 5 with 196 reviews. That’s pretty good. So guess what? I bought one.

Please note that I paid full price for the compressor. This was not a paid review and I’ve never been contacted by the seller. This is my honest opinion based on my experience with the compressor – I will get a small commission if you actually order one of Amazon but that’s it.

Introducing the GX GS3 PCP Air Compressor

Okay, there are a bunch of reasons why I bought this compressor in addition to the reviews and $499.99 price:

  • It can pressurize a cylinder to 4500 PSI
  • It can run off house current with the supplied inverter or it can clamp to a 12 volt vehicle battery
  • There is an automatic-off switch where you can set the pressure via a dial and when it reaches it, the unit shuts off. This gauge is labeled both with PSI and BAR increments.
  • It has an integral filter for oil and water
  • There are three over pressure safeties – the user sets the pressure on the dial plus there is both a safety valve and a burst disc to help prevent a catastrophe.
  • They claimed the unit ran fairly quietly at 75 decibels (this puts it somewhere between average street noise or being in a shower at 70 db and city traffic or a vacuum cleaner being at 80)
  • The unit is maintenance free – no water/antifreeze to deal with or oil or grease to add.
  • The design was elegant with a spool on the side to hold the power cable, the high pressure hose could rotate and there was a carry handle
  • The pump unit measures 10-3/4″ tall, 5-1/8″ wide and just under 9-1/2″ deep — it’s remarkably small – most of my laptop computer bags are bigger and these measures are based on my unit.
  • The duty cycle is 30 minutes run-time and then 20 minutes to cool
  • The unit only weighs 19 pounds 6 oz (I weighed my pump unit)
  • The AC adapter is separate and measures about 8.85″ long x 4.52″ wide x 2.36″ tall and weighs 1 pound 14 oz with the cord.

Here’s a link to the unit on Amazon:

2/8/23 Update: GX is really taking the affordable PCP high pressure compressor market seriously. The CS3 model, that this blog post is about, is aimed at 1.5 Liter and smaller air cylinders. They now have a CS4 aimed at tanks up to 6.8 Liters (I now have a CS4 and really like it) and they even have smaller and larger capacity units. By doing this, they are giving you a bunch of selections that you can choose from given the air capacity you need and your budget. Click here for the GX lineup on Amazon.com.

Unboxing it

I ordered the unit on a Monday and it was delivered five days later on Saturday by UPS. The pump and power adapter were packed together in one amazingly well packed box. How often do you here somebody comment on a box? This thing was made from thick cardboard and was practically like opening a wood crate and inside was thick foam cushions protecting the air pump and power adapter from all angles.

I had removed the upper right corner reinforcement already when it dawned on me I better take a quick photo. Tip: Just remove the corner braces and the end cap will slide off. You do not need to disassemble the whole box.
I don’t know who the packaging engineer was but he needs some serious recognition, a beer or both. It was one of the best packed tools that I have seen in a long time. It’s no wonder that my unit arrived in great shape.
Here’s a quick photo of the unit out of the box. Everything was in great shape.
This is the 12 volt power adapter. It’s very straight forward – plug it in and it is running and the fan keeps it cool.

Video Of It Running

I’m going to put this video both here and in the set up blog post. Today, I recorded a quick video as I topped off my tank today – January 7, 2022. It ran for about 20 minutes as I took that tank from about 3,000 to 4,500 PSI.

When done, I let the unit’s fan run for about 10 minutes until the air coming out was cool again. Since the unit is air cooled, give it time for the fan to do just that. I also bled off the unit to replace air pressure and get rid of any condensation.

Note the odd double filter rig I am running in the video – that’s just because the double-male Foster fitting will not seat all the way in the big filter’s female fitting. I need to replace it with an Air Venturi brand fitting some day when I have time.

Safety comment: Never try to force fittings apart after a fill. Most likely there is high pressure air that needs to be bled out of the lines. With that big inline filter, the output side from it to the tank stays under pressure so I need to bleed down both the compressor and tank sides before I can safely disconnect the various fittings. Just remember to think things through carefully before you force a fitting off – high pressure air dangerous.

9/15/2022 Update: They now also have a version of the compressor, the CS3-I, that includes the 120 volt AC power unit inside the compressor. It’s getting good reviews so far – the only thing that is different is there integrating the AC power into the unit.

2/4/23 – GX has released the CS4. The CS3 is aimed at 1.5L and smaller cylinders. The CS4 can handle 6.8L cylinders as it is water cooled. You have two options now. Click here for a new blog post about the CS4.


https://blog.roninsgrips.com/setting-up-and-testing-the-gx-cs3-pcp-air-compressor/The unit arrived in great shape and as described. In the next post, I’ll review how to set up, test and use the unit. Again, here’s the link on Amazon and I will jump ahead a bit and tell you that I recommend the unit based on my experience with it so far:

01/07/2022 Update: Just topped off my tank. Still working just fine. Added a video above so folks can see and hear it run.

10/23/2021 Update: Still no problems. I’m very happy with this purchase. So you know, at this point I am using 1-2x per month to refill my Omega bottle. I’m not shooting as much as I was earlier this summer.

3/4/2021 Update: Still no problems at all. I use my Omega 18 cu ft air tank to top of the FX Compact Impact until it gets down and then I use the GX GS3 to top the bottle back off. I’m really pleased with how this has worked out.

2/2/2021 Update: The compressor is still working great. No problems at all!

2/4/2023 Update: Still working just fine!

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at info@roninsgrips.com. Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Here are some well rated hand pumps on Amazon. While I do not have personal experience with them, they do get good reviews: