Using N2 with GX pump

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bchannell

bchannell

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Nov 1, 2020
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Parkersburg, WV USA
Ok, I made my maiden voyage of feeding N2, to the inlet of one of my CS2 pumps. I work on AC's and refrigeration all the time, so I had everything I needed to give it a go. I used 1/4" and 3/8" flare fittings so I could use refrigerant hoses. I also used a digital stubby gauge to measure pressure on the output of the regulator, simply because it's more precise than the output gauge on my N2 reg. I regulated it at around 6 psi, and had no bouncing to speak of. It did fill quite a bit faster than using air, because I have a rather large filter to pre fill., and without that inline, it zooms right in. The compressor sounded different too, much quieter and smoother, go figure. This was an initial test with my Challenger so I didn't go from empty or anything taxing, just a "proof on concept" run, but it worked so easily, I'm wondering why mess with using air and filters at all. I had 1000psi N2 in my cylinder and when I finished a top off of my Challenger, I couldn't tell it went down at all. The stubby gauge also gives me an inline valve to open the N2 and shut it off.
I started the N2 flowing, and set it at 6psi to atmosphere, then hooked everything up, and opened the outlet bleeder on the compressor, then started up.
Here's my procedure after setting the reg and hooking up the rifle.
1) with bleed open, start the compressor and open the N2 valve at the same time
2) close the bleed and fill the rifle
3) when finished filling, open the bleed, then shut off the compressor, and close the N2 valve at the same time
4) shut N2 cyl and bleed the minimal pressure in the inlet

On my first run, I also adjusted the reg while filling to maintain 6psi, it never dipped to zero, but it's a digital gauge, so I may try an analog next time, but I don't think it's necessary.
I've never had a moisture problem at all, I've opened most, if not all of my guns, and not a trace of damage. BUT, i use a large filter and lots of desicant and cotton filters, so it's a concern and a hassle. If I decide to go N2, then all I need is a bottle of N2 (which I always have a few) by my bench and leave it hooked to my pump, and no having to wait to pre fill my large filter. Thus the speed increase I saw in filling my rifle.

I really doubt it's all that necessary, but hey, it's 100% dry and no doubts, I may keep using it for a while and see which way is easier.
 
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Just inquisitive here. I’m pretty sure you keep yourself aware of N2 tank pressure so that you don’t run the tank dry. Having worked with sophisticated systems for manufacturing systems for a number of years we learned NEVER to trust a human for monitoring something that can go bad if they’re distracted. If I were going to add an N2 supply to my compressor, I would add a duckbill style or similar one way valve so that IF the N2 was interupted the compressor would not start pulling a vacuum. But that’s just me.
Whenever I run my manual shut off Alkin I sit there with a timer for water draining, hearing guards and a chair and don’t get up till the session is over. The only other thing I could add are handcuffs or a seat cut out switch that shuts it down if I stand up. Fortunately my refill sessions are only about five minutes, which is one minute short of my attention span. 😳😜
 
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I'm not too worried about it going into a vacuum. I have some pretty reliable regulators we use for a/c purging/pressurizing etc. I don't use N2 on my CX3 with auto shutoff, that does seem like a recipe for disaster. I only use it on my manual CX2, and I'm there watching it all the time. I too worked in industry where we used all kinds of compressed gasses and chemicals, so I'm aware of what I'm doing, but it never hurts to be reminded of safety.
I just filled my Katran for the first time, (only the second time trying N2) and everything went smoothly. I bumped the inlet pressure to 12psi, and it all went without a hitch. It now fills so quickly I don't have much time to be bored. I'm used to work where we had to watch critical things or there could have been a disaster, so I'm fairly vigilant.
I have to admit, on my CX3, I use it in manual mode more often than depending on the auto shutoff, although I trust it to shut down. I still only use it when I'm right there close by and I've learned when it should shut off, so if it doesn't I'm on it. I also rarely fill to max pressure on any gun, unless I'm testing something, so I have that bit of extra safety margin. If I think there's a need to fill to max, you can bet i'm right there looking at the gauge.
Thanks for the great info.
 
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elwoodblues said:
No oxidizers no water no C02 no enviromental contaminates no Detonation in pumps or guns and its a smaller molecule so faster pellet speed (a little)
Click to expand...
I know you've done a lot of work on this, so can you give me some idea how you arrived at the pressure/flow rates?

I tried 6 psi on my first run and it seemed fine. I used 12 psi on the second run and it too seemed fine. I use a very, very accurate digital a/c gauge on the outlet of the regulator/inlet to the GX to determine pressure as the N2 regulator gauge is just not accurate at that low pressure. I'm concerned that my digital gauge would not catch any blips going too low, but so far it just hovers around 11.5-12 psi or previously right on 6 psi. My thinking is to try an analog gauge and see if it moves much during filling.

I am in the process of reading all I can find, so if I missed a post about all this, please let me know.
I'd appreciate any guidance.

By the way, from my chem plant days, isn't N2 molecule larger than air molecules? That's one of the obscure reasons to fill tires with N2 as it leaks less being a larger molecule.
 
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No the nitrogen molecule is smaller o2 and co2 are both larger and heavier and no if want to seal a gas in your windows for example you use Argon as it is much heavier and larger but don't bother trying it in your gun it shoots slower. they use nitrogen in scope because its inert and has NO moisture. oh and its very cheap to make. same with tires no moisture and less temp sensitive because of that .
As to flow if you use a analog gauge and set low you will see it bounce a little I set it about 10psi and as it goes thru an 1/8 orifice that slows the flow rate down and still keeps the pump fed on my GX CS4 I went with a flowgauge type regulator and set it for 25cfh seemed about right as it takes about three hours to fill my 6.8 ltr aka 66cf bottle. Hope this helps in your quest.
 
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I misunderstood the molecule thing, sorry bout that, thanks for the info.
As to the flow, we're on the same page there, I ordered a n2 flow rotometer. I used to have one for purging a/c systems, but now we use a plain adjustable orifice and feed it 50psi N2, so there's no fussing with adjustment, just set and forget. It is calibrated, but I doubt it's very accurate since it's for purging line sets and to eliminate O2 in the line while brazing. I will take you flow suggestion and start there when it arrives. I just want to put a analog gauge on it to see fluctuations, as my digital, I'm sure, isn't fast enough to catch it, but the fact that it never zeros or even comes close to dropping, and runs so consistent is a good sign.

I really appreciate all the work and info you're provided, this is an interesting setup and I would love to dispense with filters and all that mess. I have a small table in the garage that I'm planning on setting up to hold a 40 ft3 bottle of N2 and the compressor, and I'll add permanent setup of flow gauge and pressure feeding the compressor. You're aware I'm sure, it sounds like a lot, but it's really nothing.

I'm trying to do some calculations on how long a 40 ft3 N2 cylinder would last filling guns at 3500psi, just to get an idea.
 
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One way to help think of the speed impact of feeding under pressure is to remember that atmospheric pressure is about 14.5 psi, although it varies and is less at altitude. Using that value, you are feeding it at about 20 psi net, or roughly 40% more gas than normal. That is where most of the speed increase is coming from.

While I don't recommend going nuts with the inlet pressure, the physics of it are such that feeding under pressure actually lowers the load on the compressor as the outlet pressure climbs. So you are doing really good by your compressor this way - shorter run time with lower load!
 
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delooper said:
Can't you just purchase nitrogen-filled tanks at the appropriate pressure, so that you don't need a compressor?
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As far as my area, N2 comes in only 2215psi cylinders of many different sizes. Anything significantly higher ie 6000psi, is VERY heavy, VERY costly, and in most areas, simply not available. I checked into it, and got the "are you crazy?" look. With a compressor and a 23" high 40 ft3 cylinder, I would expect to get many fills, even on my 480cc bottles.
Setup was relatively easy, a few hoses, fittings and a cheap N2 purge regulator, and you're all set.
 
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bchannell said:
As far as my area, N2 comes in only 2215psi cylinders of many different sizes. Anything significantly higher ie 6000psi, is VERY heavy, VERY costly, and in most areas, simply not available. I checked into it, and got the "are you crazy?" look. With a compressor and a 23" high 40 ft3 cylinder, I would expect to get many fills, even on my 480cc bottles.
Setup was relatively easy, a few hoses, fittings and a cheap N2 purge regulator, and you're all set.
Click to expand...
What is the demurrage charge per month/year ?
 
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A couple of things I've noticed from using N2.
1) I'm not sure it can be completely attributed to a shorter run time to fill guns due to no huge filter to fill first, but it seems to fill much faster. Thus, it does not heat up very much at all. I mean it's barely warm to the touch when I fill my Katran to 300bar. Since you're feeding your compressor a slight amount of pressure, it does help the compression ratio, so makes sense it fills faster and cooler, but seems so slight it wouldn't make the amount of difference I'm seeing.

2) The idea to use a N2 flow meter, for me, was a bust. I tried one and during the run cycle you can't get any useful flow info from the thing. The ball bounces from top to bottom. I can get useful info from a 0-30 psi gauge on the outlet of my regulator. I just adjust it so the swing is not hitting zero. For me, the no-flow setting of around 8-9 psi will give a swing of 5-10 psi when running. A setting of 7 psi static will swing from 2.5-7.5 psi when running.
 
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bchannell said:
A couple of things I've noticed from using N2.
1) I'm not sure it can be completely attributed to a shorter run time to fill guns due to no huge filter to fill first, but it seems to fill much faster. Thus, it does not heat up very much at all. I mean it's barely warm to the touch when I fill my Katran to 300bar. Since you're feeding your compressor a slight amount of pressure, it does help the compression ratio, so makes sense it fills faster and cooler, but seems so slight it wouldn't make the amount of difference I'm seeing.

2) The idea to use a N2 flow meter, for me, was a bust. I tried one and during the run cycle you can't get any useful flow info from the thing. The ball bounces from top to bottom. I can get useful info from a 0-30 psi gauge on the outlet of my regulator. I just adjust it so the swing is not hitting zero. For me, the no-flow setting of around 8-9 psi will give a swing of 5-10 psi when running. A setting of 7 psi static will swing from 2.5-7.5 psi when running.
Click to expand...
My only past use of flow meters has been on welders with a set specific flow which is unrestricted at the tig torch or mig gun.
In your case you have a suction going on which is cyclic. That is probably what’s causing the irregular reading.
I do recall one time tinkering with a flow meter where I would place my finger over the outlet of a flowing flow meter and the ball reacting (the ball drops because flow ceased). So when ever your compressor is in its compression cycle, the flow is temporarily stopped.
In a related post a year or so ago I posted a post that to assure an adequate flow rate on an N2 set up it would be helpful to have a partially inflated bag that needs to be at least partially inflated at all times while compressor is running.
An initial psi or flow rate could be set to see that the bag stays somewhat inflated.
Back in WWII bomber pilots wore O2 masks that had a latex bag that would inflate and partially deflate during breathing cycles. The user would adjust the flow so that O2 wasn’t being wasted. I’m thinking that design was used before reliable demand regulators were used.
The second photo is a first responder kind of mask we used when teaching scuba diving emergencies. Before putting mask on victim we turned on O2 to a recommended liters/hour, then we placed our finger over the outlet in the masks face piece which caused the bag to inflate. The first responder then took a breath or two out of the mask to assure the bag stayed inflated, then mask was placed on victim and first responder watched to make sure bag did not collapse from over inhalation.
First photo shows the latex bag.

IMG_0899.jpeg


IMG_0898.jpeg
 
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The whole bag idea is great, but it will keep the input at ambient pressure. If you want to maintain the advantages of feeding under added pressure but stabilize the input pressure some, I'd point out that you simply need to add a buffer of volume into the input line - that will reduce the pressure drop that is occurring on the intake stoke.

Maybe you could empty out and repurpose your output filters for this use? Or you could simply add more line between the regulator and the compressor. I'm sure you could find something to use . . .
 
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I'm wondering if thre's a real need to add anything. As long as the pressure never goes to zero, then you're feeding the compressor all it needs. Now, there is some sense to the theory that "adding" pressure will increase the speed of fills, but in all honesty, the speed is really good now.
However, having said that, I like the idea of adding the empty filter housing to the inlet, and stabilize the input pressure, which you could add just a bit more pressure to add even more speed if desired. I may try that, and it also might work with one of the smaller filter housings. Something to play with, but I don't want to complicate the process too much.
 
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