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MikeSD · Member

Updated to correct typo. Pressure in scuba tank is 3300 psi (230 bar).

I have a 3300 PSI tank. When it's filled, they actually put about 10% more in it.

My question is twofold.

1) I have a fill tube and guage, that maxes out at 3000 psi + some redline area.

Does that present a safety risk? When I open the valve, it can go to 3300 psi on the tank end but I manage the valve so that I only put just under 3000 psi in the pistol. Is that safe or should I invest in another fill adapter?

I just don't know if the 3000 psi on the fill adapter is the maximum the tube and guage can take.

2) When I fill my pistol, I can't get it to actually reach 3000 psi. Even if the guage on the tank is reading well over 3000psi. Is there some limitation in the gun that prevents overfilling. Or might the guage just be off. Even if the tank is wide open, the gun won't go into the red area. Seems odd. The pistol functions fine and has good power and holds the fill very well (no leaks).

Thanks,
Mike

rsterne · Moderator

If you have one gauge reading low, particularly if it's the small one on the gun, go by the higher one for safety....

If you "manage" your fills so that you don't go above the recommended fill pressure of your guns you will be OK.... IF, on the other hand, your hand slips and you dump the full SCUBA pressure into your gun you may experience valve lock, or at least very low velocities for the first few shots....

All HPA devices have a MSWP (maximum safe working pressure) that you should never exceed.... If you do, however, and if the device is properly constructed, you should be OK with slight overfills.... ie it shouldn't blow up on you.... This doesn't mean it's a good idea, it just means that if things are properly constructed you should have a safety margin.... SCUBA tanks, for example, are tested (by law) to 5/3 of their MSWP....

Bob

MikeSD · Member

Updated to correct typo. Tank is 3300 psi, but problem is the same.

When I first filled the gun, about 6 fills ago, it would easily reach 3000, according to the guage on the pistol. It's been filled about 6 times now.

The tank is an 80cu ft. steel tank that was filled to 3300 psi.

Now the pistol won't reach 2900 psi, no matter how long I let air it fill, or how slowly, or regardless of the 2nd guage reading (it reads over 3000 psi.

If my tank pressure was down to 2900 psi, I could understand this. But the tank should be capable of more than 6 fills, before dropping to 2900 psi. And even if it was the tank pressure, it would then require something also to be wrong with my fill guage, since it's still reading over 3400 psi.

It's just odd that I can no longer get my pistol to refill to 2900-3000 psi. I guess one way of verifying part of this is to take my tank in for a refill, and have them check the pressure, to be sure. But my calculations said from an 80cu-ft tank, at 3300 psi, I could get over 100 fills. hmmm.

ellerja · Member

if your tank has a pressure of 3000 and your putting it directly into your gun then one of the gauges has a wrong pressure reading if using a regulator then it maybe a reg problem.i am a certified diver and havent seen to many steel tanks that are rated above 2600 unless there HP steel tanks.make sure your tanks have a current hydro inspection on them.jacking up steel tanks often can be a bad idea.and there not cheap either.hope this helps.

MikeSD · Member

I made a typo. It should be 3300 psi (230 bars). But the problem is the same. I'm reading well over 3000 psi on the one guage but maximum on the pistol guage. I cannot reach 2900 psi now. I'll go back and update my original question, to show I meant 3300 psi.

I bought the tank at a scuba shop and they put the inspection sticker on it and said they can only fill it, if the sticker is current. So the inspection is current and the tank filled to maximum of 3300psi. But the problem is the same.

I guess I'll have to take the tank back and verify the current pressure reading. I have no way to know which guage is incorrect or if either is wrong. I only know they are different. Regardless, the pressure guages measure two different values. There is no regulator. I control the fill by opening the valve only a small amount, until the pressure on the gun is the desired value (actually I can't reach 2900 psi). To do this, the guage on the fill adapter is over 3000 psi. Those who fill PCP guns should be able to tell me if it's normal that the guages read different values, during the fill.

The fill adapter has a guage where it clamps to the K valve. There is also a small guage on the pistol. I used an online calculator to determine the number of fills. It indicated that with this size tank and pressure I could get over 120 fills, to 2900 psi. I've only filled the gun about 10 times now. I would expect the tank to still be well over 3000 psi, which is what is being displayed on the guage on the fill adapter clamp. So the guage on the clamp reads what I would expect.

The problem is, if I just go by the clamp guage, the pistol will be well below the 2900 on it's guage, when the clamp guage is held at 3000. BTW, the pistol initially would easily reach the 3000 psi. And both guages read different values, from the initial fill. The pistol guage always lagged the guage on the fill clamp.

This is very strange behavior, especially since the gun seems to work fine. I guess I can chrono some pellets and see where I stand. But this is frustrating, since this is the 2nd pistol I have had. The first did the same thing (i.e. guages didn't match) but would easily get to 3000 (albeit not at the same rate as the guage on the clamp). The problem with the first pistol was that it leaked and had to be returned. This one doesn't leak and hold a full charge. And seems to have good power. It's just that I can't get it to fill past a little over 2800psi, according to it's guage.

Let me ask this of those who have this pistol. When you fill the gun, is the pistol guage always in sync during the fill process, with the guage on the fill adapter clamp?

SMP · Silver Status Member

Mike what your seeing is normal. Neither of those gauges are certified calibrated gauges and therefore they are both only representative.

I would suspect that the gauge on the pistol is reading very low and when you filled it to a representative 3000psi the actual pressure was 3200-3300psi.. I recently bought a couple of those Crosman PCP gauges and they were about $12. I guarantee that a that what you get for $12 is reference at best.

I work on board ships and we have hundreds of gauges and no two ever read exactly the same. Especially in the 200 Bar range. We install one certified gauge on critical systems and everything else is referenced against that.

If you need to know with guaranteed accuracy what your fill pressure is then install a calibrated gauge in the fill system and use that as the only reference. Marshall Instruments is a good place to purchase such a gauge. Beyond that you will have to remove the calibrated gauge once a year and take it to a certification lab for recalibration.

http://www.marshallinstruments.com/products/test-d.cfm

MikeSD · Member

Update

Found the source of all my problems. The reason I couldn't get the guns to fill to max, was because my tank was a bit low. After use, the pressure was only at 2900psi.

What confused me about this was my larger gauge (not the ones on the gun) was still reading 3300psi+. Since the tank was originally filled to 3600psi (3300 + 10%), I assumed that gauge was correct.

I was wrong

I took the tank to the shop to have them tell me the actual pressure, so I could compare it to my fill gauge on the clamp. They said it had only 2900 psi, which is all my guns would fill to.

So, my other problem was my fill tank gauge (Air Force Fill Adapter), was reading over 300psi high. I contacted the manufacturer and they sent me a new gauge. I replaced the gauge and all is now right with the world.

All three of my gauges (2 on the guns and 1 on the clamp) read approximately the same. Also, all my guns now hold air essentially indefinitely.

Now for some shooting Very Happy

I have built a 50' range downstairs in my house. My wife's not too happy about that but now I can shoot indoors. But, with spring coming, I guess I'll move to the outdoors and make her happy. Wink

Thanks to all who helped. Sorry it took so long to post the resolution to my problem.

radar · Silver Status Member

Hooray!