TargetTalk

I'm a newbie to compressed airguns and noticed that when I fill my air cylinder it becomes warm. I'm sure there is some rational scientific explanation for this, however I'm curious because it becomes noticeable.

If this is normal, could the heat effect shot dispersion if you fill and shoot right away. Your thoughts and knowledge of this will greatly be appreciated.

Thanks,

Peter.

Yes it is normal for the AP cylinder to get warm as you fill it and feel warm for a minute or so after you fill it. I have not noticed any affect on the pellets and there should be none. What you will notice is that if you fill your cylinder in a warm room and then take it somewhere where it gets chilled the pressure will go down. Also if you have to take your scuba tank in for a refill and they have to do the visual inspection on it, they will have to drain all the air and as the air comes out of the tank the tank gets very cold. They cannot do it quickly because of this so if there is significant air left in the tank when your tank is due for inspection, drain it at home. I had to take mine in to be refilled yesterday for the first time. I had shot for over six months on one fill but the tank was getting so that it only filled the AP cylinder about a third of the way into the green. When I took the 3000psi scuba tank in, it still had about 2000psi in it and the scuba guy said that if the cylinder was high pressure that would be at about the point where it would not fully fill the AP cylinder. Isabel

If you fill the small cylinder too fast it will heat up. This can be bad for the seals. You should crack the valve slightly, letting in a little air, then shut it off, Repeat as necessary until filled, keeping heat down in the gun cylinder. Gasses heat up when going through a venturi (restriction) and when being pressurized (that's why you don't dry fire springer type airguns), while they cool when being depressurized (per the prior poster).

Thanks for all the great replies. They were very informative. Just to clarify, I have a compressed air rifle and those cylinders are larger than the air pistol cylinders.

I will open the valve slowly and only allow a small amount of air to be exchanged into the cylinder at intervals as you suggested. However, will there be a time where the pressure in the tank will equal the pressure in the cylinder? If so, prior to closing the valve, would it be beneficial to completely open it, then close it?

Thanks again!

Peter

Please, Guest, don't make this more complicated than it has to be. The following is my recollection of Don Nygord's instructions when I bought my K2s from him. Crack the tank valve ever so slightly, so that you get minimal air flow into your cylinder. After a few seconds when the cylinder has filled (you can't hear the air moving), open the valve wide; at this point the cylinder should be slightly warm to the touch. Leave the cylinder on the tank for a few minutes while temperatures equalize.

Don't forget to shut the valve before removing the cylinder. I did once and was amazed at how far it blew my papers around the room.

PV=nRT forever!

william wrote:After a few seconds when the cylinder has filled (you can't hear the air moving), open the valve wide;

Do not open the valve wide.

Unless the pressure in your tank has fallen to the pressure you want in the cylinder you will over-fill the cylinder.

Open the valve a little until either you can't hear the air moving or you reach the desired pressure in your cylinder. If you still need more of a fill then open it a lttle bit more. Keep doing this until you reach the desired fill pressure. When the tank is approaching needing a refill you might land up with the valve fully open, but you should not include fully opening it as part of your normal procedure.

william wrote:Please, Guest, don't make this more complicated than it has to be. The following is my recollection of Don Nygord's instructions when I bought my K2s from him. Crack the tank valve ever so slightly, so that you get minimal air flow into your cylinder. After a few seconds when the cylinder has filled (you can't hear the air moving), open the valve wide; at this point the cylinder should be slightly warm to the touch. Leave the cylinder on the tank for a few minutes while temperatures equalize.

Don't forget to shut the valve before removing the cylinder. I did once and was amazed at how far it blew my papers around the room.

PV=nRT forever!

Yes the cylinders get a little warm. I have been using the technique that William posted for the 5 or so years that I've owned my Morini 162EI. Most times I hear a little squeal when I reach a certain point when opening the valve and I use that as a warning that I'm opening the valve too quickly. I open the valve wide open at the end of the fill. I haven't experienced any problems.

Misny wrote:I open the valve wide open at the end of the fill. I haven't experienced any problems.

What pressure do you have in your tank and what pressure to you end up with in your cylinder.

Are you filling through a pressure regulator?

Take note of what David says
If you are filling the Rifle cylinder from a 3000psi cylinder into a 2000psi rifle cylinder,without a pressure regulator fitted,if you open the valve wide open you will cause the rifle cylinder to be over pressurized.

Hello,

Thanks again for all the replies! I am using a Scuba tank with a 200 Bar valve. According to the scuba shop, the tank is filled to 3000psi, 200bar. I am using a 200bar cylinder. The only device between my Scuba tank valve and the tank is the adapter the manufacturer provided.

Peter.

Guest. wrote:According to the scuba shop, the tank is filled to 3000psi, 200bar. I am using a 200bar cylinder.

If you are only getting the tank filled to 200 bar then yes, you will be OK fully opening the valve at the end of a slow fill.

Here in the UK we tend to get tanks filled a bit higher, letting us get more cylinder fills between tank fills.

I have a 15 litre 300bar cylinder and a 9 litre 232 bar cylinder, both fitted with 232 bar DIN valves. I get then both filled to 230 bar. Fully opening the valve after a tank refill would over-pressurise the cylinder. Even worse would be a 300 bar cylinder with a 300 bar valve (although a special adaptor would be needed to fill a Morini cylinder)

David, in the US, it is very rare to find 300 bar air. 200 bar is the norm.

Getting rarer in Australia as well - still available, but a number of dive shops no longer fill above 230bar

Yup ... not just normal ..... it's the LAW!

PV=nRT forever indeed!

jhmartin wrote:Yup ... not just normal ..... it's the LAW!

Goodness; they trust you with pistols but not with air.

Do you want to swap ;-)

David, it's OK. In an ideal world we can be trusted with ideal gas. ;-)

Misny wrote:

william wrote:Please, Guest, don't make this more complicated than it has to be. The following is my recollection of Don Nygord's instructions when I bought my K2s from him. Crack the tank valve ever so slightly, so that you get minimal air flow into your cylinder. After a few seconds when the cylinder has filled (you can't hear the air moving), open the valve wide; at this point the cylinder should be slightly warm to the touch. Leave the cylinder on the tank for a few minutes while temperatures equalize.

Don't forget to shut the valve before removing the cylinder. I did once and was amazed at how far it blew my papers around the room.

PV=nRT forever!

Yes the cylinders get a little warm. I have been using the technique that William posted for the 5 or so years that I've owned my Morini 162EI. Most times I hear a little squeal when I reach a certain point when opening the valve and I use that as a warning that I'm opening the valve too quickly. I open the valve wide open at the end of the fill. I haven't experienced any problems.

Could you clarify that on the 162EI fill? You mentioned you wide open the valve at the end of the fill. I just refilled my 162EI for the first time since I bought it, and both tubes started releasing air at the connection to the fill probe when the guage needle got close to the red zone. Actually one cyclinder only got about 80% of the way to the red zone, the other went about 90%. I thought it was a safety release, but your post seem to imply yours do not do this as otherwise there'd be no point in opening the valve wide open at the end, unless your SCUBA tank pressure is much lower than 2900psi.

BobRI wrote:I just refilled my 162EI for the first time since I bought it, and both tubes started releasing air at the connection to the fill probe when the guage needle got close to the red zone.

I've never heard of that. Unless this is some modification they have made to the latest cylinders, I think you have a problem.

I allways fill my 162EI cylinders to the green/red line and have never had them releasing air.

Thanks David I'll have to look into that, strange that it doesn't happen until the tubes are almost to the red before it happens, and no leaks after I shut off the SCUBA valve, and two tubes are unlikely to have the same issue.

A-h-h-h-h yes the Ideal Gas Equation---wonderful piece of fiction---but it works so don't knock it----"PV=nRT forever" "Doc"