SpudFiles

Xamllew wrote:I didn't know that about HPA, thanks for the info.

Gas density has a lot to do with performance, see the velocities that some people have obtained filling their PCP airguns with Helium instead of HPA.

jackssmirkingrevenge wrote:

Xamllew wrote:I didn't know that about HPA, thanks for the info.

Gas density has a lot to do with performance, see the velocities that some people have obtained filling their PCP airguns with Helium instead of HPA.

Speed increases with lower gas density? Is this what you explain?
I ask because I have noticed that at approximately the same air pressure used to fire the same ammunition, with the same firing barrel, when the air is less dense because it is hot, (in a hybrid), the ammunition shoots out faster, than using air at normal temperature ...

hectmarr wrote:

jackssmirkingrevenge wrote:

Xamllew wrote:I didn't know that about HPA, thanks for the info.

Gas density has a lot to do with performance, see the velocities that some people have obtained filling their PCP airguns with Helium instead of HPA.

Speed increases with lower gas density? Is this what you explain?
I ask because I have noticed that at approximately the same air pressure used to fire the same ammunition, with the same firing barrel, when the air is less dense because it is hot, (in a hybrid), the ammunition shoots out faster, than using air at normal temperature ...

Hotter gases move faster because they have increased kinetic energy from the heat (hot gases also have higher pressures as seen in P1/T1=P2/V2).

As for the difference between CO2 and HPA: CO2 has a molar weight of about 44 g/mol while air has an approximate molar weight of the average atmospheric air is only 28.97 g/mol.
With these weights into account, basic physics formulas such as m1v1=m2v2 or KE=1/2mv^2 will show that the lighter particles will move faster (which means better flow).


This being said, I still love CO2 for it's availability without needing a pump.

I get it. Thanks for the explanation.

*Grumble*

It seems the check valve in HEAL's trigger group is leaking air back through it. (Again rather vindicating my decision to incorporate redundant safety features - this isn't the first time a check valve has failed on me, although last time was a little more spectacular, as the valve actually split open).

In fairness, it is a hydraulic valve (I upgraded to something more butch after the last one gave up), so not really intended for the low pressures and viscosity of air, but the odd thing is that it's sealed well before. Disassembling it, it looks like it's relying on a metal-metal seal, but I think I should be able to introduce some sort of gasket to get it to seal properly for pneumatic operation.

Is it a ball bearing to seat or spool valve design type of check valve? Most pneumatic check valve designs are reeds type that I've seen.

jrrdw wrote:Is it a ball bearing to seat or spool valve design type of check valve? Most pneumatic check valve designs are reeds type that I've seen.

Of those, "ball bearing to seat" is the closest description to both the current valve and the one before, although it's actually a tapered cone.

I can't remember having seen any reed type check valves in what I've used in the past, although I have to admit that's been an eclectic mix of mains water, pneumatic and hydraulic valves.

Do you think that the screw clamp might be putting just enough side pressure to cause the damage under the conditions during firing? Maybe some shimming in between the valve and tubing above.

jrrdw wrote:Do you think that the screw clamp might be putting just enough side pressure to cause the damage under the conditions during firing?

It's been some years since HEAL was configured that way. These days, everything is mounted in a wooden stock:


In any case, I'm sure it's not damage to the valve, as I replaced it with an identical spare I had, which immediately started doing the same thing. The mystery seems to be more why the first one sealed well before, not why it started leaking.

Do you have a data sheet on that valve? Use it for comparison to what you now have. Did you save the recently replaced valve for studying?

Does the valve use a spring to help close it? Spring fail? Lubrication?

It's my guess the hardened steel ball bearing is beating up the seat it rides in to close the valve. Causing distortion of the sealing area.

jrrdw wrote:Do you have a data sheet on that valve? Use it for comparison to what you now have. Did you save the recently replaced valve for studying?

I've certainly still got the one I removed a couple of days ago, but there's nothing visibly wrong with it (although the sealing face is very hard to inspect, as it's deep within the valve).

Does the valve use a spring to help close it? Spring fail?

The spring is fine, as far as I can tell.

It's my guess the hardened steel ball bearing is beating up the seat it rides in to close the valve. Causing distortion of the sealing area.

If you mean during recoil, that's essentially out of the question. Apart from the fact it also happened with the completely unused spare, the recoil forces are less than 20G, which is a fraction of the pneumatic forces holding the valve closed.

If you mean during pressurisation, that also seems unlikely, as it's not like the pressure on the upstream side is suddenly dropping every time to let the valve slam home - it's really only a small spring pushing it back into place.

Well when it's something like this a good squirt of carb cleaner and some forced air just might fix things right up. A good cleaning never hurts.

Playing with the BFG removable magazine a bit more, this bit seems to work nicely

Have they really got something new Lightspeed™ valve

https://www.umarexusa.com/blogs/airgun- ... -air-rifle

[youtube][/youtube]

farcticox1 wrote:Have they really got something new Lightspeed™ valve

There's speculation that it uses this system.