Helium instead of HPA

Building or modifying BB, Airsoft, and Pellet type of guns. Show off your custom designs, find tips and other discussion. Target practice only!
Eljefe13
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Fri Dec 08, 2017 12:11 pm

Has anyone had experience with helium instead of HPA? My latest homemade air rifle was already performing pretty well with HPA (38 FPE).
Then I tried helium and it increased to 53 fpe!!!
Apart from the cost, are there any other down sides to using helium?
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jackssmirkingrevenge
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Fri Dec 08, 2017 3:26 pm

Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
Air2theBrain
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Fri Dec 08, 2017 3:54 pm

Any chance of a video with you speaking whilst shooting it? :lol:

http://www.spudfiles.com/pneumatic-cann ... 26691.html
Eljefe13
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Fri Dec 08, 2017 5:37 pm

jackssmirkingrevenge wrote:Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides ;)
Yes I already knew about it being more likely to leak compared to HPA but haven't had that problem yet, I made the valve stem out of hardened tool steel and delrin after many failed attempts using rubber o-rings.

I've also heard that it is less likely to create valve lock compared to HPA.
Also heard that it performs at a less efficient rate than HPA so it might turn out to be too expensive to continue with it.
Eljefe13
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Fri Dec 08, 2017 5:47 pm

Air2theBrain wrote:Any chance of a video with you speaking whilst shooting it? :lol:

http://www.spudfiles.com/pneumatic-cann ... 26691.html
Haven't got any videos yet but plan to do a couple in the near future, got a few pics though so I'll try and upload them.
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D_Hall
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Fri Dec 08, 2017 11:34 pm

jackssmirkingrevenge wrote:Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides ;)
OP,

In addition to what JSR said...

There are some advantages, to using helium... The smaller molecule means better flow under choked conditions. This means that if the performance of a gun is being dominated by the (lack of) performance of an undersized valve, helium can significantly improve performance as you noted.

HOWEVER....

Unless your gun is shooting near sonic conditions for the gas in question (ie, Mach 1 for air), this should not be an issue. If it *IS* an issue, it is a sign that your valve has been poorly designed. A better solution than using helium would be to redesign the valve.
Simulation geek (GGDT / HGDT) and designer of Vera.
Eljefe13
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Sat Dec 09, 2017 9:56 am

D_Hall wrote:
jackssmirkingrevenge wrote:Helium is a smaller molecule than Nitrogen or Carbon Dioxide and therefore often has problems with sealing system made for air, but aside from this, the cost and the dangers of a hilarious death if firing repeatedly in a confined space, no other downsides ;)
OP,

In addition to what JSR said...

There are some advantages, to using helium... The smaller molecule means better flow under choked conditions. This means that if the performance of a gun is being dominated by the (lack of) performance of an undersized valve, helium can significantly improve performance as you noted.

HOWEVER....

Unless your gun is shooting near sonic conditions for the gas in question (ie, Mach 1 for air), this should not be an issue. If it *IS* an issue, it is a sign that your valve has been poorly designed. A better solution than using helium would be to redesign the valve.
Cheers for the advice, yeah I get what you're saying but I'm pretty sure choking won't be a problem.
I've designed the valve and stem a bit large if anything so the only drawback would be decreased shot count.
Which is something I'll gladly give up in exchange for more power.
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D_Hall
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Sat Dec 09, 2017 5:52 pm

What are your muzzle velocities?
Simulation geek (GGDT / HGDT) and designer of Vera.
Eljefe13
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Sat Dec 09, 2017 9:27 pm

D_Hall wrote:What are your muzzle velocities?
At 2000 psi I'm getting 1150 fps.
Might try 2500 and then 3000 today and see how it goes.

Pic attached.
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Eljefe13
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Mon Dec 11, 2017 12:33 am

Best so far is 1198 fps for a total of 58 foot pounds @ 2500 psi from a .22 18.13gr pellet.

Groupings of half inch @ 25 metres.
Air2theBrain
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Mon Dec 11, 2017 1:58 am

Chrono pics please :)

How long is your barrel?
Eljefe13
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Mon Dec 11, 2017 3:10 am

Air2theBrain wrote:Chrono pics please :)

How long is your barrel?
Just got 1320 fps when shooting a 19.09gr pellet.
73.88 foot pounds.

24" barrel.
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Air2theBrain
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Mon Dec 11, 2017 5:20 am

Nice..so that fps was achieved with a 2000psi shot of air?
Eljefe13
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Mon Dec 11, 2017 1:54 pm

Air2theBrain wrote:Nice..so that fps was achieved with a 2000psi shot of air?
The gauge was sitting on about 2,200 psi of Helium.
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jackssmirkingrevenge
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Mon Dec 11, 2017 3:23 pm

That must make quite a crack! Interesting rifle build, I'm guessing it's a home made hammer valve?
hectmarr wrote:You have to make many weapons, because this field is long and short life
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