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high pressure valves

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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high pressure valves

Unread postAuthor: wngovr » Fri Sep 04, 2009 9:31 pm

I found a qev at McMaster-Carr that can handle 1200 psi. At 170.00$ I want to make my own valve. Can we make valves that can handle that kind of pressure with the information we have here on Spudfiles? Nitrogen tanks go to 4500 psi. I want to make an all metal launcher that can use extreme pressures. As far as I can tell, the valves are the limiting factor. So what is nessesary to make a 2000 or 3000 psi barrel piston, or quick dump valve? 1/4 inch o'rings? Is it even possible? What is the highest pressure I can expect to use with a quality made valve?
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Unread postAuthor: btrettel » Fri Sep 04, 2009 9:58 pm

"Can we make valves that can handle that kind of pressure with the information we have here on Spudfiles?": To the best of my knowledge, very little details about high (3000+ psi) pressure design are available here. Pressure ratings depend on far too many factors to make any general rules so I'll say some general things...

There basically is no limit to pressure rating. Given thick enough material you can contain essentially any pressure differential.

To understand how to make high pressure valves you basically need a good background in solid mechanics, in particular, pressure vessels and seals. I know the basics (being an undergraduate mechanical engineer) but I lack experience with valve design in practice. I'll give some suggestions you should find helpful, however.

Here's a good introductory website for design with seals: http://www.applerubber.com/sdg/guide2/index.cfm

As for the stress in the metal parts of the valve, any good CAD program will also include some FEA software (finite element analysis--basically breaking up the model into parts and looking at the stress in each individual part). This will allow you to simulate the effects of pressure on the material and see what works and what doesn't.

Below is a screenshot from Moonbogg showing what FEA does (from the design of his excellent Cobra Venom). Note the red areas--those are areas of higher stress.

Image

A "safety factor" of 2.5 is a good start for pressurized components. A safety factor is how many times the failure stress (yield stress generally for us) is higher than the maximum operating stress. If possible, shoot for a SF of 5 or higher.

Generally, the smaller the valve, for the same thickness of material, means the valve can handle higher pressures. The reason is surface area--larger surface areas have more force applied to them because the force of a pressure differential is the area of application multiplied by the pressure differential. Circular tubes and spheres can hold significantly more pressure than rectangular cross sections as well. This is due both to surface area and the problems the sharp corners introduce.
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Unread postAuthor: Hotwired » Fri Sep 04, 2009 10:01 pm

Very good seals and thick walled metal.

The pressure is limited by just your design, materials and engineering knowledge and of course your abilities to manufacture it.

Why would you want to make a piston valve at that pressure? Seals would be a menace and it would still need a high pressure valve to pilot it.
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Unread postAuthor: jor2daje » Fri Sep 04, 2009 10:32 pm

I'd check out gippeto's high pressure co-axial I think he says its capable of EDIT: 3000 psi (haha thanks inonickname) Its a good example of a high pressure valve, and after seeing your machining skills on your last gun I'm sure you could produce something similar.
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Last edited by jor2daje on Fri Sep 04, 2009 10:40 pm, edited 1 time in total.
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Unread postAuthor: inonickname » Fri Sep 04, 2009 10:37 pm

Jor, it was "go past 9000 and it will probably explode". The intended operating pressure was around 3000, for a safety factor of 3.

Just up your materials until it works. As for sealing faces, look into "hard" faces such as teflon or nitrile.
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Unread postAuthor: POLAND_SPUD » Sat Sep 05, 2009 1:35 am

I found a qev at McMaster-Carr that can handle 1200 psi.
could you provide a link?? I couldn't find it

for a start it would be a good idea to use that QEV because that would really make things much easier.... for pilot valve you could use a hp ball valve...

add to that a couple of hydraulic fittings or HP air fittings and an air reservoir rated that high

sure it wouldn't be cheap but definitely easier and cheaper than building one from custom parts
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Unread postAuthor: wngovr » Sat Sep 05, 2009 9:19 am

Thanks for the links and suggestions guys. I'll do my home work.

Hotwired, I'm not very familiar with fabricated valves. which valve (s) would you suggest? I just figured a piston valve looked relatively simple to build and easy to beef up, and a quick dump valve illuminates the need for a pilot valve.

POLAND_SPUD Here's the part no. for the qev at McMaster-Carr

49895K32 .

The mod for this valve would require some thought and fabrication. another reason I thought I would fabricate my own valve.
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Unread postAuthor: POLAND_SPUD » Sat Sep 05, 2009 1:19 pm

ohh that explains a lot... 49895K32 is not a qev
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Unread postAuthor: Brian the brain » Sat Sep 05, 2009 3:42 pm

and a quick dump valve illuminates the need for a pilot valve.

eliminate is what you meant right?

At higher pressures O-rings do not suffice.
You appearantly need V-rings ( or so I have been told)

Now..as tempting as a 3000 psi gun seems...What would you need it for?

Most likely, small caliber.
I can't imagine a 2" cannon at 3000 psi.

This is what 300 psi does in a 2" porting piston valve cannon shooting a light 250 gram projectile:
http://www.youtube.com/watch?v=X0SOzNTsZPo

the guy weighs a good 220 pounds and he almost lost his footing.
It's my cannon and this video is about as far as I dare to go when it comes to force..

Now imagine 10x the pressure...


The true question is, why need 3000 psi.Even for small bore, since it prooves to be very difficult to exceed Mach 1, the only way up in power seems to be : a heavier projectile.
And this again means a LOT of kick.

Unless you just want big cannon results out of a very short one, I don;t see the need for any pressure over 1000 psi...
S.O.S and recoil kinda set the limit...
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Unread postAuthor: THUNDERLORD » Sat Sep 05, 2009 5:08 pm

...and recoil ...


Recoiless design??? :roll: 8)
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Unread postAuthor: POLAND_SPUD » Sat Sep 05, 2009 6:05 pm

@btb
Igenerally I agree with you but sos is not such a big deal for some calibres.... imagine a gun shooting 1/2" lead balls (mass - about 12g)

I quickly GGDT'd it... with 100ccm chamber, 1.5 cm valve and 500 psi it could achieve about 150m/s... at 1000 psi 212m/s...

@THUNDERLORD
Recoiless design???

personally, I love recoil - it adds coolness factor to spudgunning... I am sure others think the same

:twisted:

but a muzzle break would be cool
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Unread postAuthor: Hotwired » Sat Sep 05, 2009 6:31 pm

Wngovr I'd point you towards a hammer valve and possibly multiple shots. They're more economical with gas and have a mechanical opening system.

The one seal required for a hammer valve is simpler than the dual seals of chamber sealing/floating spool (Tech's QDV) pistons and is more practical to make suitable for extreme pressure than the seal of a barrel sealing piston.

As for being able to avoid a pneumatic piloting system, well it goes without saying that it would be cheaper and simpler, the less moving parts while sealing against 3000psi+ the better.

In a hammer valve it's very difficult for the seal to go wrong as it's simply compression and if it does it can only allow gas to escape through the break in the seal. The valve will still be held "shut" by chamber pressure and will be heavily restricting flow even with a weakened seal, it can't fire by accident.

Things can be more interesting with dual sealing valves as one of the seals failing can cause the piloting of the piston. Even a floating spool valve which you don't think of as a piloted valve will still be piloted if it gains pressure on one side.

O-rings crossing the valve ports are another issue, firstly they can be damaged as they expand from and then get compressed back into their slots by passing the port another thing is they can be physically blown out of the cannon with the air blast going past them.

It's just a whole lot simpler with hammers ^^

Having said that. The avalauncher uses a positive pressure piloting system for its floating spool valve and runs off HPA so if you're up to the machining it has been done.
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Unread postAuthor: maverik94 » Sun Sep 06, 2009 8:35 am

If it's single shot you want, just make your own piston valve (I'd suggest barrel-sealing), you can build them to go up to VERY high pressures.
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Unread postAuthor: daccel » Sun Sep 06, 2009 10:38 am

To add to BTB's note about o-rings not working, I was looking at the piston for an airless paint sprayer a while ago, which operates at around 3,000 psi and it indeed used v-rings made out of some kind of plastic. Interestingly it had square leather rings as well.

But I was under the impression that hydraulics that operate at high pressures did use o-rings, maybe it's different with a thicker fluid. Can anyone clear that up?
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Unread postAuthor: wngovr » Sun Sep 06, 2009 11:35 am

Brian the brain,

Now..as tempting as a 3000 psi gun seems...What would you need it for?


Thats a funny question. does anyone need a spudgun? Its all about power and damage, right? I shot the XM2 at 300 psi many times, then I went up to 400 psi. I noticed a definite improvement. Now I want MORE! The XM2 cant handle much more pressure, so if im going to build another launcher, I figured Id build one that can handle allot. Then I could find a happy spot for the pressure depending on the ammo I use. (40 cal.) My goal is 1000 F.P.S. or more.

Then again maybe thats not it. Maybe its the challenge of making a quality launcher that can handle those pressures.

B.T.W. Nice launcher. (Red Bull)

Hotwired,
Ill check into hammer valves, thanks.
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