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How much Pressure could this handle?

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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How much Pressure could this handle?

Unread postAuthor: Lockednloaded » Tue Oct 12, 2010 6:32 pm

I need an air ram that can handle very high pressures, but hydraulic ones and HP ones are way out of my budget. I am looking at 6498K141 on McMaster Carr, and it says it is rated to 250psi, but thats about the same rating as commercial QEVs that have been used up to 700 psi. The cylinders are made from Type 304 Stainless steel, and seem to be of solid construction. I would like to keep a good safety margin, but I also don't want to be limited to 250 psi.
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Unread postAuthor: saefroch » Tue Oct 12, 2010 6:48 pm

Define "very high pressures." For any normally discussed pressure, that air ram can probably take it.
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Unread postAuthor: POLAND_SPUD » Tue Oct 12, 2010 6:53 pm

well you can use a pressure reducing fitting that I posted once... that should work just fine. The ones I have only bring pressure down by 8 bar but that's better than nothing
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Unread postAuthor: Technician1002 » Tue Oct 12, 2010 7:01 pm

High pressure air rams are not common due to the volume of air consumed due to compression. Safety is another factor. Stored energy is too high to be safe when there is a failure. Go non compressible hydraulic for high pressure.

Air over oil is sometimes used.
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Unread postAuthor: POLAND_SPUD » Tue Oct 12, 2010 7:09 pm

I think he wants to build a semiautomatic gun based on QEV + 3 way + air cylinder combo. Sure... he could use hydraulic cylinders but it's easier and cheaper two use a seperate low pressure circuit for controlling the air cylinder (either with the use of a 5 way valve not a 3 way valve or directly with the use of a pressure reducing fitting)
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Unread postAuthor: Lockednloaded » Tue Oct 12, 2010 8:44 pm

I'm thinking in upwards of 500 psi. How much do those pressure reducing things run? and could I make one myself?
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Unread postAuthor: lozz08 » Tue Oct 12, 2010 8:53 pm

POLAND_SPUD are you saying there is a fitting available that acts like a pressure regulator? Reduces pressure downstream? How?
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Unread postAuthor: Ragnarok » Wed Oct 13, 2010 8:54 am

Are you just going with an air cylinder coupled straight to the chamber to run an auto loader? If so, I wouldn't recommend running the cylinder at full pressure for that.

One, it'll probably be so powerful as to damage the mechanism.
Two, it's a completely unnecessary waste of air.

I cooked up something a while ago that was intended to regulate down pressure for HEAL 2's loading mechanism, but I later switched to a pump action design, so have no real use for the plans now.

It was basically a combination of regulator, check valve and pop-off - regulating the chamber pressure down to 3 bar (or whatever you choose - I elected for a lower pressure and a higher diameter ram to allow it to cycle even at low power) with a vent for any over pressure and allowing the cylinder pressure to flow back through once the chamber had fired.
It can be built with reasonably basic tools and parts if you're careful enough.

Unfortunately, I don't think I ever put the plans for it down on paper and as I'm busy with work at the moment, it's going to take at least a few days before I can spare the time to draw them.
If you're not interested or find some other solution before then, fair enough.
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Unread postAuthor: POLAND_SPUD » Wed Oct 13, 2010 9:31 am

@lozz08
POLAND_SPUD are you saying there is a fitting available that acts like a pressure regulator? Reduces pressure downstream? How?
Of course there are fittings like that. I was reffering to push-to-connect fittings but there are all threaded versions as well. The best thing about them is that they reduce the pressure but also allow you to vent the air cylinder or anything else you've got hooked up to it

I found the ones I posted on SF -> http://www.spudfiles.com/forums/viewtop ... tml#279388
You can find them using google too.

Unfortunatelly, most of this stuff is rated to standrad pneumatic pressure (that is 10 bar maybe up to 20 bar). There are verions rated higher but they are pretty difficult to find.
The good news is that most of the standard ones can fit inside 1/2" or 3/4" iron fittings - so you can do that if you are worried about their rating.

Of course you can build your own fitting that works like that.
Technically these things act like a shrader valve when you don't depress its stem while pumping. It will reduce the pressure of the gas by X psi.

So get a shrader valve and epoxy it in a fitting. Add a check valve (again it can be a shrader valve but with the spring removed and inserted the other way round) that will allow venting the other side when the pressure there is higher than on the inlet side and........ voila! it works in the same way

(it would be best if you could replace the stock spring in a shrader with a stronger one - for obvious reasons)
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Last edited by POLAND_SPUD on Wed Oct 13, 2010 9:32 am, edited 1 time in total.
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Unread postAuthor: Lockednloaded » Wed Oct 13, 2010 9:32 am

Well in my particular case, the air cylinder would be the bulk of the chamber, so not much air is being wasted on loading.

Also, this cylinder could be put to use on a low mix hybrid if I can trust that it will handle pressure. This may sound rather abusive for an air cylinder, but the ignition will not be slamming the piston forward, it will already be extended at preignition pressure
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