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Pcp hammer valve, max allowable pressure

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Pcp hammer valve, max allowable pressure

Unread postAuthor: Tasmaniac » Sat Mar 10, 2018 4:30 am

G'day boys, first time poster long time reader of this sweet forum. Im in the process of building a pcp hammer valved, rifled barreled .22 cal repeating airgun. I am building my valve with 1/2 bsp threaded nipple (150psi rated) around 80mm long with 2x20mm sockets that screw up the nipple adding around 3mm wall thickness all epoxy resin'ed into place, they are galvanised steel by a company called kinetic. They are rated to 150psi max working pressure but i think they would be capable of alot more. Im no pneumatic engineer but my abs or pvc sprinkler valve gun does 150psi no worries (140 psi rated) i plan on leaving around 20mm of exposed brass nipple on each end for securing to cylinder and hammer tube. I plan on filling the 1/2 nipple with an oxy torch and brazing rod drilling the valve stem hole and chamfering the valve seat at around 45°. Would this method be safe to hold 1000psi? I am worries of thread stripping on the brass tails mainly or the nugget of solder to simply fly out with 1000 pounds on one end of it. Cheers dudes!
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Re: Pcp hammer valve, max allowable pressure

Unread postAuthor: Gippeto » Sun Mar 11, 2018 2:41 pm

Large blocks of type are annoying as frig. :roll:

Break out the paper and pencil..(or paint...or cad if you have it) and draw it to scale or reasonably close. Post that...clarity is everything.

Can look into Barlows formula to help determine pressure ratings of tubing. There are thin and thick wall variations...using the thick wall variation is more conservative, but doesn't make for much of a weight penalty in a shoulder fired size.

Personal preference is a MINIMUM designed safety factor at MWP of 3x using yield strength. If that requires clarification... for a pcp build that will see 1000psi fills, the WEAKEST point in the system should not suffer a yield failure until 3000psi or more.

Tapered valve seats will be more challenging to seal than a flat valve seat...even if you have machine tools. They also have a tendency to "wedge" themselves closed (assuming they seal in the first place), requiring heavier hits to pop them open.

Draftsight is a good FREE 2D cad program...I use it for construction drawings.

https://www.3ds.com/products-services/d ... -download/
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