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Piston valve not sealing (Pictures)

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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Piston valve not sealing (Pictures)

Unread postAuthor: Matt_NZ » Thu Apr 15, 2010 5:18 am

This is my first spud gun (attempt) from stainless steel pipe fittings.
The piston is just simple hot glue housed inside a 3/4 tee have a look at the pictures and see if you have any theories as to why it won't seal.
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Attachments
M01A0202.JPG
Gun without barrel or chamber.
M01A0203.JPG
Piston, closeup.
M01A0204.JPG
Looking inside 3/4" tee
M01A0205.JPG
Piston inside hex nipple.
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 15, 2010 5:31 am

Diameter of the screw holding the rubber too big? Maybe it's hitting the seat. Love the 316 fittings btw, overkill FTW :D
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Unread postAuthor: Matt_NZ » Thu Apr 15, 2010 5:49 am

jackssmirkingrevenge wrote:Diameter of the screw holding the rubber too big? Maybe it's hitting the seat. Love the 316 fittings btw, overkill FTW :D


Yeah, they are beautiful fittings. (You wouldn't believe the price I got them for though *cough* staff price :shock: .)

Looking down barrel end it doesn't look like the screw is too big, any other ideas.
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Unread postAuthor: Crna Legija » Thu Apr 15, 2010 6:02 am

maby the screw is lose and air gets under the rubber then out the hole where the screw is try to glue the hole or tighten the screw
if that dosent work try to dump air into it.

what pressure are you going to use? max out those ss fittings
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Unread postAuthor: jackssmirkingrevenge » Thu Apr 15, 2010 6:06 am

As above, some araldite/JB weld between the screw/piston/face. At what pressure did you try it out?
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Unread postAuthor: boyntonstu » Thu Apr 15, 2010 11:53 am

The threads are leaking.

Been there, done it.

BTW Not using a machine screw is dangerous.


I suggest that you drill out the piston from the rear to within about 3/8" from the face large enough for a screw driver, use a screw, nut, thread sealer, and Teflon tape.

I fixed a leak this morning using the thread sealing method above.

Holds air at 600 psi.
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Unread postAuthor: FighterAce » Thu Apr 15, 2010 4:23 pm

Hot glue piston at 600 psi?
I'd say thats more dangerous then not using machine screws and nuts above 150psi.
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Unread postAuthor: Matt_NZ » Thu Apr 15, 2010 5:41 pm

Trail was done at 100psi. You've got me convinced that air probably is getting around the screw. BTW Hot glue piston is only going to be temporary, til i find some nylon.

The threads are leaking.


I hope not I put a crap load of Teflon tape on those joints, guess I'll have to test in water.

what pressure are you going to use? max out those ss fittings


I would like to use up to 500-600, however i was told my quick connect fittings would only hold 250psi.

Edit:
BTW Not using a machine screw is dangerous.


Ok, I understand what you mean now. Will definitely use machine screws when i build a nylon piston. For now, Hot glue piston at lower psi.
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Unread postAuthor: iknowmy3tables » Thu Apr 15, 2010 6:54 pm

are you sure it's the piston, how did you secure that barb that your using as a seat, is it secured and airtight?
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Unread postAuthor: Matt_NZ » Thu Apr 15, 2010 7:41 pm

iknowmy3tables wrote:are you sure it's the piston, how did you secure that barb that your using as a seat, is it secured and airtight?


Barb is screwed in with some Teflon tape, then nipple is screwed hard against it. Are piston valves meant to be so frustrating.
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Unread postAuthor: Gun Freak » Thu Apr 15, 2010 7:42 pm

Matt_NZ wrote:
iknowmy3tables wrote:are you sure it's the piston, how did you secure that barb that your using as a seat, is it secured and airtight?


Barb is screwed in with some Teflon tape, then nipple is screwed hard against it. Are piston valves meant to be so frustrating.


Haha apparently they don't like me either :P
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Unread postAuthor: jhalek90 » Thu Apr 15, 2010 7:53 pm

Just a small bit of help.

MY piston valve would not seal until i removed the screw holding the rubber gasket in place, and simply super glued the gasket on.

Its still on there, after 30-40 shots at 250-600 psi.

Ditch the screw, use some glue.
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Unread postAuthor: boyntonstu » Thu Apr 15, 2010 10:23 pm

jhalek90 wrote:Just a small bit of help.

MY piston valve would not seal until i removed the screw holding the rubber gasket in place, and simply super glued the gasket on.

Its still on there, after 30-40 shots at 250-600 psi.

Ditch the screw, use some glue.


What is the diameter of your piston and the shape of the gasket?

A photo would be appreciated.
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Unread postAuthor: Crna Legija » Fri Apr 16, 2010 12:31 am

i would not take out the screw, the sealing face will blow out at 600

i don't think the hot glue will be brake at 600 coz my sealing face is some rubber it dosent get cut
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Unread postAuthor: Matt_NZ » Fri Apr 16, 2010 4:07 am

-_- wrote:i would not take out the screw, the sealing face will blow out at 600

i don't think the hot glue will be brake at 600 coz my sealing face is some rubber it dosent get cut


Ok, cheers. I've got a bit of fine tuning, then hopefully the piston will be sealing. Fingers crossed.
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