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D*mn d*mn d*mn ...how not to test a piston valve

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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D*mn d*mn d*mn ...how not to test a piston valve

Unread postAuthor: dongfang » Sat Jul 21, 2007 7:48 am

Hi,

This is getting absurd ....

I have completed assembly of my Schweizer-Valve. It's a 63mm barrel leaking/sealing tee valve, hand made in Switzerland.

OK it did not quite seal. I could see that by placing a powerful lamp at the barrel port, and looking into the chamber port. I wanted to be sure that was in order before solvent welding on the chamber - after all, access to the valve seat is best from the chamber port. So I just siliconed the chamber on, assuming that I could just tear it off again, or maybe that it would shoot off by itself as soon as the thing was able to hold a little pressure.

Problem: Valve seals beautifully (well opening and bumper are not tested), and the chamber is stuuuuuuuuuuuuuuuck in the tee.

What the sch%ç&*!! can I do? More pressure? It would probably just do damage to itself and its surroundings when finally coming off.

Well I have these 40 ft of hose .. guess I have to dump the gun in a scenic Swiss lake, discretely inflate it from 39ft away, and pretending to have nothing to do with the depth charge like blast that will follow when I finally the enough pressure on it.... (but the damping effect of the water should keep the valve intact)...

ARGH. To have to put a hacksaw on a new and working valve....

Well, on the other hand, I have discovered that a 75mm version of the same valve is also feasible. That would be something: Firing 0.5l pop bottles filled with water at 200-300 fps; what a recoil...

Regards
Soren
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Attachments
opstilling.JPG
What not to do ... chamber is siliconed on, "so I can just test and remove it if necessary".. Right. I have too slow flow from the pump to get it to seal properly, so that is why I put the 'bird on the wrong way around: To slam the piston shut with air from its chamber. Unfortunately, I don't have a second bird around to trigger the main gun.
saede_stempel.JPG
Valve seat and piston.
set_fra_kammer.JPG
View from chamber port.
split_ventil.JPG
Valve body, piston, bumper and end cap to go directly into a sprinkler valve.
samlet_ventil.JPG
The completed valve.
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Unread postAuthor: Gepard » Sat Jul 21, 2007 7:55 am

Can I see a picture of the side of the 'exploded view' (split_ventil.JPG).

It's hard to see what it is from that angle.....

Cheers,

Michael
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Unread postAuthor: dongfang » Sat Jul 21, 2007 8:11 am

OK, next time I take it apart...

It's a 50 mm ID / 60 mm OD curved end cap == piston.

Thick 62 mm rubber gasket thingy == bumper

A 63 mm OD to 1 inch threaded reducer, with a 50 mm to 40 mm reducer glued into it == end cap. A groove is cut for an O-ring.

The valve seat is a 50 mm bushing (I think it is called -- a female to female thing for joining pipes) cut in half, with a 50 mm to 40 mm reducer glued in. A groove is cut in it for a 43.82 mm ID x 5.34 mm O-ring.

Regards
Soren
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Unread postAuthor: Gepard » Sat Jul 21, 2007 8:55 am

So, your sealing the piston with an oring?

Michael
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Unread postAuthor: dongfang » Sat Jul 21, 2007 9:05 am

Hi,

Finally, I managed to twist loose the silicone and then blast off the chamber @ 1 bar ... will now weld it on properly. (I can't find any good threaded fittings to cut apart and use for threaded sockets in the valve).

The piston fits so damn well in the tee body that no extra sealing on its sides is necessary. It's almost as if the designer of this series of parts is a spudder himself. Just needed to grind a tiny bit of material off the inside of the tee body; it is not quite round. And anyway, in a barrel sealer, the seal between the main chamber and the pilot chamber is uncritical; as long as it leaks less than an open sprinkler valve it is OK :lol: .

The piston seals against the seat at the end of the barrel with the said 43.82 x 5.34 mm NBR 90 hard-rubber O-ring, yes.

Regards
Soren
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Unread postAuthor: spud yeti » Sat Jul 21, 2007 9:10 am

That looks like a really nice piston valve youve got... pity about the silicon.. Cant you twist it/scrape it etc etc off though???
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really good quote/phrase here
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Unread postAuthor: dongfang » Sat Jul 21, 2007 9:15 am

Hi,

No problem with the silicone now; I have gotten it off. No humans or animals were killed, injured or molested this time; not even a scratch on the valve either. But for a moment it looked bad...

PS: Can anyone tell me if my bumper is too small .. .. it is about 10 mm thick (argh, there is no good view of it on any of the pictures).
The alternative is 2 softer dampers of each 6 mm stacked, but that will impede piston travel somewhat.

Regards
Soren
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Unread postAuthor: spud yeti » Sat Jul 21, 2007 9:31 am

It is probably OK as it is, but why dont you cut the hard bumper in half, and cut a soft bumper in half, glue them together... and Viola! (This might be a very stupid idea though!)
I think the hard one should be fine though.
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really good quote/phrase here
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Unread postAuthor: dongfang » Sat Jul 21, 2007 10:14 am

Hi, Spud Yeti,

Naaah I don't like to make irreversible changes to parts, assuming without really knowing, that something is wrong with them :wink:

The piston is very light compared to those solid epoxy ones and what else we see, and the end cap is heavy. That lead me to assume (hmm) that if anything will get smashed, it is the piston. So I'll try to go with just the hard damper right now.

Waiting for the PVC cement to cure now .. 24 h. After sitting with pressure on for an hour, the valve now seals with just the air from the bike pump alone.

Regards
Soren
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Unread postAuthor: spud yeti » Sat Jul 21, 2007 10:21 am

Ja, I agree with you that its always nice to be sure. I hope It will work, but Im sure it will. Whats the piston made of?
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Unread postAuthor: dongfang » Sat Jul 21, 2007 10:40 am

Hi

The piston is a PVC end cap with a rounded end. ID is 50, OD is 60 mm.

I might want to fill it up with balsa wood in a restless moment, to reduce pilot volume. But there should really not be any need of that.

Regards
Soren
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Unread postAuthor: spud yeti » Sat Jul 21, 2007 11:44 am

Yeah, I would fill it with something light to reduce pilot volume, it makes quite a difference actually. What you can also do is fill it with foam, then make a thin hot-glue layer on the top to seal it off, it works well.
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Unread postAuthor: turbohacker » Sat Jul 21, 2007 12:34 pm

Jam a piece of round PVC sheet into it.

Great valve!
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If it walks like a dog, sratches like a dog, and barks like a dog, than its probobly a...-TURTLE, it's a TURTLE!!! Cant you see?!!!

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Unread postAuthor: dongfang » Sat Jul 21, 2007 1:33 pm

Hi all,

Thanks for the ideas.

Plan is now:

- let it dry (he he the cement can reads: For repair work, the rule is 1 hour per bar of pressure. That must be 8 hours then :lol: :lol: :lol: Nah ok I will give it a whole day.

- Performance test, evaluation of bumper.

- Find or wind a suitable spring to make it self returning.

- Take it apart again, install spring and fill piston (for the spring, I suppose I need to put a pipe into the piston, on the same axis.. nice spring holder). Maybe install other bumper.

- Build 75 mm version (he he heeeeeee that's gonna be one evil valve .. in the class of Spudtecs's hyped Megah-valve, just metric. Does anyone make and sell valves of that size?)

Regards
Soren
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Unread postAuthor: Gepard » Sat Jul 21, 2007 1:48 pm

The megah valve is the next size up - I should know 'cos I'm building one now :D

Michael
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