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400psi piston vavle

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Unread postAuthor: ALIHISGREAT » Mon Dec 31, 2007 5:48 am

Hotwired wrote:
ALIHISGREAT wrote:it would be hard to get a piston that can take 400psi repeatedly :(

Get a piston QEV. Unscrew it. Remove piston thing. Insert custom piston. Screw it together again. Use at 400psi.


thats a good idea but i reall want to have a crack at making my own piston and i want higher flow than a 3/4" qev aswell.
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Unread postAuthor: Hailfire753 » Mon Dec 31, 2007 9:02 am

Hotwired wrote:Get a piston QEV. Unscrew it. Remove piston thing. Insert custom piston. Screw it together again. Use at 400psi.


jackssmirkingrevenge wrote:My epoxy pistons do that all the time, it's not such a big deal.


So, lets say I removed the piston from a 3/4 QEV. To make a custom piston, I could make a mold from melted wax, then neatly cut it in half. Fill mold with epoxy, let it set. Put epoxy piston in QEV. Withstand 400 psi?

Is there a better way to make a mold? And Jack, would a thin piston like that still work @ 400?
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Unread postAuthor: Carlman » Mon Dec 31, 2007 1:21 pm

go epoxy, it solves the worlds problems, or at least the spud world :D
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Unread postAuthor: POLAND_SPUD » Mon Dec 31, 2007 1:36 pm

hmm has anyone did something like that before ?
any idea what is the working and burst pressure of a brass QEV body ?
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Unread postAuthor: Carlman » Tue Jan 01, 2008 12:46 am

ive heard about it on another website along time ago, im not sure where. but im sure someone on here has done it before or at least something similar.
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Unread postAuthor: ALIHISGREAT » Thu Jan 03, 2008 9:00 pm

Hailfire753 wrote:
Hotwired wrote:Get a piston QEV. Unscrew it. Remove piston thing. Insert custom piston. Screw it together again. Use at 400psi.


jackssmirkingrevenge wrote:My epoxy pistons do that all the time, it's not such a big deal.


So, lets say I removed the piston from a 3/4 QEV. To make a custom piston, I could make a mold from melted wax, then neatly cut it in half. Fill mold with epoxy, let it set. Put epoxy piston in QEV. Withstand 400 psi?

Is there a better way to make a mold? And Jack, would a thin piston like that still work @ 400?



i would't do that because pistons in qevs are relitivly thin and epoxy is brittle (i think?) so unless the epoxy was reinforced pycrete style :idea: then i wouldn't try it, the other idea i had was to get a tougher harder rubber (or similar) to use as a piston, it would affect the opening time of the qev but it would be safer at higher pressures.
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Unread postAuthor: BigJon » Thu Jan 03, 2008 9:13 pm

What about polycarbonate? I think i've seen some people use that for pistons before and I've heard that its really impact resistant.
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Unread postAuthor: ALIHISGREAT » Fri Jan 04, 2008 6:22 am

BigJon wrote:What about polycarbonate? I think i've seen some people use that for pistons before and I've heard that its really impact resistant.


i did wonder about using plastic, and it would be quite easy to do because i would just have to buy a rod and cut off the desired amount then stick a sealing face on :)

another option for a piston is to use PTFE rod as a piston which would be super low friction 8)
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Unread postAuthor: POLAND_SPUD » Sat Jan 05, 2008 3:44 am

ALI how much space is left inside a qev for a piston....? I assume you've already opened the valve...

PTFE is going to be expensive... I would try rubber discs first...
for example my father has lots of rubber discs with a tiny little hole in the center (i don't really know how this thing is called but ive seen this here on spudfiles as well )
you could take 2 such rubber discs and put a small metal disc with a hole drilled between the two and finally fasten the whole thing with a bolt and nut...
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Unread postAuthor: ALIHISGREAT » Sat Jan 05, 2008 6:10 am

i think you mean rubber washers? but i'm not sure. i haven't opened it up yet but i will do it this afternoon and post some pics maybe and the ptfe won't be that expensive its under £5 for 250mm of 25mm rod and i would have spare for future projects.

p.s. i think someone opened up a qev and posted on uksgc hmmm

http://www.uksgc.co.uk/forums/index.php?showtopic=475&hl=qev

by the look of it the piston is reasonably thick, the only problem i can see is equilization :?
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Unread postAuthor: POLAND_SPUD » Sat Jan 05, 2008 7:53 am

thx for the link...

yes possibly you can call them rubber washers - but they are quite thick and have large diameter.

I don't think that equalization would be a problem - air will pass if there is any gap between the piston and the valve casing... so I wouldn't worry about that - I would rather worry that a qev modded in this way would be less sensitive to pressure drop on the pilot side....
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Unread postAuthor: ALIHISGREAT » Sat Jan 05, 2008 8:47 am

POLAND_SPUD wrote:thx for the link...

yes possibly you can call them rubber washers - but they are quite thick and have large diameter.

I don't think that equalization would be a problem - air will pass if there is any gap between the piston and the valve casing... so I wouldn't worry about that - I would rather worry that a qev modded in this way would be less sensitive to pressure drop on the pilot side....


yes it would become less sensitive and have slower opening times made worse by the fact that a non-qev piston would not act as a check valve but the advantage is that higher pressures can be used.

another option i thought of is to simply reinforce the piston with epoxy or something which would fill in the rear of the piston if ii is the kind show in the link although this might restrict equilization.
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Unread postAuthor: ALIHISGREAT » Wed Jan 09, 2008 2:24 pm

bump!

updated design so please look and tell me what you think :)
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Unread postAuthor: BigJon » Wed Jan 09, 2008 4:50 pm

The new design looks good and should work. I don't see anything wrong with it :)
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 09, 2008 8:27 pm

looks good, but what are you going to do with a pilot volume so massive you could fit a medium sized pink elephant into it?
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