Piston: Good or Bad?

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Postby Velocity » Mon Jul 10, 2006 4:46 pm

Here are a few pictures of my piston for the upcoming valve that I am about to build. It is made from 3" of 1 7/8" PVC stock, along with neoprene disks, a spring, and assorted screws and bolts.

<img src="http://www.spudfiles.com/uploader/uploadFiles/pistonside124134.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/pistonangled2352435.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/frontpistonangled23423.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/frontlightpistonangled23432.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/backpiston23423.JPG">

The back end is the one with the spring. As you can see, I added a neoprene disk there. This is not to seal anything; rather, it aids in holding the spring tightly against the piston.

The front sealing face is made up of two layer. The outer layer is a tough neoprene, which actually does all of the sealing. The inner layer is soft foam rubber, which provides some shock absorption and may aid a small amount in sealing.

Just tonight, I added a few layers of duct tape to the outside, giving a much better fit inside of the 2" sch. 40 it will be sliding in.

My question is, are there any factors/parts of this piston that will hinder performance? I used a very similar piston in my Plinker, and it yielded weak results. But in that particular cannon, other factors such as low chamber volume and too big of an equalization passageway on the piston may have contributed to this problem as well.

Does anyone see any obvious problems? Or does it look ok?

Thanks
Velocity
 
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Postby ishallstabyouwithabluntsp » Mon Jul 10, 2006 5:39 pm

The sealing rubber looks very wonky, could you not lathe it to get a better fit. Thats what I did with mine- just sandwich the rubber sheet between some scrap sheet(I used mdf but anything should work)
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Postby Velocity » Mon Jul 10, 2006 5:58 pm

...wonky??:?:
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Postby markfh11q » Mon Jul 10, 2006 9:27 pm

Larger than the diamter of the piston...

So this is a coaxial piston?
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Postby Velocity » Mon Jul 10, 2006 9:34 pm

no... its a regular ole tee valve.

The rubber is larger than the diameter of the piston, but smaller than the ID of the 2" pipe it will go into. This is just to insure a good seal everytime... I could easily cut it down, but why take the chance of making it too small when it has no ill effects as it is?
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Postby markfh11q » Tue Jul 11, 2006 7:20 am

Do you have an extension off one side of the tee the piston slides through? That's a long piston, which is why I thought it was a coaxial.
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Postby Velocity » Tue Jul 11, 2006 9:59 pm

Kinda... the piston valve body is a 2" tee with a 2" female adapter off of one leg.

I put the piston into place today on my valve... it would not seal properly. I spent about an hour trying to smooth the surface of the pipe which the piston was sealing against. It had some effect, reducing the lost air by about 70%. But I dont know what else to do to achieve a better seal.

<img src="http://www.spudfiles.com/uploader/uploadFiles/PistonValve.JPG">

This is what my valve looks like... its pretty accurate in terms of scale... I think the actual piston may be longer however, and the spring shorter
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Postby Velocity » Tue Jul 11, 2006 10:28 pm

Ok, here are actual pictures of my unfinished valve
(sorry for the blurry pictures; i hope everyone can get the general idea):

<img src="http://www.spudfiles.com/uploader/uploadFiles/all23423423.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/empty32423.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/backview23432.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/sealed234235.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/open324324.JPG">
Velocity
 
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Postby brian the brain » Wed Jul 12, 2006 4:10 am

make sure no air is leaking between the rubber disk and the bolt that holds it.

Take out the pipe it seals against and polish the sealing surface as best you can rubbing it flat on a piece of paper.( takes some time)cut the drubber disc down a little so it can't snag on the "chamber port".

If this doesn't work,you could try glueing some neoprene to the sealing surface and cutting off the rest resulting in a rubber ring on the sealing surface.

Also I see your port is too big.The one going to the barrel I mean.It's too close to the inside diameter of the tee.This valve might open too slowly.
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Postby markfh11q » Wed Jul 12, 2006 7:36 am

He's got .765" difference. That coupled with the fact that he's probably actuating it with a QEV means he should be okay. If you're still worried, you can do some stuff to reduce the pilot volume, but I'd just use it as is first.
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