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Whats wrong with my 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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Whats wrong with my piston valve?

Unread postAuthor: gwoloshyn » Sat Sep 01, 2007 9:15 pm

As you can see, I finished my piston valve and launcher here (my first piston). Here is the setup. The problem im having is that the chamber will fill up and the barrel does seal, however when I use the ball valve to actuate it all the air just escapes and my piston doesn't open up. Below are some more pictures of the valve.


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Unread postAuthor: wannabie » Sat Sep 01, 2007 9:19 pm

Do you have a kind of lubricant (sp?) on your piston to help it slide more smoothly, how tight is your piston in the T?

When you say escapes im assuming you meen around the piston?
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Last edited by wannabie on Sat Sep 01, 2007 9:20 pm, edited 1 time in total.
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Unread postAuthor: CannonCreator » Sat Sep 01, 2007 9:20 pm

there is a number of things.

1. your actuation hole may be to big, and the air desides to escape from there.

2. Your piston may cuase to much frition and the piston sticks to the side of the Tee.

I would try to lube the piston with somehting like 3 in 1 or cooking oil
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Unread postAuthor: Marco321 » Sat Sep 01, 2007 9:21 pm

The pipe it seals against isn't level so it wont seal properly.

EDIT: Just saw other posts. Yeah you might need some lube and the EQ hole might be too large. if you have a spring it might be too strong.
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Unread postAuthor: mopherman » Sat Sep 01, 2007 9:34 pm

what is connected to the other side of your ball valve?
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Unread postAuthor: CannonCreator » Sat Sep 01, 2007 9:38 pm

mopherman wrote:what is connected to the other side of your ball valve?


I think thats were he hooks it up to a compressor to fill it bro
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Unread postAuthor: gwoloshyn » Sat Sep 01, 2007 9:43 pm

Thats my quick disconnect fitting.

The piston slides very smooth, in fact i thought it was supposed to have SOME clearance around it to act as the equalization hole so i wouldnt need one. I figured the air would go around the outside of the piston you know? Maybe thats my problem.
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Unread postAuthor: goathunter » Sat Sep 01, 2007 9:45 pm

I'm with marco, Your problem is the sealing surface isn't flat.In saying that the piston is warping itself due to the "suction"(pressure of air behind the piston onto a space of normal atmosphere/the barrel) of the hole.In essence when you fill the gun you are canting the piston, so that when the ball valve opens the air escapes from the tank around the enlarged openings caused by the warping and out the ball valve.The increased friction of a warped piston doesn't help it to actuate either.
Sorry buddy but you are back to square one. :cry:
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Unread postAuthor: gwoloshyn » Sat Sep 01, 2007 9:57 pm

That sucks. I kinda figured it would be a 50/50 chance using that for a piston face. I guess I'll order some rubber discs and make a new piston. Just sucks that now I need to use my dremel and remove/repair/replace that cemented in pvc fitting :(
thanks
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Unread postAuthor: MrCrowley » Sat Sep 01, 2007 10:03 pm

CannonCreator wrote:there is a number of things.

1. your actuation hole may be to big, and the air desides to escape from there.

2. Your piston may cuase to much frition and the piston sticks to the side of the Tee.

I would try to lube the piston with somehting like 3 in 1 or cooking oil


That would increase performance, all the air in the pilot area is going to get wasted anyway, you can't save it by having a smaller pilot valve.
So instinctivly you should think that if its going to get wasted, you may as well get rid of it as fast as possible, hence the big pilot valve. I have a 1/2" pilot valve on my piston valve thats smaller then this, it's fine.

I agree with the others, try lube, make sure the seat is pefectly flat and level(the barrel) and make sure the piston fits well, if its a bit stuck, try some lube, it can never really be too tight, and if it is too tight you will just loose pilot volume and your chamber would probably have little to no air in it anyway.

You don't have to remove it, just stick your dremel down there and then smooth it of with some sand paper. Spend a hour on it and it should be fine.
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Unread postAuthor: wannabie » Sat Sep 01, 2007 10:06 pm

Mr. crowley

thats what i made my second post about but then i realised what he ment....

I think he ment the size of the equalization hole. Which would make sense
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Unread postAuthor: MrCrowley » Sat Sep 01, 2007 10:15 pm

wannabie wrote:Mr. crowley

thats what i made my second post about but then i realised what he ment....

I think he ment the size of the equalization hole. Which would make sense


Okay....I wasn't quoting you, I quoted what CC said, nothing to do with you.

Yeah thats what I thought as well, guess we will soon find out.
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Unread postAuthor: wannabie » Sun Sep 02, 2007 12:15 am

What? i didnt say you were quoting me. I ment thats why i edited my second post becuase i realised what he was saying.
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Unread postAuthor: MrCrowley » Sun Sep 02, 2007 12:20 am

wannabie wrote:What? i didnt say you were quoting me. I ment thats why i edited my second post becuase i realised what he was saying.


Oh right, well I didn't need to know that, I don't think anyone did.
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Unread postAuthor: dongfang » Sun Sep 02, 2007 7:13 am

Hey,

I made that mistake on (the first try at) my first piston valve, too. My mistake was in assuming that the valve seat (barrel end, in your case) had to be cut off at a right angle. I did that, and just glued it in - and the thing didn´t seal.

I made the next valve right by gluing some sandpaper on the from of the piston with water soluble glue, and then used the piston as a tool to grind the seat in shape (all at their places in the tee). For a different valve, I used carbon paper to see where seat and piston touched first - and carefully filed down until they contacted around the whole circumference....

If it´s really just your barrel pipe sticking down there, maybe you can salvage the rest. Like, cut it off, and file away at it like crazy. A large coarse file is better than a Dremel....

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