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Piston valve help again

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 help again

Unread postAuthor: Procrastinator » Tue Oct 11, 2011 1:09 am

Hi again, I just finished my piston valve and gotten really bad results :( (100psi shooting a battery 3 metres) I thought the problem might be the piston being too short leaving alot of space for the piston to move back, but I put a new washer further forward behind the piston and it still continued to blow 75% of the air though the pilot. I really can't figure this one out, could someone give me some advice? I think I'm just going to buy a QEV. Here is the basic setup of my Piston valve if it helps. (MRR's plans)
[/img]
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Attachments
IMG_0106.jpg
Together.
IMG_0107.jpg
Where the piston face seals.
IMG_0108.jpg
The new washer I put in.
IMG_0110.jpg
Hot glue piston.
IMG_0111.jpg
Everything.
Goats spudz wrote:omg i launched a fart ut of an airgun and it really smells
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Unread postAuthor: jvw1979 » Tue Oct 11, 2011 1:17 am

Maybe some more experienced guys can pitch in as well, My first valve had the same issue, turns out it wasn't tight fitting enough so a lot of air were allowed to escape through the pilot as it seeps around the piston.

Don't know the tolerances on your piston, but try a few turns of tape around it to get it more "snug" and try again.
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Unread postAuthor: Procrastinator » Tue Oct 11, 2011 1:27 am

Don't know the tolerances on your piston, but try a few turns of tape around it to get it more "snug" and try again.


Thanks for your reply.
The piston is a perfect fit in the tube apart from the equalization ridge I cut out. If I taped it, the piston wouldn't even fit in the tube :?
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 11, 2011 1:27 am

your piston should fit this description:

[youtube]http://www.youtube.com/watch?v=gu31VyXlTzo&feature=related[/youtube]

Procrastinator wrote:the equalization ridge I cut out.


There's your problem.

No o-ring = no need for equalisation holes
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Unread postAuthor: Procrastinator » Tue Oct 11, 2011 1:33 am

No o-ring = no need for equalisation holes
Darn, I was kinda wishing it wasn't my piston. How could have MRR's have worked then?
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Unread postAuthor: daniel0663 » Tue Oct 11, 2011 1:36 am

Have you tried using a larger pilot vavle? e.g. 1/2" or a 1/4" ball valve.
There might be lots of problems/manfunctions which may contribute to this problem.

I don't think it may be the piston tolerance, unless the piston is dramatically undersized, which will cause all kinds of sealing issues in the first place.

Your piston seems to be the same length as the nipple so i don't see any problems there.

I presume the hose is your "air tank" which you use to help you maintain a muli-shot, without refilling.

If it is, you have a exceeding amount of pilot volume ( air volume behind your piston ) which JSR will happily go over the problems relating to pilot volumes :P which may be the problem in the first place...

also, is that a nail holding the rubber againts the piston? :P
if it is, you are rebellious, not to mention it is dodgy :shock:
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Unread postAuthor: Procrastinator » Tue Oct 11, 2011 1:44 am

also, is that a nail holding the rubber againts the piston?
if it is, you are rebellious, not to mention it is dodgy

Yeah it is, That was the result of my failed attempt at using epoxy :oops:

I presume the hose is your "air tank" which you use to help you maintain a muli-shot, without refilling.
That was my original idea in which I ran into another problem :cry: the threads were all wrong.
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Unread postAuthor: MrCrowley » Tue Oct 11, 2011 2:07 am

While in a perfect world that closely resembles jackssmirkingrevenge's workshop, one could pilot such a piston with a blowgun but without o-rings and the large pilot volume you're probably best going with a 1/4" ball valve.

Usually, it is a combination of a bad fitting piston with a small pilot valve but you can have the worst fitting piston and the largest pilot valve and see sh|t results whereas you can have an excellent fitting piston and only see slightly worse results and perhaps a small delay in firing with a small pilot valve.

Tip: Buy some lubricant, it will help seal the piston around its edges.
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Last edited by MrCrowley on Tue Oct 11, 2011 2:13 am, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 11, 2011 2:12 am

MrCrowley wrote:While in a perfect world that closely resembles jackssmirkingrevenge's workshop


:D

I'm running out of space to support my compuslive accessory buying habit!
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Unread postAuthor: Procrastinator » Tue Oct 11, 2011 2:22 am

New piston is setting. Hopefully with the help of a little lubricant it will work.
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Unread postAuthor: Crna Legija » Tue Oct 11, 2011 3:53 am

what in the last pic is your tank the fire extinguisher? and its connected by hose, if so id say thats your problem.
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Unread postAuthor: Brian the brain » Tue Oct 11, 2011 4:03 am

I see a couple of problems.

The pilot volume is massive.
Even more so when compared to available chamber volume.
The chamber should be the elephant, pilot volume should be the mouse.

That hose is a well known snake: Floa Constrictor.. :D
So the volume is really only restricted to the valve itself.

I can see light passing between the piston and it's housing.
Not what you would call " Toight like a toiger" now is it?

You don't need the airchannel.If it slides there is enough room for air to pass.

So throw out the snake, and bring in the tiger, have the elephant ready to fight the mouse and you're ready.

:?

And Jack...leave me out of this.
I'm in a bad mood 'cause I lost my mustache in a nasty ssssssmelting accident!
:D
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: jackssmirkingrevenge » Tue Oct 11, 2011 4:11 am

:D :D :D

Brian the brain wrote:I'm in a bad mood 'cause I lost my mustache in a nasty ssssssmelting accident!


How will people know you're Dutch now :wink:
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Unread postAuthor: Brian the brain » Tue Oct 11, 2011 4:15 am

Cause of my wooden shoes.
Mine are painted in metalflake.

I looooooove metal.


Call me steelmember... :D

@Procrastinator:
I suggest using a bolt and washer type piston.
That way you can bolt on the sealing face.Much stronger.
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: Procrastinator » Tue Oct 11, 2011 4:58 am

I can see light passing between the piston and it's housing.

That isn't light its blue teflon tape I forgot to remove :)
EDIT: That isn't my piston either, Its the rubber washer I put infront of a metal washer.

About the chamber, I didn't plan for that huge volume. I bought the fire extinguisher then found out the threads weren't 3/4 so then for some stupid reason I decided to attach it with a hose :roll:

I will buy some 3/4 pipe to make the chamber. The piston I was thinking about but that's for another day.
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