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Coaxial Piston not actuating

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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Coaxial Piston not actuating

Unread postAuthor: iisthemuffin » Thu Aug 28, 2008 6:27 pm

I started a mini coaxial a few mopths ago. I couldnt get it so i gave up on it for a while.

Ive since decided to retry.

Today i noticed i have quite a bit of pilot room. Could this be the reason its not actuating?

It seals fine. I have a half inch chamber and my barrel is 3/8 inch copper tubing. My piston is made of epxoy. It is about an inch long. I am trying to pilot via shrader. My pilot area is roughly 2.5 inches. Yes i realize this is quite alot but i could not make it any less because of the adapter used to screw in the back plug
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Unread postAuthor: ALIHISGREAT » Thu Aug 28, 2008 6:29 pm

maybe a bigger pilot valve such as a ball valve or blowgun would get the job done?
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Unread postAuthor: iisthemuffin » Thu Aug 28, 2008 6:38 pm

Thats what i was told before. I put the project on hold until i had time to get a ballvalve.

Do you think the larger pilot valve would solve the problem with the large pilot volume?
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Unread postAuthor: MrCrowley » Thu Aug 28, 2008 9:32 pm

iisthemuffin wrote:Do you think the larger pilot valve would solve the problem with the large pilot volume?

Yes.

Go for 1/4" ball valve or a blowgun IMO. But performance may suffer with the blowgun.
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Unread postAuthor: VH_man » Thu Aug 28, 2008 9:58 pm

as JSR s once said:

Less pilot volume is ALWAYS better.

and a larger pilot valve will NEVER hurt.
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Unread postAuthor: blind909 » Thu Aug 28, 2008 10:05 pm

You could try the above, but also make sure you can move your piston with little effort with your pinky. If you cant, your pistons too tight, and that would be your problem.
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Unread postAuthor: VH_man » Thu Aug 28, 2008 10:31 pm

might i reccomend lithium grease?

It worked on Mike the HP marblegun...... in fact the grease is still there after about 40-50 firings at high pressure...... and it makes the piston movement go from hard enough that you need a hammer to get it in all the way to the point where i blow on it and it goes in..........
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Re: Coaxial Piston not actuating

Unread postAuthor: Gippeto » Thu Aug 28, 2008 10:55 pm

iisthemuffin wrote: My pilot area is roughly 2.5 inches. Yes i realize this is quite alot but i could not make it any less because of the adapter used to screw in the back plug



2.5"...Yes, ... yes that is a lot. :shock:

Do you mean to say that your piston TRAVEL is 2.5" ?

As you can access the piston, I would recommend you place a thick walled tube behind the piston to eliminate this excess volume. (drill a hole through a 1/2" dowel and wrap it with tape to fit)

Using the D/4 rule to determine the proper amount of total piston travel you get : .375"/4=.09375" or 3/32"

So, make a "spacer tube" with a length of 2 13/32 and see what happens.
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Unread postAuthor: iisthemuffin » Sat Aug 30, 2008 12:15 am

Oh no sorry Gippeto. My piston will onl travel about .5 inches. The extra space is the adapter. My piston will not travel though the adapter without being foreced. I may try the Dowel to lessen the pilot volume and also to insure that the piston does not jam itself in the adapter.
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