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Pilot volume and remote mounting of pilot 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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Pilot volume and remote mounting of pilot valve

Unread postAuthor: High-PSI » Wed Dec 07, 2011 9:48 pm

Hey Guys,

I am setting up the final configuration for my 1/2 inch barrel, 600 psi cannon and I have a question for you;

The main valve is a brass diamphragm "Sprinkler" style valve that is piloted by a direct acting valve. Right now the pilot valve is directly on top of the pilot chamber on the main valve, sticking straight up. I want to remote mount it to make room up there for a scope. Also, these brass bodied valves weigh a ton. I need to get more weigh up front because the gun is very tail heavy. So, I want to move the pilot valve out of the way toward the front of the cannon a bit (and lower) for CG reasons and scope mounting. Now, with that background information, I was curious what the increased pilot volume from the remote mounting would do. GGDT shows that in this style cannon, the pilot volume can be increased an order of magnitude without any performance drop.

Now, what I am curious about is, why is the performance not affected or is it and I am not programming GGDT properly? I would assume a smaller pilot volume would allow the valve to open more quickly and increase performance. But, that does not seem to be the case.

What are your thoughts?

Matt
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Unread postAuthor: Gun Freak » Wed Dec 07, 2011 9:53 pm

In my experience, GGDT produces the same results if not marginally different when comparing sizes of pilot volumes. In practice though, of course, it will change performance. Drastically? Probably not in your case. Can you not put the direct acting pilot facing downwards?
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Unread postAuthor: High-PSI » Wed Dec 07, 2011 10:00 pm

That is exactly what I was wondering. I am going to put in a call to the manufacturer tomorrow. I have a good relationship with their engineers (one of them).

My only concern with that is the diaphragm slug has no spring. So, the brass slug hanging up-side-down may stretch the diaphragm down and possible make it not want to innitially seal?

Anyway, I will call them tomorrow and ask. I can always bench test it to see if there is any difference either way.

Matt
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Unread postAuthor: Gun Freak » Wed Dec 07, 2011 10:32 pm

Hm, you could add a spring, or pilot fill it (I assume you're filling chamber). It might not even need a spring. Try holding your gun upside down and filling it.
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 08, 2011 12:38 am

Gun Freak wrote:In my experience, GGDT produces the same results if not marginally different when comparing sizes of pilot volumes. In practice though, of course, it will change performance.


If it didn't, much of my preaching over the years would have been futile ;)
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Unread postAuthor: mark.f » Thu Dec 08, 2011 8:25 am

Depends on the pilot volume already present in the valve and the hose diameter. ;)

I've made several cannons over the years with remote mounted pilot valves.
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Unread postAuthor: High-PSI » Thu Dec 08, 2011 9:51 pm

The pilot tube is a 1/2 inch pipe into the pilot valve. So, any added length will really add to the pilot volume.

I spoke with the valve manufacturer today. I think I will mount it upside down and install a light spring inside to compensate. That should make plenty of room for my scope and make the gun more stealth.

Matt
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