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Can qev's be piloted by schrader valves?

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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Can qev's be piloted by schrader valves?

Unread postAuthor: MisterSteve124 » Tue Aug 28, 2007 9:06 pm

I'm making a cannon and using a qev. I plan to fill it with a schrader valve. Do I need to add a ball valve there because I heard that sometimes qev's can be piloted just by the air comming out when you pull the hose off the schrader valve.
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Unread postAuthor: Novacastrian » Tue Aug 28, 2007 9:11 pm

I had the same thought about the schrader activating the pilot on my up and coming high pressure gun. It would be a serious hazzard if that were the case. I was going to use a blow gun but Jack reckons that the schraders work fine. :shock:
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Unread postAuthor: Flying_Salt » Tue Aug 28, 2007 9:46 pm

Yes, they can be piloted, but sometimes they may only half open and the air will kinda leak out the barrel. Also my old bike pump likes to leak a little air sometimes and that can even stop it from sealing.

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Unread postAuthor: MisterSteve124 » Tue Aug 28, 2007 10:01 pm

but has anyone actually had it happen to them?
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 28, 2007 10:30 pm

I heard that sometimes qev's can be piloted just by the air comming out when you pull the hose off the schrader valve.


If your pilot volume is small, then yes it can happen.

I had the same thought about the schrader activating the pilot on my up and coming high pressure gun. It would be a serious hazzard if that were the case. I was going to use a blow gun but Jack reckons that the schraders work fine.


Whoops, here's something I forgot to mention :oops: What I do to get around this is to put an o-ring between the schrader and the attachment on my shock pump. This means that the stem of the schrader isn't being pressed down and effectively acts as a check valve, being opened only by the pressure of the filling air. This means that when I disconnect the fitting, the schrader is already closed and no air is lost from the pilot chamber.
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Unread postAuthor: jon_89 » Tue Aug 28, 2007 11:08 pm

what do you use to push the valve inside with?
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Unread postAuthor: jackssmirkingrevenge » Tue Aug 28, 2007 11:11 pm

jon_89 wrote:what do you use to push the valve inside with?


You don't have to push it in - the stem is only held in place by a weak spring, so if the air pressure your pump or compressor is putting out is greater than that in your chamber, it will still pass through the schrader.
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Unread postAuthor: mike1010 » Tue Aug 28, 2007 11:39 pm

cool i will have to try that sometime thanks jsr
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Unread postAuthor: Novacastrian » Sat Sep 01, 2007 10:48 am

point taken :)
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