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Quick Exhaust Valve VS 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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Quick Exhaust Valve VS Piston Valve?

Unread postAuthor: Spudnik Tweaker » Fri Sep 28, 2007 2:39 am

Hi all. I just needed some help from members with the real hands-on experience/knowledge.

From my interpretation, according to Wikipedia (not the "Spud Files" Wiki), the commercially-made QEVs are suppose to open up faster than even the custom-made piston valves (like the ones that we spud cannon hobbyists build). Here is the info:

"Quick Exhaust Valve (QEV) - a commercial piston or diaphragm valve in a metal body intended for the quick venting of pneumatic cylinders. In spudgunning they are ideal barrel sealing valves with faster opening times than custom piston valves and high flow rates. They can be commonly found in sizes from 1/8" to 1.5" and sometimes even larger models. It provides an easy option for inexperienced spud-gun builders but the cost is usually greater than for any other valve type. (An exception to this is within the UK, where QEVs are relatively inexpensive.)"
http://en.wikipedia.org/wiki/Spud_gun

1) So is this true? Are QEVs capable of opening up faster, thereby releasing the precious pressurized more efficiently than the typical custom piston valves? (I am refering to the QEVs that are 3/4" on up BTW)

2) Why are they cheaper in the UK?

If QEVs are the way to go, than I am more than willing to cough up the extra bucks for one. They would be much more compact and would be more durable than custom-made PVC piston valves.
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Unread postAuthor: jackssmirkingrevenge » Fri Sep 28, 2007 2:57 am

A QEV is basically a piston/diaphragm valve internally and works in the same way was a "custom" piston valve.

You can make a piston valve faster than a QEV but it depends how you make it - in the sense that you must have a lightweight piston that's tight but friction free and keep the pilot volume to the bare minimum (the piston shouldn't move back more than 1/4th of the barrel diameter) - if you're up to that, well and good, if not, invest in a QEV ;)
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Unread postAuthor: Hotwired » Fri Sep 28, 2007 6:21 am

Y'know I really don't think they ARE cheaper in the UK.

They are more reliable than home made ones, they are guaranteed to seal perfectly and unless you can mould thin stiff rubber you can't get a home made valve to open faster.

Mind you, 'faster' is a matter of small fractions of a second but their reliability is certainly worthwhile.

Not worthwhile for over 3/4", the last 1" one I saw was about 5 times the price of the 3/4" version beside it :o
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Unread postAuthor: Spudnik Tweaker » Fri Sep 28, 2007 12:55 pm

Thanks for the replies.

Ok, so now I think that QEVs are the way to go. I mean, come on: QEV VS Modified Sprinkler Valve? I'll take the QEV.

By the way, how do the commercial QEVs actuate? It seems that a lot of them aren't ready to use when purchase, as if they need a switch to be connected to them for a pilot.

Can anyone share with me their QEV setup, as far as how they have it actuated?

BTW, it would be so nice if this forum had the "subscribe" feature -- that way one can keep track of things and not have to dig around.
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Unread postAuthor: jrrdw » Fri Sep 28, 2007 5:27 pm

Spudnik Tweaker wrote:Thanks for the replies.

Ok, so now I think that QEVs are the way to go. I mean, come on: QEV VS Modified Sprinkler Valve? I'll take the QEV.

By the way, how do the commercial QEVs actuate? It seems that a lot of them aren't ready to use when purchase, as if they need a switch to be connected to them for a pilot.

Can anyone share with me their QEV setup, as far as how they have it actuated?

BTW, it would be so nice if this forum had the "subscribe" feature -- that way one can keep track of things and not have to dig around.


You see below the post reply field there is a check box to notifiy me when a reply is posted. Put a check in it. No exspearance with QEV's, try the Wiki.
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Unread postAuthor: Spudnik Tweaker » Mon Oct 01, 2007 4:23 am

jrrdw wrote:
Spudnik Tweaker wrote:Thanks for the replies.

Ok, so now I think that QEVs are the way to go. I mean, come on: QEV VS Modified Sprinkler Valve? I'll take the QEV.

By the way, how do the commercial QEVs actuate? It seems that a lot of them aren't ready to use when purchase, as if they need a switch to be connected to them for a pilot.

Can anyone share with me their QEV setup, as far as how they have it actuated?

BTW, it would be so nice if this forum had the "subscribe" feature -- that way one can keep track of things and not have to dig around.


You see below the post reply field there is a check box to notifiy me when a reply is posted. Put a check in it. No exspearance with QEV's, try the Wiki.
Yeah, I am aware of that check box. The trouble I am having isn't tracking my current threads that I happen to be waiting for replies, though.

The problem with the check box feature is that you cannot track the threads that you are interested in/following. There are so many threads out there that I am following and they just seem to move all around.

This problem could be solved by having a program set up like the V Bulletin-powered message boards -- that allows you to subscribe to threads and organize each individual one into your own custom folders (nice and neat). For instance, i would be able to create a folder labelled "valves" and have all of the threads whereas I'm researching different designs into that single folder. Then I could have another folder labelled "different ideas", etc. etc.
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Unread postAuthor: Lentamentalisk » Mon Oct 01, 2007 7:06 pm

with a commercial QEV, the way to trigger it is the same way that you fill it. you simply release the pressure on the side of the input, and that will trigger the valve
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