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QEV Cascade

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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QEV Cascade

Unread postAuthor: Slauma » Mon Mar 01, 2010 4:48 pm

Anyone ever tried cascading 2 or 3 QEVs in a series? It seems to me like it would be useful for piloting a large area with a very small (or slow) valve. I know that using a setup like this would not allow the final pilot volume to be exhausted any faster than with a single properly piloted QEV. So there's no potential for increasing valve speed, but it does seem like it would work very well for minimizing the size (flow) of the valve needed to pilot the entire system. Anyone tried this or have anything to say about it?
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 01, 2010 5:01 pm

If the flow is limited, then a slight difference in valve speed isn't really going to make much of a difference in the valve being piloted. A 1" pilot opened at the same speed as a 1/2" pilot will dump air 4 times faster than the smaller valve. You might be able to improve the opening time on the 1/2" by using another QEV to pilot it but the flow restriction remains.
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Unread postAuthor: potatoflinger » Mon Mar 01, 2010 5:15 pm

I did something similar a few months ago. My golf ball cannon uses a 1/4" QEV to pilot two 3/4" QEVs that both vent to the barrel. It didn't make a noticeable difference in performance so I wound up just replacing the pilot QEV with a ball valve so that I could use the QEV for something else.
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Unread postAuthor: Slauma » Mon Mar 01, 2010 6:38 pm

jackssmirkingrevenge wrote:If the flow is limited, then a slight difference in valve speed isn't really going to make much of a difference in the valve being piloted. A 1" pilot opened at the same speed as a 1/2" pilot will dump air 4 times faster than the smaller valve. You might be able to improve the opening time on the 1/2" by using another QEV to pilot it but the flow restriction remains.


I think you may have misunderstood, or maybe I'm misunderstanding you.

I'm not looking to improve opening time or flow, I'm talking about using a smaller QEV to pilot a larger one. And maybe even pilotting the smaller QEV with an even smaller QEV

eg.
Large volume that > 3/4" QEV > 3/8" QEV > 1/8" QEV > Small(Flow restricted) valve
needs pilotted


It seems like a setup like this would allow you to pilot a large volume using a small, low flow valve
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Unread postAuthor: POLAND_SPUD » Mon Mar 01, 2010 7:46 pm

yeah I did something like that a couple of days ago... I normally pilot a 1/2" QEV with a 1/8" 3 way valve and there is some noticeable drop in performance when I squeeze the rigger rather than pull it

so I attached the 3 way valve to a 1/8" QEV and that to the main QEV...
and damn it seemed that I gained a few J with this... and the gun seemed more consistent too

I still have to find a good place where I can put the 3 way valve on the gun... the place where it was when attached directly the the piloting side of the QEV was almost ideal
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 02, 2010 2:43 am

What I was saying is that this example:

Large volume > 3/4" QEV > 3/8" QEV > 1/8" QEV > Small(Flow restricted)


would not be significantly more powerful than:

Large volume > 3/4" QEV > blowgun


POLAND_SPUD wrote:when I squeeze the rigger


You have this little guy on your launcher?

Image

:D :D :D

Or was it a spelling mistake and slavery has not been outlawed in Poland ;)
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Unread postAuthor: POLAND_SPUD » Tue Mar 02, 2010 3:00 am

lol it could have been worse ('N' not 'R')

would not be significantly more powerful than:

Large volume > 3/4" QEV > blowgun

but blowguns are not 3 way valves... and it's simpler to increase flow of a 3 way valve with the use of a small QEV than to mod a blowgun to act as a 3 way valve
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 02, 2010 3:12 am

POLAND_SPUD wrote:lol it could have been worse ('N' not 'R')


Hence:

jackssmirkingrevenge wrote:Or was it a spelling mistake and slavery has not been outlawed in Poland ;)


;)
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Unread postAuthor: Brian the brain » Tue Mar 02, 2010 3:19 am

Oh come on JSR..

You squeeze your rigger on a regular basis.


A large QEV piloted by a smaller one piloted by a blowgun

Image

well it works...even when battling constant flow coming in.

More than 2 is not neccesary..picking the right sizes is.

The secondary pilot QEV is usually only added when a larger pilot volume is created in order to place the blowgun in a particular position ( extra plumbing) or when additional systems are attached.
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 02, 2010 3:38 am

Brian the brain wrote:You squeeze your rigger on a regular basis


rather than pull it, of course ;)
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Unread postAuthor: D_Hall » Tue Mar 02, 2010 10:48 am

Slauma wrote:eg.
Large volume that > 3/4" QEV > 3/8" QEV > 1/8" QEV > Small(Flow restricted) valve needs pilotted

It seems like a setup like this would allow you to pilot a large volume using a small, low flow valve

You've got more steps in there than you really need, but the general concept of a QEV being used to pilot another QEV which is in turn piloted in any number of ways is not only common around here, it's also done on commercial valves. For example: An Asco 1.5" QEV actually is two valves in one. The 1.5" QEV, obviously, and a 3/8" QEV. All built into the same housing. How you open the 3/8" QEV is up to you, but by design the 1.5" valve is opened by the 3/8" valve.
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Unread postAuthor: Slauma » Tue Mar 02, 2010 11:44 am

jackssmirkingrevenge wrote:What I was saying is that this example:

Large volume > 3/4" QEV > 3/8" QEV > 1/8" QEV > Small(Flow restricted)


would not be significantly more powerful than:

Large volume > 3/4" QEV > blowgun




I understand that this wouldn't allow for any performance increase. I've never actually been able to pilot a 3/4" QEV with a blowgun though. I've only tried one of those cheap generic ones, but even after modding it for better flow it still wasn't enough to pilot the QEV.

Brian the Brain wrote:The secondary pilot QEV is usually only added when a larger pilot volume is created in order to place the blowgun in a particular position ( extra plumbing) or when additional systems are attached.


That's exactly the issue I'm having. All the configurations I've tried either work well for piloting but not aesthetically or work aesthetically but have too much plumbing and too much volume to pilot the QEV. Stacking QEVs seemed like it would be a good way to allow some extra plumbing to be added or a smaller pilot to be used without affecting the final performance of the valve
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Unread postAuthor: D_Hall » Tue Mar 02, 2010 3:24 pm

Slauma wrote:I understand that this wouldn't allow for any performance increase. I've never actually been able to pilot a 3/4" QEV with a blowgun though. I've only tried one of those cheap generic ones, but even after modding it for better flow it still wasn't enough to pilot the QEV.

What are you doing?? I've had zero problems piloting 3/4" QEVs with off-the-shelf blowguns. Zero modifications beyond throwing the blowgun's flow restrictor away (but I hardly count that as a mod).
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Unread postAuthor: Slauma » Tue Mar 02, 2010 8:03 pm

I wish I had my camera so I could upload a video.

I use the 3/4" QEV to pilot a 2" piston valve (PVC tee). The blowgun is not enough to pilot it with a 3/4"x1/4" adapter connected to a 1/4" tee with the blowgun on one side and a schrader on the other. Do you think this could happen because of lower pressures? I typically only operate it at 20-40 psi.
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