Mk IV QEV Popoff. Updated 22 Feb

Carlman · Fri Jun 05, 2009 8:40 pm

Yea thought as much lol

twizi · Sat Jun 13, 2009 6:34 pm

any up dates of mkIII

SubsonicSpud · Thu Jul 16, 2009 6:07 am

twizi wrote:any up dates of mkIII

Sorry, I have not made any more progress on Mk III, have had to put spudgunning on the bench for a while. Will post when I get back onto it again.

Cheers

Subsonic

Copperboy · Thu Jul 16, 2009 9:56 am

Sorry for necro an old thread, but just curious about the homemade QEV. When the piston OD and seat diameter are almost equal, is there really enough cross area around the seat to provide sufficient amount of air to the barrel? Is there a magic formula?

Technician1002 · Thu Jul 16, 2009 11:06 am

Copperboy wrote:Sorry for necro an old thread, but just curious about the homemade QEV. When the piston OD and seat diameter are almost equal, is there really enough cross area around the seat to provide sufficient amount of air to the barrel? Is there a magic formula?

The magic is the piston has length. The chamber is large and surrounds the piston area so when the piston retracts into the pilot area the chamber pressure is able to flow freely from the chamber into the barrel.

The two common configurations are built into a T so the air arrives from one side and coaxial with the chamber on all sides. Coaxial has the best flow and highest COF of piston styles.

If the piston is very short such as a diaphragm, then yes, there is only a very small gap for air to get in when used in a close ratio valve. This is why diaphragms are never close ratio valves unless the diaphragm has an extension so it resembles a piston. This is why well built piston valves beat diaphragm valves almost every time. The open further and have less flow restriction when open.

To understand how the close ratio piston flows, look at the Quick Dump Valve, a 1:1 version that could never be built as a flat diaphragm.

Copperboy · Thu Jul 16, 2009 3:37 pm

Yeah, I think I got it then. From the pictures it wasn't obvious (to me

) that the chamber got access directly (from the side that is) to the barrel when the bolt retracted.

SubsonicSpud · Mon Feb 07, 2011 1:31 am

Well after a long period not doing any spudding, a friend wanted help making a pneumatic tennis ball machine, and I finally got the bug again

Started doing some more work on the QEV popoff concept. One problem I have had with the popoff valve is the rubber seat getting worn very quickly. After driving around half the day trying to buy a few new popoffs and not finding anyone that actually keeps them in stock, I thought bugger it I will make my own. took several hours, but now have a nice alloy adjustable popoff.

Uploaded with ImageShack.us

Uploaded with ImageShack.us

I was going to put a Teflon seal on the tip of the popoff piston, but I may just machine the whole piston out of Teflon or Delrin. Now that I have worked out how to cut threads on my lathe I am going to remake brass QEV previously posted on this thread, but with screw on components. Also my material of choice has changed to Aluminium.

jackssmirkingrevenge · Mon Feb 07, 2011 2:09 am

Nice! And good to see you back

SubsonicSpud wrote:Well after a long period not doing any spudding, a friend wanted help making a pneumatic tennis ball machine, and I finally got the bug again

Sounds like a great project, is there a point to it or is it just because you CAN

SubsonicSpud · Mon Feb 07, 2011 2:49 am

jackssmirkingrevenge wrote:Nice! And good to see you back

SubsonicSpud wrote:Well after a long period not doing any spudding, a friend wanted help making a pneumatic tennis ball machine, and I finally got the bug again
Sounds like a great project, is there a point to it or is it just because you CAN

The tennis ball machine is not related to this thread, It just got me back into it again. I'm still developing the 1/4 BBMG with a QEV and tee mag in the same block, thats what this popoff valve is for. I am also toying with using HPA and a hammer valve repeater perhaps instead of the Popoff.

SubsonicSpud · Tue Feb 22, 2011 6:22 am

Well I manged to get some time to do some more work on the new QEV/Popoff Tee mag design. After spending a while redesigning the idea, I have started making a Coax style QEV Popoff. The Custom made QEV will be in a coaxial configuration with the barrel . The tee mag will be positioned in front of the QEV inside the air chamber, in a block bridging between the barrel and air chamber outer wall. (this probably does not make any sense, I'll do up a diagram to make things clear) In the mean time, here is the start I have made on the air chamber and QEV housing.

Air chamber is 150mmx31mm 6060alloy tube:

Threading in air chamber for QEV popoff section:

QEV block ready to be machined:

Thread cut on QEV block:

Woohoo it fits:

twizi · Tue Feb 22, 2011 6:34 am

very nice
how long did that take you

SubsonicSpud · Tue Feb 22, 2011 7:17 am

Has been several hours work so far, but still lots more to go. Had to Remake the QEV block as I stuffed up the last thread cut on the lathe. Would have been less work if did not have to make it twice

LovableAirGuns · Tue Feb 22, 2011 7:34 am

what size is your lathe and i see you have some really great lathe skills.
cant wait to see more pictures of what you are currently working on.

SubsonicSpud · Tue Feb 22, 2011 7:50 am

LovableAirGuns wrote:what size is your lathe and i see you have some really great lathe skills.
cant wait to see more pictures of what you are currently working on.

The lathe is only a little 14inch between centers with an 80mm chuck, perfect for this sort of thing. I don't think I am that good at lathe work, just spend way too much time playing with it.

wyz2285 · Tue Feb 12, 2013 6:06 am

Sorry I know old thread.
But any updates?

Mk IV QEV Popoff. Updated 22 Feb

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