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How Hot Have You Run This

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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How Hot Have You Run This

Unread postAuthor: ThornsofTime » Sun Oct 17, 2010 3:35 pm

Ok, so for the build im planing im really wanting to be able to run 500psi (500psi stated for safety reasons... normal operation to be ~350-400).

Heres the QEV
https://www.fastenal.com/web/products/d ... 203&ucst=t

QUESTIONS
a) whats the hottest you PERSONALLY have ever run one of these?
b) what would you recommend as a SAFE normal operating pressure?
c) Is there a different 1/4" QEV that would better suit my build?? (must be a QEV)
d)There is the option to choose the SAME QEV from two different materials; cast zinc OR cast brass zinc plated. Whats the difference??

(yes I read the product info and see the recommended psi, but i seem to remember reading in a few places that these can handle MUCH more without even hinting at stress.)

In advance-Thanks for the help :) :)
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Unread postAuthor: Gun Freak » Sun Oct 17, 2010 3:39 pm

A) I have never used one and don't intend to.
B) The highest I would take one is 600 psi, but I tend to be on the safe side so probably 400.
C) This type of QEV has been used to 40 bar ( or is it 60, I don't remember) and it is most common. I don't remember seeing another type of QEV that handled even mroe pressure.
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Unread postAuthor: Big-E » Sun Oct 17, 2010 3:44 pm

Get the cast brass/zinc plated ones, they take more pressure if I'm not mistaken. I would think that the zinc casting would not be as good under pressure.

I use a 1/2" one on Thunderbess, the highest pressure I've ever personally fed to it was 300 PSI (before I added the reg) and it handles that no problem. In theory, it should be good to 450 PSI or so, although I have heard of people running them at higher pressures than that.

It's also important to note that some QEV's use thinner diaphragm-like piston, while others use thicker pistons. if you can, get one with a thicker piston.
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Unread postAuthor: ThornsofTime » Sun Oct 17, 2010 5:24 pm

I think the one I currently have is a diaphragm type... when I took it apart its internal sealing mechanism looks like a hard rubber washer, tapered from the pilot side towards the exhaust side (no equalization hole, air just slips past that tapered edge, then cant get back into the pilot side).

Has anyone ever tried machining a new piston for one of these?? just taking a guess here... but I would put my money towards saying the "piston" is the weakest link in the QEV... and at high enough pressure it would fail, blowing out into the barrel before the housing cracked.

Any "I second that" votes for the brass/zinc plated version OVER the solid zinc??
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Unread postAuthor: Gun Freak » Sun Oct 17, 2010 5:42 pm

The piston is definitely the weak part of the valve. You could either reinforce it or make a new one to use the QEV at higher pressure.
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Unread postAuthor: D_Hall » Mon Oct 18, 2010 12:05 am

From the link....

Working Pressure 30 - 125 psi

...And that's my answer. Pressure ratings are pressure ratings for a reason. There's no performance goal in spud gunning that is so important that I'll knowingly exceed pressure ratings.
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Unread postAuthor: MrCrowley » Mon Oct 18, 2010 12:22 am

D_Hall wrote:There's no performance goal in spud gunning that is so important that I'll knowingly exceed pressure ratings.

Think the working pressure on those big Asco Pulse Valves is 125PSI, not the 150PSI you took yours too if you didn't know :wink:
Though, I could be wrong. That's just from memory.

Back on topic, I would feel pretty comfortable with these at 400PSI or so. I would imagine the piston/diaphragm would fail before anything else and if you adhere to basic gun safety rules, in the event it did fail, you shouldn't have the barrel pointing at anything worth a damn.
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 18, 2010 12:26 am

D_Hall wrote:Pressure ratings are pressure ratings for a reason. There's no performance goal in spud gunning that is so important that I'll knowingly exceed pressure ratings.


That said, the piston will fail long before the casing does and I doubt the pressure needed to blow the casing apart is anything near what an amateur spudder can achieve.

This is of course conjecture, but using it at 300-500 psi is what I would call and extremely calculated "risk".
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Unread postAuthor: Crna Legija » Mon Oct 18, 2010 12:32 am

ThornsofTime wrote:I think the one I currently have is a diaphragm type... when I took it apart its internal sealing mechanism looks like a hard rubber washer, tapered from the pilot side towards the exhaust side (no equalization hole, air just slips past that tapered edge, then cant get back into the pilot side).


i have taken a 1/4'' festo qev to 700psi and its still woking fine.

the one you opend could the rubber move freely? or was it clamped in between the two parts of the shell of the valve.
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Unread postAuthor: ThornsofTime » Mon Oct 18, 2010 12:38 am

It moved freely... unscrew back "cap" (pilot side) and it was a hollow chamber with the "piston" sitting inside. It was a semi-tight fit, but all I had to do to get it out was blow from the barrel side w/ my thumb over the exhaust port.

EDIT- If I HAD to change to a Tee fitting valve I guess I could... I just have no idea how to makem... the one I thought up was slightly poo-pooed
http://www.spudfiles.com/forums/no-more ... 21823.html
ANY valve really... im still in the design phase... so if you know of a valve that can dump a lot of air that is cheap or makable...lemme know lol

EDIT EDIT- Just noticed that the lowest psi rating on any of my parts was 1200 (except the QEV naturally)... If I were to say "im making a 1000psi launcher"... what valve would you say to use??
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Unread postAuthor: jackssmirkingrevenge » Mon Oct 18, 2010 1:03 am

ThornsofTime wrote:so if you know of a valve that can dump a lot of air that is cheap or makable...lemme know lol


The best valve isno valve at all ;)
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Unread postAuthor: ThornsofTime » Mon Oct 18, 2010 1:08 am

Like we talked about in that thread... cool idea, but I think I want something a bit simpler to reload. Some ammo variations and a standard breach is what im going for, its going to be a pretty classy rifle :D
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Unread postAuthor: lozz08 » Mon Oct 18, 2010 5:22 am

Why dont you take a look at technician"s QDV. The chamber is coaxial around the barrel.
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Unread postAuthor: ThornsofTime » Mon Oct 18, 2010 8:40 am

hehe read ma mind Lozz08, currently have another thread going that I just updated with a new valve design largely based on Technicians... except mine is built into a tee fitting instead of in a tank.

check it out, tell me whatcha think.
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