SpudFiles

For a repeating pneumatic I plan on using a QEV. I have heard that for them to repeat a hole on the piston/diaphragm and a spring is required. I think I have the spring part down but, I'm having trouble getting my head around the need for the hole. I would appreciate it if someone would explain the purpose . (I'm using a 1/2" deltrol diaphragm QEV from McMaster Link)

If you're filling from the pilot side, you don't need an equalisation hole, but if the air is coming from the chamber side, you need a hole to let air get in behind the piston/diaphragm, and the spring allows this to happen without it firing.

So if I am filling through pilot I need no modifications?

Well, almost everybody fills through the pilot, and nobody mods it, so if you gonna fill through pilot, no.

irisher wrote:So if I am filling through pilot I need no modifications?

Just make sure that your pilot valve has a much better flow than the connection you're feeding through, otherwise it will never fire...

To prevent messing up a good QEV, use and aquarium or other needle valve and place this external to the QEV. The advantage is it is adjustable unlike a hole in the piston.

Assuming a fire extinguisher is serving as chamber, will a QEV with spring and no hole in the diaphragm achieve multiple shots from the tank if the pilot is only momentary open?

with a hammer valve yes blow gun no

twizi wrote:with a hammer valve yes blow gun no

How about with a 1/4" direct acting solenoid 3-way valve?

if your making it like polands gun thay you dont need to mod it at all

so you have an external airsource?

It has a large onboard air tank that will be replenished from an outside airsource.The problem is, if the entire tank is dumped each shot then I will not have enough flow to fill it up before the next shot. If I can not get a QEV to repeat with the 3-way and pilot side filling then my design needs some serious revision.

a QEV + 3way will work and you will not need to mod it at all.
that is why poland like the 3 way idea no need to mess around with your QEV and its more air efficient than a QEV+pop off

I just want to stress the fact that in real life QEVs are normally used with 3 way valves... QEV stands for Quick Exhaust Valve

they are used to speed up return spreed of a single acting air cylinder... single air cylinders are normally controlled with a 3 way valve.. so in other words:
QEVs were designed to be used with 3 ways

if the entire tank is dumped each shot then I will not have enough flow to fill it up before the next shot.

what sort of pressures and volumes are we talking about ??
you can calculate how much time it takes to fill the chamebr to x pressure if you know the flow of the valve you want to use...

unless you want to build a fullauto gun that uses a lot of air for each shot this shouldn't be a problem

what sort of pressures and volumes are we talking about ??

I plan on Co2/HPA system but, it would be nice for it to work on a fridgy or normal air compressor. Here is my setup with AA for size comparison.

unless you want to build a fullauto gun that uses a lot of air for each shot this shouldn't be a problem

Problem is I want a full-auto gun. Although I don't mind having low amounts of air per shot.