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Posted: Sat May 07, 2011 5:46 am
by jackssmirkingrevenge
Alster370 wrote:I think this is because my pilot is a 15mm ball valve and that its too big?
There is no such thing as a pilot valve that's too big
If you open your ball valve fast enough it should work even at lower pressures.
Posted: Sat May 07, 2011 6:54 am
by Alster370
wouldn't it allow more air to flow out of the pilot rather than the barrel?
Posted: Sat May 07, 2011 7:02 am
by jackssmirkingrevenge
Most QEVs have cup pistons that effectively act as one-way valves, allowing air to flow from the pilot to the chamber but not vice versa.
This means that the air that can flow out of the pilot cannot flow out of the barrel.
Posted: Sat May 07, 2011 8:38 am
by Alster370
From visual inspection mine seems to be just a flat face piston, not a cup one. Which would explain some air coming from the pilot when firing.
Posted: Sat May 07, 2011 8:45 am
by jackssmirkingrevenge
Alster370 wrote:From visual inspection mine seems to be just a flat face piston, not a cup one.
Photo?
It could be a diaphragm with a equalisation hole, like in a piston valve.
Posted: Sat May 07, 2011 8:57 am
by Alster370
sure, but I can only take one from the barrel side as the pilot side is epoxied already.
I could give you the site I bought it off in the meantime if that helps
http://www.hosefit.co.uk/catalog/produc ... cts_id=357
Posted: Sat May 07, 2011 9:06 am
by jackssmirkingrevenge
That should look like the diagram I posted earlier, have you ever taken it apart?
Posted: Sat May 07, 2011 9:27 am
by Alster370
Nope, I didn't think I needed too. It works unlike my piston valve so I was pretty chuffed.
Posted: Sat May 07, 2011 9:29 am
by jackssmirkingrevenge
A good test would have been to plug the chamber end and blow through the barrel end to see if air comes out of the pilot end, is this possible?
Posted: Sat May 07, 2011 9:51 am
by Alster370
yeah I could give that a try, ive got the chamber epoxied shut. Il will do it in an hour or so as my fittings have been redone with epoxy and are drying.
So if I blow into it and no air comes out the pilot , do I have a cup piston after all?
Posted: Sat May 07, 2011 9:53 am
by jackssmirkingrevenge
Alster370 wrote:So if I blow into it and no air comes out the pilot , do I have a cup piston after all?
Technically yes, though what might happen if tolerances are not too good is that your breath alone will not provide sufficient pressure for the cup to seal against the sides of the valve body.
Posted: Sat May 07, 2011 10:52 am
by Crna Legija
jackssmirkingrevenge wrote:Alster370 wrote:So if I blow into it and no air comes out the pilot , do I have a cup piston after all?
Technically yes, though what might happen if tolerances are not too good is that your breath alone will not provide sufficient pressure for the cup to seal against the sides of the valve body.
thats exactly what happens with my qevs.
Posted: Sat May 07, 2011 10:59 am
by Alster370
no air came out of the pilot at all when I tested it.
I have a new problem though, when pressurising I get a tiny bit of air leaking from the qev down the barrel. This is rather annoying because it just pushes the ammo out of the barrel before ive pressurised it fully. I think its because the 1/2 to 15mm fitting is not sealing at the bottom of the threads. would an o ring fix this?
Posted: Sat May 07, 2011 11:04 am
by Crna Legija
umm no fittings on the out side should make the qev leak, id say you have a bit of dirt on the piston or seat.
Posted: Sun May 15, 2011 1:29 pm
by Alster370
Well its been a productive last week and the gun is nearly finished (mechanically) just one tiny leak to get rid of
and then I can clean it up and move onto the stock. I managed to get the qev to seal at 6psi which is pretty good and stop the air leaking past it.
Not bad to say that a fridge freezer is my workbench and I have to use an adjustable spanner that doesn't lock in place properly
Let me know what you think so far