SpudFiles

Today I just finished putting a QEV on my copper ball valve cannon but when I pressurised it to about 100psi it let out an ear piercing series of short squeaks. I have no idea what it could be and it's fine at lower pressures.
Anyone know what's happening or had this problem?

sharpshooter11000 wrote:Today I just finished putting a QEV on my copper ball valve cannon

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Leak in the pilot chamber?

I meant upgrading the ball valve to a QEV. The pilot chamber is completely airtight. It was about as loud as a smoke alarm but it didn't actually fire it, I did that after a few squeaks.

Check all of your connections, def. sounds like a leak to me! Submerge in water to find the leak!!

I'll try that but every connection is very tight, I even bent the old barrel using it as a lever

Sounds like it's honking, what's the diameter of the QEV and pilot?

Zeus wrote:Sounds like it's honking, what's the diameter of the QEV and pilot?

Yeah i reckon too, id try pilot it with a bigger valve.

It's a 1/2"bsp QEV and 1/2"bsp ball valve for a pilot.
Bear in mind though that it happens as soon as it reaches about 80-100psi when I'm filling it. Do you think drilling an EQ hole in the QEV piston would help because it fills quite slowly and the noise might be air from the pilot chamber trying to equalise with the chamber?

Wait, are you filling from the chamber side?

If so it seems like your QEV is acting like a pop-off valve...

Nope filling from the pilot.
It goes quick connect > reducer > ball valve > QEV

Your piston might be dirty. You might have a small pec or something like this on the sealing face. Try to open the QEV and see if the rubber piston is all clean. I've had a similar problem on my new airsoft coaxial. Rubber was deformed and allowed air to pass in the barrel.
OR: you ball valve can be defective, let a light stream of air pass trough, decreasing pressure but not enough to pilot, until the pressure has dropped enough so that this little flow causes piloting.

spray a bit of wd40 or whatever inside the qev and give it a good blast in all 3 ports with shop gun, will save pulling it apart to clean it.
What is your chamber size?
I constructed a small bb muzzle loader with small main chamber filling through the pilot...quick fitting > 1/4 ball valve > 1/4 brass T piece> tyre chuck valve off bottom of T piece for the trigger >straight off the other end off T to the qev > ugly as sin 3/4 male female fittings stacked as a chamber approx 10-11inch long 3/4 qev > 6.5mm stainless 4.8mm bore barrel 14 inch long. add a couple of reducers where needed and voila.
ugly as sin but that small chamber made the qev honk like a mountain duck.. changed the qev over to a 1/4 inch and it works flawlessly.. for a single shot anyhow.
Air leaks in the pilot side of the qev is bad.. did i say it was bad... i meant VERY bad.. drops of pressure in the pilot side acts the same as a trigger.. that's right a self triggering air gun... DANGEROUS. always load projectile BEFORE filling with compressed air. take your time teflon taping the fitting on the pilot side.
check my posts and u should find some photos somewhere of a simple off the shelf parts BB pinger.

Fexo.

I should think that any dirt inside should have been loosened after a spray of WD40 and a few test shots The chamber is a small oxygen tank, about the size of a small fire extinguisher. The pilot seals completely as far as I can tell, all the fittings are taped loads. I'll dip it in some water to test tonight. Did yours honk when you piloted or filled?
Thanks for all your help guys! It's so confusing

So I tested it last night and found a leak on the chamber side. I don't understand though why it would be screeching. Could it be the air trying to equalise, going from the pilot chamber to the chamber and squeezing past the piston?

Hmmm, have you checked with soapy water and looked foer bubbles? i find that's the best way to look for leaks. Again, as most people said it sounds very like a leak in the pilot, my QEV gun does that if i pilot it through the schrader. The sound is horrible, something that would be good for anti-riot gear...