Tank valve problem

I let a new tuner work on my gun and also the tank valve.
I have had the gun for months and shot it just enough to sight in a night vision scope, then the gun sits in the corner.

Yesterday I decided to see how well it was tuned on the Chrony.
Well, before I could shoot 2 ten shot strings, the tank valve starts blowing all the air out after a shot.
Besides the gun having no more power etc than a stock gun, the roughness of the parts, etc, etc. That is besides the point, anyone konw what is wrong with the bottle valve? What would the “fix” be?
Walt in Ha. is making a 25cal barrel, so not would be a good time to get it repaired correctly.

What pisses me off is I spent several 100 dollars and it turns out to be a piece of shit.

To ALL-
ONLY ALLOW TUNERS WITH A LONG HISTORY OF QUALITY WORK TO TUNE YOUR GUN.

Now I am stuck, laid off and do not have the $$$ to repair the gun as it should have been tuned in the 1st place.

I wish a million times over I would have sent it to Talon Tunes or Airhog to have the work done…, but me being me, trying to help someone out, trying to help him build a name working on these guns, just starting out, giving him a chance to build a reputation…, you know…, now I am “stuck”. The gun can not shoot, I have no extra $$$ to get it repaired and no night vision gun as I needed for varmints.
All because I always try to help out the “small guy”, the underdog, someone starting out, etc.
I always seem to get screwed when I try to help out people. I always get it in the end, one way or the other.

Rant over, I did not mean to rant, it just came out, LOL!
Anyhow, can anyone help with the valve problem?

Thanks:)