[mcguyver]

Are you using a manual valve? If so, this is your problem.

Now comes the censure. If you did not know that you should not be using a manual valve, you have no business building this. Seriously. And, you should not be using PVC pipe with those kinds of pressures. PVC can be unpredictable, expecially during temperature changes and can shrink or expand quite significantly. I know, I use it all the time at work.

You should be using steel. The pressures generated here can be hazardous if you have a failure, especially in your smaller pipe sections.