737 low pack 20psig
 

I'm currently troubleshooting this gripe and Im not sure what I'm coming up with, fault iso list: down to turning apu bleed on and turning the prsov valve to open and check for leaks when I do it to the right engine I hear the high stage valve really loud(the side that's low) but I do the same step on the left engine and the high stage is much quieter. The "split" happens at climb and sat at cruise. Looking at the diagram I'm seeing 5th stage takes over but could the high stage valve be faulty that would cause the low pressure to go through the prsov?

What does the FIM say?

Johnnygoodguy,

Check the sense/muscle lines just above the PRSOV. They are prone to cracking around the welds on the lines in that area.

Rgds McHale.