Mark

We had a leak on a static system that was not showing leak detector bubbles when we pumped the static system up with 450 Knts (approx - 5PSI pressure).

With some trepidation, we applied 20 PSI to the system which did help us locate a cracked fitting.

We used (100 PSI) nitrogen bottle pressure stepped down with a pneumatic system test unit. We were able to slowly bring up pressure from 0 to 20 PSI. We could have gone higher, but the leak was located within 5 minutes of using this modified procedure.

Bottle and regulator.....
  
     
  
Red adapter hose with 100 PSI pressure relief valve (located at bottom of image).
  
     
  
Pneumatic tester.....
  
     
  
Pressure indication.....
  
     
  
Leak found at a "through floor" fitting behind the F/O's static source select switch.
  
     
     
  
Connections at back of switch. (Most aircraft have these switches removed. Crews don't use them. They are a continual problem area because of unnecessary lines and fittings.)
  
     
  
Fitting crack.....
  
     
  
This was the first aircraft I encountered with quick disconnect fittings at the probe. These are usually flex line "B nut" connections.