static system leak chasing

[RFguy]

Troubleshooting a static leak is hard. Things under pressure  can be done with soapy water or ultrasonic leak detectors.

The fancy static/pitor test boxes seem to only read out the leak rate once per second. 

So I made a box on a saturday to make it far easier and quick to find the trouble.
I bought a blade adaptor from a manufacturer of said boxes and passed across my ideas. I dont consider them secret and propreitary ....

The big deal for leak finding is that I update the pressure change  (or absolute pressure) indication  every 20mS or so wiith an audible loud tone or clicking from a box.  with the box at the wing, I can hear it while under the instrument panel.

The fast update rate enables connections to be wiggled and instant responses, rather than most test gear that updates the digital readout  at once per second.... And if one person is doing the job,  its impossible otherwise, because generally you are lying on your back under the instrument panel. 

I have plans to add voice control of the pump etc or at least a remote pair of wires and a little keypad . and also add VOICE announciation of what is on the pressure displays.

There are a few diifferent modes I came up with . I use a differential pressure sensor of course.

(2) RATE of negative pressure leak. (leaking from neg pressure toward zero. ) 
This is the one I use for looking for static leaks.
Zero freq tone at 0 leak.  increases up to 3kHz  at equiv 500ft/min leak.
that is generated by a click sent to the loudspeaker. This way , a very small leak is 10-20 clicks per seconds, rises up to 200-400Hz for moderate leaks. Harder to hear in a noisy hanger but very precise. IE falling altitude indication.

(3) RATE of positive leak (leaking from  + toward zero) 
This is the one I use for looking for pitot leaks.
similar to (2) , but other sign of pressure (ie falling ASI indication) 

(3)  absolute pressure negative offset. Zero pressure is 440 Hz (middle A). increases up to 5kHz  at 10,000ft negative pressure. used on static
(4) absolute pressure positive offset . zero pressure is 440Hz,,  increased up to 5kHz for 1 psi (used on pitot side) 
(5) + and -  absolute pressure, with tone centred at 1.5kHz . IE can go u up or down.
that's  a nice sine wave tone. really just my testing.

3 and 4 are easier to hear  in a noisy hanger

 

Edited 1 hour ago by RFguy

[RFguy]

and

In my case it was a bad AN3  3/16" aluminium tube flare. it was tight but had a crack in the flare and on removal the aluminium AN3 to 1/8 NPT fitting on the flare side  had been cross threaded maybe once or twice. .

I have replaced the entire 50 year old patched up system with the Nylo-seal system . An excellent system! 

it sealed up first go. I teed off each instrument from a single long series of Ts, rather than daisy chained from instrument to instrument, which enables isolation .

Note you must use the tube inserts in the commonly used polyflo tube. 

 

Highly recommended ! 
Note be VERY careful of applying vaccuum and pressure to the system (with a box or syringes) 

Think about what you are doing.  Run the numbers !  1620 Pa is 100 kts (sea level STP) or 0.235 psi, so if you blew into the pitot, you would blow its brains out.

same with, for example, putting 10,000 feet across it is about  30kPa/4psi

 

you can VERY easily exceed the absolute maximum pressure differential across the ASI . For chasing static leaks, I suggest removing the ASI off the static line to eliminate any  accidents. Other practice is to T the pitor and static together so the asi doesnt see high diff pressure. (although then you might get high case to diagram pressure differential, that might also be bad) hence disconnect it. 

glen