Instrument Vacuum system woes

[jeffsvan]

I tried a forum search and could not find what I needed.

A few questions about an older vacuum system please.

I am tidying up an older instrument vacuum system and trying to get it working optimally - replacing fraying hoses and filters ect.

1. How does one check for a vacuum leak in the system?
I know how to check for pressure leaks, and pitot static leaks, but not aircraft instrument vacuum.

2. I understand teflon tape, and pipe dope are a big NO for the barbed fittings that screw into the back of the flight instruments (attitude indicator) . How then does one get a good seal on the fittings that are screwed into each instrument?

[gasman]

Originally Posted by jeffsvan

I tried a forum search and could not find what I needed.

A few questions about an older vacuum system please.

I am tidying up an older instrument vacuum system and trying to get it working optimally - replacing fraying hoses and filters ect.

1. How does one check for a vacuum leak in the system?
I know how to check for pressure leaks, and pitot static leaks, but not aircraft instrument vacuum.

2. I understand teflon tape, and pipe dope are a big NO for the barbed fittings that screw into the back of the flight instruments (attitude indicator) . How then does one get a good seal on the fittings that are screwed into each instrument?

#1 The vacuum system is a continuous leak. Just make sure your vacuum gauge reads within required volume.

#2 I like to use quality electric marking tape. 3M Scotch #35 Electrical Tape Value Pack (10457NA). This tape is thinner than normal electric tape. Cut it long enough to just overlap in trail... one layer only. Leave one thread exposed. Install hand tight + 1/4 turn.