Best sealant for pipe threads holding a vacuum

[Old Codger]

What is a good substance to seal pipe threads with when connecting a vacuum pump to a system? I tried Teflon tape and I still have a leak. Should I use regular pipe thread putty? Should I just keep tightening the brass to steel fitting? Something else?

Thanks,
OC

[Grizzly]

What is a good substance to seal pipe threads with when connecting a vacuum pump to a system? I tried Teflon tape and I still have a leak. Should I use regular pipe thread putty? Should I just keep tightening the brass to steel fitting? Something else?

Thanks,
OC

Hi OC.
Provided the pipe thread is a tapered type or a compression style fitting.
Then I have found LEAKSTOP perfectly good.
BUT it does work on the principle that the paste (blue) is subjected to compression forces.
Hence the reference to the thread being tapered.
With a parallel thread then ptfe should be fine?
Just wrap more passes around the threads!
In the past I have used a soft putty compound around a leaking Shaft Seal to allow a 12hr Vacuum test. H.M. Navy requirement.
Cheers Steve.
Cheers GRIZZLY

[chemi-cool]

What is actually sealing between the brass connection and any port on the system is the rubber that seats in side the brass connector, if it is too short or damaged, you will have a leak.

[Old Codger]

The vacuum pump port is just a straight piece of brass pipe with a 134A fitting and a ***** 12 fitting at one end and threads at the other end. No flange for any kind of gasket, just a threaded hole in the steel block at the vacuum pump that the port screws into.

Kep

[nike123]

The vacuum pump port is just a straight piece of brass pipe with a 134A fitting and a ***** 12 fitting at one end and threads at the other end. No flange for any kind of gasket, just a threaded hole in the steel block at the vacuum pump that the port screws into.

Kep

If you want to use it where you don't need to dismantle joint frequently, like in your case, then use Loctite 569 (http://tds.loctite.com/tds5/docs/569-EN.PDF)

[Chillin']

Do not use Teflon Tape for anything on refrigeration! The manufactures specify that their product is designed for 'lubrication only' not a sealant. I have done numerous repairs on leaking threaded systems and have found that the ' blue stuff ' just doesn't seal. The Loctite 567 is good for smaller fittings and anything over 3/8" you should use Loctite 271.

Just my 2 cents - it's free!