sealing NPT threads
sealing NPT threads
(OP)
I am building a blending station for mixing SCUBA breathing gases. The system will handle pure oxygen and helium at up to 2500 psi and Nitrox II (air with reduced nitrogen (@68%) and increased oxygen (@32%)) at pressures of up to 4000 psi. The manifolds are machined brass and the fittings going into the manifolds are either brass (line valves) or SS (316) check valves or #6 tube to #4 NPTM fittings. I have had large number of leaks, almost all of them between the manifold and SS fittings. I have tried using teflon tape with no success. I have tried using a thread sealant called LOX-8, with greater but not complete success. After reading other threads on this topic, I am considering trying both teflon tape and the LOX-8. The various components are all new and appear to be in good condition and manufactured to the stated specs.
My question is: "Are any other suggestions for things to try if this fails to stop the leaks?"
Thanks for your suggestions.
My question is: "Are any other suggestions for things to try if this fails to stop the leaks?"
Thanks for your suggestions.





RE: sealing NPT threads
It seals a little better than PTFE tape.
Greetings
RE: sealing NPT threads
We've had good luck using heavy (>1.1 s.g.) teflon tape with a top-dressing of an anaerobic pipethread sealant.
RE: sealing NPT threads
Mike Halloran
Pembroke Pines, FL, USA
RE: sealing NPT threads
RE: sealing NPT threads
Fluoramics suggested that the tape might be unnecessary with the LOX-8, but no luck, hence my question here.
Hacksaw - can you give me a more specific suggestion for an appropriate metal to metal seal? Thanks.
RE: sealing NPT threads
h
Ted
RE: sealing NPT threads
NPT is only considered on "low pressure" hydraulic cylinders.
G straight pipe threads with o-ring face seals are used on high pressure.