I want to connect two parts by threading. Usually
to seal it you need to put tape or sealant. But I
saw some peek connectors that just threading two parts
together and there is no leakage problem. I tried
regular die and tapping tool, it doesn't work.
Any ideals how the threads made with sealing function?
Thanks a lot for help!
Dept. of Mechanical Engineering
Univ. of Maryland, Baltimore County
1000 Hilltop Circle
Baltimore, MD 21250
Dear Tom Song:
Having the threads made with the same tolerances, thread forms, etc. will
make all the difference in the world. And it is the worst possible method
of sealing. I strongly recommend engineering an o-ring seal, or simply
using one of the standard methods that already incorporates an o-ring. SAE
is an example of the latter. There is a company that makes a face-seal
o-ring, but this is proprietary.
In direct answer to your question, assuming we are speaking of a tapered
pipe thread, the sealing occurs on exactly the peak of one full thread, and
then across the "valley" between the two "ends" of the fully seated thread.
Which is why thread sealing is a really bad idea... too much chance of
damaging a knife edge.
David A. Smith
American Standard taper pipe threads (ASA B2.1) use a tapered thread for the
male connection and a
straight thread for the female connection. As the result, a single thread is
(generally) the only
one that actually seals. The nature of the process to cut threads is NOT
accurate enough and the
thread is NOT smooth enough to guarantee that seal requiring the use of tape or
For the few threaded connections (shut off valves) that I have in my home, I
make certain that I use
two wraps of tape on the thread. The tape works better than paste for me.
You may look into *Dryseal* threads. See this page:.
You did not define *pressure* with a value so this may or may not apply to your
connections can not be trusted for high pressure use. We used ASTM A106 grade B
fittings and SAE 4 bolt flanges for our high pressure applications. For your
check with the fitting manufacturer for the rated maximum pressure of the
fittings. Remember when
you *cut* a thread in pipe, you create a high stress area in the thread area in
addition to reducing
the wall thickness.