This is really unlikely to work. The reason the tape fits easily into
the female side of pipe threads is because IP* threads are tapered.
The purpose of this thread design is twofold and quite different from
straight threads like on machine screws and fliter threads. It combines
strong mechanical coupling with sealing of gas/liquid under pressure
without any additional seals/gaskets. The tapered thread causes a tight
friction fit as the nose of the tapered male thread comes into full
contact with the female thread. You will notice that these connections
are designed so that the male never 'bottoms' in the female and there is
always male thread remaining outside the joint, the threads must be what
limits travel, or the joint will fail to seal. The tight physical
contact of the threads also does most of the sealing. However, consider
the nature of the connection. The deepest part of the thread is in very
tight contact, but the contact gets less and less as you move out from
the deepest point of contact. That is why the other component of the
seal is needed, joint compound or tape. What is needed is something
which will go into the joint with the male threads without pulling away
from the threads and fill the widest gap in the first full turn of
thread and somewhat beyond without being blown out by pressure or
degraded by the substance it seals. That's why there are different
sealing compounds for different uses. It turns out that PTFE tape works
wonderfully for this purpose for many needs, adhering nicely to the
threads, allowing the tightest threads to simply cut or crush through it
and providing a good seal under compression between the not quite so
close threads. Thus, the lubricating properties of tape or compound may
make setting the joint easier, but are secondary to their primary purpose.
Untapered threads do not inherently seal and require a separate sealing
fiunction at the tip or head if they are to act as seals too. They are
not designed to accomodate additional materials between the threads.
Moose
* IP = Iron Pipe, the material for which this tapered design was first
created.
piers@xxxxxxxx wrote:
>I will try out some PTFE tape - of the kind used to seal gas pipe threads.
>It's white, thin and very slippery, with sufficient 'give' to make a tight
>but not too tight seal, while preventing the aluminium thread and mount
>'gripping' each other. I think. We will see!
>
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