Thread Seal Type
- A seal is obtained by applying a sealant to the male
thread before engaging.
- The sealant is used to prevent spiral leakage.
- Thread tape or paste is the preferred sealant in this type of
Washer Seal Type
- A seal is obtained when the male thread is tightened
down onto the washer of the female assembly.
- The washer should be inspected regularly and replaced as
needed to prevent leakage.
Mechanical Seal Type
- A seal is obtained through metal to metal contact or metal
to seal contact, i.e. JIC couplings have a metal
to metal seal. Boss Ground Joint couplings have a metal to seal
contact, (shown above).
- The couplings should be retightened as needed to
Thread Sealing Tips
Sealing NPT threads can be an exasperating experience
if certain techniques are not followed. The following tips will
help alleviate many common problems in thread sealing:
- Always use some type of sealant (tape or paste) and apply
sealant to male thread only. If using a hydraulic sealant, allow
sufficient curing time before system is pressurized.
- When using tape sealant, wrap the threads in a clockwise motion
starting at the first thread and, as layers are applied, work
towards the imperfect (vanishing) thread. If the system that
the connection being made to cannot tolerate foreign matter (i.e.
air systems), leave the first thread exposed and apply the tape
sealant as outlined above.
- When using paste sealant, apply to threads with a brush, using
the brush to work the sealant into the threads. Apply enough
sealant to fill in all the threads all the way around.
connecting one stainless steel part to another stainless steel
part that will require future disassembly, use a thread sealant
that is designed for stainless steel . This stainless steel
thread sealant is also useful when connecting aluminum to aluminum
that needs to be disconnected in the future. These two materials
gall easily, and if the correct sealant is not used, it can
be next to impossible to disassemble.
- When connecting parts made of dissimilar metals (i.e. steel and aluminum), standard tape or paste sealant performs satisfactory.
- For sizes 2" and below, tape or paste performs satisfactory.
When using thread tape, four wraps (covering all necessary
threads) is usually sufficient.
- For sizes 2½" and above, thread paste is recommended.
If thread tape is used, eight wraps (covering all necessary
threads) is usually sufficient. Apply more wraps if necessary.
- For stubborn to seal threads, apply a normal coating of thread paste followed by a normal layer of thread tape. 9. For extremely stubborn to seal threads, apply a normal coating of thread paste followed by a single layer of gauze bandage followed by a normal layer of thread tape.
When this procedure is done, the connection becomes permanent.
Extreme measures will be necessary to disconnect these components.
All other measures to seal the threads should be explored
prior to use of this technique.
- Over-tightening threads can be just as detrimental as in
sufficient tightening. For sizes 2" and below, hand
tighten the components and, with a wrench, tighten 3 full
turns. For sizes 2½" and above, hand tighten the components
and, with a wrench, tighten 2 full turns.