Page 617 - DixonCatalog20092010

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T
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
application.
• Please refer to page 585 for thread tape options.
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.
• Please refer to pages 270, 283 and 565 for replacement
washers.
Mechanical Seal Type
• A seal is obtained through metal to metal contact or metal
to seal contact, i.e. JIC couplings (page 372) have a metal
to metal seal. Boss Ground Joint couplings (pages 93,
96) have a metal to seal contact, (shown above).
• The couplings should be retightened as needed to
prevent leakage.
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:
1. 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.
2. When using tape sealant, wrap the threads in a clock-
wise 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.
3. 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.
4. When 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
(see page 585). 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.
5. When connecting parts made of dissimilar metals
(i.e. steel and aluminum), standard tape or paste sealant
performs satisfactory.
6. For sizes 2" and below, tape or paste performs
satisfactory. When using thread tape, four wraps
(covering all necessary threads) is usually sufficient.
7. 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.
8. 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.
Caution!
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.
10. Over-tightening threads can be just as detrimental as
insufficient 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.