TM 9-2510-247-13&P
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GENERAL HYDRAULIC SYSTEM REPAIR - Continued
The following information is provided to familiarize personnel with the various types of hydraulic
fittings. Refer to this section and the warning and cautions on the previous pages when working on
hydraulic systems.
1.
National Pipe Thread (NPT) is commonly found in hydraulic systems. It differs from other
fittings because it is tapered. In order to obtain a proper seal with this thread, you must use a
sealant. The sealant should be applied to the male fitting.
CAUTION
Do not apply sealant to the leading edge or the first thread of hydraulic fitting or
sealant may get into the hydraulic system and contaminate it. Failure to comply
may result in damage to equipment.
Figure 100. National Pipe Thread (NPT)
2.
An O-ring (preformed packing) boss has a straight thread. The seal for this termination is a
preformed packing that fits at the top of the threads on the male fitting. This packing is
squeezed into the extra space at the top of the threads of the female fitting and seals the
connection. The installed packing must be free of nicks and cuts to seal properly. If packing is
nicked or cut, it must be replaced.
CAUTION
Do not apply sealant to the leading edge or the first thread of hydraulic fitting
or sealant may get into the hydraulic system and contaminate it. Failure to
comply may result in damage to equipment.
Figure 101. O-Ring (Packing) Boss
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