Mate a fitting only with a fitting designed to mate. Because two fittings will
s c r e w together is no guarantee they will not leak. Never depend on trial
a n d error. To do so could result in damage to equipment.
Fittings must be installed and hand-tightened. If a fitting cannot be
h a n d - t i g h t e n e d , it may be cross-threaded or have damaged threads. Use
w r e n c h only for final tightening. Failure to do so could result in damage to
Do not use pipe dope as sealer on any fitting. Pipe dope can separate
from fittings causing control valves and relief valves to become
c o n t a m i n a t e d and fail.
It is possible to screw a male NPT into a female straight thread, but fitting
will leak. NPT has a slight taper.
Do not attempt to use parts of a 37-degree flare fitting and a flareless
fitting with each other. Fitting will leak.
When connecting NPTs, use care not to overtighten. If overtightened,
female pipe thread will split.
Do not apply sealant to first thread of NPT fitting. If sealant enters
h y d r a u l i c system, it may cause components to fail.
Be careful when installing preformed packings. Sharp threads can nick
packing, causing it to leak.
Do not overtighten a flareless connection. Overtightening can cause leakage
r e q u i r i n g replacement of entire tube assembly.
When connecting a hose to fitting, always use two wrenches. Use one
w r e n c h to turn swivel nut onto fitting and other wrench to keep hose or
t u b e from rotating. Failure to do so could result in damage to equipment.
The following describes the types of fittings used in the vehicles. Refer to this information when
performing hydraulic maintenance tasks.
NATIONAL PIPE THREAD (NPT)
1. National Pipe Thread (NPT). This thread differs from others in that it is tapered. To obtain a
proper seal with NPT, a sealant must be used. The sealant should be applied to male threads.
Use care not to overtighten.