GENERAL HYDRAULIC SYSTEM REPAIR - Continued
· Always clean around fittings before disconnecting or connecting hoses or fittings. Ensure
area is clean before installing hydraulic components. Failure to comply may result in
damage to equipment.
· Cover, cap, or plug all openings, ports, and tube or hose ends when they are
disconnected. Failure to comply may result in damage to equipment.
· Ensure you mate only fittings designed to be mated with each other. Never depend on
trial and error. Just because two fittings will screw together is no guarantee that the
connection will not leak. See illustrations of fitting types in this work package. Failure to
comply may result in damage to equipment.
· Fittings must be installed and hand-tightened. If a fitting cannot be hand-tightened, it may
be cross-threaded or have damaged threads. Use wrench only for final tightening. Failure
to comply may result in damage to equipment.
· Do not use Teflon tape as a sealer on any fittings. It can separate from the fittings and
cause control valves, relief valves, and actuators to become contaminated and fail.
· It is possible to screw a male National Pipe Thread (NPT) into a female straight thread,
but the fitting will leak. Learn to recognize the very slight taper which an NPT has. Do not
attempt to connect NPT and female straight threads.
· Do not apply sealant to the first threads of NPT fittings. If sealant enters the hydraulic
system, it may cause components to fail.
· When connecting NPTs, care must be exercised. If overtightened, the female pipe thread
will split. Replace it. If a connection leaks, disconnect and apply thread sealant.
Reconnect the threads and snug up with an open-end wrench. Failure to comply may
result in damage to equipment.
· Be careful when installing preformed packings. Sharp threads can nick the packing,
causing it to leak. If fitting leaks, check packing for nicks or cuts and replace if necessary.
· Do not overtighten a flareless connection. Observe torque values in appendix for
hydraulic fittings. Overtightening can cause leakage, requiring replacement of entire tube
· When connecting a hose to a fitting, always use two wrenches. Use one wrench to turn
the swivel nut onto the fitting, and use another wrench to keep the hose from rotating. If
the hose rotates, it can loosen the other end of the hose, or loosen the fitting at the other
The following information is provided to familiarize personnel with the various types of hydraulic fittings. Refer to this
work package and the WARNINGs and CAUTIONs on the previous pages when working on hydraulic systems.