Whenever possible, we highly recommend using SAE O-ring or JIC fittings. Both of these provide a highly reliable, reusable connection. Since these fittings don’t rely on mechanical deformation to create a seal, the risk of a broken fitting or port is virtually eliminated.
SAE O-ring (O-Ring Boss) are straight thread fittings that seal using an O-ring between the thread and the wrench flats of the fitting. The O-ring seals against the machined seat on the female port.
Fittings with O-rings offer advantages over metal-to-metal fittings.
O-ring fittings can either be adjustable or non-adjustable. Non-adjustable fittings are screwed into a port where no alignment is needed. Adjustable fittings can be oriented in a specific direction.
JIC 37° flare fittings seal with metal to metal contact between the flared nose of the fitting and the flared tube face in the female connection.
NPT, National Pipe Thread fittings seal using a metal-to-metal connection. The metal of the male and female threads deforms during installation to create this seal. As a result, pipe thread connections tend to leak after a connection is made, disassembled, and re-assembled. If the connection leaks after re-assembly, you may need to replace one or more of the fittings. Continuing to tighten the connection will not necessarily eliminate the leak and can easily result in a split fitting or port.
Over-tightening the connection can easily split the female portion of a pipe thread connection. This is especially true when installing male pipe thread fittings into cast iron ports on valves, motors, and cylinders. Split ports are not covered by manufacturer’s warranties!
Under or over-tightening any fitting can allow leakage, but all-metal fittings are more susceptible to leakage because they must be tightened to a higher and narrower torque range. This makes it easier to strip threads or crack or distort fitting components, which prevents proper sealing.
Using a liquid thread sealant for NPT connections is recommended over using Teflon tape. If using Teflon tape, only use one-and-a-half wraps around the male portion of the thread. Start two threads up from the end of the male portion of the fitting. Keep in mind that liquid thread sealant and Teflon tape are potential contaminants to the hydraulic system.
Leaks can also result from vibration, thermal cycling and from loads being supported by the connection (i.e. using the fitting in the connection to support mechanical loads).