How to Install Hydraulic Fittings & Adapters
A clean, properly seated, correctly tightened connection is what keeps a hydraulic system leak-free and safe. Here's how to install threaded port fittings and adapters the right way.
Before you touch a connection: depressurise and lock out the system, and let hot components cool. Hydraulic fluid can be under extreme pressure — never crack a fitting on a live line.
Get set up
Before you start
Most early failures come down to contamination or a damaged seal — not the fitting itself. A few minutes of prep prevents most leaks.
- Work clean. Dirt and metal chips are the number-one cause of premature seal failure.
- Inspect the threads, bore and sealing faces for burrs, nicks and grit. Don't install a damaged part.
- Confirm the seal is the right size and material for your fluid and operating temperature.
- Have a torque wrench and a back-up (second) wrench on hand.
Procedure 1
Straight-thread (O-ring) port fittings
- Inspect the fitting and port — threads, bore and sealing face clean and undamaged.
- Check the O-ring. Right size and material for the fluid and temperature; replace it if it's nicked or flattened.
- Fit the O-ring onto the male thread and seat it at the base. Make sure it isn't twisted or pinched.
- Lubricate the O-ring lightly with system fluid or a compatible lubricant.
- Fit the back-up ring (if the fitting uses one) over the O-ring and seat it evenly.
- Tighten by hand first, then to the specified torque or turn count.
- Inspect — O-ring seated, fitting square to the port, no leaks under pressure.
Procedure 2
Adjustable port fittings (elbows & tees)
- Prepare the seal — follow steps 1–5 above so the O-ring is fitted and lubricated.
- Back off the locknut and back-up washer all the way, so the threads are fully exposed.
- Thread in until the washer just contacts the spotface. Don't overtighten yet.
- Aim the fitting. To orient an elbow or tee, back it out to the direction you need — no more than one full turn.
- Hold and torque. Hold the body steady with a back-up wrench while you tighten the locknut to spec.
- Inspect — seal and washer seated, orientation correct, no leaks under pressure.
Quick reference
Notes by connection type
How a connection seals changes how you tighten it. A quick guide:
37° flare (JIC)
Seals metal-to-metal on the 37° cone. Assemble to spec by torque or by the flats-from-finger-tight turn count. Don't over-tighten — it distorts the flare and starts leaks.
O-ring face seal (ORFS)
The O-ring in the flat male face does the sealing. Bring the faces together squarely and tighten to spec — the threads just hold the joint together.
O-ring boss / straight thread
Seals on the O-ring against the port spotface (Procedures 1 & 2 above). The straight thread carries the load, not the seal.
Tapered pipe (NPT / BSPT)
Seals on the threads themselves. Use a compatible thread sealant and tighten the right number of turns past finger tight rather than chasing a torque number.
Need the numbers? Tightening torque and turn counts vary by size, seal type and material. Our torque chart lists the values to SAE/ISO spec.
Open the torque chartTorque and turn values depend on the fitting's size, material and seal type, and these procedures are general guidance. Always follow the fitting manufacturer's published specification where one is given, and verify the assembly under operating pressure.
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