This Resource Centre provides general guidance only. Always follow the equipment manufacturer’s instructions, the product technical data sheet and your site’s safe system of work. Isolate stored energy before maintenance. For safety-critical, regulated or uncertain applications, ask a competent engineer or the product manufacturer to confirm the specification.
Not every hydraulic fitting seals on its thread. Understanding the sealing point prevents overtightening and incorrect use of tape or compound.
Common sealing arrangements
- Tapered thread: interference between male and female threads creates the sealing path, usually with a compatible sealant where specified.
- Elastomeric seal: an O-ring seals against a machined face or port; the thread holds the parts together.
- Metal flare or cone: accurately machined metal faces meet under controlled tightening.
- Bonded seal or washer: a washer seals beneath the fitting shoulder.
- Compression fitting: an olive or ferrule deforms in a controlled way around tube.
Before assembly
Confirm the connection family, size, material, pressure rating and seal. Inspect the sealing face and O-ring groove. A scratched cone or twisted O-ring may leak even when the thread is correct.
Sealant rules
Use only a sealant approved for the thread type, fluid and operating conditions. Keep excess material out of the system. Do not apply thread tape or liquid sealant to a connection that seals on an O-ring or metal face unless the manufacturer specifically instructs it.
Tightening
Follow the fitting manufacturer’s assembly procedure. “As tight as possible” is not a specification. Excessive tightening can distort a sealing face, crush a washer, damage an O-ring or crack a port.
Never check a pressurised hydraulic leak with your hand. Use a safe detection method and treat suspected injection injury as an immediate medical emergency.
Need help sourcing the item?
Send the manufacturer, reference, photographs and operating details.