Why Hydraulic Fittings Leak: Torque & Sealing FAQ
What causes a hydraulic fitting to leak?
Most hydraulic leaks come from incorrect torque, mismatched thread types, or damaged sealing surfaces. Proper thread matching and torque are the keys to a leak-free connection.
How tight should hydraulic fittings be?
Hydraulic fittings should be tightened to the manufacturer's torque spec for the size and thread type, since both under- and over-tightening cause leaks. Flare and o-ring fittings rely on precise, not maximum, torque.
Does over-tightening cause leaks?
Yes, over-tightening can deform sealing surfaces and threads, creating gaps that leak under pressure. Correct torque, not maximum force, produces the best seal.
Should I use Teflon tape on hydraulic fittings?
Use PTFE (Teflon) tape only on tapered thread fittings like NPT, never on flare or o-ring fittings that seal mechanically. Applying it to the wrong type can cause leaks.
Why does Teflon tape fail in high-pressure systems?
Teflon tape can extrude, shred, or fail to seal reliably under high pressure, and loose pieces can contaminate the system. Engineers often specify thread sealants or mechanical seals instead.
How does torque affect sealing in hydraulic systems?
Correct torque compresses the sealing surfaces just enough to block fluid, while too little leaves gaps and too much deforms the seal. Torque is critical to whether a connection seals or leaks.
Can I reuse instrumentation ferrules?
Reusing ferrules is risky because they permanently deform and bite into the tube on first installation, so a reused ferrule may not reseal reliably. Fresh ferrules are recommended for a dependable seal.
Why is my JIC fitting leaking?
A leaking JIC fitting is usually caused by improper torque, a damaged or scratched 37-degree flare seat, or a mismatched flare angle. Inspect the sealing surfaces and re-torque to spec.
What is the correct torque for stainless steel fittings?
Correct torque depends on the fitting size and thread type, so always follow the manufacturer's torque chart, and remember anti-seize can lower the required torque. Under- and over-tightening both cause leaks.
Why do hydraulic fittings leak?
Most hydraulic fitting leaks come from improper torque, either under-tightening that leaves gaps or over-tightening that deforms the sealing surface. Matching the correct thread type and torque spec is the key to a leak-free seal.
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