Thread sealant for hydraulic fittings
Hydraulic fittings must remain leak-proof under high pressure and must not loosen due to vibration. Anaerobic thread sealants fill the thread gap, harden between the metal surfaces, and provide a reliable seal – without the drawbacks of PTFE tape or hemp. This article shows which product is suitable for hydraulic threads.
To the point
For metallic hydraulic and pneumatic threads, a medium-strength anaerobic thread sealant like LOCTITE 542 the classic choice; for high-performance applications, LOCTITE 586. Permabond offers equivalent types. The seal provides a low initial seal and a full seal after curing – and remains disassemblable at medium strength.
Why anaerobic sealing instead of tape or hemp?
PTFE tape and hemp provide a mechanical seal, but can slip, tear, and release particles during tightening – a risk to valves and fine bores in hydraulic systems. In contrast, an anaerobic thread sealant fills the entire thread gap and hardens completely: no leakage path, no particles, no contamination of the hydraulic oil. It also slightly secures the connection against loosening due to vibration.
Conical and cylindrical threads
Anaerobic sealants work on both tapered (e.g., NPT, BSPT) and cylindrical (e.g., BSPP, metric) threads because they fill the gap instead of just clamping. They are particularly advantageous on cylindrical threads, where tape doesn't adhere well. Curing is anaerobic: in the absence of air between the metal surfaces; on passive metals (stainless steel, zinc-plated), an activator accelerates the process.
Product selection
| Requirement | Loctite | Permabond |
|---|---|---|
| Fine thread, medium strength, demountable | 542 | MH052 |
| High requirements / larger threads | 586 | A1044, HM163 |
A different principle is responsible for the surface sealing of housings (FIPG) – see, for example, the guide to high-strength bonding and the brand comparison under Permabond & Loctite overview.
Application
Clean the threads of any coarse dirt, apply sealant all around the external thread (leaving the first few threads clear), screw in the fitting, and allow to cure according to the data sheet; use an activator for passive metals or in cold conditions. Background information on curing: Understanding adhesive curing; for preparation: Surface preparation.
Frequently Asked Questions
Anaerobic or PTFE tape for hydraulics? Anaerobic sealants provide a seamless seal, do not release particles and protect against vibration – usually the safer choice in hydraulic systems.
Will the seal withstand the pressure? Yes, cured anaerobic thread sealants are designed for high pressures; the exact pressure rating is specified in the data sheet for the respective type.
Can the screw connection be loosened again? Medium-strength types can be disassembled with tools; high-strength types are designed to be more durable.
Consultation and samples
Tell us the thread type, material, medium, and pressure – we'll recommend the right sealant and provide a sample. Contact us or write to info@silitech.ch.
