Hydraulic Connectors

Choosing Threaded Connectors

Choosing connectors in high pressure hydraulic circuits is important for preventing leaks

• This was made clear in a recent in-person interview with a professional in the hydraulics industry. The claim was that in circuits with more than 200 PSI, connectors with "Parallel Threads" should be used instead of those with "Tapered" or "Pipe" threads.

• The key issue is that tapered threads do not seal completely and must employ a "sealant" to seal the threads completely. When fluid pressure is applied, the metal threads remain in place, but the sealant can give way and allow leaks to form. Leaks may not occur at first, but they will develop over time as the sealant weakens and as the connections experience movement and vibration.

Tapered vs Parallel Threading

• Designations for tapered pipe threads are:
  • NPT (National Pipe Taper)
  • BSPT (British Standard Pipe Tapered)

• Designations for connections with parallel threads:
  • BSPP (British Standard Pipe, Parallel)
  • UN/UNF (or "SAE Straight Threads")
  • Metric

Summary

• In summary, parallel threads are preferred for OSE hydraulic applications, since they reduce the potential of leaking.
• The most common straight threads available are "SAE" threads.

Reference

• Here is a document from Parker Hannifin explaining the details:

Pipes Fittings

Identifying unknown connectors

If interfacing to a piece of equipment with unknown connectors, the following resources can be helpful in identification.

How to Identify Fluid Ports and Connectors

Fitting Identification Guide

Surplus Center port identification flyer

Name that thread