Hydraulic Flanges & Fittings

What is the purpose of flanges in fluid power?

Flange connections are used where standard threaded fittings cannot guarantee sufficient sealing and durability—typically in systems with extremely high working pressures or in areas subjected to severe vibrations and hydraulic shock. A solid metal flange (or a pair of split flanges), bolted down with socket head cap screws and sealed with an O-ring, guarantees an absolute leak-free seal at the ports of gear pumps, piston pumps, and hydraulic motors.

SAE Standards - 3000 PSI vs. 6000 PSI Series

The most widely recognized global standard for flange connections is SAE J518. It categorizes fittings into two main pressure classes:

• SAE Standard Pressure (3000 PSI Series / Code 61): Designed for medium to high-pressure systems (up to 210-350 bar depending on size). They feature a smaller bolt hole pattern.

• SAE High Pressure (6000 PSI Series / Code 62): Heavy-duty, thicker flanges for extreme heavy-duty applications and very high pressures (up to approx. 400-420 bar). They have a larger, wider bolt hole pattern.

How to correctly measure and select a flange or fitting?

To avoid ordering mistakes, accurate measurements must be taken on the pump housing or the old fitting. The key dimensions are:

• The exact center-to-center bolt hole spacing.

• The flange size (e.g., 3/4", 1").

• The type and size of the output thread (if it's a threaded flange adapter).

• The size and thread pitch of the mounting bolts (Metric or UNC).

If you are unsure whether a specific straight or elbow flange fitting will match your pump, simply provide us with the pump's part number. Our specialists will select the appropriate connection components, complete with the correct bolts and O-rings.