When Hydraulic Flange Fittings Are the Better Choice

Fluid power systems have moved toward connection styles that use elastomeric O-ring seals to reduce leakage. That group includes SAE straight thread, face seal, ISO 6149, and SAE J518 flange connections such as Code 61 and Code 62.

Hydraulic flange fittings are especially useful when the connection is large, highly pressurized, difficult to access, or easier to service as a bolted joint than as a large threaded joint.

Captive Flanges

For tube-to-tube, pipe, or hose work, a captive flange may be used. A captive flange slips over the flared tube or fitting and connects to the mating flange or component.

Captive flange fittings are commonly associated with straight flange adapters where there is clearance for the flange to slide over the fitting and seat on the flange head.

Split Flanges

Split flanges are commonly used with 45 degree and 90 degree flange fittings. A split flange kit for Code 61 or Code 62 typically includes two flange halves, the O-ring face seal, and four bolts and washers.

The split halves fit around the flange head and let the connection be secured to the port without sliding a one-piece flange over the entire fitting geometry.

Why Flanges Are Useful

Flange fitting connections are often easier to assemble in tight spaces and easier to disassemble for maintenance or system changes. They can be a strong option for larger diameter applications under high pressure.

Code 61 flanges are commonly used on larger tube or pipe sizes, while Code 62 can provide higher pressure capability on selected sizes. Flange connections also reduce the torque required compared with tightening a comparable large threaded fitting.

Single-Point Sealing

A flange connection creates a single sealing point between tube, pipe, hose, or component port. That seal must be compatible with the fluid and supported by the correct flange code, O-ring, bolts, and port face.

When the size, pressure, and access conditions favor a bolted connection, a hydraulic flange fitting can be the better choice than a large threaded connection.