For any hydraulic system using subplate-mounted proportional directional valves, the ISO 4401 standard defines the interface that determines whether installation goes smoothly or ends in leakage.
The standard specifies port patterns from NG6 through NG32. An NG6 subplate uses four M5 bolts on a 40.5mm × 31mm bolt circle, with P, T, A, B ports arranged symmetrically. The surface flatness must be within 0.01mm per 100mm. A common failure point is the O-ring counterbore depth - ISO 4401 requires ±0.1mm tolerance; exceeding this causes either extrusion or insufficient compression, both resulting in external leakage under system pressure.
For engineers working with Rexroth Type proportional valves - including direct-acting models like 4WRAE and 4WRPEH, or pilot-operated valves like 4WRKE and 4WRZE - the mounting interface follows ISO 4401 exactly. This means a proportional valve from one source can be mounted on any standard subplate without re-machining. The interchangeability also simplifies spare parts management when maintaining mixed fleets across injection molding presses, die casting machines, and hydraulic press lines.
Design tip: Always verify that the P, T, A, B port identifications on the manifold match the valve markings before final assembly. Mislabeling during manifold fabrication remains one of the most frequent commissioning failures in electro-hydraulic systems.
