Proportional Valve

Canonical Definition

A hydraulic directional control valve that modulates flow and pressure proportionally to an electrical input signal using a solenoid-actuated spool. Proportional valves operate with internal spool-bore clearances of 5–25 µm — larger than servo valves but still highly sensitive to particle contamination above 10–15 µm. Target cleanliness codes for proportional valve circuits are typically ISO 17/15/12 to 16/14/11. Proportional valves are widely used in mobile hydraulics for boom, arm, and bucket control on excavators, and in industrial presses for force and position control.

Engineering Context

Contamination-induced stiction in proportional valves causes control instability, poor positioning accuracy, and premature spool and bore wear. Unlike servo valves, proportional valves can typically tolerate small, non-cutting contamination events without catastrophic failure, but repeated contamination events progressively degrade metering performance. The valve manufacturer's cleanliness specification must be verified against the system's achievable and maintained cleanliness target.

Applicable Standards

Related Technologies

Protection Systems

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