Home › Collections › Proportional & Servo Valves

Proportional & Servo Valves

Proportional and servo valves convert continuous electrical command signals into proportional hydraulic flow or pressure output, enabling variable-speed actuation, closed-loop control, and precision force management across industrial fluid power systems. PLC Direct stocks proportional and servo valve hardware from Parker Hannifin, Bosch Rexroth, and Moog through independent suppliers, available as surplus sealed, refurbished, and used hardware for replacement in existing installations.

Where Are Proportional & Servo Valves Used in Industrial Environments?

Proportional and servo valves are specified whenever standard on/off directional control is insufficient, requiring the actuator speed, force, or pressure to be varied continuously in response to an analog command signal. They appear across manufacturing, test, process, and energy industries that require variable-rate hydraulic actuation with repeatable cycle-to-cycle consistency.

Facilities and operations that depend on proportional and servo valves include:

Plastics injection molding machinery, where proportional valves control injection velocity and hold pressure at variable set points across each molding cycle.

Hydraulic press and forging operations requiring proportional valve control of ram approach speed, contact velocity, and applied force independently across each stroke phase.

Materials testing and fatigue test systems using continuously variable flow and force control in response to transducer and displacement sensor feedback signals.

Steel mill roll gap and continuous casting equipment relying on electrohydraulic servo valves for high-bandwidth position and force regulation under varying load.

Industrial simulation and flight test rigs where valve response bandwidth directly determines actuator dynamic accuracy and usable frequency range.

Replacing a proportional or servo valve with a mismatched unit alters the closed-loop system's gain and response characteristics, making exact series and model code matching critical before ordering.

Which Brands of Proportional & Servo Valves Does PLC Direct Stock?

PLC Direct stocks proportional and servo valve hardware from Parker Hannifin, Bosch Rexroth, and Moog across four confirmed product families, sourced through independent suppliers.

Parker Hannifin D1VW series proportional directional control valves: Direct-operated proportional spool valves in the D03 mounting pattern for variable-flow directional control in industrial hydraulic circuits requiring analog command input.

Bosch Rexroth VT series analog amplifier modules: Control electronics that convert analog command signals into calibrated solenoid current output for proportional hydraulic valve pressure and flow control applications.

Moog D662 series two-stage electrohydraulic servo valves: Pilot-operated servo valves rated to 5,000 PSI and 15 GPM for high-bandwidth closed-loop applications in injection molding, materials testing, and precision industrial circuits.

Moog D663 series direct drive servo valves: Pilot-stageless servo valves rated to 4,500 PSI providing contamination-tolerant proportional flow control for die casting, plastics machinery, and general-purpose industrial servo circuits.

All listed hardware is available as surplus sealed, refurbished, and used. Contact PLC Direct for part-level availability and current pricing.

What Should You Know Before Ordering Proportional & Servo Valves?

Hardware condition options: Surplus sealed units are unused and in original manufacturer packaging. Refurbished units have been inspected and restored to functional operating condition. Used units are tested and operational, with conditions stated on each product listing.

Compatibility and part identification: Proportional and servo valves must be matched by valve series, flow rating, pressure rating, mounting pattern, and input signal type. For Rexroth VT series amplifier modules, the module version must be compatible with the specific proportional valve it drives, as VT series cards are engineered for particular valve families and signal configurations.

Warranty: All proportional and servo valve hardware purchased from PLC Direct carries a standard 1-year warranty covering defects and functionality, applicable to surplus sealed, refurbished, and used products. PLC Direct supplies proportional and servo valve hardware for replacement and maintenance purposes and does not provide system design, programming, or integration services.

Frequently Asked Questions

A proportional valve positions its main spool in proportion to the applied solenoid current, producing a continuously variable flow output rather than a fixed on/off state. This allows actuator speed, force, and pressure to be commanded across the full operating range via an analog input signal from a PLC or process controller.

Proportional directional valves are required whenever the actuator must move at variable speeds, follow a velocity ramp, or smoothly transition between operating phases. Standard solenoid valves switch between fixed positions only, making them unsuitable for applications requiring speed profiling, soft start, or controlled deceleration between cycle stages.

In open-loop proportional control, the controller issues a command signal without feedback from the actuator, relying on valve linearity to achieve the target position, speed, or force. In closed-loop control, a position or pressure transducer feeds actual values back to the controller, which continuously adjusts the valve command to eliminate error, providing the repeatability required in injection molding, press force control, and similar precision applications.

PLC Direct stocks Rexroth VT series amplifier modules and Parker D1VW series proportional valves as separate line items, allowing individual component replacement without sourcing a complete valve-and-amplifier assembly. Contact PLC Direct with the specific VT amplifier or D1VW part number to confirm current availability across surplus sealed, refurbished, and used condition grades.

Surplus sealed proportional valves are unused units that retain their original factory calibration settings, making them the first choice where null adjustment and gain parameters need to be preserved. Refurbished units are restored to operational condition but typically require null and gain verification against the installed system's requirements before returning to closed-loop service.