Passes 200-micron particles – Unique jet construction enables model 420 to receive and pass particles as large as 200 microns through both stages without malfunction.

No unbalance from oil contamination – Because there is only one source of oil in the first stage, the valve will not become unbalanced or produce false “hard over” signals due to oil contamination of that stage.

Low hysteresis – Hysteresis is normally less than three percent of rated current for all input signals (4% maximum).

Low threshold – Normally less than 0.1 percent of rated current (0.25 percent maximum).

No filters – First-stage oil passes through a single 90-micron screen easily removable for inspection without disassembling the valve.

Low temperature drift – Maximum null shift resulting from oil or environmental temperature changes is held to approximately two percent for each 100°F through symmetrical torque motor design.

Servo-controlled second stage – Second-stage piston is precisely controlled by a high-gain, null-balance, and force-feedback servo. Pressure balance of the hydraulic preamplifier prevents displacement of the second-stage piston due to variations in supply or return oil pressure.

Wide dynamic range – Characteristics of phase and amplitude versus frequency are virtually the same for inputs from a few percent to 50 percent of full flow.

Dry torque motor – The hermetically sealed torque motor is completely isolated from the hydraulic fluid.

Low “G” sensitivity – First stage is balanced among all three axes against the effects of lateral acceleration and vibration. Acceleration and vibration tests show almost no effect on load output from 0 to 2000 Hz.