Moog D936 and D937 Servo-Proportional Valve, ISO 4401 Size 03/05

Overview

The Moog D936 and its larger sister the D937 form the Moog D93x series of direct operated servo-proportional valves with integrated electronics. They are driven by a proportional solenoid, yet use a servo valve style spool and bushing with closed-loop position control, combining the robustness of solenoid technology with the accuracy expected from Moog. The Moog D936 uses the ISO 4401 size 03 mounting pattern with rated flows from 4 to 40 l/min, while the D937 uses size 05 with 50 or 100 l/min, both at 35 bar pressure drop per spool land and a maximum operating pressure of 350 bar. Moog states that the valves are suitable for electrohydraulic control of position, speed, pressure and force in open and closed loop systems.

Seven Star LLC supplies the Moog D936 and D937 valves, mating connectors and spare parts to OEMs, hydraulic service companies and plant maintenance teams in Muscat, across the Sultanate of Oman and the GCC. We provide engineering support in Muscat for selecting flow size, spool type, fail-safe option and signal interface from the Moog ordering code.

Operating Principle

The Moog D936 is an electrical feedback valve. The spool sits in a hardened steel bushing and is deflected by the proportional solenoid against a return spring. An LVDT position transducer measures the actual spool position, and the onboard electronics compare it with the command signal received through the main connector. The electronics then adjust the pulse width modulated current to the solenoid until the spool reaches the commanded position and hold it there, so spool position is proportional to the electric command. Because this loop is closed inside the valve, flow follows the command accurately even when supply pressure or temperature changes.

The valve is a 4/4-way design that includes a fail-safe position, which Moog notes can reduce the need for additional safety components. Three fail-safe options are offered on the Moog D936. With option 1 the spring moves the spool to a fourth position connecting A and B to T, relieving the actuator; with option 2 all ports are blocked, although some internal leakage remains; with option F the spool moves to about 110% stroke towards P to B and A to T. Moog points out that the spool passes through the fully open position on the way to the fourth position and that the spring force limits the pressure drop at which the fail-safe position can be reached.

Engineering Design of the Moog D936

The Moog D936 is a one-stage valve weighing 2.9 kg, mounted on ISO 4401-03-03-0-05 with or without a Y port, and it may be installed in any position. The D937 weighs 6.8 kg and uses ISO 4401-05-05-0-05. The electronics sit on top of the solenoid for a compact shape and are mechanically uncoupled from the housing, giving vibration resistance of 30 g in three axes from 10 Hz to 2 kHz and shock resistance of 50 g. Moog specifies an MTTFd of 150 years to EN ISO 13849-1 for the D936. The electronics use a digital core with energy efficient components to reduce thermal stress.

Electrical connection is through a 6-pole plus PE connector to EN 175201-804. The supply is 24 V DC (18 to 32 V), with maximum current of 1.4 A for the Moog D936 and 2.7 A for the D937. Command signal options are ±10 V, ±10 mA or 4 to 20 mA, and the actual spool position is available as ±10 V or 4 to 20 mA for monitoring and fault detection. Degree of protection is IP65 with the mating connector fitted. Optimised overlaps and clearances between spool and bushing give low internal leakage and high resistance to contamination.

Key Features

Key features of the Moog D936 and D937 according to the Moog D93x catalog are:

• Direct operated servo-proportional design with proportional solenoid and closed-loop spool position control.
• Fully hardened spool and bushing for high accuracy and wear resistance.
• ISO 4401 size 03 (D936) and size 05 (D937) mounting patterns.
• Maximum operating pressure of 350 bar on ports P, A and B.
• Step response for 0 to 100% stroke of 11 ms (D936) and 18 ms (D937).
• Threshold and hysteresis both below 0.2%.
• 4/4-way design with selectable fail-safe position.
• Electronics decoupled from the housing for high vibration and shock resistance.

Industrial Applications

The Moog D936 and D937 are used in industrial hydraulics where a robust valve with near-servo performance is needed. Typical applications include position and speed control of cylinders in presses and forming machines, injection moulding and die casting, test rigs, material handling, steel and metal processing lines, wood and paper machines, and pressure and force control on hydraulic power units. The Moog D936 suits smaller actuators and pilot functions with flows up to 40 l/min, while the D937 serves larger cylinders and motors with 50 or 100 l/min rated flow.

In Oman and the GCC, the Moog D936 is relevant to metal and steel plants in Sohar, aluminium and cable manufacturing, oil and gas equipment such as hydraulic control units, pipe handling and test benches, marine and port machinery, and power generation hydraulics. Its tolerance of vibration and an ambient range of −20 to +60 °C suit harsh plant environments. Seven Star LLC supplies the Moog D936 and D937 for new machines and as replacements, and can assist with hydraulic fluid cleanliness recommendations given by Moog.

Technical Specifications

The Moog D936 and D937 data below are taken from the Moog D93x series catalog, Rev. E, February 2026.

How to Order

To order a Moog D936 or D937, send Seven Star LLC the full Moog part number or ordering code from the valve label, or your required size, rated flow, spool type, fail-safe option and signal interface, and we will prepare a formal quotation. The Moog D93x catalog is available as a download on this page. Seven Star LLC supplies Moog hydraulic valves in Oman and the GCC with engineering support in Muscat. Related products include the MOOG G761 Electrohydraulic Servo Valve, the Moog 79 Series Flow Control Servo Valve and the Moog Servo Valves and Proportional Valves – Hydraulic Control.