Moog 72 Series Two-Stage Flow Control Servo Valve

Overview

The Moog 72 Series are two-stage flow control servo valves with an analog interface, designed as throttle valves for three-way and preferably four-way applications. Moog describes the design as simple, rugged and dependable for long life, and the valves cover rated flows of 95, 150 and 225 l/min at 35 bar pressure drop per spool land, with a maximum flow of 355 l/min. The Moog 72 Series is intended for electrohydraulic position, speed, pressure or force control with high dynamic response, and it uses the standard ISO 10372-06-05-0-92 mounting pattern, so manifolds are readily available. Intrinsically safe and explosion proof versions are certified to FM, ATEX, CSA, TIIS and IECEx standards for hazardous locations.

Seven Star LLC supplies the Moog 72 Series, including the intrinsically safe 72K versions, together with connectors, pilot filters and seal kits, to turbine operators, oil and gas equipment users, steel plants and hydraulic service workshops in Muscat, the Sultanate of Oman and the GCC. We provide engineering support in Muscat for matching the full Moog model and type number.

Operating Principle

The Moog 72 Series consists of a polarised electrical torque motor and two stages of hydraulic amplification. The armature sits in the air gaps of a magnetic circuit, supported by a flexure tube that also seals the electromagnetic section from the hydraulics. A flapper fixed to the armature passes between two nozzles, forming two variable orifices. When a current flows in the two motor coils, the armature and flapper deflect, one nozzle orifice grows and the other shrinks, and the resulting pressure difference acts on the ends of the second stage spool. The spool moves and deflects a cantilevered feedback spring attached to the flapper, until the feedback force balances the input signal torque. At a fixed pressure drop, output flow is then proportional to spool displacement and therefore to input current.

This mechanical force feedback means the Moog 72 Series needs no onboard electronics; it is driven by a current from a servo amplifier, with standard coil options of ±8, ±15 or ±40 mA rated current in parallel connection. As general engineering background, a current feedback amplifier with high output impedance is recommended because copper coil resistance changes with temperature, and Moog notes that this practically eliminates the effect. Most valves are set to return to a fail-safe position when the command signal is lost, and an external null bias adjustment lets technicians trim the hydraulic null on the machine.

Engineering Design of the Moog 72 Series

The Moog 72 Series uses a dry torque motor, eliminating contamination in the motor air gaps, with dual coils for redundancy and dual precision nozzles. The spool and bushing are hardened 440C stainless steel for wear resistance and low friction, and the feedback mechanism uses a carbide ball-in-hole design that Moog states extends life compared with slotted spool and sapphire ball designs. Each valve is 100% factory tested, and the design complies with the SAE-ARP-490 servo valve design standard. A field replaceable pilot stage filter supports preventive maintenance, and a field configurable fifth port allows a separate pilot supply for low pressure applications.

Three body options are offered: aluminium for up to 210 bar, steel for up to 350 bar, and a filterless body for up to 490 bar. The steel body valve weighs 7.26 kg and the aluminium body valve 3.52 kg, and installation may be in any position, fixed or moving. Ambient and fluid temperature range is −29 to +135 °C, with higher temperature options, and vibration resistance is 30 g in three axes from 10 Hz to 2 kHz. Electrical connection is through a standard MS3106F14S-2S four-pin connector with all four coil leads available for single, series or parallel coil operation. Seals are FKM or EPR, with other materials on request.

Key Features

Key features of the Moog 72 Series listed in the Moog catalog are:

• Two-stage servo valve with nozzle-flapper pilot and mechanical spool position feedback.
• Rated flows of 95, 150 and 225 l/min at 35 bar per spool land, maximum flow 355 l/min.
• ISO 10372-06-05-0-92 mounting pattern for standard manifolds.
• Aluminium (210 bar), steel (350 bar) and filterless (490 bar) body options.
• Dry, dual-coil torque motor with redundancy and contamination resistance.
• Hardened 440C spool and bushing with carbide ball-in-hole feedback.
• Field replaceable pilot filter, external null adjustment and configurable fifth port.
• Intrinsically safe and explosion proof versions certified to FM, ATEX, CSA, TIIS and IECEx.

Industrial Applications

The Moog 72 Series is a long-established choice for servo control of large actuators where reliability matters more than onboard electronics. Typical uses include steam and gas turbine control and stop valve actuators, fuel and inlet guide vane positioning, hydraulic presses and forming machines, rolling mill gauge and tension control, test rigs and simulation tables, and offshore and marine hydraulic systems. Step response times are 11 ms for the 95 l/min valve, 18 ms for 150 l/min and 33 ms for 225 l/min, and high-response pilot options are available. The wide temperature range and Ex certified versions allow the Moog 72 Series to be installed close to hot equipment and in classified areas.

In Oman and the GCC the Moog 72 Series is found on gas turbines in power and desalination plants, compressor stations, refinery and petrochemical turbine drives, oil and gas test and control equipment, and steel plants in Sohar. Because many units are installed in critical control systems, exact model matching, including body material, coil, pilot stage and seals, is essential. Seven Star LLC supplies the Moog 72 Series against the nameplate model and type numbers and can advise on Moog cleanliness recommendations of 17/14/11 for functional safety.

Technical Specifications

The Moog 72 Series data below are taken from the Moog 72 Series catalog, Rev. AC, May 2024.

How to Order

To order a Moog 72 Series servo valve, send Seven Star LLC the complete model and type number from the nameplate, or the required flow, body material, coil, pilot and seal options and any hazardous area certification, and we will prepare a formal quotation. The Moog 72 Series catalog is available as a download on this page. Seven Star LLC supplies Moog servo valves in Oman and the GCC with engineering support in Muscat. Related products include the Moog 79 Series Flow Control Servo Valve, the MOOG G761 Electrohydraulic Servo Valve and the Moog D792 High-Flow Servo Valve.