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ITT Air Motors 

What is an Air Actuator Motor? Versus: What is an Air Motor?

Generally speaking, a pneumatic actuator consists of a piston inside of a cylinder. When pressure is supplied from an external compressor the piston inside the cylinder moves along the axis of the piston, creating a linear force. That force turns the actuator shaft, often 90-degrees for quarter-turn valve actuation. Unfortunately, the terms “Air Actuator” and “Air Motor” have been used interchangeably for actuation or diaphragm valves. Air motor is the correct description, although both air actuators and air motors can be spring-loaded. 

Air motors are small and can be stopped and started instantly. The axial torque and difficult environments unaffected by stalling or overload. ITT Grinnell 3100 Series Fail Open Air Motors, 3200 Series Fail Closed Air Motors, and 3300 Series Double Acting Air Motors have lower torque and power-to-weight ratios than a comparative air actuator. Compressed air offers advantages that make air motors desirable on low-pressure piping. 

 ITT Engineered Air Motors, Dia-Flo Diaphragm Valves, ITT Grinnell Valves, ITT Diaphragm Valves, ITT Engineered Valves, Grinnell Valves and Grinnell Air Motors can be combined as complete valve assemblies by Authorized Parts, Inc. See our selection guide at:

Actuated Diaphragm Valve Component Parts

The Bill of Materials for actuated Weir Type and Straightway Diaphragm Valves manufactured by ITT Grinnell include the air motor, valve stem, EPDM or Buna O-Rings, Valve Body, Valve Block, Compressor, Diaphragm (Elastomer or PTFE), Thrust Washers, Tube Nut, Bearings, and Bolting. 

Diaphragm Valve Air Motor Component Parts

The Bill of Materials for Weir Type and Straightway Diaphragm Valves with an Air Motor manufactured by ITT Grinnell include 3100 Series Fail Open Actuators(Spring to Open – Air to Close), 3200 Series Fail Closed Actuators(Air to Open – Spring to Close) and 3300 Series Double Acting Air to Open – Air to Close

Actuators. The Fail Open Actuators and Fail Closed Actuators have replaceable springs. Other replaceable parts are the top cover, spindle, spindle nut, diaphragm plate, actuator diaphragm, O-Rings, Lube Fitting, Compressor, and valve diaphragm. The air motor may have optional parts as well. Position indicator, travel stop, limit switches, solenoid valve, positioner, and proximity switches. Be sure to specify the valve size and diaphragm type when ordering parts. See the complete list of component parts at Authorized Parts, Inc. website:

Diaphragm Valve Replacement Diaphragms

Weir Type and Straightway Replacement Diaphragms are available in the following materials:

Soft Natural Rubber (FDA), Black Butyl, Hypalon, EPDM (FDA), Commercial Grade EPDM, BUNA N (FDA),

Natural Rubber, Neoprene, White Butyl (FDA), Direct Load DP BUNA N, Viton, Type R2 PTFE (FDA) and Type TM PTFE (FDA). Air Motor Diaphragms are made of Buna-N and are marked by size with the stamping “ITT Engineered Valves” on the diaphragm, with corresponding size numbers os 12, 25, 50, 75, 101, 130, and 250. See our ITT Air Motor Maintenance Manual at:

Sizing an ITT Air Motor

Torque output for an air motor is a function of differential pressure. Properly sized, torque should be constant for a given operating pressure. An air motor should be selected based on the peak power point, when possible, to ensure that the motor is operating at its greatest efficiency. Air motors are sized by their horsepower at rated input air supply, a maximum of 85 psig on ITT Air Motors. 

Selection of the correct air motor involves the following factors:

  • Line Pressure is the service media pressure in the pipeline against which the actuator must close.
  • Pressure Drop: 100% – when the actuator is closed, then pressure is applied or 0% – when the
  • actuator needs to shut the valve off against the line pressure.
  • Operating Pressure is the air pressure required to power the actuator.
  • Valve Size is the nominal size of the valve body (2”, 4”, etc.) in inches.
  • Valve Type, either weir type or straightway 
  • Diaphragm Type: PTFE faced diaphragms are more rigid and require higher operating pressures

When these factors have been determined, choose the appropriate actuator from the performance graphs available in our reference guides or submit your RFQ on Authorized Parts website easy to use form at:

Actuator Spring Sizing

Available Operating Pressure, the air pressure required to power the actuator, may on occasion be low, or abundantly available, permitting economy by way of using a small actuator with an oversized spring, or conversely, a large actuator with an undersized spring. The spring in any diaphragm valve actuator requires the force on the stem equal to zero. The formula is generally calculated using the following input: the area of the diaphragm, operating air pressure, spring constant, spring displacement, and process pressure drop at shut-off pressure. The force of the acting air is in a positive direction (direct acting) and is opposed by spring compression force and force due to process flow. Air consumption, the operating pressure of instrument air is a cost factor in installations. Ample air at adequate pressure to produce stroke speed and movement is concerned, which will determine the air volume and consumption of the air motor. The delta factor is the sole determinant in spring size, thereby allowing for, in some cases, the economy of air motor size. 

How to Order ITT Air Motors or Actuated Valve Assembly

ITT Engineered Air Motors, Dia-Flo Diaphragm Valves, ITT Grinnell Valves, ITT Diaphragm Valves, ITT Engineered Valves, Grinnell Valves, and Grinnell Air Motors. 303 Weir Type and Straightway Diaphragm Valves, or complete 303 valves with Air Motor can be quoted by RFQ or ordered online by the complete figure number, 303 Number, or by providing some or all the following information: 


If a valve recommendation is preferred, send all pertinent application data as an RFQ to:


If no Figure Number is visible on the nameplate and the air motor needs replacing, or the air motor diaphragm needs replacing, the casting on the air motor will be marked with the Grinnell name, or with 

ITT Engineered Valves No. then the corresponding size numbers of 12, 25, 50, 75, 101, 130, and 250. It is also important to specify whether the air motor is Fail Open, Fail Closed, or Double Acting.

Yes. Other manufacturer’s valves cross-reference to ITT Grinnell 303 Valves. Saunders, Dia-Flo, Pure-Flo, Dow, Resistoflex, Century and Hills-McCanna are examples of manufacturers with equivalent products. However, not all design features are the same, so care should be taken when evaluating. Be especially careful when reviewing the face-to-face dimensions when making comparisons. 

Yes. All valve and air motor testing requirements can be made available. MTR’s, NDE, Pressure Testing, Radiography Testing, Magnetic Particle, Dye Penetrant, PMI, Positive Material Identification, Hardness Testing, Failure Analysis, spark testing, or electrostatic and hydro-testing per ASTM 1545. Note: The Pressure Rating of the valve is influenced by the diaphragm material. The hydrostatic test pressure must not exceed the maximum pressure rating of the diaphragm.

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