What To Consider When Selecting an Air Motor

Air motors are used in many applications where compressed air is available and represents a better option than electrical power for logistical or environmental concerns.

– Air motors are non-electrical, so the likelihood of explosion from igniting flammable gases is greatly reduced.
– Speed can be varied with use of a simple valve placed between the air source and air motor.
– Air motors can be stalled against a load and will not burn out.
– Air motors run cool with the expansion of compressed air.

Rule of thumb for selecting an air motor: Choose an air motor that will provide the horsepower and torque required, using only two-thirds (2/3) of the available line air pressure available. The full pressure will then be available for overloads and starting.

Bottom line: Air motors have different operating characteristics from other mechanical power sources, such as electric motors. Electric motors typically have start and run windings, where the start windings momentarily provide greater torque. Air motors are a mechanical device where greater air pressure will produce greater torque.

Example: Customer is calling out a starting torque requirement of 110” lbs. Available line pressure is 100 PSI. Would Gast 6AM or 8AM Series be the best choice? 8AM Series would be best, as 60 PSI line pressure would produce approximately 115” lbs. of starting torque. 100 PSI line pressure would be required to produce similar starting torque with a 6AM Series air motor. See attached Spec Sheets for the Gast 6AM and 8AM Series of air motors.

Tip: Pressure is just half of the equation! Make sure there is adequate CFM flow to maintain performance @ the desired RPM. Sizing of the compressor, plumbing and related air line accessories are critical considerations. Air quality is critical too! Compressed air that is loaded with water, rust and other contaminants is sure way to kill air motor performance and operation.

Four-vane or Eight-vane: Four-vane units meet most requirements, but it is wise to specify eight-vane models for more precise inching control and in applications where the motor is operating in a stalled condition. Bottom Line: Use 4 vane air motors for constant run applications like fans, pumps and mixers. Use 8 vane air motors in applications where RPM speed control is more critical, such as winching, reeling, positioning and tensioning.

For further info, check out https://gastmfg.com/products/air-and-gear-motors or purchase a Gast Air Motor


Ed Walker
GAST Product Specialist
[email protected]

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