Selection Guide | Air Motors | Ingersoll Rand

Selection Guide

Ingersoll Rand offers two basic types of Air Motors:
Vane Motors

Are smaller, lighter and less expensive than piston motors or similar power. Simple in design and construction, they can be operated in most any position. Vane motors are available in a broad range of speeds, torques and power and are the most widely used type of air motor.

Radial Piston Motors

Operate at lower speeds than vane motors. Have excellent starting and speed control. Especially good for "lugging" heavy loads at slow speed. Standard operational position is horizontal.

Reversible / Non-Reversible Air Motors

Non-reversible air motors are rated at slightly higher speeds, torques, and horsepowers than reversible motors of the same family.

Air Pressure

When selecting air motors, remember that the specification listings show only one set of performance figures, at a particular pressure — 90 psig. Air motors are designed to produce optimum performance at this pressure.
Many other speeds, torques and power can be obtained from the same motor by regulating the pessure, air supply or exhaust. While they will operate at pessures below 40 psig, their performance may not be consistent. They can also be operated above 100 psig, but often at the expense of increased maintenance.
A good rule to follow is to size an air motor based on approximately 70% of the lowest available air pressure. This will allow additional power for starting and possible overloading.

Maximum Power

Ungoverned air motors develop maximum horsepower at approximately 50% of free (unloaded) speed while governed motors reach their peak horsepower at about 80% of free speed.

Desired Operating Speed

The desired operating speed, not the free and unloaded speed should be considered when selecting air motors.
Ungoverned air motors should not be run unloaded. The performance curves in this catalog indicate the maximum speeds at which the motor should be operated. The nameplate stamped speed is present for identification only.

Required Torque

Equally important as the speed at which an air motor is to be run is the required torque. The combination of the two factors—speed and torque—determine the power of the desired motor. Care should be taken to differentiate between stall (maximum) and running torques when selecting air motors.

Speed and Torque

Starting torques are approximately 75% of stall torques.
Operating or running torques at any speed can be approximated from motor performance curves—or calculated using the formula:

                        Horsepower x 5250
Torque (lb.ft.) = --------------------------------
                   speed (revolutions per minute)

                      Kilowatts x 9550
Torque (Nm) = --------------------------------
               speed (revolutions per minute)
                    
Shaft Radial Loads

When an air motor is to be used with a pulley, sprocket, or gear on the shaft, the overhung load (perpendicular to the shaft), commonly called "shaft radial loading" must be considered. It is shown in the performance curves and is generally assumed to be applied at the mid-point of the keyway of the shaft.

 

Torque and Power Curves

 

 

Air System and Supply

Once an air motor has been selected, it is important to insure that the desired air pressure is available at the motor, while the motor is operating. A pressure reading at the compressor does not mean that the same pressure will be available to an operating air motor, because of possible restrictions and friction losses in the air system. Exhaust restrictions can also affect air motor operation, and are often the cause of performance problems.

Inlet Controls

When installing reversible air motors, a four-way valve or two three-way valves should be used to prevent blockage of the secondary Exhaust Port. This is the opposite Rotation Port to that which is being pressurized.

Replacing Electric Motors with Air Motors

Electric motors, with the exception of series wound direct current motors, have entirely different performance characteristics than air motors. Therefore, their torque and speed curves will not match. Many electric motors are oversized to allow for overloading and lower power air motors can be used as replacements.

 

 

Torque and Power Curves

Torque and Power Curves

 

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