vane motors

8/14/2019 Vane Motors

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Pneumatic gear motor

Known industry wide for their rugged construction and reliability, Gast Air Motors and airpowered Gearmotors are available in both lubricated and oilless models.

These air motors and gearmotors are used in many industrial applications, from mixingequipment to running pump drives.

Self-sealing vanes take up their own wear, ensuring consistent output for thousands of hoursof use

Variable speed capabilities allow flexibility and versatility in any number of applications

Cool-running operation means air motors can be used in ambient temperatures of up to 250F (120 C)

Non-electrical operation reduces the possibility of explosion from igniting flammable gases

ATEX (II 2 GDc T4) compliance as standard on catalogue listed Air Motors. (Availableonly on European spec. Geared Air Motors upon request.)

Piston motors

Piston air motors are used in applications requiring high power, high starting torque, andaccurate speed control at low speeds. They have either two, three, four, five, or six cylindersarranged either axially or radially within a housing. Output torque is developed by pressureacting on pistons that reciprocate within the cylinders.

Motors with four or more cylinders provide relatively smooth torque at a given operatingspeed because power pulses overlap: two or more pistons undergo a power stroke at any timewithin a revolution. Motors designed with overlapping power strokes and accurate balancing

are vibration-free at all speeds.


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Power developed by a piston motor depends on the inlet pressure, the number of pistons, andpiston area, stroke, and speed. At any given inlet pressure, more power can be obtained from amotor that runs at a higher speed, has a larger piston diameter, more pistons, or longer stroke.Speed-limiting factors are the inertia of the moving parts (which has a greater effect in radial-than in axial-piston motors) and the design of the valve that controls inlet and exhaust to the

pistons.Radial- and axial-piston motors have one significant limitation: they are internally lubricated,so oil and grease supplies must be checked periodically and replenished. They must bemounted in a horizontal position to provide proper lubrication to bearing areas. However, atleast one manufacturer offers a radial-piston motor with the shaft vertically-down as astandard configuration. Other mounting positions from any manufacturer require speciallubrication configurations.

Radial-piston motors feature robust, oil-lubricated construction and are well-suited tocontinuous operation. They have the highest starting torque of any air motor and are

particularly beneficial for applications involving high starting loads. Overlapping powerimpulses provide smooth torque in both forward and reverse directions. Sizes range to about

35 hp for speeds to 4,500 rpm.

Axial-piston motors, Figure 1, are more compact than radial-piston motors, making themideal for mounting in close quarters. Their design is more complex and costly than vanemotors, and they are grease lubricated. However, axial-piston motors run smoother anddeliver maximum power at much lower speeds than vane motors can. Smaller and lighter thanelectrical gear motors of the same power rating, axial-piston motors also tolerate higherambient temperatures. Maximum size is about 3-1/2 hp.

Turbine motors

Efficiency of an air motor is defined as the ratio of the actual power output to the theoreticalpower available from the compressed air for the expansion ratio at which the machine isoperating. Turbines convert pneumatic power to mechanical power at about 65% to 75%efficiency. Turbine efficiency is higher than other air motors because sliding contact of partsdoes not occur to cause internal friction. As a result, there is no need for extensive lubrication.The absence of lubricating oil dramatically improves cold-weather performance.

Until recently, turbine air motors typically were used for applications requiring very highspeed and very low starting torque - dental drills and jet aircraft engine starters being mosttypical. Now, however, turbine technology is being applied to starting small, medium, andlarge reciprocating engines. Turbine technology offers simple, highly efficient pneumaticstarters that require no lubrication of their supply air, tolerate contaminants in the supply air,and need little maintenance. Turbine starters include a planetary gear reduction to bring theturbine's high rotor speed down to normal engine cranking speeds.

Turbine motors are relatively compact and light for their power-delivery capability. Highergear ratios - from 9:1 through 20:1 - provide high stall torque and versatility for a variety ofengines. Turbine horsepower is easily changed by limiting air flow through the motor.

Operation of a turbine air motor involves a nozzle that directs and meters air to a turbine

wheel or rotor. It changes high-pressure, low-velocity air flow to low-pressure, high-velocity.The mass-flow rate of air passing through a turbine determines its horsepower. Changing the


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number of nozzles or nozzle passages changes power output proportionally. If a 16-nozzlestarter is reduced to 8 nozzles, the altered starter will produce half the power of the original.Therefore, within the same basic starter configuration, many models can be designed thathave a wide range of inlet pressures, cranking speeds, and cranking or stall torques. Thiscapability, combined with various gearboxes, allows production of low-cost starters for a

wide variety of applications. For example: turbine starters are available to crank engines withdisplacements from 305 to 23,800 in.3 at pressures from 40 through 435 psig.

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