Air motors harness the power of compressed air to generate torque and rotational motion in applications ranging from powering production machinery and rotating turntables to operating mixers and actuating valves. They’re often an engineer’s “go-to” solution for jobs an electric motor can’t handle. That’s because in many instances, air motors outperform their electric counterparts.
Advantages of air
One big advantage is safety. Because they do not require electricity and have no sparking hazards, air motors can be used in volatile atmospheres. Explosion-proof electric motors, on the other hand, require costly special housings. Air motors can also be overloaded and stalled without harm. Overloading an electric motor, however, can trip circuit breakers and damage the motor.
By their nature, air motors tolerate adverse environments well. Dust and dirt that can shorten the life of electric motors has little effect on air motors, provided the air supply sees proper filtration. Likewise, air motors withstand wet, humid, and aggressive washdown conditions. High temperatures also tend to limit the performance of electric motors. Air motors, however, are self cooling and generally perform well to 300°F and, in some cases, even higher. Cool-running air motors can also be a better choice in applications with frequent starts and stops, because electric motors must be greatly oversized to dissipate heat generated by high starting torque.
Air motors generally have a higher power density than electric motors, so they can transmit more power from the same envelope or the same power from a smaller envelope. This is especially true when loads must be driven at less than the nominal speed of the electric motor — which necessitates using an electric gearmotor or separate gear box.
Finally, electric motors typically cannot be repaired by the average maintenance technician. They must be sent to a facility that specializes in electric motor repair to be re-wound and insulated. In contrast, technicians experienced in repairing rotating equipment — such as pumps, compressors, and gear boxes — can usually work on air motors. This reduces downtime and overall maintenance costs.
Motor types
Air motors are available in different designs, but vane and piston versions are most common in industrial settings.
Piston air motors deliver high power, high starting torque, and precise speed control at low speed, making them well-suited for tasks where the motor must start under load. They usually have from two to six cylinders arranged either axially or radially within a housing. Pressure acting on pistons that reciprocate within the cylinders generates output torque.
Power developed by a piston motor depends on the inlet pressure, the number of pistons, and piston area, stroke, and speed. Speed-limiting factors are the inertia of the moving parts (which has a greater effect on radial-piston than axial-piston motors) and internal valves that control cylinder inlet and exhaust.
Radial-piston motors are robust units, typically oil-lubricated, and well-suited to continuous operation. They have the highest starting torque of any air motor. Radial-piston motors deliver torque and horsepower at relatively low speeds — under 3000 rpm – and are commonly used for driving conveyors, rotating large drums and tumblers, and for rotating positive-displacement pumps.
Axial-piston motors are more compact than their radial-piston counterparts, making them suited for mounting in close quarters. Their design is more complex and costly than vane motors, but they deliver maximum power at much lower speeds than vane motors can. Axial-piston motors also offer the ability to precisely control speed.
Rotary vane motors normally deliver low to medium power. Simple and compact vane motors are an excellent option in applications that require a high-speed, low torque power source. They most often drive portable power tools but are used in a host of other applications as well.
Vane motors have axial vanes fitted into radial slots running the length of a rotor, which mounts eccentric with the bore of the motor’s housing. The vanes are biased to seal against the housing interior wall. Torque develops from pressure acting on one side of the vanes. Torque at the output shaft is proportional to the exposed vane area, pressure, and the distance (moment arm) from the rotor center line to the center of the exposed vane. Vane motors operate at speeds from 100 to more than 25,000 rpm and deliver more power per pound than piston air motors. Though many require lubricated air, more and more are designed to operate non-lubricated to serve critical applications and address environmental concerns.
Piston and vane air motors offer power ranges from 0.13 to 32 hp, speeds from 0 to 10,000 rpm, and torques to 155 Nm. Features include explosion-proof operation, stalling safety, stepless speed control, and instant reversibility. The modular motors can be equipped with gear reducers, brakes, and hand or remote pendant controls as options. They’re used in hazardous environments for hoists, winches, mixers, pump drives, choppers, grinders, and mining equipment.
Tonson Air Motor, (800) 318-3233, www.tonson-motor.com
ATEX certified
These vane air motors are used in applications like mixers, ventilators, winches, pump drives, aftercoolers, and conveyors. They feature simple, adjustable torque and output speed, can be stalled under load without harm, and are instantly reversible. Oilless and ATEX certified versions are available. Products range from the VA1, rated at 0.44 kW and 1.05 Nm stall torque, to the VS10C with a maximum power of 9.5 kW and 44 Nm torque. Maximum speed ranges from 2400 to 6000 rpm, and multiple mounting configurations are available.
Globe Airmotors North America, (905) 949 1750, www.globeairmotor.com
Small and light air motors hold distinct advantages in many hand-held devices and automation applications. According to officials at Deprag Schulz GmbH, Amberg, Germany, the typical air motor has only one-third the size and one-fifth the mass of an equivalent electric motor. However until now, speed regulation posed a problem.
A characteristic of air-motors is that when operated without load, the motor runs at its rated no-load-speed. If load increases, motor speed decreases. So, an air-motor can operate from 100% down to approximately 15% of its nominal speed, depending on the load.
This can cause problems, say in an agitator or mixer that needs a constant speed for accurate production. A change in the mixture’s viscosity or its volume in the container can cause an undesirable speed change.
A speed regulator from Deprag overcomes this issue. A non-contact speed sensor mounts between the vane air motor and its gearing, monitors the motor’s speed, and sends the data to the air motor circuit’s regulator. Any variation between actual and required speed commands a special proportional valve to actuate, which regulates air flow to the motor and, therefore, output speed.
The regulator was originally used with the company’s model 67-028R stainless-steel air motor on a chemical agitator. The nominal speed of the 1200-W motor is 1250 rpm, no-load speed is 2500 rpm, and nominal torque is 9.2 Nm, based on an operating pressure of 6 bar. Although mixtures in the agitator range in viscosity from 1 to 300 mPas, the regulator maintains motor speed within ±5 rpm—and readjusts the speed when loads change within 2 sec.
he regulator can be used across Deprag’s complete product range, even at speeds to 80,000 rpm.
Click here to read an article describing an application using this product.
Deprag North America Inc., (800) 433-7724, www.depragusa.com.
Cleco air motors (formerly Gardner Denver) come in several versions. Rotary vane motors range in size from 0.3 to 7.5 hp and feature heavy-duty bearings. Small, light, axial-piston units are suited for limited-space installations, heavy starting loads, and start-stop operations. Large spindle bearings permit overhung loads with no external support. Heavy-duty radial-piston motors deliver high torque and handle heavy starting loads, with at least two pistons always on a power stroke.
Apex Tool Group, Power Tool Div., (800) 688-8949, www.apexpowertools.com
LZL 05 stainless steel air motors meet strict hygiene requirements and handle hazardous or corrosive environments as well as heat and vibration. They also run lubrication free, making them suited for mixing chemicals, pharmaceuticals, and other solutions. Weighing 8.6 lb, LZL 05R SL is EX-certified to level Ex II 2G T4 IIC D110°C according to the ATEX directive. Maximum output is 2.2 hp, 2.2 ft-lb torque, and speed of 5000 rpm.
Atlas Copco Tools and Systems, (248) 373.3000, www.atlascopco.us
A wide range of vane air motors in stainless steel and lubrication free versions have output power ranging from 0.21 to 3.9 hp. Most can be supplied as either unidirectional with a threaded shaft, or reversible with a keyed shaft. The air motors can also be ATEX certified for potentially explosive environments. They are suited for applications in material handling, packaging, strapping, and printing machinery; petrochemical and agricultural equipment; and food processing machinery.
Desoutter, +33 2 40 80 2000, www.desouttertools.com
An air motor with a free-floating piston design is capable of precise position control. Maximum torque is available on start-up and it can be finely adjusted with standard air-flow valves. The piston motor reportedly consumes up to 80% less air than a vane motor, providing significant cost saving even at maximum torque. It comes with a corrosion resistant or acetyl housing, can run on non-lubricated air, and has recessed fasteners that reduce trapped debris. This makes it suited for food preparation and packaging systems, and washdown applications.
Huco Engineering Industries Ltd, Altra Industrial Motion, (815) 389 3771, www.huco.com
Rugged air motors and air-powered gear motors are available in many operating and mounting configurations. Seven basic lubricated versions produce up to 9.5 hp with motor speeds from 300 to 10,000 rpm. Oilless versions come in three basic models ranging from 0.18 to 2.5 hp and deliver speeds up 4000 rpm. Mounting options include hub, foot, face, NEMA C-flange, and Metric D Series. Right-angle and in-line air powered gearmotors generate from 73 to 5200 lb-in. torque with single-reduction gear ratios from 10:1 to 60:1.
Gast Mfg Inc., (269) 926-6171, www.gastmfg.com
Taiyo offers a full line of vane and radial piston air motors. For example TAV1 vane motors are compact and light with power output ranging from 66 to 500 W, 0.05 to 16 Nm torque, and speeds as high as 14,000 rpm. TAM1 radial-piston air motors are low-speed high torque units with maximum power of 735 W, 23.5 Nm torque, and speed of 300 rpm.
Taiyo America Inc., (877) 544-8775, www.taiyoamericainc.com
More than 200 cataloged models of direct-drive and geared air motors include vane and piston configurations. Reversible and non-reversible types come with an extensive range of options. Ratings range from 0.10 to 30 hp, speed ratings from 23 to 26,000 rpm, and torque output from 0.10 to 1090 ft-lb. Standard motors withstand temperatures to 150°F, and up to 300°F with high-temperature lubrication.
Ingersoll Rand, (800) 866-5457, www.ingersollrandproducts.com
Miniature air motors are suited for medical, aerospace, robotic, and industrial use. They operate on compressed air, nitrogen, and inert gases at pressures to 150 psi. They have aluminum and stainless-steel construction and precision ball bearings to virtually eliminate friction and wear. Hardened planetary gears can increase torque transmission capabilities. The 0.75-in. diameter models produce stall torques from 2.8 to 1200 oz-in., at free speeds of 7 to 40,000 rpm. Motors are available with either direct drive or internal gearing.
Pro-Dex Inc., (800) 562-6204, www.pro-dex.com