Written Report (air Motors)

Alcaraz, Ronalyn Z. 200713098 BSCoE 5-1 Air Motors •

Air motors are used to produce continuous rotary power from a compressed air system.

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Air motors are similar in construction and function to hydraulic motors, and are most commonly of the rotary vane, gear, radial piston, or axial piston type. They can operate at speeds in excess of 10,000rpm.

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Torque of Air Motor • •

When load resistance to the air motor is increased, the running speed of the motor reduces and the torque is increased to match the load. if the load decrease the speed goes up but the torque reduces in matching proportion to the load.

Power Air Motor •

Air motors are available in the market from very low to very high kilowatt rating. There are air motors manufactured by some firms with fractional kW of as low as 0.05 kW while the higher limit ranges up to 20 kW. 10 kW is a more moderate and maximum acceptable size under normal working conditions for general pneumatic application.

Comparison of Air Motor to Electric Motor • • • • • • •

Air motors develop more kW/N weight and per cubic meter of displacement than most standard electric motor. They are inherently shock and explosion proof which is not the case with electric motors. Air motors are not affected by hot, wet or corrosive atmosphere. Because they operate under internal pressure, dust, moisture, and fumes cannot enter the air motor case. Dust or explosion proof enclosures for electric motors involve extra cost. Air motors are not damaged by overloading, rapid reversals, or continuous stalling; when an air motor stall, it continues to produce high torque with no damage to itself, but electric motor can be severely damaged due to overload. Speed can be varied over a wide range without complicated control arrangements in air mass, but in electric motors, it is expensive.

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Because of their low inertia, air motors accelerate and decelerate quickly-from zero to full speed in milliseconds – ideal for fast cycling. Electric motors take more time to do this. Air motors are simple in design and construction is relatively inexpensive. They are reliable or easy to maintain and there is no heat build up even if it stalls for longer period. The harder an air motor works, the cooler it runs- because air expands as it passes through the motor, the air creates a cooling effect which permits air motors to operate in environments where ambient temperature may reach as high as 125 C which is simply the opposite in the case of electric motors.

Disadvantages • •

Air motors are less efficient and noisier unless their exhaust ports are muffled. Electric motors are more efficient, because air motor speed varies with load, they cannot hold constant speed without governor controls. Electric motors are better in this respect.

Types of Air Motors • • • •

Vane Motors Piston type Motors Turbine Motors Gerotor

Vane Motors • • •

Rotary vane motors normally are used in applications requiring low- to mediumpower outputs. Rotary vane air motors are available with three to ten vanes. Increasing the number of vanes reduces internal leakage or blow-by and makes torque output more uniform and reliable at lower speeds. However, more vanes increase friction, cost of the motor, and decrease efficiency.

Piston Type Motors •

PISTON-TYPE MOTORS are the most commonly used in hydraulic systems. They are basically the same as hydraulic pumps except they are used to convert hydraulic energy into mechanical (rotary) energy.

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Radial-piston motors feature robust, oil-lubricated construction and are wellsuited to continuous operation. They have the highest starting torque of any air motor and are particularly beneficial for applications involving high starting loads. Overlapping power impulses provide smooth torque in both forward and reverse directions. Sizes range to about 35 hp for speeds to 4,500 rpm.

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Axial-piston motors, are more compact than radial-piston motors, making them ideal for mounting in close quarters. Their design is more complex and costly than vane motors, and they are grease lubricated. However, axial-piston motors run smoother and deliver maximum power at much lower speeds than vane motors can. Maximum size is about 3-1/2 hp.

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Turbine Motors • •

they convert low velocity high pressure air to high velocity low pressure air by passing it through metering nozzles. One advantage of this is that there is no rubbing or sliding contact between the rotating parts and the body cavity. Turbines convert pneumatic power to mechanical power at about 65% to 75% efficiency.

Gerotor • • •

deliver high torque at low speed without additional gearing. Gerotor power elements provide torque at speeds down to 20 rpm. These motors are well suited to hazardous-environment applications where relatively high torque is needed in limited space.