A compressed air motor works with the conversion of energy of compressed air to
perform mechanical work. The compressed air expands to generate a rotary or
linear motion that has given rise to numerous applications. The hand-held power
tools are one area where the pneumatic motors are successfully employed. From
spinning of a dentist’s drill at 50,000 rpm to a burly heavy-duty jackhammer, the
pneumatic motors are at the heart of the process. Pneumatic motors have existed in
one form or other over a long time.
Linear motion commonly uses a system of pistons. The air is fed to an airtight
chamber which pushes a piston fitted with a coiled spring. As the pressure
develops, the piston moves down the chamber and at maximum length, the air is
released and the spring coils back the piston to the original position. The kinetic
energy of air is thus converted to mechanical energy. In rotary system, rectangular
vanes are fixed to a rotating element, and air thrusts the vanes to move creating
rotational motion. The rotational speed varies with air pressure.
In hand held tools, the pneumatic motors have added another dimension in their
use. There are air power drills, impact wrenches, grinders, nut runners, sanders to
name some. Pneumatic motors have several advantages over electric motors. They
offer greater power density, especially higher power-to- weight ratios to generate
more torque, can work in hazardous environments, don’t need an auxiliary speed
controller making it compact and lighter, have good compliance. Unlike electric
motors, when overloaded, they just stop and don’t get overheated or sparked out.
At the same time, there are some control problems known to be associated with air
tools. A hose connects the tool to an air tank which consumes some time to
develop the required pressure whereas an electric motor is ready to function as
soon as plugged to the power supply. Air compressors are not only costly but also
are noisy, heavy, needing periodic maintenance.
The tools which use pneumatic motors are a type of power tools. Among the
factors which govern a particular pneumatic tool are air pressure and air
consumption. The air in the compressor is maintained in psi (pounds per square
inch) while a constant air flow at any given pressure is crucial for a tool to work
and it is measured in cubic feet per minute (CFM). If the pressure is increased, the
volumetric flow of air also increases. The output of a pneumatic motor is relatively
constant, when load increases, the speed decreases, and torque rises. While
specifying air input requirements of different tools, the air flow in CFM varies
while the pressure is maintained constant. Some commonly used pneumatic tools
and their air flow requirements are listed below:
Pneumatic Drill, which does its job of drilling holes quickly with precision,
needs about 3-6 CFM airflow at 90 PSI pressure.
Socket Wrench for lessening of hardened bolts in no time needs 2.5 to 3.5
CFM for the wrench of ¼” dia. at 90 PSI pressure. And 4 to 4.5 CFM air
flow for 3/8” dia. also at 90 PSI pressure.
Air Hammer to drive long thin nails needs only 0.3 CFM air flow at 90 PSI
Angle Grinder which allows cutting or fine trimming of metals needs 5-8
CFM airflow at 90PSI pressure.
Riveter for fastening of metals with a long metal rivet needs 4CFM airflow
at 90 PSI pressure
Speed Saw for cutting of fine edges as it is easier to keep its movement
straight, needs 5CFM at 90 PSI pressure
Sander smooths the rough edges and even exposed the fine grains as it
randomly moves in any direction, needs 8 – 12 CFM airflow at 90 PSI
It is important to note that specifications are made at the same air pressure. The
rate of air consumption thus plays an important role. The selection of right motor
calls for minimizing air consumption. Another crucial factor in deciding an air
motor is its speed. The speed or rpm rate decreases with the load administration, so
the motor speed is adjusted with a mix of planetary reduction gears. Pneumatic
motors have fewer moving parts, that makes them more compact, easier to handle
and maintain. Though a bit costlier, pneumatic tools last longer than corded or