Glossary

The volume of air a compressor delivers in one minute. Match tool CFM demand to compressor CFM output at the pressure you use.

The force or pressure of compressed air. Most shop tools run at 90–100 PSI; check the tool nameplate.

Pressure measured relative to atmospheric pressure. Tank and line gauges read PSIG, not absolute pressure.

The compression element of a rotary screw compressor. It contains the male and female rotors and the housing that forms the compression chambers.

A compressor that uses pistons moving up and down in cylinders to draw in and compress air.

A reciprocating compressor that compresses air in two pistons or stages, usually reaching higher pressure and better efficiency than a single-stage unit.

A heat exchanger between compression stages that cools air and removes moisture before the next stage of compression.

A heat exchanger at the compressor discharge that cools hot compressed air and knocks out water before it reaches the dryer or tank.

The storage tank that holds compressed air, smooths out pulsations, and provides reserve capacity so the motor does not cycle constantly.

A one-way valve that lets compressed air flow toward the tank but prevents backflow into the pump when the compressor stops.

A valve that vents pressure trapped in the pump head or discharge line so the motor can restart without a heavy load.

The control that starts the compressor at cut-in pressure and stops it at cut-out pressure.

The low tank pressure that causes the pressure switch to start the compressor.

The high tank pressure that causes the pressure switch to stop the compressor.

The percentage of time a compressor can run in a given period without overheating. A 50% duty cycle means half on, half off.

The unit of electrical current. Motor current draw in amps tells you how hard the motor is working.

The unit of electrical pressure or potential. Common motor voltages are 115 V, 230 V, 460 V, and 575 V.

The unit of electrical resistance. One ohm allows one amp to flow with one volt of pressure.

A three-phase motor winding arrangement where one end of each coil connects to a common neutral point, usually for reduced starting current.

A three-phase motor winding arrangement where the coils connect in a triangle, typically for full running torque.

A heavy-duty electrically operated switch that connects the motor to the power supply when the control circuit energizes it.

A protective device that monitors motor current and trips to shut off the motor if it overheats or draws too much current.

The brief surge of current a motor pulls when it first starts, often five to seven times the normal running amps.

The current a motor draws if the rotor is locked and cannot turn. This is the worst-case startup current.

The expected current a motor draws at rated horsepower, voltage, and frequency under normal full load.

AC power with three voltage waveforms, common in industrial motors. It provides smooth, high-torque starting.

AC power with one voltage waveform. It is common in residential and small shop equipment and often needs a starting capacitor.

An insulation resistance tester used to check if motor windings or cables are breaking down to ground.

The temperature at which moisture in compressed air begins to condense. Lower dew point means drier air.

The liquid water and oil mixture that drains from tanks, filters, dryers, and drop legs. It must be disposed of properly.

A dryer that cools compressed air to remove water vapor, typically reaching a pressure dew point near 35–40 °F.

A dryer that passes air through a drying material such as activated alumina to reach very low dew points.

The replaceable cartridge inside a compressed-air filter that traps particles, oil aerosols, and water droplets.

A valve that removes condensate from low points, tanks, filters, and dryers. Manual, timed, or zero-loss styles are common.

The working fluid that absorbs and releases heat as it circulates through an HVAC or refrigeration system.

The amount a refrigerant vapor is above its saturation temperature at a given pressure. It proves the evaporator is starved of liquid.

The amount a refrigerant liquid is below its saturation temperature at a given pressure. It proves the condenser is full of liquid.

The coil where refrigerant absorbs heat and boils from liquid to vapor, cooling the surrounding air or fluid.

The coil where refrigerant releases heat and condenses from vapor back to liquid.

A measure of heat energy. HVAC capacities are often rated in BTU per hour or tons, where one ton equals 12,000 BTU/hr.

The safety procedure to shut off, isolate, and secure energy sources before performing service or maintenance.

Safety gear worn by technicians, such as safety glasses, gloves, hearing protection, and steel-toe boots.

Scheduled inspections and service such as oil changes, filter replacements, belt checks, and condensate drain cleaning.

Taking a small oil sample and sending it to a lab to check for contamination, wear metals, and oil degradation.

Measuring machine vibration to detect problems like bearing wear, imbalance, misalignment, or looseness.