20 - Compressors

semihermetic compressor

A compressor that contains an electric motor and compressor that can be accessed by opening the casing. It is a field service ready version of a hermetic compressor, combining the benefits of the hermetic and open-type compressors. Also called semihermetics.

hermetic compressor

A compressor that contains an electric motor that is connected directly to the compressor within a sealed shell. Also called hermetics.

open-type compressor

A compressor that is driven by an external source of power, usually an electric motor. The motor may be directly connected to the compressor, or it may use a V-belt to transmit the turning power.

screw compressor

A compressor that uses a pair of matched augers (or "screws") to compress refrigerant gas that enters at low pressure at one end of the pair and discharges at high pressure at the other end.

rotary compressor

A compressor that uses a rotor that interacts with rotating or stationary blades to compress gas. These are classified as either rotating vane or stationary blade.

reciprocating compressor

A compressor that uses an electric motor to turn a crankshaft that operates reciprocating pistons within cylinders to draw in and compress refrigerant. These operate much like an automobile engine. Reciprocating compressors are one of the most widely used types of compressors in HVACR.

crankshaft

A device used to change the rotary (circular) motion of the electric motor into a reciprocating (up-and-down) motion in a reciprocating compressor.

precooler

A heat exchanger that desuperheats hot gas refrigerant in the compressor discharge line. A precooler only removes some of the sensible heat (measured in temperature). It does not remove enough heat to cause a phase change.

connecting rod

A part that attaches the piston to the crankshaft in a reciprocating compressor.

flywheel

A pulley (sometimes weighted) that is attached to the external crankshaft of a motor.

access opening

A small stub on a hermetic compressor that allows access to the normally sealed refrigerant circuit.

valve plate

A specially milled steel plate located between the head and the piston cylinders of a compressor. It holds the valve reeds and serves as a division point between the low-side pressure and high-side pressure.

compliant

A term meaning yielding. It describes compressors (used in heat pumps and other applications) that can pump liquid without damage. It eliminates the need for installing an accumulator and crankcase heater to prevent slugging/liquid floodback.

rotary

A term used to describe a circular motion around a central point or axis.

reciprocating

A term used to describe a motion in one direction and then in the opposite direction, such as back and forth or up and down. Many HVACR compressors operate using a reciprocating motion to draw in and then compress refrigerant.

full-floating

A term used to describe a piston pin that is free to rotate within the connecting rod and the piston.

valve reed

A thin piece of steel located on top of the compressor cylinder and under the valve plate. The valve reed flexes to open and close as gas is compressed inside the cylinder. The suction valve reed admits refrigerant into the cylinder, and the discharge valve reed releases compressed refrigerant from the cylinder.

scroll compressor

A type of compressor that involves the orbiting of one scroll (spiral) that is intertwined with another scroll to form a series of crescent-shaped pockets that reduce in size and increase in pressure. During compression, one scroll remains stationary while the other scroll orbits around the space between it and the fixed scroll.

centrifugal compressor

A type of compressor that uses centrifugal force to compress refrigerant gas. Also called a turbo compressor.

revolutions per minute (rpm)

A unit used to measure the speed of motors and other rotating devices.

disc-type compressor valve

A valve design that uses discs to virtually eliminate the clearance pocket at the top of the piston stroke, which minimizes the re-expansion of gas. This design increases compressor capacity up to 25% by improving volumetric efficiency.

hermetic

Airtight; totally sealed against all external forces.

direct drive

An open-type compressor drive arrangement in which the rotor is coupled directly to the compressor's crankshaft.

discharge line stub

One of the stubs on a hermetic compressor. It feeds the compressor's high-pressure exhaust to the hot gas discharge line leading to the condenser.

augers

Screwlike devices used to compress refrigerant gas in a screw compressor.

piston rings

Sealing rings that fill the gap between a piston and the compressor cylinder wall. Piston rings are typically used only on compressors rated at 10 horsepower or higher.

stubs

Short copper-coated steel pipes welded to openings in the housing of a hermetic compressor for attaching tubing or valves.

clearance pocket

Space formed at the top of a reciprocating compressor cylinder to prevent the piston from striking the valve reed.

orbiting

Term describing the form of motion that compresses gas between the two scroll components in a scroll compressor.

vanes

The blades mounted on a rotor inside a compressor or other rotating machine.

volute

The case containing the spinning rotor in a centrifugal compressor or pump.

eccentric

The crank throw in a reciprocating compressor.

piston

The device that moves up and down inside a reciprocating compressor's cylinder to compress refrigerant gas.

suction line stub

The short copper-coated steel pipe welded to an opening in the housing of a hermetic compressor for attaching the suction line tubing.