Chapter 15 Compressors

belt driven compressors

An open drive compressor that is connected to its drive motor by a belt and pulley system

direct-drive compressors

An open drive compressor that is driven by a motor connected directly to the compressor by a coupling between their shafts.

oil slugging

Excess amounts of oil being pumped out of the compressor due to oil foaming

piston ring

In reciprocating compressor's, a split metal ring installed in a groove on the piston. Piston rings push outward to form a seal between the side of the piston and the cylinder wall.

shaft seal

On open drive compressors, a sealing device that is installed between a shaft and the case where it emerges.

compression rings

Piston rings that are designed to prevent pressurized refrigerant vapor from blowing past the piston and into the crankcase

piston pins

Small metal cylinders that connect a reciprocating compressor's piston to its connecting rod

volute

Spiral shaped, with a gradually decreasing cross sectional area along the perimeter. Used to describe the shape of the stator of a centrifugal compressor.

stator

The stationary part of an electric motor that is attached to the inside of the motor housing. Also called the frame.

viscosity

A fluids resistance to flowing. A high viscosity fluid flows more slowly and a low viscosity fluid flows freely.

scroll compressors

A compressor in which vapor compression takes place between a fixed scroll and an orbiting scroll.

rotary compressors

A compressor in which vapor compression takes place in spaces between the cylinder wall and sides of an off center rotor that spins inside the cylinder.

screw compressors

A compressor in which vapor is compressed by a pair of meshing helical rotors.

semi-hermetic compressors

A compressor that contains the motor and compressor inside a multipart shell that is bolted together.

serviceable hermetic compressors

A compressor that contains the motor and compressor inside a multipart shell that is bolted together.

reciprocating compressors

A compressor that functions by changing the rotational movement of the crankshaft into the reciprocating motion of the pistons.

hermetic compressors

A compressor that includes an integrated drive motor in a sealed unit.

external drive compressor

A compressor that is driven by a motor that is separate from the compressor unit. Also called an open drive compressor.

open drive compressors

A compressor that is driven by an external motor. Also called an external drive compressor.

mufflers

A cylinder with internal baffles that mute the noise caused by refrigerant vapor pulsation , thereby reducing sound and vibration.

O-rings

A flexible ring (usually made of elastomers) installed at the joints between mating parts to prevent leaks.

centrifugal force

A force that acts outwards from the center of rotation

splash system

A lubrication system that relies on the moving internal parts of the compressor to distribute oil by splashing.

pressure lubrication system

A lubrication system that uses a pump to pressurize oil, which is then distributed to all bearing and other high wear surfaces through dedicated oil passages.

unloader

A mechanism that reduces the load on a compressor to aid startup or to modulate the compressors capacity.

connecting rod

A reciprocating compressor component that connects the piston to the crankshaft

pistons

A reciprocating compressor component that moves up and down in the cylinder and compresses the refrigerant vapor.

eccentric

A shaft section that is larger and has a different center than the rest of the shaft

gaskets

A thin seal installed between the mating surfaces of a case or housing to prevent leaks at the joint, such as between a compressor and its service valves. In refrigeration cabinet construction, a flexible rubber material pressed into a channel on a door to perform an airtight seal between the door and cabinet when the door is closed.

scotch yoke

A variation of the reciprocating compressor that has a long piston with an elliptical slot at the bottom of the skirt. The piston is connected directly to the crankshaft pin, which slides from side to side in the slot as the crankshaft rotates. Scotch yoke compressors have no connecting rods.

impeller

In a hydronic system, the part of a circulating pump that spins and forces water through the system. In a rotary or centrifugal compressor, the compressors rotor.

oil ring

In a reciprocating compressor, a piston ring that lubricates a cylinder wall and prevents excess oil from entering the cylinder

valve plate

In a reciprocating compressor, the metal plate between the cylinder head and the cylinder block on which the valves are installed.

clearance space

The volume of space between the top of the piston head and the bottom of the valve plate when the piston is at top dead center (TDP)

reciprocating

Up and down, or back and forth movement in a straight line.

centrifugal compressors

a compressor consisting of an impeller with radial blades and a volute casing. As the rotor spins, it flings refrigerant vapor outward, where it compresses against the volute casing.

cylinder head

a metal plate positioned on top of the valve plate and bolted to the cylinder block. The cylinder head holds the valve plate in position and seals the cylinder.

crankcase heater

an electric device on or in a compressor that supplies heat to the crankcase in order to evaporate any refrigerant that may be trapped in the oil or prevent refrigerant inside the compressor from condensing into liquid