25-09-2013, 04:57 PM
COMPRESSORS
COMPRESSORS.ppt (Size: 639 KB / Downloads: 105)
FUNCTION OF THE COMPRESSOR
Considered the heart of the refrigeration systems
Compressors are vapor pumps
Responsible for lowering the pressure on the suction side of the system
Responsible for increasing the pressure on the discharge side of the system
Suction gas from the evaporator enters the compressor
Refrigerant is discharged to the condenser
COMPRESSION RATIO
Compares pumping conditions for compressors
Defined as the high side pressure (psia) divided by the low side pressure (psia)
High compression ratio can lead to overheated compressor oil
High compression ratio leads to reduced refrigerant flow through the system
Reduced refrigerant flow reduces system capacity
TWO-STAGE COMPRESSION
Lowers the compression ratio
Utilizes two compressors
One compressor discharges into suction of the other
Also referred to as compound compression
Often used when the compression ratio of a single compressor system exceeds 10:1
Often used in low-temperature commercial and industrial storage applications
TYPES OF COMPRESSORS
Reciprocating
Fully welded, hermetic compressors
Semi-hermetic compressors
Open-drive compressors
Belt-driven and direct-drive compressors
Screw compressors
Rotary compressors
Scroll compressors
Centrifugal compressors
SEMI-HERMETIC COMPRESSORS
Bolted together, can be field serviced
Housing is made of cast iron
Has a horizontal crankshaft
Smaller compressors are splash lubricated
Larger compressors use pressure lubrication systems
Often air cooled
Piston heads are located at the top of the compressor
BELT-DRIVE MECHANISMS
Motor pulley is called the drive pulley
Compressor pulley is called the driven pulley
Pulleys can be adjusted to change compressor speed
Drive size x Drive rpm = Driven size x Driven rpm
Shafts must be properly aligned
Pulleys with multiple grooves must used matched sets of belts