Components:
Compressors
The refrigeration system consists of
four basic components—t h e compressor, the condenser, the liquid receiver, the
evaporator, and the control devices. These components are essential for any system to
operate on the principles previously discussed. Information on these components is
described in the following sections.
Compressors
Refrigeration compressors have but one
purpose—to withdraw the heat-laden refrigerant vapor from the evaporator and compress
the gas to a pressure that will liquefy in the condenser. The designs of compressors vary,
depending upon the application and type of refrigerant. There are three types of
compressors classified according to the principle of operation— reciprocating,
rotary, and centrifugal.
Compressors will not be explained
further here except to discuss the special methods used to seal compressors to prevent
escape of refrigerant. Many refrigerator compressors have components besides those
normally found on compressors, such as unloaders, oil pumps, mufflers, and so on. These
devices are too complicated to explain here. Before repairing any compressor, check the
manufacturer's manual for an explanation of their operation, adjustment, and repair.
External Drive Compressor.—An
external drive or open-type compressor is bolted together. Its crankshaft extends through
the crankcase and is driven by a flywheel (pulley) and belt, or it can be driven directly
by an electric motor. A leakproof seal must be maintained where the crankshaft extends out
of the crankcase of an open-type compressor. The seal must be designed to hold the
pressure developed inside of the compressor. It must prevent refrigerant and oil from
leaking out and prevent air and moisture from entering the compressor. Two types of seals
are used—the stationary bellows seal and the rotating bellows seal.
An internal stationary crankshaft seal
shown in figure 6-15 consists of a corrugated thin brass tube (seal bellows) fastened to a
bronze ring (seal guide) at one end and to the flange plate at the other. The flange plate
is bolted to the crankcase with a gasket between the two units. A spring presses the seal
guide mounted on the other end of the bellows against a seal ring positioned against the
shoulder of the crankshaft. As the pressure builds up in the crankcase, the bellows tend
to lengthen, causing additional force to press the seal guide against the seal ring. Oil
from the crankcase lubricates the surfaces of the seal guide and seal ring. This forms a
gastight sea whether the compressor is operating or idle.
An external stationary bellows
crankshaft seal is shown in figure 6-16. This seal is the same as the internal seal,
except it is positioned on the outside of the
http://www.sweethaven02.com/MechTech/Refrig01/crankcase.
An external rotating bellows crankcase
seal is shown in figure 6-17. This seal turns with the crankshaft. This seal also consists
of a corrugated thin brass tube (seal bellows) with a seal ring fastened to one end and a
seal flange fastened to the other. A seal spring is enclosed within the bellows. The
complete bellows assembly slips on the end of the crankshaft and is held in place by a
nut. The seal ring that is the inner portion of the bellows is positioned against a
nonrotating seal fastened directly to the crankcase.
During operation, the complete bellows
assembly rotates with the shaft, causing the seal ring to rotate against the stationary
seal. The pressure of the seal spring holds the seal ring against the seal. The expansion
of the bellows caused by the pressure from the crankcase also exerts pressure on the seal
ring. Because of this design, double pressure is exerted against the seal ring to provide
a gastight seal. |
