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Figure 6-1. Diagram of an R-12 refrigeration system |
CHAPTER 6
REFRIGERATION AND AIR CONDITIONING
As an EN1 or ENC you have already learned
the principles of refrigeration and air condition-
ing, and the components and accessories that
make up the system. You have learned how to
start, operate, and secure refrigeration plants. In
addition, you have performed routine
maintenance jobs such as trouble shooting, and
servicing the system, and used correct procedure’s
for leak detecting, and changing the lubricating
oil in refrigeration compressors. As you advance
in rate, you will be expected to have a greater
knowledge of the construction and operating
principles of refrigerating equipment. You will be
required to perform more complicated
maintenance jobs, to make repairs as required,
and to determine the causes of inefficient plant
operation and accomplish the necessary correc-
tive procedures.
This chapter provides information that sup-
plements related information in other training
manuals applicable to your rating and related to
the qualifications for advancement. Information
is included on the construction and maintenance
of refrigeration and air conditioning equipment,
and the detection and correction of operating
difficulties.
You should refer to the manufacturer’s
technical manual for details of the plant on your
ship.
The main parts of an R-12 refrigeration system
are shown in figure 6-1. The primary components
of the system are the thermostatic expansion
valve, the evaporator, the compressor, the con-
denser, and the receiver. Additional equipment
required to complete the plant includes piping,
pressure gages, thermometers, various types of
control switches and control valves, strainers,
relief valves, sight-flow indicators, dehydrators,
and charging connections.
In the following discussion, we will deal with
the R-12 system as though it had only one
evaporator, one compressor, and one condenser.
However, a refrigeration system may (and usually
does) include more than one evaporator, and it
may include additional compressor and condenser
units.
COMPRESSORS
Many different types and sizes of compressors
are used in refrigeration and air conditioning
systems. They vary from the small hermetic units
used in drinking fountains and refrigerators, to
the large centrifugal units used for air con-
ditioning.
One of the most commonly encountered com-
pressors on today’s modern ships is a high speed,
continuous running unit with a variable capacity.
This compressor is of the multicylinder,
reciprocating design, with a positive unloaded
system built into the compressor to control the
compressor’s capacity.
SHAFT SEALS
Where the crankshaft extends through the
crankcase, a leakproof seal must be maintained
to prevent the refrigerant and oil from escaping
and also to prevent air from entering the
crankcase when the pressure in the crankcase is
lower than the surrounding atmospheric pressure.
This is accomplished by crankshaft seal
assemblies. There are several types of seals
including the rotary seal, and the diaphragm.
6-1
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