Refrigeration cycle and components

NAVEDTRA 14075 §6-1

The vapor-compression refrigeration cycle Refrigeration moves heat from a cold space to a warmer one, against its natural direction, by repeatedly evaporating and condensing a refrigerant in a closed cycle. It works because a liquid absorbs a large amount of heat (its latent heat) when it boils, and gives that heat up again when it condenses; by controlling the pressure, the refrigerant can be made to boil at a low temperature in the space being cooled and to condense at a higher temperature where the heat is rejected. The vapor-compression cycle has four essential components connected in a loop: the compressor, the condenser, the metering (expansion) device, and the evaporator. Following the refrigerant around the loop: low-pressure liquid refrigerant boils in the evaporator (the cooling…

NAVEDTRA 14075 §6-2

Compressors The compressor is the heart of the refrigeration system: it draws low-pressure vapor from the evaporator, compresses it to a pressure high enough that the refrigerant will condense at the available cooling-water or air temperature, and so keeps the refrigerant circulating and the heat moving. Most marine refrigeration and air-conditioning plants use reciprocating compressors, in which pistons draw vapor in through suction (reed) valves on the down-stroke and force it out through discharge valves on the up-stroke; they may be open (driven by an external motor through a coupling or belt, with a shaft seal) or hermetic/semi-hermetic (motor and compressor sealed in one housing). Larger air-conditioning plants often use rotary screw or centrifugal compressors, which give smooth, hi…

NAVEDTRA 14075 Ch. 6 — 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 conditioning. One of the most commonly encountered compressors 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.

NAVEDTRA 14075 Ch. 6 — Correcting Troubles

Faulty operation of the refrigerating and air conditioning plants is indicated by various definite symptoms. Information in figures 6-12 and 6-13 indicates some possible troubles that may be encountered, the possible causes of these troubles, and the corrective action which may be taken. But remember always consult the manufacturer’s technical manual before attempting any repair or adjustment on your equipment. Trouble Possible Cause Corrective Measure High condensing pressure. Air or non-condensable gas in system. Purge air from condenser. Inlet water warm. Increase quantity of condensing water. Insufficient water flowing through condenser. Increase quantity of water. Condenser tubes clogged or scaled. Clean condenser water tubes. Too much liquid in receiver, condenser tubes submerged in…

NAVEDTRA 14075 Ch. 6 — Refrigeration and Air Conditioning

As an EN1 or ENC you have already learned the principles of refrigeration and air conditioning, 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 corrective procedure…

NAVEDTRA 14075 Ch. 9 — Engine Maintenance ¶14

8-27. During plant operation, which of the following symptoms will indicate a clogged R-12 liquid line strainer? 1. The temperature of the tubing on the outlet side of the strainer is much warmer than the tubing on the inlet side 2. The temperature of the tubing on the inlet side of the strainer is much warmer than the tubing on the outlet side 3. The pressure on the outlet side of the strainer tubing is much higher than on the inlet side 4. The pressure on both the inlet and outlet sides of the strainer tubing are the same 8-28. Which action should you take prior to tightening the cap on a liquid line strainer that has been cleaned? 1. Test the strainer for leaks 2. Open the strainer outlet valve 3. Purge the air out of the strainer 4. Replace the strainer screen spring 8-29. Which of the…