Starting

The compressor motor is started. The lube oil pressure should reach the correct value. The first stage drains and then the second stage drains are closed and the machine will begin to operate. The pressure gauge cocks should be adjusted to give a steady reading. Where manual drains are fitted they should be slightly opened to discharge any moisture which may collect in the coolers. The cooling water supply should be checked as well as operating temperatures.

Stopping

To stop the compressor the first and second-stage cooler drain valves should be opened and the machine run unloaded for 2 or 3 minutes which will clear the coolers of condensate. The compressor can now be stopped and the drains should be left open.

Maintenance and operating troubles and remedy

Maintenance involves the usual checks and overhauls common to reciprocating machinery, e.g. crankcase oil level, cooling water system, operating temperatures and pressures, etc. The suction and delivery valves are most troublesome. These valves are automatic requiring a small pressure differential to operate.

The constant rapid opening and closing action of the valves may require seats to be refaced. Overheating, use of incorrect lube oil or the presence of dirt may result in sticking or pitting of the surfaces. The suction and delivery valves should be stripped and all parts carefully cleaned and examined and worn parts replaced and the valve seat and plate lightly lapped before reassembly to ensure a good seal.

Heat exchangers words and expressions

to require conducting surface opposite counter or contra flow fairly heat transfer shell and tube cooler plate type heat exchanger tube bundle corrosion resistor visible joint radial flow circular baffles safety expansion ring double joint removable cover shell frame plate carrier bar support post tie bolt plate pack guide bar

требовать проводящая поверхность противоположный противопоток довольно теплопередача трубчатый охладитель пластинчатый охладитель пучок труб антикоррозийный протектор наружное соединение направляющие пластины потока предохранительное расширительное кольцо рамовая плита балка корпус, кожух поддерживающая опора стяжной болт зд: двойное уплотнение съемная крышка пакет пластин направляющая балка

TEXT

Heat exchangers on board a ship are mainly coolers where a hot liquid is cooled by sea water. There are some instances where liquid heating is required, such as heavy fuel oil heaters and sea water heaters for tank cleaning.

In the heat exchange process the two liquids pass on either side of a conducting surface. The heat from the hot liquid passes to the cold liquid and the conducting surface is at a temperature between the two. Marine heat exchangers usually have the two liquids flowing in opposite directions, i.e. counter or contra flow which provides a fairly constant temperature difference between the two liquids and therefore the maximum heat transfer.

Coolers at sea fall into 2 groups: the shell and tube and the plate type. Heaters are similar in construction to coolers.

In the shell and tube design a tube bundle is fitted into a shell.

Figure 4.2. Shell and tube cooler,

The plate type heat exchanger is made up of a number of pressed plates surrounded by seals and held together in a frame.

Figure 4.3 Plate-type heat exchanger: (a) construction.