Low pressure, submerged tube plants differ from ship to ship, but the operating conditions and the maintenance procedures are basically the same. In almost all instances, the personnel who stand watches on distilling plants are also respon-sible for the maintenance of the plants. This gives them ample opportunity to detect abnormal operating conditions before such conditions reach advanced stages. When operating troubles do occur, it is the responsibility of the EN1 or ENC on duty to locate the trouble and to make the necessary adjustments or repairs.

Steady operating conditions are essential for satisfactory results. Except under emergency con-ditions, no plant should be forced beyond its rated capacity, because higher steam pressures will be required and the resulting higher temperatures will cause more rapid scaling of the evaporator tubes. During operation, the various elements of any plant are interdependent due to the heat and fluid balances throughout the plant. Adjustment of any one control can produce widespread effects on these balances. For example, an increase in the feed to the first effect will raise the liquid level in the first effect. More heat will be required to raise the feed to the boiling point, so that less heat will be available for evaporation in the first-effect shell and a smaller amount of heat will flow to the second effect tube nest. These changes would work out to a new balanced condition, but other adjustments would be required to make the new balance satisfactory. Under such circumstances, overcontrolling can cause many readjustments. The operator will always find it is better to make adjustments singly and in small increments, allow-ing enough time between each adjustment for the conditions to become steady.