A Practical Manual On Sea Water Distillation
With A Description Of The Necessary Machinery For The Process

MULTIPLE DISTILLATION. 215 Economy Effected by using Pump Exhaust. 101. The pump is driven by the high-pressure steam coming direct from the boiler, therefore, the most econ- omical and convenient manner of saving or retrieving the heat that is used is to let the exhaust steam impart its latent heat, either inside the first evaporator coils, or to the boiler feed-water (which requires to be made as hot as possible), and to let the water or the condensed exhaust steam go into the distilling condenser to be cooled along with the rest of the drinking water produced. The arrangement has already been explained, and need not be repeated here. 102. If the pump exhaust steam, instead of heating the boiler feed-water, is conducted back into the steam pipe leading the primary steam to the first evaporator, a non- return steam valve should be placed on the main or primary steam pipe to the apparatus, at a convenient place between the point where the live steam branches off to the pump and the point where the pump exhaust pipe rejoins the main steam pipe. By this means the non- return valve can be adjusted so as to reduce the pressure of the primary steam to the first evaporator sufficiently, so as not to overpower the exhaust steam or cause too great a back pressure upon the pump. This, however, involves the pressure in the boiler being kept somewhat higher than is necessary, in order to have a sufficient excess of pressure for driving the pump. 2. Feed-Water Pump. 103. The pumps, when drawing the regulated feed-water from the various compartments of the feed regulator, are prevented from sucking in air, by the arrangement of