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

 166 SEA WATER DISTILLATION. ®S (12) Duration of Trial—Four consecutive hours on the above conditions, with a production of 10 per cent, more than ordinary output specified; and during the trial there must be no altering of the steam valves or feed inlet, nor any manipulation of the automatic feed. This margin (10 per cent.') is sometimes increased to 20 per cent, for trial before delivery, and 10 per cent. on subsequent trial when the apparatus is fixed on board ready for use. Note.—In H.M. ships of cruiser and battleship type, it is usual to have a combination of two evaporators working with one distilling condenser. This saves space, but the arrangement is not so simple as a single evapo- rator working with its own distiller. General Observations. 7. For ordinary working of a double distiller, an atmospheric pressure for the gained steam is clearly preferable to a minus pressure or vacuum. Perhaps the strongest argument in support of this is, that whereas a few years back, specifications required the double distiller to work always at a considerable minus pressure, now specify that practically atmospheric pressure is to be the condition for normal working. Where, however, the latter system (i.e., a vacuum) is specified it is always complied with. N