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

200 SEA WATER DISTILLATION. Fire doors should be kept shut, and the steam pressure regulated by careful use of the dampers. Steam should not blow off to waste at the safety valve. (3) The boiler should not be worked at an unnecessarily high pressure. The pressure of steam should not be more than sufficient to supply the evaporator with steam when the steam valve is full open—that is, the pressure of the steam in the boiler should not be very much above that inside the first evaporator coils. A little extra pressure may be needed to drive the pump. (4) In prolonged runs of a distilling apparatus, it will be found that the pressure of the boiler will be low at first, and that it will require to be gradually increased as the scale deposits on the heating surfaces. (5) The level of water should be kept as steady as pos- sible. Blowing off too much brine and filling up with feed to make up is wasteful. The feed regulator should be designed to give a feed in proportionate excess of the evaporation, so that there will be a constant discharge of brine if the blow-off cock is carefully regulated. (6) Once a day the safety valves should be just lifted by hand to see they are acting properly. (6) THE EVAPORATOR—1. Heating Surface. 63. What has been already said as to evaporators (Chap, vi.)—viz., as to their heating surface, brine, and other details regarding double distillation—applies to multiple evaporation just as minutely. 64. The heating surface has to be calculated, as was shown, for a pressure mside the coils counteracted by a lower pressure (more or less great) owfeide the coils—i.e., the difference in temperature is taken between the sens-