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

102 SEA WATER DISTILLATION. (c) Zinc Plates. 75. To preserve the casings of evaporators, zinc plates are sometimes fitted inside the casings, in order to take the galvanic action ; but they do not appear to be needed in casings made of gun-metal. These zinc blocks, as already stated in a former page, very soon corrode away and require some care in replacing, for if badly fixed they may be worse than useless. The gun-metal parts of an evaporator have been known to last for a considerable number of years without showing any signs whatever of perishing. (<Z) Fittings and Mountings. 76. The usual fittings on the evaporator are as follows :— A steam valve for regulating the steam supplied to the in- terior of the coil. A coil drain—i.e., a valve or cock for opening or closing the passage—for the escape of primary water condensed inside the coil. A jeed inlet, which may, or may not, have a non-return valve, according as the feed-water is to enter, or not, against pressure inside the casing. A filling pipe and cock for cpiickly charging the evaporator with feed-water to start with. A brine outlet for the brine to discharge either into a brine receiver or elsewhere. A secondary steam pipe on the top of the evaporator, fitted with a valve, for getting up a pressure in the casing when desired. A presslire gauge for indicat- ing the pressure of the steam inside the coils. Another pressure gauge, to indicate the pressure inside the casing. A ivater gauge, for indicating the brine level inside the casing. A safety valve, when pressure is got up inside the casing. A test cock, for use with the salinometer. A large door, facing the coils or evaporating surfaces, for