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

98 SEA WATER DISTILLATION. however, necessary to make the small elbows of this metal, as a good gun-metal casting will be found easier to make, and give greater satisfaction. 64. If the coil ends are expanded into the gun-metal elbows, a couple of small grooves inside the elbow socket (as shown in Fig. 9a) will make a tighter fit when expanded. A screw or thread is sometimes put instead of grooves, but this does not make such a tight joint as the grooves, which will stand a test pressure without the chance of leaking round the thread. Coil Drain. 65. Before leaving the subject of the evaporator coils, a few words are necessary to explain the action of the coil drain. 66. As the primary steam inside the coils is condensed into water when giving out its latent heat for the purpose of generating steam from the water outside the coils, this primary water is blown away at the end of the coils, and the coil drain is usually a cock with a by-pass of suitable size for passing water only, as blowing away primary steam would be very wasteful. 67. This by-pass must not, however, be too small, otherwise the primary water would not escape freely, and the coils would become water-logged, and their heating power very considerably reduced. The exact size of the hole for the by-pass depends on the pressure inside the coil, and the quantity of water that has to escape, and can only be determined by experience. 68. It is important to note that the primary water is practically at the same pressure and, therefore, of the same temperature as the “ sensible ” heat of the primary