All About Engines

Engines for Ships 287 ing at the lowest possible temperature so as to remove the greatest possible quantity of air per stroke. The efficiency of the wet air pump, on the other hand, depends upon the removal of the condensed steam at the highest possible temperature, so that it will require the smallest amount of heating before it goes back to the boiler. The temperature in the dry air pump is kept down by means of an injection of cold water. Another device of Messrs. Weir, who have made a speciality of auxiliary machinery, not only of ships but also of land stations, is the direct contact feed water heater shown in Fig. 160. The steam for heating is drawn from the low-pressure receiver of the main engine and the exhaust of such auxiliary engines as pumps, electric light, and fan engines, etc., and it is led into the heater through the non- return valve B. From thence it passes through the perforated cylinder and mixes with feed water de- livered through the spring-loaded valve d and the conical spray piece in the form of a fine spray. Any air contained in the water is liberated and escapes into the condenser or into the atmosphere through the cock k. The level of the water in the heater is kept constant by an ingenious self-regulating device. The float e is a pan, suspended on levers so that the levers are horizontal when the pan is full of water and immersed to half its depth. The position of this float regulates the amount of steam supplied to the feed pump through the regulating valve f. Probably the most popular pump for marine