All About Engines

The Gas Engine 203 exactly like the swing of a pendulum. So long as the swings are not very large their magnitude does not matter : they each take the same time. But for our purpose the time of swing is not of much conse- quence. The essential fact is that if you give water in a tube of this form a push, it will always come back again. And that is just what a gas engine piston linked up to a crank will do. So that this column of water, once it is set in vibration, will draw in, or Fig. 116.—Diagrammatic section of the Humphrey pump compress, or expel gases just like the solid piston of an ordinary gas engine. At the Chingford Reservoir of the London Water Board there are five pumps constructed on this plan and represented diagrammatically in Fig. 116. The horizontal portion, called the play pipe, is of cast iron, 6 feet in diameter and 60 feet long. The left- hand limb, forming the pump proper, is 7 feet in diameter and 10 feet long. It is provided (a) with gas and air inlet valves, and (b) with exhaust valves, in the upper end, and with a water inlet valve in the