A section of a Pulsometer is shown in Fig. 98. It consists of two bottle-shaped chambers _A_ and _B_ with their necks communicating at the top and each opening into the outlet chamber _O_ through a check valve. Steam is admitted at the top and enters chamber _A_ or _B_ according to the position of the steam valve _C_ as shown. This steam valve is a ball which is free to roll either to the right or left and forms a steam-tight joint with whichever seat it rests upon. In normal operation chamber _A_ would be filled with water as the steam enters the cylinder. At the same time a check valve at the top opens to admit a small quantity of air which forms a cushion insulating the steam from the water, reduces the condensation of the steam, and serves as a cushion for the incoming water on the opposite stroke. The pressure of the steam depresses the surface of the water without agitation and forces the water through the check valve _F_ into the discharge chamber _O_. When the water falls to the level of the discharge chamber the even surface is broken up and the intimate contact of the steam and water condenses the former instantaneously. This forms a vacuum in chamber _A_ which, assisted by a slight upward pressure in chamber _B_ caused by the incoming water, immediately pulls the ball _C_ over to the other seat and directs the steam into chamber _B_. The vacuum in chamber _A_ now draws up a new charge of water through the suction pipe into the chamber. [Illustration: FIG. 99.—Emerson Steam Vacuum Pump. ] A section of the Emerson pump is shown in Fig. 99. The pump consists of two vertical cylinders _B_ and _C_. Each chamber has a suction valve _L_ at the bottom, opening upward from a common chamber from which the discharge pipe _U_ extends. On the top of each chamber is a baffle plate _G_ which operates to distribute the steam evenly to the two chambers and to prevent it from agitating the surface of the water in the chambers. A condenser nozzle _F_ is connected with the bottom of the opposite chamber by a pipe into which a check valve opens upward. As the pressure in the chamber alternates water will be injected through _F_ into the opposite chamber and condense the steam therein, promptly forming a vacuum. An air valve _P_ admits a small quantity of air while the chamber is filling with water, the air acting as an insulating cushion as in the Pulsometer. Valve _O_, just above the top connection _S_ is used to regulate the amount of steam that enters the pump. The top connection _S_ has two ports, one leading to each chamber. An oscillating valve enclosed in it admits the steam through these ports to the two chambers alternately. This valve is driven by a small three-cylinder engine, the crank shaft of which extends into the top connection in the center of the bearing on which the valve oscillates. A positive geared connection is made between the valve and the engine and so arranged that the engine will run faster than the valve.