. The steam-engine and other heat-motors. Fig. Air-pump.—The condensed steam flows continu-ously by gravity from the condenser into the base of the pump 272 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. and is there dealt with mechanically by the conical bucket workingin connection with a base of similar shape. Upon the descent ofthe bucket the water is projected silently and without shock ata high velocity through the ports into the working barrel. However slowly an air-pump with foot- and bucket-valvesmay be running, the pressure in the condenser has to be sufficientlyabove that in the
. The steam-engine and other heat-motors. Fig. Air-pump.—The condensed steam flows continu-ously by gravity from the condenser into the base of the pump 272 THE STEAM-ENGINE AND OTHER HEAT-MOTORS. and is there dealt with mechanically by the conical bucket workingin connection with a base of similar shape. Upon the descent ofthe bucket the water is projected silently and without shock ata high velocity through the ports into the working barrel. However slowly an air-pump with foot- and bucket-valvesmay be running, the pressure in the condenser has to be sufficientlyabove that in the pump to lift the foot-valves, overcome the inertia. Fig. 144. of the water, and drive the water up through the valves into thebarrel. The higher the speed of the old type of pump the greateris the pressure required to overcome these resistances owing to thevery short space of time available, and as any increase of pressurein the condenser is accompanied by a corresponding increase ofback pressure in the cylinder, it will be seen that in an air-pump fitted with foot- and bucket-valves, increase of speed meansloss of efficiency. Under ordinary working conditions, when the bucket descendsand the ports are open, there is absolutely no obstruction betweenthe condenser and the pump; the air has a perfectly free entranceinto the barrel (Fig. 142), while immediately afterwards the water COXDEXSERS AXD AIR-PUMPS. 273 is injected into the barrel at a high velocity. Thus, instead ofobstructing the entrance of the air, the water tends to compressthat already in the barrel and to entrain or carry in more airwith it. In the old type of pump the
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