Fig. 357.
It will thus be seen that the engine is suited to meet the demand of the large power on one stroke, and very little on the other, thus adapting itself admirably to its requirements.
The valves are of the Corliss type, and do not trip; the cut-off being set by hand, does not require to be changed or altered, as the speed is controlled by a throttling governor.
Fig. [357] shows a cross section through the steam cylinder of this vacuum pump.
Fig. 358.
The Edwards air and vacuum pump is shown in Figs. [358], [359] and [360], in which it may be perceived that both foot and bucket valves are dispensed with; the only valves used are those which in other pumps are known as head or discharge valves.
The following brief description of its leading features will be understood by reference to the illustrations: Fig. [358] is a sectional view through the center of the air pump, but the piston and rod are shown as a full view.
The action of this pump is as follows: the condensed steam flows continuously by gravity from the condenser into the base of the pump, and is there dealt with mechanically by the conical bucket working in connection with a base of similar shape. Upon the descent of the bucket the water is projected silently and without shock at a high velocity through the ports into the working barrel (see Fig. [359]). The rising water is followed by the rising bucket, which closes the ports, and, sweeping the air and water before it, discharges them through the valve at the top of the barrel.