The gain to be secured by using a condensing apparatus may be measured in two ways: first, by the decrease in fuel consumption over that necessary when running non-condensing, which will represent a constant decrease in running expenses; or, second, by the increase of power working quite up to its economical limit, in a non-condensing engine.
By the use of a condenser a further increase of power is realized in raising the mean effective pressure of steam within the engine cylinder without increasing the demand upon the boiler.
The application of a condenser to a steam engine increases its economy from 20% to 25% depending upon circumstances, while by compounding and condensing an economy of 35% to 40% is effected.
SINGLE AND CROSS COMPOUND DOUBLE ACTING VACUUM PUMPS.
The vacuum pump shown in the engraving, Fig. [346], represents a single cylinder double acting vertical design having but one set of valves and those used exclusively for the discharge.
The suction port is in the middle of the cylinder, A, shown in the sectional view, Fig. [347]. The piston, E, when it passes this port imprisons the water beyond it and pushes this water out of the discharge valves, D D, if the piston is rising, and out of the valves, C C, if the piston is descending. The main discharge pipe is attached to a flange at B.
This pump is made to work easily and steadily by adjusting the cushioning valves, F. F.
The discharge valves are reached through the holes provided for that purpose and covered by plates shown in the engraving, Fig. [347].
The main slide valve moves horizontally for the reason that if it moved up and down the force of gravity would seriously interfere with its regular action.