American Milk- Condensing/ Factories. 
125 
possible the unequal wearing of the cylinder. K is the pump- 
cylinder, one-hall of which is shown in section, to exhibit the 
Figs. 4 and 5. — Plan and Section of the Improved Vacuum-Pump. 
Fig. 4. ■ 
arrangement of the valves. The end of the cylinder forms the flat 
valve-plates, in which are imbedded the induction-valve M, and 
the eduction-valve N, the former connecting with the induction- 
passage O, and suction-pipe Q; the latter with the eduction- 
passage P, and exhaust-pipe R. L is the pump-piston, which 
moves up to the valve-plate, as closely as the case will admit, 
to expel as much air as possible. A small quantity of water 
is also admitted for this purpose at T in the suction-pipe. 
In what is known as a dry vacuum-pump, to which class of 
machmes this belongs, it is of the greatest importance to leave 
the least possible amount of dead space in the cylinder between 
the piston and the valves, when the piston is at the end of its 
stroke; because, on expelling the vapour, the amount that fills 
this space remains, and reduces the capacity of the pump, in the 
proportion that this space bears to the capacity of a single stroke 
•)1 the pump, multiplied by the ratio of the density of vapour, 
