504 APPLIED MECHANICS 
generally used. - The piston A has an area twice that of the piston: 
B. During the outward stroke the water to the left of the piston is dis- 
charged through the passage C and valve D to the accumulator, and 
water at the same time enters. by the suction valve E and passage F,. and. 
fills the space to the right of the piston. During the inward stroke ‘ 
water to the right of the piston is discharged through the passage Fa 
valve H into the passage K, but only half of this water goes through the 
valve D to the accumulator ; the other half goes by the passage C to the 
annular space in the barrel or cylinder to the left of the piston. A volume — 
of water, equal to half the volume swept through by the piston, - 
evidently discharged to the accumulator during each stroke. ‘The valve 
D is not absolutely necessary, but it acts as a check on the others when th e 
pump is not working. To make the valves close promptly they are load ed 
with springs, which consist of rubber rings separated by metallic washers. ~ 
438. Air and Vacuum Chambers.—In a pump of the single-acting 
type water is delivered during alternate strokes only, and the ioe , 
through the delivery pipe is therefore 
intermittent. The result of this is 
that in the neighbourhood of the 
delivery valve there is a great fluctua- 
tion of pressure due to the inertia of 
the water, and a consequent series of 
shocks. To remedy this defect an 
air chamber A (Figs. 806 and 807) 
is placed over or near the delivery 
valve D. 
The theory of the action of the 
air chamber is as follows. Referring 
to Fig. 808, the base line is a time > ‘1G. 807. 
base. The height of the straight line bi at a 
MN above the base represents the static pressure of the water due ~ 
to the head in the delivery pipe. The height of the line marked “total — 
Pie suet To er 
1 eae: “Soe7 1 Se l 
nae <= ees ese 
‘ i ' 
Pe. | ' | | | ' | 
“AL By GD ie Foyt 
Lime of first | i ime of second Lime of third, | 
! stroke! ' stroke ! s “at 
——e— —>l tate fede! | bee aS ee >! ' 
Fia. 808. 
resistance” above MN represents the additional pressure required to 
overcome the friction in the delivery pipe. Suppose that the pump — 
starts from rest. The water in the delivery pipe being at rest, the — 
pressure of the air in the air chamber is equal to the static pressure of the 7 
water. At the beginning of the first delivery stroke the delivery valve — 
opens, and the water, flowing through, finds two passages open to it, 
