CHAPTER XXX 
PUMPS 
431. Distinction between a Piston, a Bucket, and a Plunger.— A 
: “ei is generally a cylindrical piece which slides backwards and forwards 
‘inside a hollow cylinder. A piston may be moved by the action of fluid 
pressure upon it, as in a steam-engine or as in certain types of water 
_ pressure motors. A piston may, however, be used to give motion to a 
fluid, as in certain types of pumps. A piston is usually attached to a 
_ rod called’a piston-rod. Numerous forms of packing are used to prevent 
leakage past the piston. In the piston shown in Fig. 797 cup-leathers are 
PISTON. © 
Fig. 797. 
used for packing ; the pressure of the water acting on the inside of the cup 
presses the leather outwards against the cylinder. 
A bucket (Fig. 798) is a piston provided with one or more valves 
which permit of the fiuid passing through it in one direction. 
A plunger (Fig. 799) may be looked upon as a piston having the same 
diameter as its piston-rod. 
432. Bucket Pump.—Referring to Fig. 800, AB is a cylinder or 
barrel, in which is made to reciprocate a bucket C. A pipe DE, called 
the suction pipe, leads from the lower end of the barrel and dips into the 
water which the pump is required to raise. A pipe FH, called the delivery 
pipe, leads from the top of the barrel to the vessel into which the water 
is to be delivered. There are three valves, all opening upwards, one in 
the bucket, one at the top of the suction pipe, called the suction valve, 
and one at the bottom of the delivery pipe, called the delivery valve. 
The action of the pump is as follows. The bucket being at the 
bottom of its stroke, and the barreliapd pipes full of air at atmospheric 
