PUMP 



given a to-and-fro motion, and fits 

 the inside of the chamber closely 

 all round. The space below it is 

 divided into two parts, X and Y, 

 connected with the suction pipe by 

 valves A 1 and A- respectively. 

 When the diaphragm is rotated 

 in a clockwise direction, water is 

 sucked into X, while 

 the contents of Y are 

 added to those of 

 J space Z by the open- 

 ing of B-, and part of 

 the total is expelled 

 through the delivery 

 pipe. During the re- 

 verse stroke X de- 

 livers and Y sucks in. 

 Fig. 4 shows a sin- 

 gle-acting force 

 pump. The second 

 valve B is here at- 

 tached to a station- 

 ary part, below the 

 Fig. 4. Single- piston, which draws 

 acting force m t h e water during 

 pump. See text ^ out . stroke> an 



presses it from the cylinder during 

 the in-stroke. A solid plunger, 

 working through a water-tight 

 gland, is often used instead of a 

 piston, especially in pumps which 

 have to work under very high 

 pressure. 



Fig. 5 is a diagram of a 

 double-acting force pump, 

 which takes in and expels 

 water from each end alter- 

 nately, A 2 working simul- 

 taneously with B 1 , and A 1 

 with B 2 . The 

 air chamber 

 on the delivery 

 pipe relieves 

 the working 

 parts of sud- 

 den shocks (by 

 virtue of the 

 compressibility 

 of the impris- 

 oned air), and 



is used where high pressures are 

 reqmred, especially on quick, high- 

 speed pumps. 



The flap valve, hinged at one 

 side, is the valve most commonly 

 used It may be of leather or 

 rubber weighted with lead or iron, 

 or be entirely of metal. 

 Conical and , mushroom 

 valves and ball valves are 

 preferable for 

 q u i c k-running 

 pumps. What- 

 ever kind of 

 valve be used, 

 the area of the 

 way through should be am- 

 ple to allow the water to 

 pass without raising the 

 valve far from its seat. A 

 slow -closing valve causes Rg - 

 serious loss of efficiency by showing principle! 

 the "slip" that occurs See text 



PUMP 



Fig. 6. Rotating 



pump. Diagram 



showing principle. 



See text 



force pump 

 text 



while the valve is seating itself; 

 and wear increases rapidly with 

 the lift of the valve. 



ROTATING PUMPS. The best- 

 known pump of this class is the 

 centrifugal, of which diagrammatic 

 side and cross sections are given 

 in Figs. 6 and 7. In principle it 

 may be regarded as a water tur- 

 bine reversed. The runner, or 

 impeller, R, 

 mounted on 

 shaftS, is open 

 at the centre, 

 and divided 

 radially into a 

 number of 

 curved com- 

 partments, 

 the vanes be- 

 tween two 

 compart- 

 ments curving 

 backwards 



from the direction of rotation. 

 The centrifugal force produced 

 by the rapid rotation of the im- 

 peller presses the liquid in the 

 impeller towards the periphery, 

 and creates a vacuum at the central 

 openings C C, into which liquid 

 streams under atmospheric pres- 

 sure from the supply chambers 

 which are connected with the 

 suction pipe. On leaving the 

 vanes, the liquid is 

 caught in part of the 

 exterior casing, so 

 shaped that its ca- 

 pacity increases 

 gradually towards 

 the delivery end, and 

 its kinetic energy is 

 converted into pres- 

 sure'. A pump of the 

 ^ simplest type can be 

 "" used for heads up to 

 100 ft., and will give an efficiency 

 up to 86 p.c. For very high heads, 

 up to 1,800 ft., multi-stage pumps 

 are employed. These have se- 

 veral impellers, and the liquid 

 passes from one to the other 

 through specially shaped passages, 

 gaining pressure at every stage. 



Centrifugal pumps are particu- 

 larly well suited for raising large 

 quantities of water against moder- 

 ate heads, and are much 

 used for draining fens, 

 dealing with storm water, 

 and emptying 

 docks. Their free- 

 dom from valves 

 renders them in- 

 valuable for pump- 

 ing liquid loaded 

 with sand, clay, and other 

 solid matter. Those used 

 in the Alexandra Docks, 

 Newport, are each able to 

 raise 100,000 galls, per 

 minute (640,000 tons per 

 day) against a head of 20ft. 



suction 



( V 



\Chomber 



.. 



The gear wheel type of pump, 

 Fig. 8, is a favourite on motor 

 cars for circulating cooling water 

 and lubricating oil. The flow of 

 liquid is shown by the arrows. 



Fig. 8. Gear wheel type of pump 

 used on motor cars 



Another kind used for the same 

 purposes, Fig. 9, has a drum A 

 placed eccentrically in a circular 

 casing, with which the ends make a 

 good fit. The leaves B are kept 

 pressed against the casing by a 

 spring, and work in and out of their 

 grooves as the drum rotates, scoop- 

 ing up liquid at the S end and 

 delivering at the other. 



Fig. 9. 



Pump with eccentric drum 

 See text 



A recent addition to the rotary 

 class is the Rotoplunge, the princi- 

 ple of which is explained in Fig. 10. 

 C is a circular casing in which a 

 number of cylinders are bored 

 radially. The pistons are all at- 

 tached at their inner ends to a 

 common connecting-piece, which, 

 by means of projections engaging 

 in eccentric grooves in the end 

 covers of the 

 casing, draws 

 each piston in- 

 wards while 

 passing from 

 A to B, and 

 thrusts it out 

 between B and 

 A. As the 

 water cannot 

 pass the points 

 A and B, each 

 cylinder in 

 turn charges 

 itself from the 

 suction side, 

 and empties its contents into the 

 delivery side. 



PRESSURE PUMPS. The Hum- 

 phrey pump is an example of 

 the third class of pumps, in which 

 an elastic fluid is used to expel the 

 water. Five large pumps of this 



Fig. 10. Rotoplunge 



type of pump. See 



text 



