BECIPKOCATING PUMPS 



585 



work, and as will be noted the ram or plunger is in compression during 

 this stroke. 



If L = length of stroke we have : 

 Work done on suction stroke = A { -n a (fr a h s ) } W L foot Ibs. 



= IF h, A L foot Ibs. 



Work done on delivery stroke = W h d A L foot Ibs. 



A separate valve box may now contain both suction and delivery valves, 



and these become more accessi- 

 ble for examination and repairs. 

 Fig. 271 shows a section of 

 such a pump having a plunger 

 diameter of 32 inches, and^ a 

 stroke of 5 feet. The valves for 

 this pump are situated on the 

 sides and top of small hexagonal 

 prisms instead of being arranged 



^Lpl ^r-f on a s i n gl e plane surface. The 



pump is directly driven by a 

 steam engine and makes 40 

 strokes per minute against 153 

 feet head. 



So far, each type considered 

 has suffered from the disadvan- 

 tage that it only delivers water 

 on alternate strokes. This diffi- 

 culty is, however, overcome in 

 the " Bucket and Plunger " 

 pump (Fig. 272). Here the piston rod of the ordinary bucket pump is en- 

 larged to form a plunger of about half the area of the bucket which it carries. 

 Suction now takes place on the up stroke, and, if a and A are the areas 

 of plunger and bucket, a volume of water = A L is drawn into the pump, 

 while a volume (.4 a) L is displaced through the delivery valves. On 

 the down stroke the plunger displaces a volume A L, and in consequence 

 this volume passes to the upper side of the bucket. Of this the volume 

 (A a) L remains in the annular space between the barrel and the 

 plunger, while the remaining volume a L is displaced through the delivery 

 valves. 



Thus for equal deliveries on the two strokes : 

 (A - a) L = a L 

 /. A = 2 a. 



FIG. 272. Bucket and Plunger Pump. 



