550 Farm Mechanics. 



amount of water is being discharged per minute as when 

 the pump was being worked on the 3-inch discharge pipe. 

 From these observations it is clear that the size of the 

 suction and discharge pipe, compared with the 'piston, 

 may make a very material difference in the amount of 

 power necessary to work the pump at a given rate. Tho 

 area of the 3-inch piston contains the area of the I -inch 

 pipe nearly 16 times and this means that when the piston 

 is driving the water through the i inch pipe its velocity 

 must be 16 times that of the piston, while when forcing it 

 through the 3-inch pipe the water travels at only the same 

 rate and therefore reouires less power. 



Influence of Elbows on the Power Required to Work 

 a Pump. In the apparatus of Fig. 259 there is repre- 

 sented, leading out of and back into the {-inch pipe, a side 

 tube, so that w r hen the inch gate valve is closed and the 

 pump worked the water is forced to travel through four 

 right angles instead of taking the straight course possible 

 when the gate is open. Under these conditions the gage E 

 shows an increase of pressure amounting to I of a pound 

 per square inch for each right angle, or a total increase 

 of three pounds per square inch on the piston and, as the 

 piston has an area of over seven square inches, the extra 

 power which had to be applied to the piston rod, in order 

 to pump around the four elbows, exceeded 28 pounds. 



697. Double-Acting Suction Pumps. In the ordinary 

 suction pump, practically all of the work has to be done 

 with the up stroke of the piston and this requires a heavier 

 pressure than would be necessary if the work could be 

 divided between the up and down strokes. An effort is 

 sometimes made in the construction of the pump to divide 

 the labor between the two strokes and one of the methods 

 employed is represented in the double acting pump of Fig. 

 260. In this pump there are two cylinders, the upper one 

 without a valve and having one-half the cross-section of 

 the lower one. With this arrangement, when the piston is 



