104 



To start a centrifugal pump the suction pipe and the pump must be 

 filled with water or primed. This may be done by closing the discharge 

 pipe with a check valve and connecting the suction end of a hand pump- 

 to the top of the casing. Where a steam engine is used a steam ejector 

 may take the place of the hand pump. For small pumps and low lifts a 

 foot valve on the end of the suction pipe may be used and the pump primed 

 by pouring water in the casing, or suction pipe. The disadvantage of a foot 

 valve is that if the water is not clear a small stone or twig may lodge itself 

 in the foot valve and prevent priming. This will necessitate that the suc- 

 tion pipe be uncoupled and the obstruction removed. 



The pump must be placed as near as possible to the water level to keep 

 the suction lift down. While theoretically the suction lift may be as great 

 as 33 feet at sea level and about 30 feet at an elevation of 3000 feet, it is 

 desirable not to exceed 20 feet and less is preferable. 



The plant efficiency can be increased by reducing the friction in the suc- 

 tion and discharge pipes. As few bends as possible should be used and 

 these should be made by using long turn elbows. The suction and dis- 

 charge pipes should be larger than the intake and outlet openings of the 

 pumps and joined to the pump with an increaser. The diameter of the 

 suction pipe and especially of the discharge pipe should be 1 % times the 

 diameter of the intake and if the discharge pipe is long it may be economy 

 to make its diameter even larger. Enlarging the lower end of the suction 

 pipe will further decrease the friction. This may be done by a funnel- 

 shaped section whose length is about 3 times the diameter of the suction- 

 pipe and whose large end is about 1 % times the diameter of the pipe. The 

 larger opening at the entrance to the suction pipe will decrease the tend- 

 ency to suck up sand or gravel. When the water carries weeds, gravel, or 

 other material a strainer should be used and the total area of the strainer 

 should be at least twice the area of the suction pipe. The discharge pipe 

 should not carry the water any higher than necessary. 



Power piston or plunger pumps. 



This type of pump consists of one or more cylinders in each one of 

 which a piston or plunger moving backwards and forwards sucks the water 

 in the cylinder and forces it up the discharge pipe. When the cylinder has 

 only one suction valve and one discharge valve the motion of the piston in 

 one direction causes suction and displacement in the opposite direction 

 forces the water through the discharge pipe. With two sets of valves so 

 arranged that there is a discharge for each displacement of the piston, the- 



