176 



FORCE-PUMP. 



the suction pipe and the lower valve into the 

 barrel. "When the piston is again pressed down, the lower 

 valve closes, the reaction of the water opens the piston 

 valve, the piston sinking below the surface of the liquid in 

 the barrel. When next the piston is raised, it lifts the 

 water above it toward the spout of the pump. At the same 

 time, atmospheric pressure forces more liquid through the 

 suction pipe into the barrel. 



295. Notes and Queries. The cistern or well containing 

 the liquid must not be cut off from atmospheric pressure, i. e., must 

 not be made air-tight. Why ? For water pumps, the suction pipe 

 must not be more than 34 feet high. Why ? Owing to mechanical 

 imperfections chiefly, the practical limit of the water pump is 28 

 vertical feet. As the lifting of the liquid above the piston does not 

 depend upon atmospheric pressure, water may be raised from a very 

 deep well by placing the barrel, with its piston and valves, within 

 28 feet of the surface of the water, and providing a vertical dis- 

 charge pipe to the surface of the ground. The piston-rod may 

 work through this discharge pipe. Deep mines are frequently 

 drained by using a series of pumps, one 

 above the other, the handles (levers) of 

 which are worked by a single vertical rod. 

 The lowest pump empties the water into a 

 reservoir, from which the second pump lifts 

 it to a second reservoir, and so on. 



296. The Force-Pump In 



the force-pump, the piston is generally 

 made solid, i. e., without any valve. 

 The upper valve is placed in a dis- 

 charge pipe which opens from the bar- 

 rel at or near its bottom. When the 

 piston is raised, water is forced into 

 = the barrel by atmospheric pressure. 

 I^EE ~~ When the piston is forced down, the 

 FIG. 114. suction pipe valve is closed, the water 



