DRIVEN MACHINES 



103 



livered is reduced because the discharge pipe is too 

 small. Doubling the diameter of a pipe increases its 

 capacity four times. Square turns in the discharge 

 pipe are obstructions ; either the pipe must be larger 

 or there will be a diminished flow of water. Some 

 pump makers are particular to furnish easy round 

 bends instead of the ordinary right-angled elbows. A 

 great many pumps are working under unnecessary 



Figure 116. Hand Force-Pump. Showing two ways of attaching 

 wooden handles to hand force-pumps. 



handicaps, simply because either the supply pipe or 

 discharge pipe is not in proportion to the capacity of 

 the pump, or the arrangement of the pipes is faulty. 

 Rotary Pumps. A twin-chamber rotary pump ad- 

 mits water at the bottom of the chamber and forces it 

 out through the top. Intermeshing cogs and rotary 

 cams revolve outward from the center at the bottom, as 

 shown by the arrows in Figure 118. The stream of 

 water is divided by the cams, as it enters the supply 

 pipe at the bottom, and half of the water is carried 

 each way around the outsides of the double chamber. 

 These streams of water meet at the top of the cham- 

 ber, where they unite to fill the discharge pipe. These 



