LAND DRAINAGE BY MEANS OF PUMPS. 
47 
hence the static head on the pump may be only the difference in 
level between the water in the canal and the water in the river. In 
this case the pipe must have an opening at the highest point for use 
in priming the pump. This opening will also be used to admit air 
to break the seal, thus preventing water from flowing back by siphon 
Section C-D _ , , . „ 
Section through A-B 
Fig. 3.— Plan and elevation of pumping plant in Muscatine-Louisa Levee and Drainage District, Iowa. 
action when the pump is stopped. If the pumps equipped with this 
type of discharge pipe are driven by motors, a flap valve should be 
used on the end of the pipe to prevent the water from siphoning back 
through the pump while it is being primed, thus turning the motor 
backward and overloading it. This valve need not fit tightly and 
