USE OF CONCRETE PIPE IN IRRIGATION. 23 
stopped, it is not to be expected that enough water will run back to 
close a check valve. Water is incompressible and pressure alone may 
be transmitted back to the pump without any appreciable back move- 
ment of the water. 
The Whittier Water Co. has equipped electric motors with heavy 
flywheels directly connected to centrifugal pumps, in order to re- 
duce the water hammer. Gasoline engines have also been equipped 
with extra heavy flywheels, the engine being connected by gears to 
the pump. The function of a flywheel on an electric motor is to pre- 
vent a sudden stopping or starting of the pump, as the momentum 
of the flywheels will keep the pump going for about one minute 
after the power is turned off. Heavy flywheels on gasoline engines 
serve the same purpose. If a belt is used to connect engine or motor 
with pump, however, the flywheel would be of no use in case the power 
is suddenly shut off, as the belt would then slip off or break. 
The engineer in charge of this work has reported excellent results 
from the use of flywheels, and has installed them in many of the 
pumping plants of the company. He has torn down standpipes as 
being less effective, and is of the opinion that blow-off valves and 
check valves are either worthless or else a never-ending source of 
annoyance. 
When concrete pipe is directly connected to a centrifugal pump, the 
best practice is to eliminate any check valve and substitute a slow- 
closing gate valve on the discharge pipe of the pump. When the 
pump is started the valve can be opened slowly and thus prevent a 
dangerous increase of pressure on the pipe. The valve can be closed 
slowly when the pump is stopped and thus prevent water hammer. 
In case of an accidental stoppage of the power water will run down 
the well until the valve is closed. 
DESIGN OF PIPE SYSTEMS FOR IRRIGATION. 
The design of an irrigation system for a new tract where pipe is 
to be used differs in many respects from that where all water is 
carried in open ditches. The chief difference in design is due to 
the fact that well-made concrete pipe may be depended upon to 
carry water under pressure. Thus it is possible to eliminate devious 
routes of main ditches that must be located on grade. It is best, how- 
ever, to make accurate contour surveys of large tracts that are to be 
irrigated by pipe. Contour maps should also be made of all possible 
routes of main lines and each subdivision should have contour inter- 
vals plotted close enough to enable the engineer to design economically 
the sizes of laterals and their location and to indicate how the indi- 
vidual units should be graded for effective irrigation. 
