Water-Lifting Devices – Pumps - Practices of Irrigation and On-farm Water Management - page 467

12.9.2.3 Operational Check

• Check to ensure that the pump is delivering liquid; if not, stop the driver

immediately, determine the cause.

• Check the pump for excessive vibration, localized heating of components, noise,

and leakage. If any of the conditions exists, stop the pump and investigate and
take corrective action.

• Check the pump discharge pressure and intake vacuum to manufacturer's speci-

fications. If not to specification, investigate and take corrective action.

12.9.3 Pump Control

The basic of pump control systems is that the pump is started and stopped by turning
“ON” or “OFF” the power supply. All pump controls are no more than a variation
on this same procedure. When we need water, we can simply plug in the extension
cord that ran to the pump, and to turn the water off we can simply unplug the cord.
The next step up in pump control is to get rid of the plug and outlet and use a
permanent switch to turn “ON” and “OFF” the power flow. Some small pumps are
stopped and started in exactly this way. But with the higher voltage and amperes
commonly used for irrigation pumps, a simple switch will not be practical. The
switch would have to be huge to handle the load. Most pump control circuits are
designed using a relay circuit that isolates the user from the pump voltage. The
relay circuit is like a messenger. You tell the relay to start the pump and the relay
starts it for you. Most relays use 12 or 24 V, a few use 120 V (Fig. 12.8 ) .

12.9.3.1 Automating the Control Circuit

To automate the control of the pump, you simply replace the manual switch in
the circuit with an automatic switch. There are several types commonly used:

Switch

Relay

Pump

24 volt 240 volt

Fig. 12.8 Typical relay control circuit