Introduction to Industrial Automation

3.5.3   Operation of Two Pumps According to Demand

Two pumps are supplying a water tank from a natural source of water, and subsequently, the tank 

supplies a consumer with a random demand. Ideally, the automatic operation of the two pumps 

is as follows:

  1. If the level of the tank is below a certain level (E

1

), both pumps should be in operation.

  2. If the level of the tank is between the levels E

1

 and E

2

, one pump should be in operation.

  3. If the level is greater than level E

2

, none of the pumps should be in operation.

As indicated in Figure 3.26, two level controllers are utilized for detecting the levels E

1

 and E

2

. The 

automation circuit is presented in Figure 3.26, along with the indicated contact status of ELS

1

 and 

ELS

2

, for the case of an empty tank. Let’s assume that, in the beginning, the tank has a certain 

amount of water. A big demand will indicate that the tank will get emptied quite fast, and thus 

the level will drop below E

1

, and with respect for the desired automation, both pumps will be in 

N

C

50 Hz 230 V

R

e

NC contact

of ELS 

RS

0-1

Pump

ELS

ELS = electronic level switch

ELS = electronic level switch

A