In this control method, the flow is controlled by switching pumps on or off. It is necessary to have a storage capacity in the system e.g. a wet well, an elevated tank or an accumulator type pressure vessel:
The storage can provide a steady flow to the system with an intermittent operating pump.
When the pump runs, it does so at the chosen (presumably optimum) duty point and when it is off, there is no energy consumption.
If intermittent flow, stop/start operation and the storage facility are acceptable, this is an effective approach to minimize energy consumption.
The stop/start operation causes additional loads on the power transmission components and increased heating in the motor. The frequency of the stop/start cycle should be within the motor design criteria and checked with the pump manufacturer.
It may also be used to benefit from “off peak” energy tariffs by arranging the run times during the low tariff periods.
Minimize energy consumption with stop/start control it is better to pump at as low flow rate a the process permits
This minimizes friction losses in the pipe and an appropriately small pump can be installed.
For example, pumping at half the flow rate twice as long can reduce energy consumption to a quarter
