Pump sumps are designed to receive liquids and be intermittently drained. The sump size depends on the capacity Q and permissible start-up frequency Z of the pump set The electric motor.
The start up frequencies of any dry motors are as follows :

Motor rating Start up frequency
Up to 7.5 kW max. 15/h
Up to 30 kW max. 12/h
Above 30 kW max. 10/h
Start up frequency is calculated using :

The maximum start up frequency occurs when Qm = 2 x Qzu, when the capacity Qm is twice the incoming flow Qzu. The max. start up frequency is there fore :

With the dry liquids, solids must be prevented from being deposited and collecting in dead zones and on the floor. 450 walls, or better still 600 walls, help prevent this

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