TABLE OF CONTENTS The pumping station must be able to adjust to the variations of wastewater flows. The smallest capacity pump should be able to pump from the wet well and discharge at a self-cleansing velocity of about 0.6 m/s (2 ft/s). It should be connected to a 100-mm (4-in) force main which would have a capacity of approximately 280 L/min or 75 gal/min. The wet well capacity should contain sufficient wastewater to permit the pump to run for at least 2 min and restart not more than once in 5 min (Steel and McGhee 1979). The pump running time ( t r) and the filling time ( t f) in the wet well are computed as
and
| where t r | = pump running time, min |
| V | = storage volume of wet well |
| D | = pump discharge |
| Q | = inflow |
| t f | = filling time with the pump off |
and the total cycle time ( t) is
The starting limitations on pump motors usually dictate the minimum size of a well. The wet well should be large enough to prevent pump motors from overheating due to extensive cycling, but small enough to accommodate cycling times that will reduce septicity and odor problems. Typically, submersible pumps can cycle 4 10 times per hour. A maximum storage volume for a cycling time should be no more than 30 min.
If the selected pumps have a capacity equal to the peak (maximum) flow rate, the volume of a wet well is...
