Environmental Engineering Reference
In-Depth Information
5.2.4.2 Wet-Well Pumping Stations
Another type of pumping station design is the wet-well
type, which
has a single compartment that collects the wastewater flow. The pump
is submerged in the wastewater with motor controls located in the space
or has a weatherproof motor housing located above the wet well. In this
type of station, a submersible centrifugal pump is normally used.
5.2.4.3 Pneumatic Pumping Stations
The pneumatic pumping station consists of a wet well and a control
system that controls the inlet and outlet value operations and provides
pressurized air to force or push the wastewater through the system. The
exact method of operation depends on the system design. When waste-
water in the wet well reaches a predetermined level, an automatic valve
is activated which closes the influent line. The tank (wet well) is then
pressurized to a predetermined level. When the pressure reaches the
predetermined level, the effluent line valve is opened and the pressure
pushes the wastestream out the discharge line.
5.2.4.4 Pumping Station Wet-Well Calculations
Calculations normally associated with pumping station wet-well
design (such as determining design lift or pumping capacity) are usu-
ally left up to design and mechanical engineers; however, on occasion,
wastewater operators or interceptor technicians may be called upon to
make certain basic calculations. Usually these calculations deal with
determining either pump capacity without influent (e.g., to check the
pumping rate of the constant speed pump) or pump capacity with influ-
ent (e.g., to check how many gallons per minute the pump is discharg-
ing). In this section, we use examples to describe instances on how and
where these two calculations are made.
Example 5.1. Determining Pump Capacity without Influent
Problem:
A pumping station wet well is 10 ft by 9 ft. To check the pump-
ing rate of the constant-speed pump, the operator closed the influent
valve to the wet well for a 5-min test. The level in the well dropped 2.2 ft.
What is the pumping rate in gallons per minute?
Solution
: Using the length and width of the well, we can find the area of
the water surface.
10 ft × 9 ft = 90 ft
2
The water level dropped 2.2 ft. From this we can find the volume of water
removed by the pump during the test:
Area × Depth = Volume
(5.1)
90 ft
2
× 2.2 ft = 198 ft
3
