Pump Stations, Lift Stations, and Force Mains
Core concepts
Understand wet well, dry well, pumps (submersible, centrifugal), controls, and force main hydraulics. Key terms: static head, friction head, total dynamic head (TDH), and system curve. Pumps operate where the pump curve meets the system curve. Know duty/standby/alternating pump logic and level controls (floats, transducers).
Force main concerns
Velocity in force mains must keep solids moving (commonly 2-5 ft/s) but not so high as to waste energy. Long detention creates septic conditions and H2S, driving corrosion and odor control needs. Air valves and surge protection matter. Check valves prevent backflow; bypass pumping is critical during maintenance.
Traps
Do not confuse static head with friction head. Do not assume a larger pump always solves low flow; it may run out on its curve or overload. Watch questions about wet well sizing (too small causes short cycling; too large causes septic detention). Alternation prevents one pump from wearing out.
Rule of thumb
TDH = static head + friction losses + velocity head (often small). If static head is 30 ft and friction is 12 ft, TDH ~ 42 ft; select a pump whose curve delivers design flow at 42 ft.
Worked example
A station needs 500 gpm at 42 ft TDH. Choose a pump whose curve passes through that point, with a standby of equal capacity and alternation controls.