What does a foot valve do in a well's pump suction line?

A foot valve is an essential component installed in a well's pump suction line that serves a specific purpose: it maintains a prime on the pump and prevents flow reversal. When the pump is shut off, the foot valve closes and seals the suction line, which helps to retain water in the line and ensures that the pump will not lose its prime. This is crucial because losing the prime would require the pump to be reinvoked to start pumping again, which can be a cumbersome process.

Additionally, the foot valve's one-way design prevents water from flowing back down into the well when the pump isn't operating. This is particularly important in applications where water may be drawn up from significant depths; without a foot valve, the water could flow back into the well, leading to inefficiencies and difficulties in maintaining a steady supply.

The other options do not correctly describe the role of a foot valve. While it does not prevent a well from drying up, increase flow rates, or filter impurities, its primary function revolves around prime maintenance and flow control in the suction line.