Sierra Leone
Water Aid and Engineering Development
- Initially, the waste valve is open, and the delivery valve is closed allowing gravity-driven water to flow down the drive pipe and into the pump, spilling out of the impulse valve.
- The flowing water picks up speed and pressure until it forces the weighted impulse valve to close.
- Since the flowing water no longer has an escape route, a water hammer is generated inside the drive pipe that causes a sharp rise in pressure in the pump body. This in turn forces the delivery valve to open, filling the air chamber with water. The air in the cylinder is compressed, which causes a cushioning effect on the impulse.
- Eventually the flow in the delivery pipe slows and then stops causing the delivery valve to close. Momentarily the flow reverses allowing a small pellet of air to be sucked into the system to replenish the gradual loss of air in the cylinder. When the water flow has stopped, the weighted waste valve reopens against the now static head, which allows the process to begin again.
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