The diagram above shows a lift pump with valves at P and Q. During a downward stroke of the piston
both valves are open
P is open while Q is closed
P is closed while Q is open
Both valves are closed
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In a lift pump, the piston moves up and down inside a cylinder, which is connected to two valves at the bottom. When the piston is moving downwards, it creates a low-pressure region inside the cylinder which causes the valve at the bottom, marked as P, to open and the valve at the top, marked as Q, to close. This allows water to enter the cylinder through the valve P. During the upward stroke of the piston, valve P closes and valve Q opens, allowing the water to be lifted up and out of the cylinder. Therefore, during a downward stroke of the piston, valve P is open while valve Q is closed. The answer is P is open while Q is closed.
