Grades 3–5 · Machines
How does a piston pump move water one way?
A piston pump can lift water in a repeating rhythm: draw some in, then push it onward. A piston slides inside a cylinder, changing the space available for water. Two one-way valves give that back-and-forth movement a one-way result.
In the diagramPiston movement and two one-way valvesInletOutletWater-filled chamberPiston rises: chamber growsInlet opens; outlet stays closed
When the piston rises in the pictured intake stroke, the cylinder's water space grows and its pressure falls below the pressure on the supply side. That difference pushes the inlet valve open and drives water into the cylinder. The outlet valve is pushed shut by the pressure on its other side, keeping delivered water from returning.
On the delivery stroke, the piston moves back and reduces the water space. Cylinder pressure rises. It presses the inlet valve against its seat, blocking the route back to the supply, while opening the outlet valve. Water is pushed along the delivery route.
The valves do not need to know which way the piston is moving. Their shapes let a pressure difference open them in one direction and press them shut in the other. Repeating the two strokes moves successive amounts of water onward; the work of moving the piston supplies the energy.
About this explanation
Starting knowledge: Recognize that moving a fitted piston changes space inside a chamber.
Sources
- U.S. Department of Energy / OSTI — DOE Fundamentals Handbook: Mechanical Science, Volume 1, Positive Displacement Pumps