A hydraulic jack has a piston rod (ram) on one side of the piston only. Fluid at equal pressure is applied to both sides of the piston. What happens?
- The piston stays where it is, because the equal pressures on its two faces cancel each other out.
- The piston moves away from the rod side and the rod retracts, because the two faces have different areas.
- The piston moves towards the rod side and the rod extends, because the two faces have different areas.
Explanation from PART66Online
Force equals pressure times area. On the side without the rod the fluid acts on the full piston area; on the rod side the rod covers part of the piston, leaving a smaller ring-shaped (annular) area. At equal pressure the full face therefore produces more force, so the piston moves towards the rod side and the rod extends. The net force equals the pressure times the cross-sectional area of the rod.
chevychase asked · 12 May 2012
surly if the ram takes up say 2 sq in and the jack piston has area of say 6 sq in, the piston minus ram area will be 4 sq in. Giving an overall advantage to the bare piston face equivelent to 2 sq in (the area of the ram) with equal pressure there is a net unbalanced force onthe bare piston face thus pushing it to the side were the ram is. Please explain how this is wrong?
Community Comments (5)
Why pressure should be different if it is applied in the same time from one source to both sides of piston? Force will be not equal as per formula you provided and this is the reason why piston will move to ram side.
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