# Force and Movement Ratios of a Double-Action Cylinder If an external force F acts on a piston, this force creates a pressure on the piston area Ak. Conversely, this force is also a resistance that the pump delivery Q meets. In this way, a pressure builds that acts evenly on all sides, including the piston area Ak. The piston can thus now exert a force itself according to the following formula:

F = p * Ak

F = p * Ar (Analogously for the return flow)

F = Piston force in [N]
Ak = Piston area

(D² *3,14)

4

in [mm²]
Ar = Piston ring area

(D²-d²) * 3,14

4

in [mm²]
D = Piston diameter in [mm]
d = Piston rod diameter in [mm]
h = Stroke length in [mm]
Q = Pump delivery in [l/min]
t = Stroke time in [s]
v = Speed in [m/s]

Since friction and pressure losses reduce the piston force, a safety margin of 15-25% should be allowed for compensation when you select a cylinder. The theoretical compressive or tractive forces of the hydraulic cylinders can be found in the documents for every series.