You spec a 63 mm bore cylinder at 6 bar. The catalog says 1860 N of force. On the machine it won’t push the part. You check the pressure, it reads 6 bar. The cylinder isn’t defective; the catalog number is theoretical and you sized to it instead of the real load.
What the catalog doesn’t subtract
The theoretical force is pressure times bore area. It ignores the piston rod, which on the extend stroke eats a small amount of area. On the retract stroke the rod area matters a lot; a 63 mm cylinder with a 20 mm rod loses about 10 percent of its retract force.
Then subtract friction. Seals drag, especially when new. Pressure drop through the fittings, tubing, and flow controls costs another chunk. A cylinder running through throttled exhaust sees less effective pressure at the piston than the gauge at the FRL reads.
Use a safety factor
Size cylinders so the theoretical force is at least 1.5 to 2 times the actual load. On push applications where friction is high or the load binds, go to 2. Running a cylinder right at its rated force means it stalls the moment the air pressure dips or a seal breaks in.
Don’t oversize to 4x either. A cylinder much bigger than needed moves too fast, hammers the end caps, and wastes air. The load moves under control when the force margin is reasonable, not enormous.
Pressure actually available
Check the dynamic pressure at the cylinder port, not the static pressure at the regulator. When the cylinder moves, the pressure in the active side drops as air flows. If the tubing is long or undersized, that drop is bigger than you expect. Measure with a gauge at the cylinder while cycling.
Side loading kills cylinders
A cylinder loaded off-axis bends the rod and wears the rod bearing and barrel. No amount of force sizing fixes that. Guide the load with linear bearings or use a guided cylinder. If you see the rod scoring or the front seal leaking, the problem is side load, not pressure.
