Cylinder Speed Calculation
Cylinder speed is found by dividing the flow rate entering it by the effective piston area. Stroke time is then calculated by dividing the stroke length by this speed. Because the area on the rod side is smaller, at the same flow rate the retract motion is always faster than the extend motion.
The calculation order is this: first find the effective area, then convert the flow rate to a compatible unit, and divide last.
- For an 80 mm piston the area is about 50 cm², and with a 45 mm rod the retract side is about 34 cm².
- A flow rate of 40 l/min means 40,000 cm³ per minute.
- Extend speed is 40,000 / 50 = 800 cm per minute, that is about 13 cm/s. Retract speed is about 20 cm/s.
This asymmetry is clearly felt in the field: at the same lever angle the return motion is faster than the forward one. Operators are used to it, but when switching to a wireless remote control it can be surprising in the first days; the issue is not in the remote control but in the cylinder's geometry. On the controller side, speeds can be brought closer together by defining different maximum currents for the two directions.
Another use of the calculation is cycle time estimation; dividing stroke length by speed tells you in advance how many seconds a motion will take.
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