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Hydraulic cylinder speed calculator

Enter bore, rod diameter and pump flow. The calculator returns extension and retraction speed, plus the time each direction takes over a given stroke — the number that decides whether a machine feels responsive or sluggish.

Bore (mm)

Rod diameter (mm)

Pump flow (L/min)

Stroke (mm)

Result

Extension speed: — mm/s; = — m/min
Retraction speed: — mm/s; = — m/min
Time to extend: — s
Time to retract: — s
Speed ratio (ext : ret): — : 1
Oil per full stroke: — L

Extension filling the full bore and retraction filling only the annulus, at the same pump flow — The same flow fills two different volumes. That is the whole reason retraction is faster, and why a flow control usually belongs on the rod side.

Why retraction is always faster

The pump delivers the same litres per minute in both directions. On the rod side, the rod occupies part of the chamber, so there is less volume to fill for the same travel. A 100/70 cylinder therefore retracts at roughly twice the extension speed, and nothing in the valve setting changes that.

This matters most on machines where speed has to be controlled: a log splitter, a press, a lift that must come down gently. Retraction speed is usually the one that needs a flow control, because it is the fast one.

Oil per stroke is the other useful output here. It sets the tank size and the accumulator, and it explains why a big cylinder empties a small reservoir in one cycle — seereservoir sizing.

The arithmetic

Extension speed: v = Q × 16 667 / A; Q in L/min, A in mm², v in mm/s. The constant is 1 000 000 / 60.
Retraction speed: v = Q × 16 667 / (A − Ar); Ar is the rod area. Less volume to fill means a faster stroke.
Stroke time: t = stroke / v; Seconds, with stroke in mm and v in mm/s.
Speed ratio: vext / vret = (A − Ar) / A; The inverse of the area ratio — the same number as the force ratio.

Before you use the number

Speed is calculated at the cylinder, before pressure-drop losses in the valve and lines. A circuit with a long return line or a restrictive valve will run slower than this, and a load-assisted retraction can run faster. Use it to size the pump, then confirm on the machine.

Need the design, not the number?

Send bore, stroke, pressure and the load case. You get a model back with the calculation behind it.

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