Speed Equation: v = Q / A

Cylinder velocity is determined by the flow rate divided by the piston area being pressurized:

v = Q / A

• v = Cylinder velocity (m/s, mm/s, or in/s)
• Q = Flow rate (L/min, GPM, or m3/s)
• A = Effective piston area (mm2 or in2)

Extension Speed

When extending, flow fills the full bore (cap end) area:

v_extend = Q / A_bore = Q / (pi x D^2 / 4)

Retraction Speed

When retracting, flow fills the smaller annular (rod end) area. Less volume is needed, so retraction is faster:

v_retract = Q / A_annular = Q / [pi x (D^2 - d^2) / 4]

Speed Ratio

The retraction speed is always faster than extension by the area ratio:

Speed Ratio = v_retract / v_extend = A_bore / A_annular = D^2 / (D^2 - d^2)

• This is the inverse of the force ratio
• Typical speed ratios: 1.25:1 to 2:1
• Same flow, smaller volume = faster speed

Velocity Limits Guidance

• Precision/positioning: < 0.3 m/s (12 in/s) - allows accurate stopping
• Normal industrial: 0.3 - 0.5 m/s (12-20 in/s) - standard operation
• High speed: > 0.5 m/s (20 in/s) - requires cushions, may cause shock
• Maximum practical: ~1 m/s (40 in/s) - oil velocity limits, heat generation

Practical Considerations

• Port size: Undersized ports create back pressure and heat
• Hose/pipe sizing: Flow velocity in lines should be < 4 m/s (suction) or < 6 m/s (pressure)
• Cushioning: Required for speeds > 0.1 m/s with significant load
• Meter-in vs meter-out: Control location affects actual speed under load