18.1: How to Calculate the Extend Speed of a Hydraulic Cylinder
- Page ID
- 117076
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The extend speed of a hydraulic cylinder is determined by how fast oil fills the cap end of the cylinder. This speed is dependent on two factors:
- The flow rate (Q) delivered to the cap end
- The volume that must be filled per inch of stroke
Since the rod is moving as the fluid fills the cap end, the effective volume being created per unit of time determines the piston’s travel speed.
The formula used to calculate rod speed during extension is:
Rod Speed (in/min) = Flow Rate (in³/min) / Cap End Area (in²)
To use this formula effectively:
- Convert the pump flow rate into cubic inches per minute (1 GPM = 231 in³/min).
- Calculate the cap end area of the cylinder using the piston diameter:
Cap Area = 0.7854 x D ²
where D is the piston diameter.
- Divide the flow rate by the cap area to get speed in inches per minute.
A 2-inch diameter piston with a 1 GPM flow rate:
Cap Area = 0.7854 × (2²) = 3.14 in²
Flow Rate = 231 in³/min
Rod Speed = 231 ÷ 3.14 ≈ 74 in/min
Understanding this calculation helps you size actuators correctly and verify that system performance matches design requirements. It also sets the foundation for troubleshooting flow-related speed issues.