KEVOS® MAKEOS · Hydraulics
Hydraulic Cylinder Sizing (Bore, Rod Buckling, Flow, Power, Pipes)
What bore and rod does this cylinder need, how much flow and power does it take, and what pipe size suits it?
Sizing a double-acting hydraulic cylinder from the duty: minimum bore for the push force at system pressure, rod diameter for Euler buckling with a mounting factor and safety factor, the largest rod that still gives the pull force, extend and retract flows for the speeds, pump input power and pipe bores for the chosen fluid velocities.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Duty | ||
| Push (extend) force | kN | Force needed when extending. |
| Pull (retract) force | kN | Force needed when retracting. |
| System pressure at the cylinder | bar | Pressure available at the cylinder after losses. |
| Extend speed | mm/s | Extend speed. |
| Retract speed | mm/s | Retract speed. |
| Stroke | mm | Stroke length. |
| Cylinder | ||
| Chosen bore (0 = minimum) | mm | Bore you intend to use (a standard size); 0 shows the minimum. |
| Buckling length (fully extended) | mm | Length used for buckling, usually the fully extended pin-to-pin or mounting length. |
| Effective length factor for the mounting | Effective length factor: about 0.5 fixed–fixed, 0.7 fixed–pinned, 1 pinned–pinned, 2 fixed–free. | |
| Safety factor on buckling | Safety factor applied to the Euler load. | |
| Rod modulus | GPa | Elastic modulus of the rod. |
| Power unit | ||
| Pump overall efficiency | % | Overall efficiency of the pump and motor. |
| Pressure line velocity | m/s | Fluid velocity allowed in pressure lines. |
| Return line velocity | m/s | Fluid velocity allowed in return lines. |
Method and formulas
- Minimum bore = √(4 F_push ÷ π p).
- Rod for buckling: Euler F_cr = π² E I ÷ (K L)² ≥ n F_push, giving d = [64 n F (K L)² ÷ π³ E]^¼.
- Largest rod for the pull force: √[D² − 4 F_pull ÷ π p].
- Flows Q = area × speed; pump power = p Q ÷ η; pipe bore = √(4Q ÷ π v).
- Example: 50 kN at 160 bar needs at least a 63.078 mm bore and a 51.462 mm rod for buckling.
Limitations
- Euler buckling for slender rods; short stiff rods are governed by stress, and cylinder tube support changes the effective length.
- Pressure is at the cylinder; allow for valve and line losses.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Specify a cylinder and power unit for a press or actuator
- Check rod buckling on a long stroke
- Size supply and return lines
Who it is for
- Hydraulic engineers
- Machine designers
- Maintenance engineers
What you get
- Minimum and chosen bore
- Rod diameter limits
- Flows, power and pipe bores
Interpreting the result
- If the buckling rod is larger than the pull force allows, choose the next bore up.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 281–286, 3421–3425. Topic reference; no source tables or recommended settings are reproduced.
WORKOS tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Hydraulic Cylinder Sizing (Bore, Rod Buckling, Flow, Power, Pipes) calculator
