How to Select the Right Hydraulic Cylinder: Bore, Stroke, Pressure and Load

Start from the load, not from the catalogue

The first number you need is the load the cylinder has to move or hold: the working load plus any over-travel, shock and friction allowance. For a push force, the theoretical force is pressure multiplied by bore area; for a pull force the rod area is smaller, so the same cylinder needs a larger bore or higher pressure. Once the required force is known, the rest follows.

Working pressure and safety factor

Pick a working pressure the cylinder can carry continuously and multiply the peak load by a safety factor, typically 1.25 to 1.5 for steady duty and higher for shock or reversing cycles. HCIC publishes working pressure ranges per model; the pressure rating in the specification table is the value the unit is tested to, not a maximum to be used continuously.

Bore and rod diameter

Bore diameter sets the push force and the rod diameter sets the pull force and the buckling resistance of the extended rod. A common mistake is to size the bore for push only and then discover the rod is too slender for the retracted length at full extension. Check the rod against the extended stroke with the applicable safety factor.

Stroke and retracted length

Stroke is the working travel. Retracted length is stroke plus the piston, rod eye and end cap dimensions; the extended length is retracted length plus stroke. Both lengths determine whether the cylinder fits the machine, so give us the available space, not only the required stroke.

Speed and flow

Extension speed is set by the oil volume entering the piston area and is limited by how much flow the pump can deliver. Always check the required speed against the pump output, and check that the return side does not over-heat the oil on fast contractions.

What to send for a drawing quotation

Send the application, the required push and pull load, working pressure, stroke, the space available for retracted and extended length, the rod end and cap mounting, the fluid, the duty cycle and the ambient temperature. With those we can return a dimensioned drawing and a firm price.