5 Critical Parameters for Selecting a Hydraulic Cylinder

Introduction

A hydraulic cylinder is the component that converts system power into linear motion. A wrongly selected cylinder either works with insufficient force, or — being larger than necessary — becomes an expensive, bulky load that increases oil consumption. Correct selection requires the correct analysis of 5 parameters.

1) Working Force and Bore Diameter

The first question: how many kN of force must it produce? The answer follows from the classic relationship between working pressure and bore diameter:

F = P × A — A = π × (D/2)²

Example: for 50 kN of force at 100 bar working pressure, the minimum bore diameter should be around Ø80 mm. In practical design a safety factor (1.2–1.5) is applied.

2) Stroke Length

Travel distance + 10–20 mm buffer. For very long strokes a buckling check is mandatory — the DIN 24333 buckling diagram is used. Stroke length cannot be selected independently of rod diameter; a longer stroke requires a thicker rod.

3) Working Pressure and Safety

The nominal working pressure (e.g. 210 bar) must stay below the fatigue limit of the cylinder body. Test pressure is 1.5x the working pressure (PED compliance). In servo / proportional systems, instantaneous responses may momentarily exceed the nominal pressure — so keep an eye on the peak pressure limit.

4) Mounting Type

Mid-flange, front flange, clevis, foot, lug — the mounting type determines how the cylinder directs the load. The wrong mounting type causes premature fatigue even when bore and stroke are correct. Axial load → flange; angular / swivelling load → clevis type.

5) Speed and Cushioning

Cylinder speed is the ratio of flow rate to bore area. If the speed goes above 0.5 m/s, a cushion option should be added — otherwise end-of-stroke impacts rapidly fatigue the cylinder and the area around the rod. In servo applications, electronic position control is preferred over cushioning.

Decision Matrix

The right cylinder is not just the right bore and stroke. It is a system decision in which all five parameters are consistent with one another. If in doubt, send us your drawing and operating conditions; our cylinder manufacturing team responds with a price and a recommendation within 48 hours.

Quick Checklist

• Has the force requirement been calculated? (F = P × A)
• Have stroke + buffer + buckling been checked?
• Is the working pressure compatible with the system nominal, and does it withstand peak pressure?
• Is the mounting type suited to the load (axial / clevis / flange)?
• If speed is above 0.5 m/s, is cushioning provided?

If all five items are covered, you have selected the right cylinder.