How to Determine Hydraulic Cylinder Size for an OEM Machine

Hydraulic cylinder size is determined from the machine load case, available pressure, required motion, packaging and service duty. Bore controls theoretical force, rod diameter contributes to tensile strength and compression stability, and stroke defines travel. A valid selection also checks mounts, pins, speed, oil volume, pressure losses, side load and load-control requirements.

This guide supports industrial engineering and procurement. Follow the machine manufacturer’s instructions and qualified safety procedures. Explore Гидравлика Чжэнцян.

Calculate cylinder force from machine geometry

Start with a free-body diagram across the full mechanism travel. Linkage angle and lever arm often make the worst cylinder load different from the largest external load.

Include payload, self-weight, friction, acceleration, impact and applicable design margins. Distinguish extension and retraction requirements.

Select bore from force and pressure

Required effective area is force divided by available working pressure. Convert area into a preliminary bore, then use the active extension or annular area as appropriate.

Allow for circuit losses and do not treat maximum relief pressure as a continuous design pressure. Validate the complete pressure boundary.

Select rod, stroke and mounts

Rod size requires tension, compression buckling, fatigue, thread and connection checks. Long stroke and poor end fixity can make rod stability govern before hydraulic force.

Mounting centers, pin sizes, bearing area and articulation must suit the real load path. The cylinder should not absorb continuous side load caused by misalignment.

Check speed, duty and environment

Flow divided by effective area gives theoretical speed. Verify cycle time, heat, cushioning, seals, contamination, temperature and corrosion exposure.

Document all assumptions in a controlled specification and confirm fit through the full machine envelope before approving production.

Practical reference

Sizing input	Primary design effect
Required force and pressure	Bore and pressure demand
Stroke and installed lengths	Travel and package fit
Rod length and end conditions	Buckling and stiffness
Flow and cycle time	Speed, losses and heat
Mounting geometry	Pins, bearings and side load
Environment and fluid	Seals, coatings and materials

Information to document

• Machine manufacturer, model, serial range and cylinder function.
• Controlled drawing, part number, photographs and verified dimensions.
• Pressure, force, flow, speed, duty cycle, fluid and temperature.
• Mounting, load direction, environment and observed failure history.
• Quantity, acceptance tests, documentation and delivery destination.

Read more in the Hydraulic Cylinder Knowledge Center.

Frequently asked questions

Can bore and stroke select a cylinder?

No. Rod, mounts, ports, pressure, speed, stability and environment are also required.

Should the largest possible bore be selected?

No. Oversizing increases oil volume, package size and cost and can change control behavior.

What information should an OEM send?

A drawing, load case, pressure, motion, duty, environment, interfaces, options and acceptance tests.