How to Measure a Hydraulic Cylinder for Repair

What it is

A hydraulic cylinder is described by its bore (inside diameter of the barrel), rod diameter, stroke (travel), retracted and extended lengths, mounting style and port size and type. With these, a shop can quote a seal kit, a repair or a replacement cylinder. Tie-rod cylinders often follow ISO 6020 or NFPA mounting dimensions. Welded cylinders are often built to the equipment maker's design. See Hydraulic Cylinders (Tie-Rod, Welded, Telescopic).

How to use it

1. Look for a tag or stamp. A part number or serial number is the fastest route to the original spec.
2. Rod diameter: measure with calipers on a clean, unworn part of the rod.
3. Bore: if the cylinder is apart, measure the barrel ID with an inside micrometer or bore gauge. If not, measure the barrel OD and record it. Bore can only be estimated from OD because the wall thickness is unknown.
4. Stroke: measure retracted length and extended length between the same points. Stroke = extended length − retracted length.
5. Retracted length: measure pin center to pin center, or mount face to mount face, fully retracted.
6. Mounts: note the style at each end and measure pin diameter, clevis width and cross-tube length.
7. Ports: identify the port thread type and size, and measure the port center-to-center distance.

Measurement record

Key points

• Measure the rod where it is not worn or pitted. Chrome damage changes the reading.
• Inch and metric cylinders can be close in size. Measure carefully and record units.
• Seal kits are made for specific cylinder designs. Matching bore and rod alone may not be enough. See Cylinder Seals and Seal Kits.
• Pressure ratings come from the maker. Do not estimate them.
• Relieve all pressure and support the load before removing a cylinder.

Common mistakes

• Calling barrel OD the bore.
• Measuring stroke from a partly retracted position.
• Missing port type and only recording size.
• Measuring a worn rod section.

Governing standards: ISO 6020 and ISO 6022 (mounting dimensions for metric cylinders); NFPA T3.6.7 (square head tie-rod cylinders); the cylinder maker's drawing and data.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.