How to Measure a Hydraulic Cylinder

How Are Hydraulic Cylinders Measured?

Selecting the right hydraulic cylinder is based on the following measurements:

• Piston or bore diameter
• Rod diameter
• Mounting length (extended and retracted)
• Stroke length

Important factors, such as port size and thread type, mounting style and dimensions, and rod-end thread and style, also play a significant role in choosing the right cylinder.

How to Measure Your Hydraulic Cylinder

Use the following steps to measure your hydraulic cylinder and determine the precise specifications you need for a replacement.

1. Identify Your Cylinder

Identifying the type of cylinder you have is the first step. Standard piston-rod cylinders feature an internal piston and a rod that retracts and extends through the end. Here are the most common types and how to differentiate between them:

• Mill-duty cylinder: A mill-duty cylinder has heavy walls and bolted flanges at the cap or head. It has no external tie rods, and its bolts are arranged around its circumference. Mill-duty cylinders are common in steel foundries, mills and presses.
• Welded cylinder: The barrel of a welded cylinder is welded to its end caps. It has no external tie rods and usually features weld beads where the end cap attaches to the barrel. Welded cylinders are common on mobile equipment.
• Tie-rod cylinder: A tie-rod cylinder features long external tie rods with nuts clamping them at the head and cap. Tie-rod cylinders are common in general industrial machinery, material handling applications and robotics.

2. Determine Whether You Have a Single-Acting or Double-Acting Cylinder

Once you identify the type of cylinder you have, you can determine whether it's a single-acting or double-acting cylinder:

• Single-acting cylinder: A single-acting cylinder features one port for hydraulic fluid to enter, forcing the rod in one direction. It retracts either by an internal spring (spring-return) or an external force, such as gravity or the weight of the load (load-return). To identify a single-acting cylinder, look for a single hose attached to a hydraulic port.
• Double-acting cylinder: A double-acting cylinder features two ports — one that allows the hydraulic fluid in and extends the rod, and one that retracts the cylinder. To identify a double-acting cylinder, look for two hydraulic hoses connected to two ports.

It is also important to determine if your cylinder is a single-rod or double-rod cylinder.

• Single-rod: If you have a single-rod cylinder, one rod retracts and extends from one end of the cylinder. Single-rod cylinders are the most common type.
• Double-rod: On a double-rod cylinder, a rod may extend and retract from each side of the cylinder.

3. Gather the Necessary Tools

Obtain the following tools and safety equipment before measuring a hydraulic cylinder:

• Personal protective equipment, such as safety glasses and steel-toe boots
• Calipers or a micrometer to measure bore or rod diameter with precision
• A tape measure
• Thread gauges to verify the sizes of your cylinder's port threads
• A physical or online document to record measurements

4. Check the Cylinder's Part Number or Nameplate Details

The fastest way to determine what type of replacement cylinder you need is to find the part number or nameplate. Some cylinders feature a standard serial number, while others have a smart part number encoded with important specifications. A reputable component manufacturer can help you decipher nameplate information.

If your cylinder's part number or nameplate information is untraceable, you can continue with the following measurement steps.

5. Measure the Diameter of the Bore

Measuring a hydraulic cylinder's bore diameter helps you determine its force output and compatibility with components and seals. You can disassemble your hydraulic cylinder to measure its internal diameter with a dial bore gauge. If you cannot disassemble the cylinder, you can measure its external diameter and subtract the combined thickness of the cylinder walls.

6. Measure the Diameter of the Rod