One question that IBT’s fluid power team is always answering is what information do I need to replace my hydraulic cylinder. This article is here to address that exact concern, walk you through measuring the size of your hydraulic cylinder, and provide the information needed to replace your cylinder.

Before we get too deep into measuring the cylinder’s size, we need to discuss the type of hydraulic cylinder that you are measuring. There are many types of hydraulic cylinders that you could be measuring. Standard cylinders are Tie Rod, Mill Duty, and Welded.  

Tie Rod, Mill Duty, and Welded are all piston-rod cylinders. They have a piston inside and a rod that extends and retracts through the end of the cylinder.  These cylinders can be single or double-acting.  A single-acting hydraulic cylinder includes one port where the hydraulic fluid enters and forces the plunger out in one direction. A double-acting cylinder consists of two ports. One for the hydraulic fluid to enter and extend the plunger and another port for retracting the cylinder.  A single-acting cylinder needs a force applied to it to retract. This force can come in the form of an internal spring or an external force. A double-acting cylinder uses hydraulic fluid pressure to retract. The most common external feature to identify a single vs. double-acting cylinder is a cylinder having a single hydraulic port/hose attached vs. containing two ports and two hydraulic hoses connected.  

Another feature to look for is a single rod vs. a double rod. A single rod cylinder has one rod that extends and retracts out of one end of the cylinder. A double rod simply has another rod that extends and retracts out of the other end of the cylinder, both rods are connected to the piston. The illustrations above are single-rod type cylinders and are most common in industrial applications.

12 Steps to Measure a Hydraulic Cylinder

Now that we have covered some of the different kinds of hydraulic cylinders, let’s get down to measuring the cylinder. Gather the proper tools and safety equipment required to quickly and safely record the measurements of your cylinder. 

Safety Equipment should include: 

• Eye protection
• Steel toe footwear.

Tools should include:

• Tape measure 
• Calipers 
• Thread gages or a known fitting size to check port and rod extension threads.  
• Other shop tools
• Something to record your measurements, or you may want to use a step-by-step form to register your measurements (Hydraulic Cylinder Questionnaire courtesy of Yates Industries).

Several features will help us define the hydraulic cylinder we are replacing:

• Nameplate Check
• Bore Diameter
• Rod Diameter
• Stroke/Rod Extension
• Rod End Style
• Mounting
• Hose Ports
• Ambient Environment
• Working Pressure
• Manufacturer Drawing Verification

Step 1:  Check for Nameplate or Part Number Information  

The easiest way to find a replacement cylinder is to find the nameplate information and the cylinder part number. Most manufacturers use “Smart” Part Numbers or have history on the Serial Number. IBT Fluid Power Specialists are experts at deciphering nameplate information.  

However, nameplate information and the cylinder part number are often unavailable or untraceable. In that case, you can continue to use these steps to help you measure and replace an existing hydraulic cylinder.

Step 2: Piston diameter

The piston diameter is the inside barrel diameter. This diameter is the primary dimension of a hydraulic cylinder. It is also known as the bore diameter. If the cylinder is disassembled, measure either the inside diameter of the cylinder tubing or the actual piston diameter.

If the cylinder is still assembled or installed, the bore diameter can be measured by using the outside diameter of the cylinder and subtracting the thickness of both tubing walls. 

For example, if the outer barrel is 2-inches and you subtract 0.25-inches for each tubing wall, then the bore is equal to 2-inches minus 0.25-inches minus 0.25-inches. This equals a 1.5-inch bore. 

Below is a collection of the most common industry-standard tubing sizes:

Piston Diameter (Bore)	Outside Barrel Diameter (Option 1)	Outside Barrel Diameter (Option 2)	Outside Barrel Diameter (Option 3)
1.5”	1.75”	1.88”	2”
1.75”	2.12”	2.27”	N/A
2”	2.38”	2.5”	N/A
2.25”	2.5”	2.65”	N/A
2.5”	2.75”	2.88”	3”
2.75”	3.12”	N/A	N/A
3”	3.38”	3.5”	N/A
3.25”	3.88”	N/A	N/A
3.5”	3.88”	4”	N/A
4”	4.5”	4.62”	4.75”
4.25”	4.62”	N/A	N/A
4.5”	5”	5.5”	N/A
5”	5.5”	5.62”	5.75”
5.5”	6.12”	N/A	N/A
6”	6.64”	6.75”	7″

 

 

 

Step 3: Rod diameter

The next step is to measure the rod diameter. The rod is the part of the hydraulic cylinder made of either chrome-plated steel or stainless steel and moves in and out of the cylinder. Using a micrometer or caliper, measure the thickness of the rod. This measurement will reveal the rod’s diameter. The rod is one of the most critical parts of a cylinder; this transfers all the forces during operation. Proper measurement of the rod diameter will help prevent future rod bending.

 

Step 4: Measuring Stroke

The stroke equals the extended length minus the retracted length of the rod. It is the distance that a cylinder travels. If your equipment is down or non-functioning, the cylinder must be uninstalled and extended, and retracted manually for precise measurement.  If you are doing this on a cylinder that is still installed and functional, always use the manufacturer and your company’s lock-out tag-out procedures before reaching into the machine to measure the cylinder. You may have to apply hydraulic pressure to the cylinder to extend the rod fully.  Use necessary precautions when doing so, atomized spray or mist of oil droplets may extend as far as 40 feet. The flammable oil spray can be ignited readily by hot surfaces and create a flash fire.  The more accurate the measurement, the better. If this measurement is inaccurate, the replacement cylinder will not be installed or operated correctly.

Stroke = Extended Length – Retracted Length

 

Step 5: Measuring the retracted length of the cylinder rod

This is the distance between a fixed location on the cylinder to the marked location on the cylinder rod while in the fully retracted position. In the example below, we used masking tape to mark the cylinder rod and measured 1.25 inches from the rod wiper to where the tape ends. 

 

Step 6: Measure the Extended Length of the Cylinder Rod

The extended length measurement is similar to the retracted length. This time, we will measure the distance when the rod is fully extended. First, extend the rod to its maximum extended position. Again, use a tape measure and measure the distance between the same fixed point on the cylinder and the marked point on the rod.  In the illustration below we measure 13.25 inches from the rod wiper to the end of the masking tape.

For this particular cylinder, the stroke is 12 inches.

13.25 in (Extended Length) – 1.25 in (Retracted Length) = 12.00 in

Again, the more accurate the measurement, the better. 

 

Step 7:  Determining Rod End Style

There are many rod-end thread styles. However, the most common are standardized by the NFPA. These are Standard Male, Standard Female, and Intermediate Male.

When measuring the rod end, you will check the threads using a standard thread gauge and calipers.  Other dimensions should be measured and noted.  These can be compared to manufacturers’ NFPA published standard sizes for accuracy.

 

Step 8: Determining Mounting Style

There are several ways to mount a hydraulic cylinder. The original equipment manufacturers (OEM) vary how their cylinders are mounted. The standard mounting for industrial cylinders would be the Flange Mount, and for Mobile equipment would be the Pivot mounts. 

Five most common hydraulic cylinder mounting styles:

• Flange Mounts – Head or Cap Rectangular or Square Flange – Head or Cap Rectangular Integral Flange – Head or Cap Square Integral flange
• Side Lug mounts – Side Tapped – side End Lug – Centerline Lug – Side Angle Mount
• Pivot Mounts – Fixed Clevis – Detachable Clevis – Fixed Eye – Detachable Eye – Spherical Eye
• Trunnion Mounts – Head Clevis Trunnion – Cap Trunnion – Intermediate Fixed Trunnion
• Tie Rod Mounts – Both End Extended Tie-Rods – Head Extended Tie-Rods – Cap extended Tie-Rods

The National Fluid Power Association (NFPA) publishes standard mounting types.  Manufacturers use this visual matrix to help you identify the mounting style on NFPA Tie Rod Cylinders. You can download the matrix using this link.  NFPA Tie Rod Cylinder Mounting Types  

As an example, the cylinder shown below would be a Side Mount-Side Lug (MS2) mounting style.

When replacing a cylinder, you will want to confirm that the replacement is the same and that the outer dimensions will work with your frame allowances for correct fitment.

Step 9: Hose Ports Size and Location

Evaluate your existing hydraulic hose ports next. The hose port is where the hydraulic lines connect to the cylinder. Without the hoses attached, your cylinder will not work. Each hose has two crimped ends with either male or female ends. The most common design features female ports on the cylinder and requires male hose crimps to be connected. Every hydraulic port has two more designations which are thread type and size. 

Hose Sizes:

• ¼-inch
• ⅜-inch
• ½-inch
• ¾-inch

Thread Types:

• SAE (O-Ring Boss)
• NPT (National Pipe Thread)
• JIC (Joint Industry Council)

If the cylinder that you have chosen is different from the thread of the hose, then an adapter can be utilized to make the correct connection, the port sizes above are a few of the options available for cylinders and the OEM could have had custom ports designed into the cylinder, always check the size closely.

To measure the ports on a hydraulic cylinder, you can use a thread gauge and caliper to measure the thread pitch and size.  You can also use known fitting to determine thread type and size as an alternative method.  Using a thread gauge to determine pitch is illustrated below.

Port location is also essential. Ports can be located on the top, sides, or bottom of the cylinder.

Step 10: Ambient Environment

External factors such as working temperature, dust contact, and corrosive materials should be noted. Knowing these factors is vital to select the correct materials, wipers, and seals for your hydraulic cylinder.

Step 11: Working Pressure

Determine the hydraulic cylinder’s working pressure. This will be determined by your application and the hydraulic system the cylinder operates in. Hydraulic pumps produce a maximum pressure and can be measured at the cylinder ports or found in manufacturer manuals. Typical Industrial Hydraulic cylinders come in Medium Duty (up to 1500 psi) and Heavy Duty (up to 3000 PSI).

In some cases, even higher pressure duties are required as high as 10,000 psi or more for excavators, hydraulic presses, hydraulic jacks, and other heavy-duty equipment.

Step 12: Compare to Manufacturer Drawing

The final step in the process is to compare your measurements to a manufacturer’s drawing before you order. Cylinders drawings can be configured using our manufacturer’s configuration tools. A two-dimension or three-dimension drawing can be provided in most cases. IBT and our manufacturers require a signature verifying the dimensions of a cylinder on all orders. It ensures that we get it right the first time and provides a good record for future orders. Here is an example courtesy of Yates Industries configuration tool.  

Learn More from IBT’S Fluid Power Solution Experts

These steps can help you determine the size of your hydraulic cylinder ensuring that the replacement part will be the correct size and fit to keep you up and running.

With our years of experience in providing fluid power options, you can rely on IBT for the best solution to your problems. Contact Brent Hanson, the IBT Fluid Power Director of Business Development, at (913) 261-2125 to learn more.

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