How to measure a hydraulic cylinder replacement?
- Issue Time
In order to measure and decide which hydraulic cylinder you need, first of all you would have to visually determine the type of hydraulic cylinder you try to replace. Here are the the main three types of hydraulic cylinders:
- Piston rod cylinder – has piston inside, can be single and double acting (ex. Clevis cylinder)
- Plunger cylinder – mostly is a single acting cylinder (ex. Snow plow cylinder)
- Telescopic cylinder – has multiple stages, can be single and double acting
Main hydraulic cylinder attributes are as follows:
- Bore diameter
- Rod diameter
- Retracted length
- Extended length
- Mounting ends
- Hose ports
- Working pressure
Here is a detailed guide on how to properly take measurements of any plunger or piston rod hydraulic cylinder. For this procedure you need such tools as a simple tape measure and a caliper.
Piston diameter or inside barrel diameter is the main dimension of the hydraulic cylinder and known in the hydraulic industry as “BORE”. Therefore it has to be measured first. If your cylinder is taken apart, simply measure either inside diameter of the barrel (cylinder tubing) or measure actual piston diameter across.
However if the cylinder is assembled and/or installed on machinery, BORE can be defined by measuring the outside diameter of the cylinder barrel (tubing) and subtracting thickness of both tubing walls. For example, outside barrel diameter is 1.88”, less 0.19” for each wall, so the BORE = 1.88” – 0.19” – 0.19” = 1.5” BORE. To make it easier for our customers, we listed the most possible options for industry standard tubing sizes below. You can compare your numbers to this table and easily analyze what BORE diameter you have on your cylinder.
|Outside barrel diameter|
|Outside barrel diameter|
Outside barrel diameter
The next step is to determine rod diameter. Rod of the hydraulic cylinder is a round chrome plated steel bar that performs reciprocating motion. As commonly described by our clients, it’s a shiny part that comes out from the cylinder. Caliper can easily take care of rod measurement. Simply measure rod diameter (thickness) with a caliper. Rod is one of the most significant parts in the hydraulic cylinder because main force during operation applies on the rod. Proper analysis of rod size and specifications will prevent bend rod situation.
Next thing to do is to measure the retracted length of the cylinder. Retracted length is the distance between centers of cylinder mounting pins (pin holes) when the hydraulic cylinder is completely retracted inside (closed). Retracted length can be measured with any standard tape measure. Without this measurement, the cylinder will not be installed and operated properly on machinery.
Extended length should be defined next. Extended length is exactly the same as retracted length described in step 3, with the only difference that hydraulic cylinder has to be fully extended (open) when measured. Just like with retracted length, use tape measure. It is a fairly simple procedure unless your piece of equipment is down and the hydraulic cylinder is not functional. In a situation like this, you would have to take the cylinder off the machinery and extend it manually.
With both above lengths on hand, we can calculate the stroke of the hydraulic cylinder. Stroke is a travel distance and calculated simply by subtracting one from another. Stroke = extended length – retracted length. Yes,it’s that simple.
After we noted all primary dimensions of the cylinder, it’s time for secondary ones. There are thousands of possible options on how to mount the hydraulic cylinder on machinery. Every original equipment manufacturer creates their own design. However the most popular type of mounting is the one with pivot pins. These pins connect hydraulic cylinder on each end with an equipment frame. Therefore to make sure that hydraulic cylinder replacement can be installed on your machinery, pivot pin diameter has to be measured using a caliper.
Huge selection of various machinery units created hundreds of different cylinder mounting end styles. However they can be separated on a few most popular segments:
- Cross tube hydraulic cylinder – cylinder with two tubes welded across on both sides
- Clevis end hydraulic cylinder – cylinder with U-shape coupler and through holes inside
- Tang hydraulic cylinder – cylinder with solid welded steel ends of different shapes
- Swivel eye hydraulic cylinder – cylinder with spherical bearings installed on each end
- Trunnion hydraulic cylinder – cylinder with two symmetrical rods welded to a barrel
Based on the selection above, you should choose which option is the one you have. You have to make sure that outer dimensions are within your frame allowances for a proper fit.
Evaluation of existing hydraulic hose ports. Hydraulic cylinder port is the place where you connect hydraulic lines with oil. Hydraulic hoses basically power up the hydraulic cylinder. Each hose has two ends with crimps which can be either male or female. The most popular design is where the cylinder has female ports and requires male hose crimps to be connected. Every hydraulic port has two more designations: thread type and size. The most common thread sizes are ¼”, ⅜”, ½” and ¾”. Where the most popular hydraulic threads in the United States are SAE (O-ring Boss), NPT (National Pipe Thread), JIC (Joint Industry Council), and Flat Face. We have a separate, more detailed guide on threads which you can find in our FAQ section. If you analyzed that your thread is different from the cylinder you chose in our catalog, no worries, it’s an easy fix. There are thousands of different adapters available online at affordable prices.
The last step is to arbitrate the working pressure of the hydraulic system. Despite enormous selection of hydraulic cylinders out there, most of the hydraulic applications work at 2500 – 300 PSI pressure. This pressure rating is sufficient to perform most of the hydraulic applications. Exceptions in pressure would be such applications as excavators, hydraulic presses, hydraulic jacks and other heavy-duty mining equipment which work at 4500 – 7000 PSI pressure.
These basic 8 steps will help you to evaluate and properly measure a hydraulic cylinder you currently have. When you have all these dimensions ready, just give us a call or send us an email (pictures preferred) and one of our customer service representatives will be more than happy to assist you in selecting a proper replacement hydraulic cylinder.