How to measurecylinderdiameter

The Mentored Engineer is a resource for mechanical engineers of all skill levels, but geared for young engineers just entering the work force. The material here will minimize the time needed to get an engineer competent in his or her field. Corey Rasmussen Managing Director

When measuring, line up the tape measure as shown and read the value where it lines up with 10″. Then subtract 10″ and divide by Pi to get the circumference.

How to measurecylinder borediameter

If the machine doesn’t have a pressure gauge already mounted on it, get one and install it. Often there is a location where a quick connect fitting is ready for a gauge. I recommend using one that goes to 5000 psi in case the pressure is higher than the expected location.

I recommend using a 1/2″ (13mm) wide or less tape measure so that the arc across the tape measure lays flat and doesn’t interfere much with the measurement.

Accurately measuring the barrel can actually be a little challenging. On an assembled machine, there my not be adequate access to the cylinder where the aren’t ports, feeder tubes, or welds. Perspective also makes it difficult to get an accurate reading of the barrel diameter. With these two issues, using a tape measure to determine the barrel size may be out of the question.

We can look at the hydraulic hoses for pressure ratings on the inlay, but that can be misleading. A hose that is rated for 4500 psi (310 bar) can be used on a 2400 psi system with no issues. You may have better luck with this method if your cylinder uses thermoplastic hoses.

https://youtu.be/Szm7tn006II We are in full production mode on our new coaster launch system and I want to update you on the status. Half of the track sections are fully welded Main cart...

For either type of tape measure, I also burn the first 10 inches of the tape. By not using the first 10″ of the tape, you prevent the end clasp from interfering with the measurement. You could use as little as 1″, but I often forget to subtract that from my measurement afterward. Ten inches is a little more obvious that something is wrong.

If you only have a 1″ (25 mm) wide tape measure, I would suggest turning the tape measure over so that the numbers are on the inside. This way the tape measure lays flat against the barrel much better.

So measuring the rod diameter, retracted and extended length of a cylinder is easy. It is far harder to take the cylinder apart and measure the ID. (It is by far very messy as well and you could damage the cylinder). Even with the giant cutout in this cylinder, getting an accurate measurement is tough.

A key element of determining the wall thickness is determining the tube’s material strength. Most tubing used in cylinder manufacturing is high strength tubing that has a tensile strength of 101.5 ksi (700 MPa).

With a simple measurement and few quick calculations, we can determine the bore diameter of a cylinder without ever looking inside. Knowing the tensile strength and the system pressure can get us close enough to accurately determine how powerful a system we have without disassembling the cylinder.

Corey Rasmussen is an award-winning professional engineer (NC and TX) with over 20 years of product design and development experience. He has two patents related to aerial lifts machinery, has advanced certifications in hydraulics and electronic controls, and specializes in designing mobile equipment. Corey is the principal engineer of Rasmussen Designs and is based out of Durham, NC.

Our bore is calculated to be 2.61 in. We can see that the thickness is 0.16 inches which is smaller than the minimum thickness. When we increase the tube wall thickness, we get very close to a 2.50 inch bore diameter. We will use that.

How to measurecylinder borewithouta boregauge

Barlow’s equation is a simple formula that measures the circumferential or “hoop” stress of a pressure vessel. This equation accounts for the pressure, average diameter and wall thickness.

Sorry, we just need to make sure you're not a robot. For best results, please make sure your browser is accepting cookies.

Now once we have the bore diameter, we have to make some judgement calls. This calculation is theoretical and you will come up with a very specific answer. It won’t be the actual diameter of the bore, but it will be close.

How to measurecylinder borewith caliper

Since cylinders are often used in overhead lifting or lifting of human life, they are designed to a 3:1 design factor at minimum on burst strength.

Cylinder manufacturers will generally limit the minimum thickness to around 3/16″ or 5 mm. This prevents dents and dings on the surface from causing issues with the seals. It also limits thermal issues, addresses axial and buckling loads. It is also easier to handle and store.

There are differing opinions on whether the OD, ID or midplane of the tube should be used for this equation. Most use the mid-plane diameter so we will use that here. It is shown as (OD – t) in the middle equation.

Knowing the system pressure is a critical first step to determining the bore ID. Most hydraulic systems operate in the 2400 psi to 3000 psi (165 to 207 bar) range.

Determining the bore or inside diameter of a hydraulic cylinder without disassembly is possible by measuring the barrel outside diameter. The wall thickness can be estimated using Barlow’s formula Finally, the bore can be calculated and then compared to common cylinder bore sizes.

Measuring cylinder borewith telescoping gauge

Many times in my career, I have found the need to determine a cylinder’s characteristics from an assembled machine. This is often the case when scoping out the competition. Most critical dimensions can be found with a tape measure in a matter of minutes. The cylinder bore cannot.

I get that you don't believe I'm actually building the world's BEST backyard coaster. Well, It's not finished yet, but we are making progress. Here are some pictures to prove it. Kiddo's...

Some design standards require a 4:1 design factor on burst pressure. There are many reasons for this high design factor:

How to measurecylinder borewith micrometer

You can see here, that the bore calculated is exactly 4.00 in, that rarely happens. We can conclude that the bore is 4.00 in. If the diameter was a little larger or smaller, we could make the same assumption.

Cylinder bores come in standard sizes which mean that they are somewhat predictable. They are 1.5, 2.00, 2.50, 3.00, 3.50, 4.00, 5.00, 6.00, 7.00, and 8.00. Greater than 8″ cylinders usually step up in 2″ increments.

Measuring the circumference is often a better way to measure the barrel diameter. You only need limited access and you can line up the numbers easier. If you have a ‘pi’ tape measure (reads diameters when wrapped around circumference), use it. Otherwise use a standard tape measure.

Yes, some manufacturers use even higher grade steels, but this is rarer than we think. When considering cost and strength, it is a good assumption to use this material.

Once the gauge is installed, power one function so that a cylinder is either fully extended or fully retracted. This will cause pressure to go over relief and our gauge will indicate the maximum system pressure. Make sure that the function selected won’t damage the machine and it doesn’t have any pressure reducing or limiting valves on it.

If I measure a cylinder that is 4.50″ and another that is 2.94″, what are the bore diameters? Both cylinders see system pressure of 3000 psi.

Ultimately we don’t want the cylinder to fail if the pressure increases by a significant amount. So we use a 4:1 design factor.