Hydraulic Cylinders Selection Guide

Posted on Jan 2, 2021

Hydraulic Cylinders

This guide intends to give you an overview of hydraulic cylinders which are a very common component in machine tools, as well as some of the factors you should consider when selecting one.

What Are Hydraulic Cylinders?

Hydraulic cylinders, also known as linear hydraulic motors, are a type of mechanical actuator system which converts the hydraulic pressure to driving force through unidirectional strokes. Hydraulic cylinders are widely used in engineering automotive, manufacturing machines, civil engineering or other industrial applications. For example, they are commonly used in earth-moving machines to lift or lower the arms, buckets and booms. This type of cylinders is also preferred in hydraulic bending machines, metal sheet cutting machines, hot press machines and so on.

The hydraulic cylinder plays a vital role as a motor or actuator in a wide variety of machinery. Actuators are the heart of industrial machines; they can direct and regulate the mechanisms to complete the tasks. For instance, they can control the movement of lifting the load or opening the valves. The actuator, like hydraulic cylinders and pneumatic cylinders require instructions and the source supplying stable energy. General sources of the actuators include the electric currents, the hydraulic pressure or the pneumatic pressure; and instructions that regulate the actuator mostly come in pressure form, computer software’s signal form or simply comes from human power. 

When it comes from the basic operating principle of the actuator, the equipment will convert different kinds of energy to unidirectional force that supplies a fixed mechanical/electrical machine system. Those hydraulic, pneumatic or electronic machinery systems that involve actuators to drive the tasks are considered automation systems, which are increasingly popular across industries. 

:: Read more : What Are Small Hydraulic Cylinders?


What to Consider When Selecting Hydraulic Cylinders?

The proper selection of hydraulic cylinders will affect the results of expected applications. So it is important that you take all of these factors into account to make sure that your selected product meets your needs.

Mass: The first factor you should consider is the amount of mass you intend to move with your machine. This is the required step prior to figuring out how much force you need to move the mass. For example, 5 tons of loads will require over 5 tons of force in order to push the mass across the ground. Otherwise, it won’t be able to overcome the friction and acceleration. Simply put, the force of your cylinders should always be high enough to allow a margin of error. 

● Geometry: Once you determine the mass, the next step is to consider the geometry needed to move it. For machines that typically move up and down (e.g., hydraulic presses), the geometry is simple and there isn’t much to consider. However, when this is not the case, you need to consider the point of lift force, and the force required by the cylinder may change. Take a crane as an example, the cylinders often push very far from the load. In most scenarios, the load distance can be up to 10 times the lift force.

Bore Size: With the above completed, what you should do next is to calculate the bore size of your cylinders. You multiply pressure by the area of the internal piston surface, and you’ll get the force produced by the cylinder. This determines the bore size you need for your cylinders.

Rod Size: After determining the bore size for your cylinders, the next step is to select a proper rod size. Even though most stock cylinders already come with a couple of rod options, you should still determine the required rod size yourself. This requires careful consideration because it is closely associated with the buckling strength of the rod. If you don’t know how to calculate it, your supply/manufacturer should be able to provide assistance. Aside from rod buckling, you should also take bearing load into consideration when selecting your hydraulic cylinders. Consider using stop tubes so that the bearing loads do not exceed the design limitation.

Cushion: Finally, you need to determine if internal cushions are required at the end of the cylinder stroke. The purpose of using the cushion is to decelerate for high speed rods to reduce the impact of the piston assembly against the end cap of the cylinder. The good news is that cushions are typically optional. But if you feel that you need them, you can place one at either end of your hydraulic cylinders. 

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