Single-Acting vs. Double-Acting Cylinders

There’s been some confusion as to how to configure and use either system effectively without causing damage to the equipment, load, or to the user. Some of this confusion results from misunderstanding the difference between single-acting or double-acting cylinders and being unsure of when either should be used. Hopefully, we can clear the air in this department.

A pump, a hose, and a cylinder round out the basic setup of a hydraulic system, often times referred to as a port-a power. Without each of these components, this system cannot be operated at all.

A single-acting cylinder is one in which the hydraulic fluid performs on just one side of the piston only. Since hydraulic oil does not compress, when applying force via a hand, electric or gas powered pump, the piston rod of the cylinder will extend. More specifically, the pump forces oil into the hose which flows into the bottom connection port of the cylinder, resulting in the ability for pushing, tensioning or jacking applications. The single-acting pump and cylinder are both equipped with one connection port at the lower portion of the cylinder body, for the oil to both advance the piston rod, and when retracting it, allow the oil to flow back into the reservoir of the pump. Many of the single-acting cylinders have springs built in to assist in the retraction process, but if not, they may be a bit more challenging to retract. The pump that you select also plays a role in the retraction process. Some manufacturers have pumps that will pull the oil back into it, rather than allow it to just flow back into the reservoir. The last consideration in selecting either single or double-acting, is whether the cylinder is considered a load-return type. Meaning, that in order for retraction to occur, the load, or a significant force is required, in addition to the pump for it to retract completely. So be careful, if you have an application that requires several complete stroke cycles, such as a jack and crib operation, you will likely want a double-acting cylinder for that task. Most single-acting cylinders are more commonly-used in light industrial and commercial applications. This of course is not an exclusive list, but the majority of single-acting cylinders in use today tend to be on the lower end of the capacity spectrum.

On the other hand, the double-acting cylinder is one in which the hydraulic fluid performs on both sides of an apron portion of the piston. The double-acting pump and cylinder are both equipped with two connection ports; one at the lower portion, the other at the top portion of the cylinder body. This system requires hoses for each port. When advancing the piston rod, oil flows in through the lower connection port. When you have achieved your desired pressure or stroke requirements, putting the pump in the neutral position will hold the cylinder at that resting point, until it is time to either continuing to advance, or when you would begin retracting operations. Double-acting cylinders are more commonly-used in heavy industrial and construction applications, such as lifting bridges to perform bearing maintenance. The majority of double-acting cylinders in use today tend to be on the higher end of the capacity spectrum.

This is a meant to act as a quick guide in the selection of cylinder types. Always work with the proper qualified sources to help select the capacity and type most suitable for your project.

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