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Hydraulic Cylinders: The Might Behind America’s Construction Crews

Hydraulic cylinders are used in large- and small-scale industry, from hand-held manual tools to massive construction vehicles and robots. A hydraulic cylinder provides the force that moves hydraulic fluid through its pipes, valves, and manifolds, where on the other end, it eventually reaches another cylinder that translates the movement of the hydraulic fluid into the movement of machinery. Hydraulic cylinders can be found in cars, cranes, oil rigs, bulldozers, draw bridges, and even in professional-grade long-reach pruning shears.

The primary components of a hydraulic cylinder are the cylinder, the piston head, and the piston rod. Mechanically, they work together much like a syringe — the piston rod pushes the piston head, which forms an airtight seal with the cylinder. The piston head forces the hydraulic fluid through the hole at the end of the cylinder. Because fluid cannot be compressed, and the entire sequence of pipes, valves, and manifolds is already full of fluid, any motion by the cylinder on one of the hydraulic series affects the cylinder on the opposite side without any delay.

Generally, the piston arm is powered by an electric motor, though there are plenty of exceptions. The outside of the cylinder and the piston arm are often painted with chrome for aesthetic purposes, but the inside of the cylinder and the piston head are under constant stress (as the hydraulic fluid pushes out equally on all surfaces of it’s container), so painting them would be counterproductive.

Cylinders come in several varieties. There are hundreds of different bores of cylinder available. They come in single-stage and double-stage (depending on whether you expect the force to some exclusively from one side or you need both sides to be able to move the other.) Cylinders are generally attached to reservoirs that contain additional hydraulic fluid and filters that keep the fluid free of impurities.

Quite often, a single powerful cylinder is used to power a variety of different motions within the same machine. In that case, a hydraulic manifold that can ‘switch’ one cylinder between several different endpoints is put into play. For any machine that only needs to make one motion at a time, a single hydraulic cylinder operating on a manifold makes for a lower cost of ownership over time.

You Use Gas Springs All The Time And Probably Never Knew It

Have you ever opened someone’s screen door and had it not slam shut on you when it closed? Congratulations — you’ve used a gas spring. Gas springs range in size and power from the tiny ones that keep screen doors from sliding shut or keep the lid of your hatchback’s trunk up to massive gas springs that act as shock absorbers on cranes and other construction equipment.

Gas springs are steel tubes that hold pressurized gas, usually nitrogen because it’s the cheapest noble (i.e. nonreactive) element. Unlike a pneumatic cylinder, however, the purpose of a gas spring isn’t to push the gas to a new location; it’s to use the physical properties of the gas to cushion impacts.

Because gas compresses when pushed upon, a gas spring acts much like a normal spring, absorbing impacts and then pushing back. Gas springs with fine holes in the cylinder will then proceed to lower the load slowly until it reaches a stopping point — as is the case with the screen doors. Other gas springs have nitrogen on both sides of the airtight seal, and thus provide impact absorption in both directions and settle toward the middle of the spring.

Other variations include locking gas springs, which use a locking shroud to keep the spring fully extended until it’s unlocked; friction-stop springs, which have a locknut that can be positioned anywhere along the spring; and adjustable-force springs that allow the amount of gas inside the spring to be adjusted on-site after installation.

A close cousin to the gas spring is the damper, which is essentially the same mechanism but filled with hydraulic fluid and with a small reservoir into which the fluid flows as pressure is exerted on the piston. A damper slows the load’s progress by forcing the fluid inside through a small hole. Like gas springs, dampers can work in one direction or in both.

If you’re working in any kind of major industry, you may be well aware of the gas springs and dampers that surround you and help you get each day’s work done. If you’re like the rest of us, you may be surprised at just how commonplace these helpful little items actually are.