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.