A gas spring, also known as a gas strut or gas damper, is a type of spring that, unlike a typical mechanical spring that relies on elastic deformation, uses compressed gas contained within an enclosed cylinder.^[1] This cylinder is sealed by a sliding piston to pneumatically store potential energy and withstand external force applied parallel to the direction of the piston shaft, loosely analogous similarly to a bicycle pump without a gas outlet.

Gas springs are used in automobiles to support hatches, hoods, and covers.^[2] They are also used in furniture and doors, as well as in medical beds.^[2] They are used industrially in machine tool presses.^[2] Fast-acting gas springs are used in aerospace design and weapons applications, and large, extended gas springs are used in passive heave compensators, which stabilize drilling operations against waves.^[2]

Gas springs are usually implemented in one of two ways. A pneumatic suspension gas spring directly compresses a chamber of air with the piston. A hydro-pneumatic suspension gas spring instead compresses a chamber of oil linked to an accumulator in which the pressure of the oil compresses the gas.^[3] Nitrogen is a common gas in gas springs because it is inert and nonflammable.^[2]

If the internal plunger features a diaphragm that extends to the side of the gas tube, it will stop moving once the applied force becomes constant and will support a weight, like a normal spring.^{[citation needed]} Some gas springs have fine holes in the plunger for additional damping:^[2][how?] these are called "slow-dampened springs"^{[citation needed]} and are common on safety gates and doors.^[2] A gas spring designed for fast operation(s) is termed a "quick gas spring" and is used in the manufacture of air guns and recoil buffers.^{[citation needed]}

It is possible to reduce the gas volume and increase its internal pressure by means of a movable end stop, or by allowing one tube to slide over another, allowing the characteristics of a gas spring to be adjusted during operation. The rod may be hollow by use of clever seals, or it may consist of multiple small-diameter rods. A small amount of oil is normally present.

The gas may be introduced by a Schrader-type valve, using a lip seal around the rod and forcing it to allow gas in by external overpressure or a shuttling O-ring system. Gas springs with high caliber contain a very large amount of energy, and can be used as a power pack. In emergency use, the gas may be introduced via a gas generator cell, similar to those used in airbags.

A gas spring can be given adjustable push-in force via a local knob or remote via a Bowden wire.^{[citation needed]}

Extended stroke is usually acquired through telescoping mechanisms, composed of one rod and multiple cylinders, where the smaller of the two cylinders actually acts as a second rod extending in and out of the larger cylinder.^[2]

There are also techniques to make variable-lift gas springs. These are intended for short production runs and prototypes, and in applications where the exact force is important but hard to estimate in advance, such as lifting a lid slowly in a known time. In this case, the cylinder is supplied filled to maximum design pressure but equipped with a bleed port to allow gas to be released once installed. The intention is that the design can be over-sprung, and then the pressure is reduced in stages to optimize behavior. If too much gas is released, a new spring must be installed.^{[citation needed]}

It's also possible to make degressive gas springs, where the spring becomes more, not less, powerful as the main cylinder expands.^[4]

• Shock absorber