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[[File:Gas-spring_simplified_numbered_120.png|thumb|Simplified constant-force pneumatic gas spring with sectional view:
Gas springs are used in automobiles to support hatches, hoods, and covers. They are also used in furniture and doors, as well as in medical beds. They are used industrially in Machine press. 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.
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. Nitrogen is a common gas in gas springs because it is inert and nonflammable.
In the ideal case of a piston moving with zero friction through a fully sealed cylinder, there are two key phenomena which can be thought of as acting simultaneously inside the spring as it is compressed. Firstly, as the spring is compressed and the piston rod is pushed into the cylinder, the effective volume of the cylinder decreases due to the extra space now being occupied by the solid piston rod. This would be the case even if there were no piston attached to the rod, as the only changing factor is the cylindrical volume of the rod itself. Second, the bottom of the piston always experiences a greater force opposite to the compressing action than the top. Even though the compressed gas exerts an equal amount of force on all the inner surfaces of the cylinder and piston rod, the force contribution in the direction of travel is practically zero for the sides of the rod, but nearly total for the bottom of the rod. The addition of a piston to the end of the rod thus does not alter the net forces involved, but instead partially separates the cylinder into two volumes with restricted flow of gas and oil between them, through flow-restriction channels in either the piston or the cylinder wall.
Gas springs whose pistons have fine holes in them for damping are called slow-damper springs and are common on safety gates and doors.
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 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, similar to those used in .
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.
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.
It is also possible to make degressive gas springs, where the spring becomes more, not less, powerful as the main cylinder expands.
There are a few common signs of failure for gas springs. To list a few: Leakage of gasses, failure to support its weight compacity, unusual noises, excessive bouncing, and sagging.
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