Gas spring

A gas spring consists of a sealed cylinder filled with a charge of high-pressure gas, a piston rod attached to a piston with a sliding seal, and some oil. The piston (or the cylinder wall) contains a number of channels that allow the gas to transfer between the lower chamber (between the piston and the closed end of the cylinder) and the upper chamber (between the piston and the head cap). Firstly, as the spring is compressed and the piston rod is pushed into the cylinder, the gaseous 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 volume of the rod displaces an equal volume of gas, but the total volume of the enclosing cylinder remains a constant. This means the pressure of the gas increases. Second, the bottom of the piston always experiences a greater force opposite to the compressing action than the top, because pressure is a scalar quantity: it acts equally in all directions. The gas on both sides of the piston will be at equal pressure due to the equalizing channels, but the gas in the "lower" chamber has more surface area of the piston available to push on than the gas in the "upper" chamber, due to the rod. Since pressure is force per unit area, more area at the same pressure necessarily means more force. This is the reason the piston is present. Other details According to Hooke's law, 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. Some gas springs have fine holes in the plunger for additional damping: these 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-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. ==Variations==

A gas spring can be given adjustable push-in force via a local knob or remote via a Bowden wire. 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. It is also possible to make degressive gas springs, where the spring becomes more, not less, powerful as the main cylinder expands. == Consequences ==

Poor manufacturing Gas springs are often used in office chairs, truck tailgates, and wheelchairs, to name a few. A rare concern with gas springs is that if it is made cheaply, using air as its internal gas, the oxygen will combust given enough force. This is because oxygen, by definition, is the reason for combustibility, whereas nitrogen is not combustible and does not enable combustibility. Oxygen is not flammable itself, but it will oxidize internal parts under high heat. The internal parts of the gas spring, under great tension and heat, then explode with any oil or grease within the gas spring. An incident in 2008 involved an elderly man who suffered severe injuries due to a rod forcefully ejected from the explosion of an office chair. There are a few common signs of failure for gas springs. To list a few: leakage of gases, failure to support its weight capacity, unusual noises, excessive bouncing, and sagging. ==See also==