A gas lift chair has springs that consist of cylinders as well as pistons that slide in and out of them. The cylinders contain pressurised nitrogen and oil, according to ExplainThatStuff.com.
How Gas Springs Work
Pushing the down lever of the chair forces the piston into the cylinder, compressing the gas and lowering the seat. Pushing the up lever pulls out the piston, allowing the compressed nitrogen to expand, thus raising the seat.
The gas spring is designed to lift a particular load at a constant speed. In addition, the oil in the spring smooths its movement. Gas springs are simple, durable, reliable and do not require maintenance. They are also smaller than metal springs.
Gas springs come in different designs and configurations. Vertically mounted gas springs work more efficiently and are less likely to collapse at full extension. Tight seals around the piston prevent the nitrogen and oil from escaping.