Adjustable office chairs that go up and down with the pull of a lever are fairly common in business and home offices. They come in many different sizes from a couple of inches of height adjustment to over 7 inches for drafting stools. The majority of cylinders have a travel height of 4.5 inches or less. They all pretty much operate using the same mechanism even though they are different heights.
How It Works
The pneumatic chair uses a cylinder or gas spring filled with air. The air chamber is connected to a plunger or piston sealed with a gasket that when activated with the lever mechanism, moves into or out of the chamber. The air is pushed by the plunger and further compressed. The air is compressed and causes a springing or lifting movement. Releasing the piston expands the air. The volume of air contained in the cylinder can be adjusted to make the spring more or less forceful in its movement. A spring makes it easier to lift the seat. Without the spring you would be required to move the seat up and down manually and use a knob or pin to stabilize the height.
Why It Fails
Eventually the pneumatic cylinder goes bad and your chair will sink down while you're sitting in it. The average life of a good pneumatic cylinder is about 5 years when used everyday and much less for cheap chairs. The reason for failure is that the rubber gasket separating the gasses in the cylinder deteriorates over time with use. It's located inside the red circle to the left. Because the spring is not strong enough to keep you up and there is no seal to trap the air, the chair will slowly sink down when you sit in it. Usually the rest of the office chair is still functional, but it becomes unusable if you can't sit at the correct height.
In the next post we will look at the pros and cons of traditional options such as buying a new ergonomic chair or trying to figure out what type of replacement cylinder to buy and what it takes to install.
