Why does my office chair sink down on its own?

The seal inside the gas cylinder has failed and nitrogen is leaking past the piston, so the cylinder can no longer hold your weight. It is a worn part, not a loose adjustment — cylinders are a standardised replacement item and swap out in minutes.

Why it happens

The cylinder is a sealed steel tube holding pressurised nitrogen above an oil-damped piston. Pressing the lever opens a valve and lets the gas move; releasing it closes the valve and the column holds. When the piston seal wears, gas bleeds past it continuously, so the chair descends under load whether the valve is open or not.

Side-loading is what kills them. Dropping into the seat, or leaning hard on one armrest, pushes the piston against the tube wall rather than straight down its axis, and that scuffing is what eventually destroys the seal. A cylinder that has started sinking will not recover — the gas is gone.

What to do about it

1. 1Confirm it is the cylinder: lower the seat fully, sit down, and raise it without touching the lever. If it settles again within a minute or two under weight, the cylinder is leaking.
2. 2Measure the cylinder's taper and diameter, or check your chair's model number. Most office chairs use a standard cone taper, which is why generic replacements fit a large share of chairs.
3. 3Replacement is mechanical, not electrical: the cylinder is held by friction in a tapered socket and is removed by tapping it free, usually with a pipe wrench and a mallet.