If your office chair slowly drops every time you sit down, or won't stay at the height you set, the problem is almost always the gas cylinder. It's the metal tube between the seat and the base. The good news is it's usually fixable in under an hour, and sometimes it's covered by your warranty.

Why office chairs sink

The gas cylinder (also called a pneumatic cylinder or gas lift) holds pressurized gas behind a seal. When you pull the height lever, a valve opens and the seat moves. Over time, the seal wears out and gas leaks past it, so the cylinder can no longer hold your weight and the seat creeps down.

It's a normal wear part. Cheaper chairs tend to wear sooner, and heavier use speeds it up.

Step 1: Check your warranty

Before buying anything, check the chair's warranty. Many brands cover the gas cylinder for several years, and some cover it for much longer. If yours is covered, the maker may send you a replacement cylinder for free.

Step 2: Try a quick temporary fix

These won't repair the cylinder, but they'll keep the chair at one height while you sort out a replacement.

  • The PVC pipe fix. Lower the chair to the height you want and measure the visible part of the cylinder. Cut a piece of PVC pipe to that length, slit it lengthwise and snap it around the cylinder. The seat now rests on the pipe instead of the gas.
  • The hose clamp fix. Set the height you want, then tighten a metal hose clamp around the cylinder just below the seat. Wrapping a bit of rubber or tape around the cylinder first helps it grip.

Both fix the chair at one height, so you lose easy adjustment.

Step 3: Replace the gas cylinder

A replacement cylinder is the proper fix. Most office chairs use a standard-size cylinder that fits a common taper, but check before you buy:

  1. Measure the old cylinder. Note its overall length and how far it can extend, and look for any markings or a class rating.
  2. Check the weight rating and choose one rated for your weight.
  3. Get the tools: a pipe wrench, a rubber mallet, and some penetrating lubricant.

How to swap it:

  1. Turn the chair upside down on a soft surface.
  2. Remove the base: tap firmly around the top of the base near the cylinder with the mallet until the base pops off.
  3. Remove the cylinder from the seat: grip it with the pipe wrench and twist while tapping, or follow your chair's instructions. A spray of lubricant helps if it's stuck.
  4. Push the new cylinder into the seat mechanism, fit the base onto the cylinder, turn the chair upright and sit down firmly to seat everything in place.

Wear eye protection and keep the cylinder away from heat. Never try to cut or open a gas cylinder.

When to replace the chair instead

If the chair is old, the seat foam is flat, the arms wobble or the mechanism is cracked, a new chair may be the better buy. Our guides to the best office chairs, budget office chairs and ergonomic chairs compare popular options, including their weight ratings and warranties.