When an office chair sinks under your weight or won't rise at all, the gas cylinder has worn out — and replacing it is one of the most satisfying, money-saving repairs you can do. A new cylinder costs a fraction of a new chair and turns a sinking seat back into a fully adjustable one. The job is well within reach of anyone with basic tools and a little patience. This guide walks through it step by step, with the safety points clearly flagged.

Safety first

Gas cylinders are sealed and pressurised. Never puncture, drill into, saw, open, or apply heat to a cylinder. Removed and refitted as a whole unit, it is completely safe. Wear eye protection and work gloves, and dispose of the old cylinder responsibly rather than tampering with it.

How the cylinder works (briefly)

The gas cylinder is the pneumatic tube between the seat mechanism and the five-star base. Pressing the lever opens a valve that lets the pressurised gas inside raise or lower the seat, and holds it once you release. When the internal seal wears, the gas leaks and the cylinder can no longer hold your weight. Our gas cylinder explainer covers the workings in more detail; here we focus on replacing it.

Step 1: Buy the right replacement

Most office chairs use a standard-size cylinder, so a universal replacement usually fits, but it's worth checking a few measurements before you buy:

  • Taper diameter at the top (where it enters the mechanism) and bottom (where it enters the base) — most are a standard size, but confirm.
  • Overall length and stroke (how far it extends) if you want to keep the same height range, or choose a taller cylinder for a higher seat.
  • Cylinder class — a higher class generally means a sturdier cylinder; matching or exceeding your weight needs is wise, as noted in our weight capacity guide.

Step 2: Remove the chair from the base

  1. Turn the chair upside down on a soft surface or lay it on its side.
  2. Remove the casters from the base if it helps you work (optional).
  3. Separate the seat-and-mechanism from the cylinder, and the cylinder from the base. The cylinder is usually held only by friction in tapered sockets — no bolts.

Step 3: Free the old cylinder

The cylinder is wedged tightly into the base and mechanism by years of pressure, so it can take some effort. With eye protection on, tap the base of the cylinder away from the chair base using a rubber mallet, working it loose gradually. For the mechanism end, gripping the cylinder with a pipe wrench (protecting the surface with a cloth) and twisting while pulling usually frees it. Penetrating oil at the joint and a little patience help with stubborn cases. Avoid excessive force in awkward positions.

Step 4: Fit the new cylinder

  1. Remove the plastic skirt (telescopic cover) from the old cylinder and slide it onto the new one.
  2. Insert the new cylinder into the five-star base, narrow end down, seating it firmly into the tapered socket.
  3. Lower the seat mechanism onto the top of the cylinder and press it on.
  4. Turn the chair upright and sit on it gently — your weight wedges the tapered joints together securely, which is exactly how the chair is designed to hold.

Step 5: Test it

Operate the height lever to confirm the seat raises and lowers smoothly and holds your weight at any setting. Give the chair a gentle rock to confirm everything is seated firmly. If the height adjustment feels off, double-check that the lever is engaging the new cylinder's valve pin correctly. That's it — your chair is restored.

Disposing of the old cylinder

Because it's pressurised, don't throw a gas cylinder onto a fire or attempt to cut it open to "release" the gas. Check your local recycling or waste guidance for pressurised metal items, or ask a scrap-metal facility. Treating it as the sealed unit it is keeps disposal safe.

When to call it a day

If, once you start, you find the base is cracked or the mechanism is also failing, replacing a single part may not be worth it on an older, inexpensive chair. Weigh the cost of the cylinder (and any other parts) against a replacement using our buying guides. But for an otherwise sound chair, a new cylinder is a genuine bargain that adds years of life.

Tools and time at a glance

It helps to know what you're in for before you start. The job typically takes twenty to forty minutes, most of which is spent persuading the old cylinder to let go. You'll want a rubber mallet, a pipe wrench or large adjustable spanner, a cloth to protect surfaces, eye protection, and ideally some penetrating oil for a stubborn joint. None of these is specialised, and most households can assemble them or borrow them easily. If you don't own a pipe wrench, locking pliers can sometimes do the job on the cylinder. Having everything to hand before you begin makes the whole process smoother, and means you won't be left with a half-dismantled chair while you hunt for a tool.

Conclusion

Replacing an office chair gas cylinder is a straightforward, affordable repair: buy a correctly sized replacement, separate the chair from the base, work the old cylinder free, fit the new one into the tapered sockets, and let your weight seat it. The only firm rule is to never puncture, open, or heat the cylinder, since it's pressurised — handled as a sealed unit, the job is safe and simple. Do it once and you'll never pay for a new chair over a sinking seat again.