How do I know when the gas cylinder on an ergonomic chair needs replacement?

The telltale sign is a chair that slowly sinks during use — you sit down, set the height, and 30–60 minutes later you're 2–3 inches lower. This happens when the pneumatic nitrogen charge in the cylinder leaks past the internal seals. Replacement cylinders are a standard part available for most commercial chairs ($20–$45), and swapping one out requires only a rubber mallet and pipe to knock the old cylinder out of the base. Most cylinders last 5–10 years under normal use. FindOfficeFurniture.com sells chairs from brands with available replacement parts — call 888-719-4960.