Why are air chambers or hydraulic pressure arrestors used in cold water systems, and what is a common limitation of air chambers?

• A. To store extra water; air chambers leak.
• B. To improve filtration; air chambers clog easily.
• C. To cool water; air chambers corrode.
• D. To absorb pressure surges; air chambers can fill with water over time, reducing effectiveness.

Answer: (C)

Air chambers are placed on cold water lines to dampen pressure surges, or water hammer, that happen when a valve or faucet is closed quickly. The trapped air acts like a cushion: as the flow trying to stop is suddenly cut off, the moving water compresses the air, absorbing the energy of the surge and reducing the spike in pressure. This protects pipes, fittings, and fixtures from damage and noisy hammer.

A common limitation is that the air can gradually dissolve into the water or leak out, causing the chamber to fill with water. Once water fills the chamber, there’s no longer an air cushion, so its effectiveness at absorbing pressure surges is greatly reduced. To restore function, the chamber can be drained and recharged with air or replaced with a newer arrestor.