Q:

What is the purpose of water hammer arresters?

A:

Quick Answer

Water hammer arresters prevent water hammer, a plumbing phenomenon that results from fast-moving columns of water inside home plumbing systems. Water hammer arresters absorb the pressure differential that causes water hammer, preventing both the unpleasant sound and the potential plumbing damage associated with this phenomenon.

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Full Answer

Water hammer occurs because water builds up momentum as it travels through pipes in a home plumbing system. When a person closes a valve in the system, the fast-moving water slams into the closed valve, producing a shock wave that travels throughout the entire system. In most cases, a trapped pocket of air exists somewhere inside the pipe that absorbs the force of the shock wave and prevents the loud banging associated with water hammer. If no air pocket is present, however, the shock wave keeps traveling until it hits another closed area of the system, producing a loud bang.

Water hammer is not just annoying to residents; powerful shock waves can eventually cause connections to come loose, and particularly frequent water hammer can even cause ruptures in copper pipe. A water hammer arrester is a very simple device consisting of a vertical pipe with an internal plastic piston. Normally, the piston rests at the bottom of the pipe, but when a shock wave travels through the system, it forces the piston up into the pipe. The piston absorbs the force of the shock wave, preventing water hammer.

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