Thermal Expansion

What is Thermal Expansion?
Thermal expansion is a result of heating water.  When water is heated, its density decreases and its volume increases.  Backflow prevention assemblies and other one-way valves installed at a customer's service connection eliminate a path for expanded water to flow back to the distribution system, resulting in increased system pressure.  This increase in pressure can result in: pressure surges, dripping faucets, chronic or continuous dripping of temperature and pressure-relief valves on hot-water heating tanks, and other mechanical problems with hot-water tanks, including distortion and rupture.
What is a closed system?
A closed system is created when an approved backflow prevention assembly or a single check valve (not approved for backflow prevention) is installed at a customer's service connection.  The backflow prevention assembly or single check valve does not allow water to flow backwards from the customer's private water system into the PWS's distribution system.