Expansion Tank & Why
The California legislature has recognized the importance of metering and has passed several bills requiring meters in California. In 1991, the legislature passed SB 229, requiring meters on new connections after 1992. The legislation, however, did not require utilities to actually read the meters or to use that data to bill customers by volume. In 2003, AB 514 required Central Valley Project water users to be fully metered by 2013 and start charging metered users volumetrically by 2010. Then in 2004, AB 2572 (Kehoe) closed the loophole in SB 229 by requiring urban water utilities to meter all municipal and industrial users by 2025 and charge metered customers based on the actual volume of water delivered. In 2009, the legislature passed similar requirements for California’s investor-owned utilities (AB 975 Fong).
Automatic meter reading (AMR) systems automatically send real-time water usage data to the utility, without the need for an employee to physically read the meter onsite. Advanced metering infrastructure (AMI) also reads usage automatically and allows two-way communication between the customer and the utility. With the installation of these new water meters also saw the installation of a check valve at each new meter, this check valve allows water to flow in one direction away from the meter to your home, this check valve is to prevent the possibility of contaminates (chemicals from your lawn or garden) from entering the public potable water system.
How can contaminates enter the public water system from my home? Well the answer to this question comes in two ways, one a broken main city water pipe can and has caused water from properties to back flow into the city pipes caused by the reverse pressure of the broken city pipe. The second and most common way is when water enters your homes pipes from the city water source the pressure will balance at approximately 40 - 65 pounds of pressure per square inch (PSI) this is the most common pressure range in the Sacramento areas. When a water heater goes through it's heating cycle you get a pressure rise of up to 20% this excessive water pressure would simply push back into the city water supply, however now with the installation of these new AMR or AMI water meters containing check valves, won't allow the excessive water pressure to push back.
This is why expansion tanks are now required per California plumbing code (CPC) in every home or business that replaces it's old water heater, expansion tanks have a ballon called a bidder bag inside this small tank this bladder bag is filled with air to match your current incoming water pressure, any pressure above this range is absorbed by the bladder bag like a shock absorber on your car.
The International Residential Code (P2903.4.2) requires the installation of an expansion tank on a hot water tank where thermal expansion may cause an increase in pressure. The tank is only required when the water supply system incorporates a backflow prevention device, check valve or similar device. Similar language can be found in the Uniform Plumbing Code under section 608.3.