THERMAL EXPANSION
THE FIX
The ideal fix involves the use of a pressure reducing valve if supply pressures are above 60 to 70 psi, and a properly sized expansion tank. The PRV reduces supply pressures to 40 to 60 psi allowing an economically priced and sized expansion tank to be used. The PRV also offers the benefit of saving water and prolonging the life of water flow valves. The PRV is not required if the system already has one or if high supply pressures are desired. A supply water pressure of 80 PSI is a maximum set by many local or state codes.
The PRV is installed between the check valve and the water heating system. The expansion tank is installed between the PRV and the water heating system. Follow the manufacturers instructions for installing the expansion tank.
Run the thermal expansion check again. The pressure should increase only slightly then hold steady throughout the recovery cycle. The expanded water is flowing back from the heater and into the pressurized storage bladder of the expansion tank. Air pressure will force this water out of the expansion tank into the supply once usage resumes.
DO NOT DEPEND ON THE TEMPERATURE & PRESSURE VALVE (T&P VALVE) TO HANDLE THERMAL EXPANSION! The T&P valve manufacturers designed the valve to be an emergency relief device only. The T&P Valve could be subject to reduced effectiveness or failure.
FIGURE
IN A CLOSED SYSTEM USE A
THERMAL EXPANSION TANK
COLD WATER SUPPLY TO FIXTURES
PRESSURE REDUCING VALVE
WITH BYPASS
HOT WATER | COLD WATER |
OUTLET | INLET |
COLD WATER INLET VALVE (SHUT-OFF VALVE)
WARNING
Thermal expansion of water, if not compensated for in system design, will lead to the early failure of components. These failures are not covered by the manufacturer’s warranty, so it is extremely important that everyone be aware of the causes, symptoms and solutions to thermal expansion in a closed water heating system.
36
