State SW 37-670 - Manual (Page 11)

11
closed water systeMs
Water supply systems may, because of code requirements or such
conditions as high line pressure, among others, have installed
devices such as pressure reducing valves, check valves, and
back flow preventers. Devices such as these cause the water
system to be a closed system.
therMal eXpansIon
As water is heated, it expands (thermal expansion). In a closed
system the volume of water will grow when it is heated. As the
volume of water grows there will be a corresponding increase in
water pressure due to thermal expansion. Thermal expansion
can cause premature tank failure (leakage). This type of failure
is not covered under the limited warranty. Thermal expansion
can also cause intermittent pressure relief valve operation: water
discharged from the valve due to excessive pressure build up.
This condition is not covered under the limited warranty. The
pressure relief valve is not intended for the constant relief of
thermal expansion.
A properly sized thermal expansion tank should be installed
on all closed systems to control the harmful effects of thermal
expansion. Contact a local plumbing service agency to have a
thermal expansion tank installed.