These valves are normally set for 150 PSI and/or 210F. If either condition is
exceeded, the valve will open and discharge water. Most codes require a "drop line"
from the outlet of the valve to a point within ten inches of the floor, to protect anyone
nearby, and to minimize damage to electrical and other components, if the valve
Pressure and temperature relief valves are not designed for use in solar collector
loops, as they open at temperatures well below typical operating conditions.
These valves are used for introducing or removing non-freezing solar fluid from the
collector loop of closed-loop systems. (Figure 2-32) Simple boiler drains can be
used, if their seats and packings are compatible with the solar fluid. In other cases,
a shutoff valve and a hose adapter perform the same function without compatibility
problems. Finally, specialized poppet valves have been used by different
manufacturers for this purpose.
As discussed in Section 2.2, the fill/drain assembly includes the two valves on each
side of a shutoff valve or check valve. As solar fluid is pumped into the system, the
center valve forces the fluid to move up through the collectors, and back out the
other side of the assembly. Since the fluid goes back into the bucket it was
originally pulled from, it moves around and around the system, forcing out the air.
After charging, the fill/drain valves are closed. If children have access to the
system, caps are normally provided to reduce the chance of tampering.
This process ensures a completely filled system, but it does require an independent
pump for charging the system.
2.7 COMPONENT OPERATION