Valves must never be installed in a way that could allow the
isolation of the solar collectors from pressure relief valves
and/or expansion tanks. Collectors have been completely
destroyed by bursting in this way.
Automatic air vents can be used only in piping loops containing water. When used
with solar fluids, an automatic air vent will eventually vent enough fluid vapor or leak
enough to render the system inoperative. (Figure 3-5)
An Automatic Air Vent
The high points of closed-loop systems containing solar fluids must be vented, but
with manual (coin) vents (Figure 3-6). The vent should be a simple needle valve,
with absolutely no plastic seals, seats, wafers or other non-metal components.
During installation and maintenance procedures, service personnel can open the
valve to check for air or to let it out. Otherwise, the vent stays closed.
The high points of draindown and drainback collector loops, and the high point of
storage water loops should use a high-pressure automatic air vent. Confirm that the
vent is capable of handling at least 125 PSI, although 150 PSI is better. Check the
pressure relief valve setting to ensure protection for the vent.
3.1 INSPECTION PROCEDURES