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. The vent must
be rated for at least 125 PSI, although 150 PSI is better.
The cap on automatic air vents is used to prevent the entry of dust which would clog
the mechanism, so it is never fully tightened.
A Manual Air Vent
The air vent should be constructed of metal. Plastic air vents are not recommended
because catastrophic failure is common.
Air eliminators, also called air scoops, are normally used only on the collector loops
of large closed-loop systems. Their internal construction includes vanes to push
entrained air bubbles upward to a holding chamber. When enough bubbles have
been collected, an automatic air vent at the top of the unit vents the air.
The air vent should allow flow only during startup operations. They must be closed
during normal operation, after all the air has been removed from the system. Again,
be sure the vent is capable of withstanding the solar fluid itself, and the system
Most air eliminators feature a threaded port on the bottom for the system expansion
tank. This is acceptable, but it means the eliminator/vent/expansion tank package
must be installed on the suction side of the solar pump.
2.7 COMPONENT OPERATION