Unique design concepts sometimes require com-ponents to operate in nonstandard conditions.
One example would be using balancing valves to regulate flow through multiple banks of solar collectors in a large drainback solar thermal system. In a more typical solar thermal system operating with antifreeze, the use of balancing valves would be routine. But in a drainback system, there is no antifreeze; water drains out of the collector array and exterior piping whenever the collector circulator turns off.