Elevated Spas - if the spa is higher than the pool, gravity will attempt to equalize
the water level between the two bodies of water UNLESS there is a check valve on the spa return line.
Fountains - if there is a fountainhead that is above the level of the water or if
there is a fountainhead that protrudes out of the water, then it should have a check valve on it.
Heaters - it is a good idea to put a check valve between the filter and the heater
to keep superheated water from leaving the heater and warping the plumbing or backwash valve between the filter and heater.
Chlorinators - if an inline chlorinator is installed after the heater, it is a good
idea to put a check valve between the heater and chlorinator to keep the chlorinator from sending corrosive gasses and liquids into the heater. This can quickly and
effectively destroy a heat exchanger.
Dual Pump Arrangements - if there are two or more pumps plumbed together, a check
valve should be installed on the outlet side of each pump to keep one pump from blowing water down the throat of the other. Otherwise you run the risk of spinning
the impeller off that other pump.
