[ChemE584]

I am working on a water filtration plant that using pumps to "vacuum" filtered/clean water from a tank and then transfer it to a clearwell. I'm not sure if I should be using an air release valve or a vacuum breaker valve. Here's the setup.

The pump vacuums water (elevation not important as I have my suction figured out), then the discharge piping from the pump immediately goes up 12 feet, where a backpressure loop is then located (another 3 feet up). From there the piping goes down (below the pump centerline) to the clearwell. The high level in the clearwell is higher than the pump centerline, but lower than the high point in the piping. I've been told to use vacuum breakers when the clearwell is lower than the discharge piping, but I'm not exactly sure why as I don't believe contamination is of concern (water is clean).

I am calculating the TDH of the pump and the use an air release valve or vacuum breaker will affect what is used for static discharge. If I use an air release valve the static discharge will be based off the high level in the clearwell (as it's a submerged discharge) and if I use a vacuum breaker valve the static discharge will be based off the high point in the piping (since it's introducing atmospheric air to the system). For some reason I have a difficult time grasping this concept!