Upflow vs Downflow Water Softener Pistons

Many modern water softener control valve manufacturers now make their control valves in both upflow and downflow configurations. This directional naming describes the flow path that the regenerating brine solution takes as it passes through the exhausted softening resin. In an upflow regenerating water softener, the brine solution is introduced at the bottom of the resin bed and is pushed upwards through the bed. A downflow regenerating softener is the opposite - it brings the brine solution into the top of the tank and pushes down through the resin bed. Most high efficiency water softeners will use an upflow brining arrangement.

Some water softener models can be be converted from upflow to downflow (or vice versa) simply by swapping out the piston and making a small programming change. Below is a picture of each of these types of piston from a Fleck 5800 control valve. As you can see, the difference between them is quite subtle:

Upflow water softeners have a couple of advantages over their downflow counterparts:

1. Since the flow of brine is in the upward direction it pushes accumulated sediment out of the resin bed as it regenerates which can allow a shorter backwash stage and significant water savings
2. In a downflow water softener the brine has to pass through the void space at the top of the tank where it is diluted. In an upflow water softener the brine is not diluted as it enters from the bottom
3. Upflow regenerated softeners tend to "super regenerate" the resin at the bottom of the resin tank, while downflow softeners do this for the resin at the top of the resin tank. Since the treatment direction is the downflow direction an upflow regenerated softener creates a "catchall" at the bottom of the resin tank to grab onto any hardness that has not been captured up higher in the resin column.

Be careful: some water softener control valves will show both "upflow" and "downflow" programming options (most Fleck systems are like this) however simply changing the programming setting is not sufficient - there will be internal components that need to be changed also.