Chap FIVE: Pressure/Flow Switches
PRESSURE SWITCH
How It Works: The lower chamber of the switch is physically attached to the
water flow of the plumbing system. The pressure internal to the plumbing is also
manifested in this chamber. This chamber expands to push a post toward a
microswitch. When the chamber is not pressurized (pump off) the post pulls back
and the microswitch opens. When the pump is turned on the post pushes out and
closes the microswitch. The distance between the post and microswitch can be
adjusted on most switches. Typically turning the adjustment wheel clockwise
moves the post closer to the chamber and further from the microswitch. Turning
the wheel counterclockwise gives the opposite result.
What it Does: The purpose of the pressure switch is to notify the board whether
enough water is moving past the heater element. If sufficient pressure closes the
microswitch, the board turns the heater on. Otherwise it does not . Due to the low
pressure of circulation you should use a 1 or 2lb pressure switch. Overtime the
microswitch can fail, the post is less responsive, or doesn’t withdraw fast enough.
Any of these failures will cause the board to fail.
FLOW SWITCH:
The flow switch performs the same function as the pressure switch.
How It Works: The flow switch is a simple device. It is installed typically after the
#1 pump discharge. It’s a reed switch and a magnet. The switch is inside the
center post of the flow switch. The magnet is on the metal armature.
What It Does: When water flows pass the armature it moves toward the center
post and closes the reed switch. This tells the board that there is enough water
flow. When water stops flowing, the armature moves back and the switch opens.
Flow switches either work or do not. The key to installing is making sure the right
21
