Zone 2 Loses Pressure Unless Another Zone Runs Simultaneously

Bizarre Zone Behavior: Zone 2 Fails Alone But Works With Another Zone

4-zone river-fed system. Zone 2 starts with zone 1, then loses pressure after minutes. Replaced 75% of diaphragm—same. Cut diaphragm center out—same. Zone 2 works fine when ANY other zone runs simultaneously. 2 HP Flowtech pump, 40 ft lift, 2" pump output reduced to 1" near top.

Valve Still Suspect

Despite diaphragm mods, the valve is the most likely culprit. The fact that it works when another zone runs suggests the combined flow keeps the valve's internal passages clear or maintains pressure differential.

Electrical Check

Use a multimeter: check controller output on station 2 during a full run cycle. Must hold 24VAC continuously. If voltage drops, controller or wiring fault.

Pump Line Reduction

The 2" to 1" reduction near the top of the lift line is suspicious. It creates friction loss. Consider increasing to 1.25" or 1.5" if pump allows.

Next Steps

1. Verify 24VAC on station 2 throughout cycle.
2. If voltage good → replace valve.
3. Evaluate pump discharge line sizing.