System

Valve qty

Meter

Function

D-NT

Interlock

2

2 meters

Two units in service at the same time. When one meter zeros out,  that unit starts regeneration. The  other unit remain in service even if it zero out during this time.

D-NT

series

2

1

Two units in service at the same time. When system meter zeros out , the  "lead" unit regenerates, another on remains in service unit the leak returns to service. The subsequent unit regenerate as needed

D-NT

Alternating

2

2

One unit on stand by, another one in service. When one meter zeros out, it goes to regeneration and the stand by one goes to service at the same time.