6
SYSTEM PERFORMANCE
Rev C
Understanding Net Driving Pressure
Net driving pressure (NDP) is pressure available to the elements for
production of permeate water. It is equal to the flowing inlet pressure at
the unit minus the pressure drop throughout the system.
Figure 3
Inlet Pressure
The first step in determining net driving pressure is finding the inlet
pressure to the Merlin. This is the flowing pressure within 12 inches of the
Merlin inlet. Often, this pressure is less than indicated by a home’s well
pump pressure gage.
NOTE:
Use the flow rate worksheet located at the end of this
document to estimate flow from the Merlin.
NOTE:
Net Driving Pressure = Inlet Pressure - System Pressure Drop.
RO Assembly
Faucet
Carbon Postfilter
Elevation
above unit
Length of permeate
tubing
Permeate Line
Inlet Pressure-
Measure as
close to unit
as possible
Obstructions - Elbows,
Tees, etc.
40 psi
80 psi
12 inches
Inlet Line