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Location of Differential Pressure Switch
The high pressure port connects to the inlet manifold between the
solenoid valve and the rotameter/rate-adjusting valve. The low
pressure port connects to the discharge side of the rotameter.
Function of Differential Pressure Switch
The differential pressure switch ensures sufficient water flow is
present before the polymer pump is energized. This integral,
automatic safety feature eliminates the problem of overfeeding neat
polymer to an application without proper dilution.
In operation, the rate valve is adjusted to produce the desired flow
through the system. This causes a pressure drop to occur across the
valve which is applied to the differential pressure switch.
If supply pressure decreases enough to affect flow rate or if back
pressure between the PolyBlend and the point of solution application
increases enough to affect flow rate, the differential pressure across
the rotameter and valve decreases. This causes power to be
interrupted to the polymer pump and prevents damage to the mixing
system caused by extremely high viscosity developing in the mixing
chamber.
NOTICE:
If system pressure or flow are not adequate, investigate the cause of
lack of flow. (For example, inadequately sized piping can produce
Inadequate flow.) To avoid undesirable water dilution conditions and
damage to equipment, do not bypass or adjust the differential pressure
switch for a lower pressure/flow setting.
Question: Why doesn't the polymer pump turn off when I turn the water off using
the rotameter?
The differential pressure switch senses flow on either side of a
pressure drop. Because the rotameter is the sensing point, the rotameter
closing is the only cause of loss of flow that the differential pressure
switch cannot see.
Test the differential switch by turning off the source water or the
discharge flow. (See step 5 on the next page.)
Differential Pressure Switch
7
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