Pd pump Systems neslab p/N 000878 Rev. 08/15/96 Service Manual

Parts List ........................................................................................................................... 44

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Identification
This section is for maintenance of positive
displacement pumps manufactured by
PROCON®. These are brass pumps which
match one of the above drawings.
Figure 1

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Application
The pump type used in a recirculating chiller system is determined
by the requirements of flow and pressure. This chart illustrates
which pump family is suitable for various combinations of flow and
pressure.
If the pump system does not deliver the required flow and pressure
on initial installation, the requirements should be compared to the
catalog pump curves to confirm the pump is correctly sized to the
application.
If the pump system has delivered the required flow and pressure
in the past, and the application/installation is unchanged; it is safe
to assume a degradation in performance has occurred and can be
corrected.
Figure 2

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Figure 3

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The PD (Positive Displacement) pump is a type of rotary vane
pump, known as a carbonator pump due to its widespread use in
the beverage industry. Four vanes are captive to a rotor which
connects to the motor shaft. The rotor spins inside a liner. The
rotor and liner are on different centers, providing an eccentric
cavity. Opposing vanes are connected by push rods. As one vane
is pushed into the rotor slot by the approaching liner, the opposing
vane is pushed out of the rotor slot, maintaining firm contact with
the retreating liner.
Fluid enters the liner cavity and is trapped between two vanes. As
the vanes rotate inside the liner, the eccentric alignment gradually
decreases the volume available to contain the fluid. When the
rotating trapped fluid finally encounters an outlet, it is squeezed out
at high pressure.
The result is a consistent flow rate, essentially regardless of sys-
tem pressure. The pump curve approximates a straight line. Thus,
this pump family is designed to deliver low flow rates and high
pressures.
Disassembly of the pump is not recommended. Restoration of
performance is unlikely due to high machining tolerances required.
Any internal pump failure should be resolved by replacing the
pump. The manufacturer (Procon®) accepts removed pumps for
rebuilding.