Flow Control Valve "Off" No Flow; Flow Control Valve "On" Slow Flow; Flow Control Valve "On" Full Flow - Wayne Dresser Vista 1 Series Service Manual

5.2.1.

Flow Control Valve "Off" No Flow

Flow control valve "Off" or no flow (see Figure 5-1. and Figure 5-4.) occurs
when the inlet to the valve is charged, but there is no flow required from the
particular valve, as in the instance, where the submersible pump motor is
running because another fueling point is being used. The inlet and the "inlet
chamber" (A) are charged with the pump pressure. This pressure passes through
a port (2) from the inlet chamber to the "outer chamber" (B). From there the
product passes through the orifice (3) into the two stage actuator (1).
The pressure in the inlet chamber and the outer chamber are equal at this point.
Because the area of the diaphragm material (5) exposed to the inlet chamber is
approximately half that exposed to the outer chamber, the force holding the
diaphragm closed is twice that which is trying to open it. Therefore, the
diaphragm material (5) remains in the closed position covering the outlet port.
5.2.2.

Flow Control Valve "On" Slow Flow

Flow control valve "On" slow flow (see Figure 5-2.) occurs at the beginning of
all sales, and again at the end of preset sales. The pressures remain the same as
described in Section 5.2.1. The difference is that the slow flow actuator coil
(omitted for clarity) has been energized. This causes the slow flow poppet (8)
to be pulled off of its seat exposing a path (4) to the outlet. The flow through
this path is so slow that the pressure in the outer chamber (B) is not reduced
significantly. Therefore, the diaphragm remains in the closed position.
5.2.3.

Flow Control Valve "On" Full Flow

Flow control valve "On" full flow (see Figure 5-3.) occurs during the main
portion of all sales. At this time, both the slow and fast actuator coils (omitted
for clarity) are energized. This pulls both the slow (8) and fast (9) poppets rear-
ward exposing a path to the outlet. This path is larger then the one described in
Section 5.2.2. Pressure is relieved from the outer chamber (B) faster than it can
be replenished. This creates a pressure imbalance between the inlet chamber (A)
and the outer chamber (B); the pressure in the outer chamber being lower.
Because the pressure in the inlet chamber is higher than that in the outer
chamber, the diaphragm material is pushed towards the outer chamber. This
opens a path directly from the inlet to the outlet, initiating full flow.
When the delivery is complete both actuator coils are de-energized, allowing
the poppets to return to their rest position. This closes both ports in the actuator
and removes the pressure drain from the outer chamber. The pressure now
builds in the outer chamber until it equals that of the inlet chamber, at which
point the effects of the higher force caused by a larger area on the diaphragm
and the spring (10) pushes the diaphragm closed stopping flow.
February 1997 Part No. 920160 Rev A
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