Flow Control Valve "On" Full Flow; Flow Control Valve Holding Back Pressure - Wayne Vista Series Service

5.2.3. Flow Control Valve "On" Full Flow (see Figure 5-4)
Flow control valve "on" full flow 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 (12) and fast (13) poppets rearward
exposing a path to the outlet. This path is larger then the one described in
Section 5.2.1.2. Pressure is relieved from the center chamber (C) faster than it
can be replenished. This creates a pressure imbalance between the inlet
chamber (A) and the center chamber (C); the pressure in the center chamber
being lower. Because the pressure in the inlet chamber is higher than that in
the center chamber, the diaphragm material is pushed towards the center
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 center chamber. The pres-
sure now builds in the center chamber until it equals that of the inlet chamber,
at which point the spring (14) pushes the diaphragm closed stopping flow.
5.2.4. Flow Control Valve Holding Back Pressure (see Figure 5-5)
Once a delivery is complete there is some amount of product which is trapped
on the outlet side of the flow control valve. This is necessary in order to hold
the meter, hose, and nozzle full. This product is held at some pressure, gener-
ally near the pressure of the last delivery. If the pressure should build up, for
instance a car running over the hose, the flow control valve would act as a
relief valve.
November 1992 Part No. 917543 Rev. A
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