Part No. 920525 Rev A - Wayne 3/VISTA series Service Manual

5.2. PROPORTIONAL FLOW CONTROL VALVE
The proportional flow control valve (see Figure 5-2) is a pilot-operated, diaphragm sole-
noid valve. It has three main functions in the dispenser:
• Positive shutoff
• Blend ratio control
• Flow rate regulation
Located between the meter and the hose outlet, the valve is controlled by a 24 VDC pulse
width modulated signal. Normally closed, the pilot opens by an amount proportional to the
amount of current sent to the valve coil. As the pilot raises off its seat, it reduces the pres-
sure to the back side of the diaphragm causing it to lift off of its seat as well. The same
applies to the valve closing; the diaphragm follows the pilot back to the closed position as
the current to the coil is reduced for blender models. The computer continually adjusts the
current to the valves during a sale based on the desired blend ratio of the two feedstocks
and maximum allowable flow rate. The high and low products remain separate until they
are mixed at the hose outlet in proportional blenders or at the outlet valve in fixed ratio
blenders.
FIGURE 5-2. PROPORTIONAL FLOW CONTROL VALVE. In 3/Vista models the valve is located at the
meter outlet.
June 2001

Part No. 920525 Rev A

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