Wayne Dresser Vista 1 Series, Service Manual

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Part No. 920160 Rev A February 1997
3.8. PROPORTIONAL FLOW CONTROL VALVE
(Blenders only.) The proportional flow control valve 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 from the blender solenoid drive board. 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 pressure 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. 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.
* The maximum allowable flow rate in the United States is 10 gallons per minute.