Proportional Flow Control Valve (Blenders Only); Figure 5-5. Proportional Flow Control Valve - Wayne Dresser Vista 1 Series Service Manual

5.3.

PROPORTIONAL FLOW CONTROL VALVE (BLENDERS ONLY)

(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 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 in proportional blenders or at the outlet valve in fixed ratio
blenders.
FIGURE 5-5. PROPORTIONAL FLOW CONTROL VALVE. The valve is controlled by a 24 VDC pulse
width modulated signal from the solenoid drive board .
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Part No. 920160 Rev A February 1997