Flow Control Valve "On" Slow Flow; Flow Control Valve "On" Full Regulated Flow; Meter - Wayne Dresser Vista 1 Series Service Manual

5.3.2.

Flow Control Valve "On" Slow Flow

Flow control valve "On" slow flow occurs at the beginning of all sales, and
again at the end of preset sales. In this case the coil is energized with current
bursts of shorter duration. This allows the pilot to slightly move off its seat,
allowing slow flow through the pilot orifice leading to the valve outlet, but not
relieving enough pressure to cause the diaphragm to open.
5.3.3.

Flow Control Valve "On" Full Regulated Flow

Flow control valve "On" full regulated flow occurs during the main portion of
all sales. At this time, the coil is energized with bursts of current of longer dura-
tion, pulling the pilot further off it's seat, relieving the pressure balance, and
allowing the diaphragm to open by an amount relative to the distance between
pilot and the pilot orifice. The position of the pilot is constantly moving in very
small increments based on the signals sent from the computer relative to
controlling a specific blend ratio and/or maintaining a maximum flow rate of 10
GPM through a hose. As the computer senses the need to increase or decrease
the amount of a particular feedstock, it will send signals to the coil of longer (to
open) or shorter (to close) duration. As a result, the pilot moves up or down
causing the diaphragm to follow its movement and achieve the proper amount
of flow.
When the delivery is complete, the coil is de-energized, allowing the pilot to
return to its closed position. This allows pressure to build on the back side of the
diaphragm, forcing it to close and seal the outlet port thereby stopping flow.
5.4.

METER

The meter is, in effect, a three-cylinder motor, using cylinders 'B' and 'C' and chamber 'D'
as the three cylinders
valve are located 120° apart, and the port openings in the valve seat are at 120°, there is no
dead-center position in the meter. The operation of filling is continuous, in that before one
chamber is fully filled, the next one is in the process of starting to fill. The same procedure
applies to the discharging operation. The filling and discharging operations each occupy
180° of rotation. Measurement of flow is determined by the fact that the displacement of
each cylinder, together with the displacement from chamber 'D', represents a known quan-
tity, and the flow has a direct and substantially constant relationship to the rotation of the
output shaft.
By connecting the output shaft to the pulser assembly, the rotary movement of the meter
can be converted into pulses, which can in turn be counted by the computer. Calibration is
made possible by the incorporation of an adjusting knob on the top of the unit. Movement
of this knob causes the throw of the crank arm on the output shaft to be varied, so that the
speed at which the shaft rotates can be accurately adjusted to the known output of the meter.
38
Part No. 920160 Rev A
see Figure 5-6. . Because the filling and discharging ports in the
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February 1997