38
Part No. 920160 Rev A
February 1997
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
(
see Figure 5-6.
)
. Because the filling and discharging ports in the
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.
Summary of Contents for Dresser Vista 1 Series
Page 1: ...1 Vista Series Blending and Non Blending Remote Dispensers SERVICE ...
Page 4: ...Part No 920160 Rev A February 1997 ...
Page 10: ...viii Part No 920160 Rev A February 1997 ...
Page 12: ...2 Part No 920160 Rev A February 1997 ...
Page 22: ...12 Part No 920160 Rev A February 1997 ...
Page 38: ...28 Part No 920160 Rev A February 1997 ...
Page 62: ...52 Part No 920160 Rev A February 1997 ...
Page 76: ...66 Part No 920160 Rev A February 1997 FIGURE 7 8 NOZZLE BOOT ASSEMBLY LIFT TO START ...
Page 77: ...67 February 1997 Part No 920160 Rev A FIGURE 7 9 NOZZLE BOOT ASSEMBLY PUSH TO START ...
Page 83: ...73 February 1997 Part No 920160 Rev A APPENDIX A TROUBLESHOOTING FLOWCHARTS ...
Page 110: ...100 Part No 920160 Rev A February 1997 ...
Page 111: ...101 February 1997 Part No 920160 Rev A APPENDIX B SERVICE INFORMATION AND CONNECTOR PIN OUTS ...
Page 134: ...124 Part No 920160 Rev A February 1997 ...
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