Two Stage Valve - Bennett 3000 Series Service Manual

210 Retail Electronics - Two Stage Valve
Two Stage Valve Control - The two stage valves that the 3000 series dispenser uses are +24 Volt dc
valves (except for the 120 or 230 volt valves that are used in the Satellite unit of a Master / Satellite
system). These valves are used to control the flow of fuel to the hose. In retail, where the fuel always
has a price displayed, you need valves to keep people on other dispensers from getting fuel from an
unauthorized hose when the submerged pump is "on" for that product. If valves were not present then a
customer on another pump could pump fuel from the same product hose as the one you are using
because that product submerged pump has that product line pressurized.
Also, the other use of the two stage valve is in a preset or prepay application to slow the flow of fuel at
the end of the transaction. As an example, on a pre-pay sale (where the sale amount is collected before
fueling), the pump is "preset" by the P.O.S. In this example we will say that the customer preset the
pump for $5.00. When the customer pumps fuel it is in fast flow all the way up to the slow flow offset
that is programmed in the pump. Let's say that that was set to .2 gallons. So, at about two tenths of a
gallon until the end of the sale the pump goes into slow flow and at $5.00 the valve closes all the way
and the pump stops.
So, a retail dispenser may have only one or up to four 2 stage valves. There is one valve per meter and
the valve is mounted on the outlet of the meter.
The upper portion of the valve is where the two coils
are located along with the two plungers. The wires
that control the coils are:
Black - Fast Flow coil/plunger
Yellow– Dribble/Slow flow coil plunger
Red - +24 Volts dc
+24 Volts dc is always present on the Red wire
(unless this is a 120 or 230 volt AC valve which can
be found in the Satellite unit of a Master / Satellite
system). The coils are not energized until the system
provides a "ground" for those coils. When the CPU
wants to open either the fast or slow flow it turns on
a Field Effect Transistor (FET) to provide a ground
for that coil. Lets look at an example:
Example: With the valve turned "off" both "coils" are
de-energized because their legs are not grounded. In
the de-energized state the spring in the fast flow
valve pushes against the flanged sleeve and both
the fast and slow are dropped down closing off any
flow.
At the beginning of a sale, the CPU will allow only
slow flow until 9 pulses are received from both
phases of the pulser. It does this by grounding the
slow flow coil (energizing it raising the plunger) by
turning "on" a field effect transistor (FET). This allows
a small amount of fluid to travel through the small
orifice in the diaphragm, up along the grooves on the
outside of the high flow valve, and then down
through the little hole in the center of the high flow
valve. This is slow flow.
Fig 1 - 2 stage valve operation
Fig. 2 - The 2 stage valve is installed between the
meter outlet and the hose outlet.
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107933 Rev E 03/01/11