The Blending Process Proportional Blenders; The Blending Process Fixed Ratio Blenders - Wayne Vista Series Service

1.1. THE BLENDING PROCESS PROPORTIONAL BLENDERS (see Figure 1-1)
Proportional blenders have two grades of fuel input to the dispenser. The dispenser can
then use these grades to "produce" as many as five different grades output to the nozzle.
Two of these are the input grades, the other three are a mix of the two input grades.
These intermediate grades are produced by mixing the two input grades at some propor-
tion. The proportion which is used will determine the octane rating of the intermediate
grade.
There are two separate sets of hydraulics inside the proportional blender. One of these
sets is used to control flow of the low octane input (also called the LO feedstock), and the
other is used to control the high octane input (also called the HI feedstock). The heart of
the hydraulics in proportional blending dispensers is the blend valve. The HI and LO
feedstocks are each input to separate chambers in the blend valve; the blend valve is
designed in such a way that the outputs from these chambers can be controlled. By
manipulating the valve the flow from one chamber can be restricted while the flow from
the other is increased, changing the ratio of one product to the other. The hydraulics
continue to be separate until the two products are mixed at the hose outlet.
The computer continually senses the flow rate of each end grade and adjusts the blend
valve in order to maintain the correct blend ratio. If for some reason the correct blend
ratio cannot be obtained the computer will shut the sale down and generate an fault code.
1.2.

THE BLENDING PROCESS FIXED RATIO BLENDERS

Fixed ratio blenders differ from proportional blenders in that only one blended product is
available. This blended product is dispensed from the blended product hose (see Figure
1-2). The feedstocks are dispensed from separate hoses.
Because the blend ratio output from the blend hose cannot be changed from one sale to
the next, the mixing of the end grades can take place immediately after the blend valve.
November 1992 Part No. 917543 Rev. A
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