Woodward 3171A, Руководство по эксплуатации продукта, Страница: 31 / 47

Manual 26731 EM35MR1/3171A Gas Valve
Woodward 21
Determining the Demand Required to Achieve
Specific Flows
To determine demand values necessary to achieve a specific flow at end or
intermediate points once the valve size is set, is very similar to the process used
for sizing the valve. First, determine the necessary valve effective area for the
flow point. Interpolate between pressure ratios and demand columns to
determine at what percent/mA/valve angle the flow will be achieved.
Notes on the Valve Sizing and Application Program
The algorithm used for sizing and demand value determination used in the
standard valve application programs available for the 3171A is basically the
same as that described above. However, the program makes use of a valve inlet
pressure compensation algorithm that enhances the accuracy of the calculation.
This compensation scheme is not easily implemented in a manual system as
described here. Therefore, the demand values determined using the methods
described here will be slightly different from those determined using the
application programs. Since this difference is small, the use of the application
program is not absolutely necessary for the sizing/application of standard valves.