Fisher Controls

Magnetrol International, Inc. SOR, Inc. Magnetrol International, Inc. SOR, Inc. Fisher Controls. International, Inc. Magnetrol International, Inc. 

George W. Gassman, B.S.M.E., Senior Research Specialist, Final Control Systems, Fisher Controls International, Inc., Marshalltown, Iowa (Section 8, Process Control)... 

Paul J Schafbuch/ Ph D / Senior Re.search Specialist, Final Control Sy.stems, Fisher-Controls International, Inc., Mar.shalltown, lA. (Controllers, Final Contr ol Elements, and Regulators)... 

References 1 and 2 were used extensive for this section. The sizing procedure is generally that of Fisher Controls Company. 

Fisher Controls Company, Sizing and Selection Data,... 

Anderson, G. D., Guidelines for Selection of Liquid Level Control Equipment, Fisher Controls Company. 

Figure 15-6. Typical single-port body control valve (left) and pneumatic actuator (right). Courtesy of Fisher Controls Internationa , Inc.]...

Lasher, R., Editor, Control Valve Handbook, Fisher Controls Co., 1965. 

Figure 10-13 illustrates the flow versus valve stem travel characteristic for various typical valve trim functions (Fisher Controls, 1987). The quick opening characteristic provides the maximum change in flow rate at low opening or stem travel, with a fairly linear relationship. As the valve approaches the wide open position, the change in flow with travel approaches zero. This is best suited for on-off control but is... 

Figure 10-13 Control valve flow characteristics. (From Fisher Controls, 1987.)...

Figure 10-19 Critical pressure ratios for water. The abscissa is the water vapor pressure at the valve inlet. The ordinate is the corresponding critical pressure ratio, rc. (From Fisher Controls, 1987.)...

Values of Km for the Fisher Controls design EB valve are given in the last column of Table 10-3, and representative values for other valves at the full-open condition are given in Table 10-5. 

The notation used here is that of the Fisher Controls literature (e.g., Fisher Controls, 1990). The ANSI/ISAS75.01 standard for control valves (e.g., Baumann, 1991 Flutchison, 1971) uses the same equations, except that it uses the notation F = (A m )1 2 and FP = rc in place of the factors Km and... 

The flow coefficient Cv is determined by calibration with water, and it is not entirely satisfactory for predicting the flow rate of compressible fluids under choked flow conditions. This has to do with the fact that different valves exhibit different pressure recovery characteristics with gases and hence will choke at different pressure ratios, which does not apply to liquids. For this reason, another flow coefficient, Cg, is often used for gases. Cg is determined by calibration with air under critical flow conditions (Fisher Controls, 1977). The corresponding flow equation for gas flow is... 

Equation (10-44), which applies at low pressure drops, and Eq. (10-48), which applies to critical (choked) flow, have been combined into one general universal empirical equation by Fisher Controls (1977), by using a sine function to represent the transition between the limits of these two states ... 

Fisher Controls. Control Valve Handbook. 2nd ed., Marshalltown, IA Fisher Controls, 1977. 

Fisher Controls. Catalog 10. Marshalltown, A Fisher Controls, 1987, Chap 2. 

FIG. 8-66 Post-guided contour plug globe valve with metal seat and raised-face flange end connections. (Courtesy Fisher Controls International LLC.)... 

FIG. 8-69 Segmented ball valve. Partial view of actuator mounting shown 90° out of position. (Courtesy Fisher Controls Interruitbrud LLC.)... 

FIG. 8-70 Eccentric plug valve shown in erosion-resistant reverse flow direction. Shaded components can be made of hard metal or ceramic materials. ( Courtesy Fisher Controls international LLC.)... 

H.C. Jones and D.J. Fisher Controlled-Potential and Derivative Polaro-... 

FIG. 8-68 Partial cutaway of wafer-style lined butterfly valve. Courtesy Fisher Controls Intemationtd LLC.)... 

FIO. 8-71 Spring and diaphragm actuator with an up fail-safe mode. Spring adjuster allows slight alteration of bench set. (Courtesy Fisher Controls Intemor-tlonal LLC.)... 

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