IEC 60534-2-1:2011 pdf – lndustrial-process control valves – Part 2-1: Fiow capacity – Sizing equations for fluid flow under installed conditions.
8.1 General
This annex presents equations for predicting the flow of a compressible fluid through multistage control valves. The basic flow equations are identical to the equations presented in the main body of this document with the exception of the following differences:
a) the equation for the calculation of expansion factor V(Equation B.3);
b) the Inclusion of stage interaction factor k and reheat factor ,
C) the addition of tables for multistage valves for values of FL and x,(Table D.2)
This technology is applicable to designs of multistage multipath control valves, multistage single path control valves and continuous resistance trim control valves. Refer to Clause 8.3 for definitions and descriptions of each control valve type.
The test data used to validate the method for multistage single and multipath with one to five stages were obtained from sizing tests carried out in accordance with IEC 60534.2.3 using air as the test medium at pressures varying from 5 x i0 Pa to 13.5 X i0 Pa and at temperatures of approximately 300 K. Some data were obtained under plant conditions using steam at pressures varying from 12 x 10 Pa to 110 x 1O Pa and temperatures from 460 K to 750 K. The method is applicable to any number of stages but has only been validated up to five stages.
The test data used to validate the method for continuous resistance trim with 4 to 30 turns was obtained from sizing tests carried out in accordance with IEC 60534-2-3 using air as the test medium at pressures varying from 5 x io Pa and temperatures of approximately 300 K. Some data was obtained under plant conditions using steam at pressures varying from 24 x iO Pa and temperatures from 500 K to 720 K. This method may be used for any number of turns, but has only been validated up to 30.
If valve specific coefficients (such as ìç or C, FL. and Xy) cannot be determined by appropriate test procedures in IEC 60534-2-3. values supplied by the manufacturer should then be used.
The conventional single stage equations presented in the main body of this document may be used for multistage valves when:
a) the valve designs fall outside the scope of the configurations presented herein. aridlor.
b) the single stage equations can be shown to be applicable to the design configuration under consideration.
B.3 Terms and definitions
For the purposes of this annex, the terms and definitions given in lEC 60534-1, those given inthis standard as well as the following. apply.
B.3.1 Multistage control valves
Globe control valve where the trim has several stages which are separated by a gap(see Figures B.1 and B.2).The geometrical contour of the apertures in all stages should be similar. The ratio ofthe second stage flow coefficient C to the first stage flow coefficient C should not exceed 1,80.The ratio of the flow coefficient C of the other stages to their previous stage should not exceed1,55 and should be uniform within a tolerance of ±9 %.Normally, for incompressible fluids theflow coefficients of the stages are approximately equal, a slightly smaller flow coefficient C beingallocated to a particular stage only if it is required to take a higher pressure drop.
B.3.2 Gap
Distance between adjacent stages
B.3.3Multistage multipath control valves
Globe control valve where the trim has multiple flow passages having several stages which areseparated by a gap (see Figure B.1).To ensure the validity of the prediction equations of thisannex，the gap should conform to the values calculated from the following equation with atolerance of+15 % and -10 %(see Figures B.1 and B.2).