Worksheet GL-b
by M. Fraganza and M. Miccio based on the Examination test of February 1, 2002
rev. 2 of April 3, 2019

Objectives

• Choose the most appropriate valve for DN and intrinsic characteristic from the table of C_vn and the plot of intrinsic characteristics
• Calculate and check cavitation at nominal conditions
• Calculate valve autority
• Calculate a preferred working point of the installed characteristic

go to data input section

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Data given by the manufacturer:

Data input for valve sizing :

Select the fluid type from the drop-down list:

upstream pressure P₁ :

downstream pressure P₂ :

vapor pressure of the liquid P_v :

mass flow rate:

Choice of valve size and its intrinsic characteristic :

Valve nominal flow coefficient (C_vn) from the given manufacturer's Table:

Valve rangeability r:

Calculating C_v at 70% stroke and comparing it to the "required" C_v :

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Estimation of C_vmin :

Calculation and plot of cavitation data (efflux characteristic curve) :

OTHER DATA:

from

"ISA Annex D"

see Magnani, Ferretti e Rocco

The relevant data points are calculated in nominal conditions, i.e., in relation to C_vn :

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We can create an asymptotic graphic representation:

Data input for the installed characteristic :

Valve authority calculation:

Flow rate calculation at nominal condition:

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Flow rate and Pressure drop calculation at a given stroke value :

relative stroke ( h ) at which flow rate is to be calculated:

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