Worksheet GL-c3

by M. Fraganza and M. Miccio based on the Examination test of February 7, 2008
rev. 2.0 of 17.04.2019

Objectives

• Sizing the valve as a function of authority: the value chosen for the authority automatically determines the inherent characteristic of the valve.
• Plotting the installed characteristic from the values of measurement rangeability and authority.

go to

data input

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Data given by the manufacturer:

Data input for valve sizing:

Select the liquid type

from the drop-down list:

upstream pressure P₁

downstream pressure P₂

vapor pressure P_v

mass flow rate

Choice of valve size and its intrinsic characteristic:

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

Valve rangeability r:

Valve authority V:

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

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YES / NO check for cavitation (IEC norm)

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Data input for the installed characteristic:

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Flow rate calculation at nominal condition:

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

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NOTE: A realistic combination of r and V values

which is independent of the previous choice of the intrinsic characteristic

that makes the installed characteristic curve as close as possible to a straight line

is:

r = 100; V = 0.9

The best theoretical combination of r and V values is:

r ---> ∞ (the characteristic is bisector of the 1st quadrant)

V = 1 ("absence of user's equipment")

Calculation of the Valve pressure drop at nominal condition ( ΔP_n ) for a given authority

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