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CONTROL VALVE SIZING


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Catégorie :Category: mViewer GX Creator App HP-Prime
Auteur Author: dodopace
Type : Application
Page(s) : 20
Taille Size: 2.28 Mo MB
Mis en ligne Uploaded: 15/09/2021 - 18:57:26
Uploadeur Uploader: dodopace (Profil)
Téléchargements Downloads: 1
Visibilité Visibility: Archive publique
Shortlink : http://ti-pla.net/a2792449

Description 

UNIVERSITÀ DEGLI STUDI DI SALERNO



Bachelor Degree in Chemical Engineering


Course:
Process Instrumentation and Control
(Strumentazione e Controllo dei Processi Chimici)



CONTROL VALVE SIZING:
SIMPLIFIED PROCEDURES FOR LIQUIDS


Rev. 4.5 of April 13, 2021
THE CONTROL VALVE SIZING PROBLEM
Choices and calculations to do:

• Valve type (globe, butterfly, modulating ball, etc.)
• Capacity (based on the concept of CV introduced in the
40’s)
• Valve DN
• Inherent characteristic, if possible
• Construction material (depending upon temperature,
pressure, corrosive and erosive properties of the fluid)
• Body shape, plug and bonnet
• Type and size of the actuator, servo-positioning device
• Safety items (e.g., action type in case of failure),
reliability, maintenance
• Noise evaluation
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 2
SIMPLIFIED CONTROL VALVE SIZING
Design case
KNOWN DATA:
• NOMINAL PIPE SIZE (NPS, DN) OF THE PIPING
• FLUID (LIQUID IN OUR CASE)
• INLET TEMPERATURE T1
• NOMINAL ΔP = (P1 - P2)
• FLOW
 mass flow rate OR volume flow rate
 design at nominal / max / min flow rate
• MANUFACTURER TABLE


1. TO BE CHOSEN:
• VALVE TYPE (GLOBE / BALL / BUTTERFLY), if possible
Taking
• TYPE OF INHERENT CHARACTERISTIC, if possible
suitable data
2. TO BE DETERMINED:
from the
• DN of the VALVE
“MANUFACTURER TABLE”
• Cvn of the VALVE
3. TO BE CHECKED:
• CAVITATION (calculation of ΔPc or ΔPMAX)


15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 3
VALVE MANUFACTURER TABLE
first examples

An angle globe valve A linear globe valve (kb1498)




Cvn Cvn Cvn

When FL is not present in MANUFACTURER TABLE:
 AnnexD_ISA_7501-1985
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 4
VALVE SIZING PROBLEM
2 different design cases

1. the valve is a stand-alone unit


2. the valve is inserted in an equipment process scheme




15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 5
DATA: liquid substance: ρ, Gf, Pv, (FF, Pc, Tc)
SIMPLIFIED
Operating Conditions: P1, P2, T1, flow rate SIZING
Piping: NPS PROCEDURE
Valve: Kc, FL, manufacturer table, intrinsic characteristic

according to
A valve is to be chosen with a DN lower than the Magnani, Ferretti
piping diameter NPS by one size (if possible) and Rocco (2007)
Calculate the required •
Flow Coefficient: ???????? = ???? ൘ (???? 1−???? 2)ൗ????????


Once NPS and Cv are known, a valve is to be chosen
from the manufacturer table such as: ???? ∗ = ???? ȁ 70% rule
???? ???? ℎ 0 7 ≥ ????????
= .


Check cavitation according to IEC 60534 norm
Δ???? ????????????= ????????2 (???? 1−???? ???? ???? ????)
A higher FL
valve has to be
False CHOKED FLOW
P  ( P1  P 2 )  P m ax choosen (low
according to pressure
IEC 60534 norm recovery valves)
True
NORMAL FLOW


(possibly)
P  (P1 P 2 )  P c
False

END OF SIZING True
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 6
CONTROL VALVE SIZING
Design case
ROTARY VALVES
The simplified procedure presented in the flow chart is valid for globe valves.
In fact, the rotary valves are not characterized by the relative stroke “h” but
by the opening angle θ.
For rotary valves, the simplified sizing procedure is referred to an angle θ*,
which corresponds the 70% max opening angle (90°):

Strictly θ* = (70/100)90° = 63°

In practice θ* = 65° or 70°


Remarks
• A rotary valve usually has one and only one inherent characteristic.
• Butterfly valves have often a S-shaped inherent characteristic with an inflection
point (such as V-port).
• Modulating ball valves have often an equal percentage inherent characteristic.

15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 7
CONTROL VALVE SIZING
Design case
The MANUFACTURER TABLE: several cases are possible

a) For each NPS, the MANUFACTURER TABLE reports Cvn as well as Cv
values for different values of h (θ)

 Inherent characteristic known “point by point” in a tabular shape


b) The MANUFACTURER TABLE only shows the value of Cvn for each NPS,
furthermore, the manufacturer gives a diagram of ϕ or Cv as a function of h (θ)

 For the inherent characteristic use the manufacturer’s diagram


c) The MANUFACTURER TABLE only shows the Cvn value for each NPS

 Use formulas for the inherent characteristic


15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 8
SIMPLIFIED CONTROL VALVE SIZING
Verify case

KNOWN DATA:
• VALVE TYPE
• NOMINAL PIPE SIZE (NPS, DN) OF THE VALVE
• NOMINAL FLOW COEFFICIENT Cvn
• INHERENT CHARACTERISTIC
• FLUID (LIQUID IN OUR CASE)
• TEMPERATURE T1
• NOMINAL ΔP = (P1 - P2)



1. TO BE CALCULATED:
• NOMINAL FLOW RATE (h = 1 OR θ = 90°)
• FLOW RATE at a given value of h OR θ


2. TO BE CHECKED:
CAVITATION (calculation of ΔPc or ΔPMAX)

15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 9
INTRODUCTION TO
INSTALLED CHARACTERISTIC
The circuit is formed by a control valve and a utility, for example a heat exchanger, to which a
pressure drop is attributed. see ch.5
A pump, not indicated, supplies the pressure PM – PS, assumed constant for simplicity.
We can evaluate the role of the pressure drop across the valve comparing it with the total
pressure drop of the circuit:
I. it should be high in order to improve the control of the flowrate;
II. on the other hand, it should be low in order to reduce costs of pump energy.
The aim is to find a good technical compromise solution between these two opposing evidences.



HYPOTHESES: w(h) ➡
• ΔP0 = PM - PS = constant
• Negligible pressure drop along the pipe:
P3
a) PM = P1
b) PS = P3
• The pressure drop at the utility depends on the square of the
velocity and therefore, for incompressible fluid, is a quadratic
function of the mass flowrate w(h): ΔPu= P2(w(h)) – P3 = w2(h) ΔPv = P1 – P2(w(h))
• No accumulation in the circuit
ΔP0 = ΔPv + ΔPu
15/09/2021 Process Instrumentation and Control - Prof. M. Miccio 10
INSTALLED CHARACTERISTIC
DEFINITIONS
w(h) ➡
INSTALLED CHARACTERISTIC:
It is the relationship between the flow rate and the (linear P3
or rotary) valve opening when the valve is inserted in the
circuit and influenced by process condition.

PRESSURE DROP across the valve: Δ????????

NOMINAL (or RATED) PRESSURE DROP ΔPn = ΔPv ȁh = 1 = ΔPv ȁθ = 90°
across the valve :

VALVE AUTHORITY: Δ????????
It is the ratio between the nominal pressure drop (ΔPn) ????=
across the valve and ...

Archive contentsContenu de l'archive

Action(s) SizeTaille FileFichier
3.06 Ko KB readme.txt
3.65 Ko KB lisezmoi.txt
1.09 Ko KB CONTROL_.hpprgm
2.28 Mo MB CONTROL_.hpappdir.zip
95 octets bytes appslist.txt

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