General Control Valve Study

Engineering Centre of Excellence
ECoE - Doha, Qatar
Instrument training – 16th July 2011
General Control valves.
Prepared by: Gavhane D.V.

2
General Control Valves.
BY:-DNYANESHWAR GAVHANE

3
INTRODUCTION :-
Control valves also called final control element are a most
important element in the control system of a process plant.
It is the last device in control loop.
DEFINITION :-
A control valve is a variable orifice used to regulate the flow
of a process fluid in accordance with requirement of process.
FUNCTION :-
It absorbs the proper amount of pressure drop to maintain
system balance under all operating conditions.

4
Features of Control valves.
THERE ARE FOUR FEATURES OF CONTROL VALVES :
Capacity
Rangeability
Characteristics
Pressure drop
CAPACITY : The capacity is normally measured as Cv
(Flow Coefficient) which is defined as :
“The number of US gallons per minute of water at 60oF that
will flow through a valves with 1psi pressure drop .
RANGEABILITY : Rangeability of a Control Valve is the
ratio of the maximum to the minimum controllable flow.

5
Control valves and Flow Characteristics.
The relationship between control valve capacity and valve stem
travel is known as the Flow Characteristic of the control valve.
The Curve shown are based on constant Pressure drop across
the valve and called Inherent flow characteristics.

6
Linear Characteristics.
Flow Capacity increases linearly with valve (stem) travel. In
which the valve differential pressure drop is Constant over the
travel range.
Linear valve plug shall for liquid level control and control
application requiring constant gain.
LINEAR VALVE TRAVEL IS DIRECTLY PROPORTIONAL TO
THE VALVE STROKE
FOR SLOW
FLUID
TRANSFER
PROCESS
MORE THAN
40%
OF SYTEM
PRESSURE
DROP
ACROSS
VALVE

7
Equal Percentage Characteristics.
Flow Capacity increases exponentially with valve trim travel .Equal
increment of valve travel produce equal percentage change in
existing Cv.
Equal Percentage valve plug shall be used where only small
percentage of system drop is available in Control valve.
EQUAL INCREMENT OF VALVE TRAVEL PRODUCE AN
EQUAL PERCENT FLOW CHANGE
FOR FAST FLIUD
TRANSFER
PROCESS
HIGH
RANGEABILITY

8
Quick Opening Characteristics.
Provides large changes in flow for very small changes in lift or in
which a maximum Cv is achieved with minimal closure member travel.
It has too high valve gain.
LARGE INCREASE IN FLOW WITH A SMALL CHANGE IN VALVE
STROKE
Quick opening valve are usually specified for “ON-OFF” Service such
as sequential operation in either batch or semi continuous process
and in self actuated control valve .
When maximum valve capacity must be obtain quickly.
Cage- A part of a valve that surrounds the
closure member & can provide Quick
opening flow characterization.

9
Cavitation.
Cavitation is condition that occurs in liquid flow where the internal
pressure of liquid at set point falls below vapour pressure and vapour
bubbles form and at downstream rises above vapour pressure again.
As this pressure recovers so that bubbles collapse and cavitation take
place.
It is possible to predict where cavitation will occur by looking pressure
condition and valve recovery factor.( sigma Method )
Cavitation sounds like stone passing through the valve.
Bubble form
Bubble collapse
Vena Contracta
P
P
Pv
PRESSURE PROFILE ACROSS
SINGLE SEATED CONTROL
VALVE

10
Effect of Cavitation.
Erosion in rotary plug valve body induced by cavitation

11
Flashing.
Flashing is condition that occurs with liquid flow where the Pressure fails
below it . There are then two phases flowing ( i.e. Liquid and vapour )
down stream.
Several damage can occur inside a valve due to erosion caused by the
impact of liquid droplet traveling at high speed.
Bubble form
Vena Contracta
Bubble continue
down stream
P1
Pv
P2
VALVE

12
Effect of Flashing.
Typical trim erosion damage due to flashing

13
Velocity Profile across Single seated Valve.
P1
P2
V 1(Liquid)
V 2
(Liquid)
VALVE
Pressure Recovery:- At vena contracta,the velocity is greatest & substantially
decrease in pressure .Further down stream, as the fluid stream expands into
a large area, Velocity decreases and pressure increases. This phenomena is
called Pressure recovery.
As a general ,globe valves have Lower pressure recovery than Ball and
Butterfly Valves.
Pv

14
Piping Influence/Reynolds Number/Choked Flow.
Piping Influenence:- Capacity reduction due to the presence of Reducer Up &
Down stream of the valve. Correction factor will be available from
manufacturer .
Reynolds Number :- For Reynolds number application such as viscous or
small flow , the basic sizing equation can not be used without
correction, since the equation is based on turbulence flow . Correction factor
will be available from manufacturer .(The ratio of dynamic forces to viscous
forces)
Usually the correction can be ignored when Reynolds number is greater than
4000,the correction will be 10% or less .
Choked Flow:- When the pressure at vena contracta drop below the vapor
pressure of the liquids, bubbles will form in the stream .The formation of
bubbles causes a crowding condition at vena contracta which tends to restrict
flow, and further increase in pressure drop will not produce increase in flow.
In case of gas , choked flow means outlet velocity reaches sonic velocity.
The limiting Pressure difference ΔPt is called Maximum allowable differential
pressure for sizing.

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Contents of Control Valve:– Data Sheet
PROJECT:- GPS DOC NO:- -
CONTRACT NO:-
SUB CONTRACTOR
DOC NO:-
SHEET NO:- 1 OF 1
DOCUMENT
NAME:-
SPECIFICATION AND DATASHEETS
FOR CONTROL VALVES
CLIENT DOC NO:-
DATE:-
REV NO:-
DATASHEET - CONTROL VALVES
1
GENERAL
DATA
TAG
2 SERVICE BLANKET FUEL GAS FROM OIL STORAGE TANK 0-T-3603
3 LINE NO. / PID NO. 0-14"-FG-43 0017-AA3-H(E) / S2-01-YS207019-PID-P-5004 Sht 1 of 2
4 FLUID TANK VENT/FUEL GAS CRITICAL PRESS. Pc
5
SERVICE
CONDITION
UNIT MAX FLOW NORM FLOW MIN FLOW SHUT-OFF
6 FLOW RATE m3/h 5166 1847 525.3 -
7 INLET PRESSURE psi(g) 0.0568 0.093 0.0975 15 bar(g)
8 OUTLET PRESSURE psi(g) 0.037 0.0087 0.00234
9 INLET TEMPERATURE Degree C 50 50 50 100(Note 1)
10 SPEC WT/DENSITY/ MOL WT
- /kg/m3 /
kg/kmole
/-/1.378/40.30 /-/1.378 /40.30 /-/ 1.381/40.30 -
11 VISCOSITY /SPEC HEAT RATIO Cp / 0.00924/1.133 0.00924/1.133 0.00924/1.133 -
12 VAPOR PRESSURE inH2O NA NA NA -
13 REQUIRED CV -
14 TRAVEL % 0
15 ALLOWABLE /PREDICTED SPL dBA < 85/ < 85/ < 85/ -
16 SET POINT inH2O(g) 2.75 2.75 2.75

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Contents of Control Valve:– Data Sheet.
17
LINE
PIPE LINE SIZE &
SCHEDULE
IN 14" & SCH20 56
ACTUATOR
(PNEUMATIC)
TYPE
SINGLE-ACTING FAIL SAFE
SPRING RETURN –DIAPHRAGM
TYPE
18 OUT 14" & SCH20 57 MFR & MODEL VTS
19 PIPE LINE INSULATION
HEAT CONSERVATION
(ELECTRICAL TRACING)
58 SIZE / EFF.AREA VTS
20
SPEC.&
CODES
VALVE SIZING ISA S75.01 59 ON/OFF MODULATING YES
21
VALVE SEAT LEAKAGE
CLASS
IV AS PER FCI 70-2 60 SPRING ACTION ON FAIL CLOSE
22 61
MAX ALLOWABLE
PRESS.
VTS
23 62 MIN REQUIRED PRESS. VTS
24 63 AVAILABLE AIR SUPPLY
PRESSURE kPag
MIN NOR MAX DESIGN
25
VALVE
BODY
TYPE BUTTERFLY 64 400 850 900 1000
26 SIZE VTS 65 BENCH RANGE VTS
27 MAX PRESS./TEMP. VTS 66
ACTUATOR
ORIENTATION
VTS
28 BODY/BONNET MATERIAL A105 or A216 WCB 67 HANDWHEEL TYPE YES VTS
29 LINER MATERIAL / ID 68
AIR FAILURE LOCK
RELAY
REQD. SET AT Note 5
30 69 AIR BOTTLE REQD. WITH ACCESSORIES
31 END CONNECTION IN/ OUT FLANGED 70 FIRE SAFE YES
32 RATING & FLANGE FACE FINI. 150# RF ASME B16.5 71
POSITIONER
INPUT SIGNAL 4-20 mA
33 END EXTENSION/MATERIAL ASTM A105 carbon steel 72 TYPE ELECTRO-PNEUMATIC (HART)
34 FLOW DIRECTION YES 73
EXPLOSION
PROTECTION
EExd
35 TYPE OF BONNET BOLTED 74
ON INCR SIGNAL
OUTPUT INCR/DECR
FIELD REVERSIBLE
36 LUB & ISO VALVE / LUBE 75 GAUGES Yes BYPASS Yes
37 PACKING MATERIAL PTFE 76 CAM CHARACTERISTIC
38 PACKING TYPE VTS 77 MFR & MODEL VTS
39 BONNET GASKET VTS 78
SWITC
HES
TYPE - QTY -
40 MFR & MODEL VTS 79 MFR & MODEL -

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Contents of Control Valve:– Data Sheet .
41
TRIM
TYPE VTS 80 CONTACTS/RATING -
42 SIZE RATED TRAVEL VTS VTS 81 ACTUATION POINTS -
43 CHARACTERISTIC VTS 82
44 BALANCED/UNBALANCED VTS 83
AIR
FILTER
MATERIAL DIE CAST ALUMINIUM
45 RATED CV VTS FL VTS XT VTS 84 FILTER SIZE < or = 25 Micron
46 PLUG/BALL/DISC MATERIAL F6 85 SET PRESSURE
47
SEAT MATERIAL
F6 SEAT HARD FACED WITH
STELLITE6.
86
INTEGRAL PRESS.
GAUGE
50mm DIAL
48 CAGE/GUIDE MATERIAL VTS 87 CONNECTION 1/2"NPT
49 STEM MATERIAL F6 88 MFR & MODEL VTS
50 89
51
SPECIALS
/
ACCESSORIES
NEC CLASS GR. DIV. 90
TESTS
HYDRO PRESS. YES
52 IEC ZONE GR. TEMP. CLASS CLASS I, ZONE 2 , GROUP IIA & T3 91 SEAT LEAKAGE TEST YES
53 92 CAPACITY TEST YES
54 93
55 94
NOTES : VTS-Vendor To Specify

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Globe Control Valve Construction. .

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General Control Valve Classification.
CONTROL VALVE
LINEAR
MOTION
ROTARY
MOTION
Diaphragm valve
Gate valve
GLOBE VALVE
Globe
Angle
Three way
Eccentric plug
Butterfly
Ball

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General Types of Control Valve.
CONTROL VALVE TYPES
VALVE TYPES BASED ON PLUG CONSTRUCTION ARE
GLOBE VALVE BALL VALVE BUTTERFLY VALVE
Control:- Linear & equal %
Use:- Throttling Service,
Flow Regulation, Frequent
Operation
Application:- Liquid, Vapour,
Gases, Corrosive Substances
Slurries.
Advantage: Efficient throttling
Available in multiple ports.
Accurate Flow control.
Disadvantage: High pressure
Drop, more expensive.
Control:- Quick opening
And linear.
Uses:- Fully open / closed
limited-throttling
Application:- Most liquids
High temperature, slurries
Advantage:- High capacity
Low leakage and Maint.
Tight sealing with low torque
Disadvantage:- poor
Throttling characteristics
Prone to Cavitation
Control:- Linear & equal %
Uses:- Fully open / closed or
Throttling services, Frequent
Operation, Minimal fluid
Trapping in line.
Application:-Liquids, gases,
Slurries, Liquids with
suspended Solids.
Advantage :- High Capacity
Good flow control, Low Press.
Drop, Low cost and Maint.
Disadvantage:- High torque
Required for control
Prone to cavitation at lower
Flows.
ECENTRIC PLUG / CAMFLEX DIAPHRAGM KNIFE GATE

21
Eccentric Plug / Camflex Valve Construction.
Side view of an eccentric plug valve
Shown in partially open…..

Eccentric Disk/Ball/Knife Valve Construction
22
V-Notch Ball Valve Knife Gate Valve
Eccentric Disk Valve

Butterfly/Angle/Three Way Valve Construction
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General Control Valves. Prepared by: Gavhane D.V.

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Diaphrgm Type Valve Construction.
Seal over a seat ( Straight type)
Weir type ( Saddle type)

25
General Types of Actuators .
Actuator is the part of the valve that responds to the applied signal and
causes modification of the fluid flow through stem & plug.
TYPES OF ACTUATORS:
1) Diaphragm Actuator
Direct Acting
Reverse Acting
Size depends on output thrust required and supply air pressure
available.
2) Piston Actuator
Use of high pressure air to 150 psig., eliminating the need of pressure
regulator.
Used where High & Fast Stroking Speed is required.
3) Electro hydraulic Actuator:
Electro-hydraulic Actuator is single unit contains Hydraulic Pump
and Reservoir & Electric Motor.
Ideal for isolated locations
4) Manual Actuator
Used where no auto control is required

26
Direct – Acting Actuators .

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Actuators Fail-Safe Requirements.
Fail Safe is the action of the actuator by which the valve CLOSES (FC)
or OPENS (FO) fully in case of air supply failure.

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General Types of Bonnet & Accessories .
Bonnet -
Bonnet is a part of the valve body assembly through which the valve
plug stem or rotary shaft moves.
Types Of Bonnets
Plain or Std Bonnet :-Operating Temp below 2000 c.
Finned Bonnet :- Operating Temp above 2000 c or Equal.
Extension Bonnet :- Operating Temp below 00 c or Equal.
Extension Bonnet :- Operating Temp above 4500 c.
Bellow Seal Bonnet :- where no stem leakage is tolerated For Toxic,
Expensive Fluids.
•Positioners
•Limit Switches
•Solenoid Valves
•Position Transmitters
•Volume Boosters
General Control Valve - Accessories

29
General Construction of Bonnet .
Forged –Valve
Bonnet
Finned
Bonnet
Bellow Seal
Bonnet ( Enviro Seal)
Std./ plain
Bonnet
Extension
Bonnet

30
Control valves Characteristics.
PROCESS APPLICATION INHERANT
CHARACTERISTICS
PRESSURE LIQUIDS
GAS (LOW FLOWS )
GAS (LARGE FLOWS)
ΔPmax/Δpmin < 5
ΔPmax/Δpmin > 5
EQUAL %
EQUAL %
LINEAR
EQUAL %
Temperature Liquids & Gases EQUAL %
Flow Load Changes
Set point change
EQUAL %
LINEAR
Level ΔPmax/Δpmin < 5
ΔPmax/Δpmin > 5
LINEAR
EQUAL %

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Control valves :- Interface
PROCESS INTERFACE
Process to provide process data to Instrument for specifying the
valve
Instrument to provide slected valve size to Process for
incorporating in P&IDs
Instrument to provide instrument air consumption figures for the
valves to Process to decide air line & header sizes.
PIPING INTERFACE
Instrument to provide Face to Face Dimensions, End Connection
Size & Rating, Actuator Height & Orientation, Envelope
Dimensions (for 3-D Model), Weight, etc.
Piping to provide location of control valves to Instrument for
deciding instrument air manifolds.
Piping to provide Pipe Material Specification to Instrument for
specifying the valves.

32
Control valves Body Material.
Frequently Used Valve Body Cast Materials Are:
CARBON STEEL (ASTM A216 GR WCC) up to 4270 C
CHROME MOLY STEEL (ASTM A217 GR WC9) up to 5930 C
CARBON MOLY STEEL (ASTM A217 GR C5) up to 5930 C
304L STAINLESS STEEL (ASTM A351 GR CF3) up to 8160 C
316 STAINLESS STEEL (ASTM A351 GR CF8M) up to 8160 C
CAST IRON (ASTM A126) up to 2320 C
Special Materials Used Depending On The Process Requirements
HASTEALLOY B
HASTEALLOY C
MONEL ALLOY

33
Control valves Trim Material.
Frequently Used Valve Trim Materials Are:
• 302 SS : ASTM A 276 TYPE 302
• 304 SS : ASTM A 276 TYPE 304
• 316 SS : ASTM A 276 TYPE 316
• 316 L SS : ASTM A 276 TYPE 316L
• 410 SS : ASTM A 276 TYPE 410
• 17-4 pH SS : ASTM A 461 GR 630
[High Tensile Strength, High Yield point, Hardened Material]
• HASTEALLOY ``B’’ : ASTM A 335
• HASTEALLOY ``C’’ : ASTM A 336

34
Control valves Codes and Standards.
ANSI B 16.34 :
• Covers Pressure, Temperature rating, Dimensions, Materials, NDT
Requirements
ANSI B 16.5 :
• Covers design of flanges and flanged fittings
MSS SP 67 :
• Covers design and test performance requirements of Butterfly valves and
divides in to three leak classes.
ANSI B 16.10:
• Face to Face dimensions
ANSI B 16.37:
Hydrostatic testing
LEAKAGE RATES AS PER ANSI/FCI 70-2
Formerly (ANSI B 16.104) for seat leak classes and testing procedures
- FCI

35
Vendor Design Documents- Sizing & Selection
Step # 1:- Define the system
Example :- The system is pumping water from one tank to another through a
piping system total pressure drop is 150psi.The fluid is water at 700F.Design
(maximum) flow of 150 gpm,operating flow rate of 110 gpm,and minimum flow rate
of 25gpm. Pipe diameter is 3 inches. At 700F, water has has a specific gravity of1.0
Key Variables:- Total pressure drop , design flow ,operating flow, minimum flow
diameter, specific gravity.
Step # 2:- Define Max. Allowable Pressure Drop For The Valve
When defining the allowable pressure drop across the valve, you should first
investigate the pump.What is its maximum available head? Remember that the
system pressure drop is limited by the pump. Essentially the Net Positive Suction
Head Available (NPSHA) minus the Net Positive Suction Head Required (NPSHR)
is the maximum available pressure drop for the valve to use and this must not be
exceeded or another pump will be needed. The usual rule of thumb is that a valve
should be designed to use 10-15% of the total pressure drop or 10 psi, whichever
is greater.
For above example step#1 system, 10% of the total pressure drop is 15 psi which
is what we'll use as our allowable pressure drop when the valve is wide open (the
pump is our system is easily capable of the additional pressure drop).

36
STEP #3: Calculate the valve characteristic

37
Step#4:-Preliminary Valve Selection
The Cv value should be used as a guide in the valve selection, not a hard
and fast rule. Some other considerations are:
a. Never use a valve that is less than half the pipe size
b. Avoid using the lower 10% and upper 20% of the valve stroke. The
valve is much easier to control in the 10-80% stroke range.
Before a valve can be selected, we have to decide what type of valve will
be used . For our case, we'll assume we're using an equal percentage,
globe valve . The valve chart for this type of valve is shown below. This
is a typical chart that will be supplied by the manufacturer.
For our case, it appears the 2 inch valve will work well for our Cv value at
about 80-85% of the stroke range. Notice that we're not trying to squeeze
our Cv into the 1 1/2 valve which would need to be at 100% stroke to
handle our maximum flow.

38
Typical Chart Supplied by Manufacturer.

39
Step# 5:-Check Cv & Stroke % at Min. Flow
If the stroke percentage falls below 10% at our minimum flow, a smaller
valve may have to be used in some cases.
Judgments plays role in many cases. For example, is your system more
likely to operate closer to the maximum flowrates more often than the
minimum flowrates?
Or is it more likely to operate near the minimum flow rate for extended
periods of time. It's difficult to find the perfect valve, but you should find
one that operates well most of the time. Let's check the valve we've
selected for our system:

40
Step#6:Check Gain across Applicable Flow Rates
• Gain is defined as:
•
• Now, at our three flowrates:
Qmin = 25 gpm
Qop = 110 gpm
Qdes = 150 gpm
we have corresponding Cv values of 6.5, 28, and 39. The corresponding
stroke percentages are 35%, 73%, and 85% respectively. Now we construct
the following table:
Flow (gpm) Stroke (%) Change in (gpm) Change in Stroke (%)
25 35 110-25=85 73-35=38
110 73
150 85 150-110=40 85-73=12
Gain #1 = 85/38 = 2.2
Gain #2 = 40/12 = 3.3

41
General Control valve Gain.
The difference between these values should be less than 50% of the
higher value.
0.5 (3.3) = 1.65
and 3.3 - 1.65 = 1.65. Since 2.2 is closer than 50%, there should be
problem with controlling the valve. Also note that the gain should never
be less than 0.50.
Turndown :- It is ratio of the calculated Cv at maximum condition to the
calculated Cv minimum.
Rangeability :- It is ratio of Cv of the valve fully open to the minimum Cv
at which it can control.
The rangebility of the selected valve must exceed the turndown
requirements of the application.

42
Any Question ?

General Control Valve Study

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