2. IN THIS PRESENTATION
CONTROL VALVES
CONTROL VALVE SIZING
VALVE CONSTRUCTION
TOP GUIDED CONTROL VALVE
CAGE GUIDED VALVES DOUBLE
DOUBLE SEATED CONTROL VALVE
CAGES/TRIM
GLAND PACKING
TURNDOWN RATIO
CAVITATION
BODY/TRIM MATERIAL
SEAT LEAKAGE
CLASSIFICATION
FAIL SAFE DESIGN
NOISE
END PREPARATION
VALVE ACTUATORS
CONTROL VALVE
ACCESSORIES
TESTS
STANDARDS
3. CONTROL VALVES
Control valves are
valves used to control
conditions such as flow,
pressure, temperature,
and liquid level by fully
or partially opening or
closing in response to
signals received from
controllers that compare
a "setpoint" to a "process
variable" whose value is
provided by sensors that
monitor changes in such
conditions.
4. CONTROL VALVE SIZING
The control valve shall be of globe body
design with single port. The valve trim,
shall be suitable for quick removal without
any cutting or welding.
Sizing shall be accordance with ANSI/ISA
75.01,01.
Valve outlet velocity does not excesed 8
m/sec for liquid service and 150 m/sec for
steam services.
5. CONTROL VALVE SIZING
The valve sizing shall be suitable for
obtaining maximum flow conditions with
valve opening at approx 80% of total valve
stem travel and minimum flow conditions
with valve stem travel not less than 10% of
total valve stem travel.
All valves shall capable of handling at least
120% of required maximum flow.
Valve body rating shall meet the pressure
and temperature requirement as per ANSI B
16.34.
6. VALVE CONSTRUCTION
Conform to requirement of ANSI for dimensions,
material thickness and material specification for their
respective pressure class.
All valves shall be globe body design and straightway
pattern with single or double port or angle body
design.
All valves connected to vacuum on down stream side
shall be provided with packing suitable for vacuum
application (e.g double vee type chevon packing).
Extension bonnets shall be provided when the
maximum temperature of flowing fluid is greater than
275 deg c.
If the downstream is subjected to vacuum, flow
direction of the fluid shall be to close.
7. TOP GUIDED CONTROL VALVE
Top-guided, single-ported
valves may be
used for tight shutoff
applications; however,
because these valves
are unbalanced, they can
require more force from
the actuator to achieve
shutoff if the flow is
under the plug.
8. CAGE GUIDED VALVES
Cage-guided valves
have a cylindrical plug
guided through a guide.
The increased guiding
area is desirable for high
pressure drop, high
noise, and anticavitation
applications
Unbalanced types can
provide a tight shutoff if
sufficient
For balanced styles, the
plug is vented and the
process pressure
interacts with the top
and bottom side of the
plug.
9. DOUBLE SEATED CONTROL VALVE
Double-seated control
valves are used to a
lot of industrial
applications due to
advantages of
reduction in actuator
force, a great flow
capacity and a deal of
slurry fluids.
Double-seated valves
cannot provide the
same shutoff capability
as the single-ported
types.
11. GLAND PACKING
PTFE if fluid
temperature is less
than 180 deg C.
Graphite if fluid
temperature is more
than 180 deg C.
All valves connected to
vacuum on down
stream side shall be
provided with packing
suitable for vacuum
application (e.g double
vee type chevon
packing).
GLAND
PACKING
12. TURNDOWN RATIO
The valve-sizing coefficient for globe
valves should be selected to limit
turndown to a ratio of about 30:1.
This limits the valve opening to
approximately 10% of maximum for
globe valves with equal percentage
trim.
13. CAVITATION
Cavitation is a two stage phenomena
with liquid flow.
The first stage is the formation of vapor bubbles in the
liquid as the fluid passes through the trim and the
pressure is reduced below the fluid's vapor pressure.
The second stage is the collapse of the vapor bubbles as
the fluid passes the vena contracta and the pressure
recovers and increases above the vapor pressure.
The collapsing bubbles are very destructive when they
contact metal parts and the bubble collapse may
produce high noise levels.
14. Cavitation
Cavitation in
control valves can
have four negative
effects;
• Restricts fluid flow
• Causes severe vibrations
• Erodes metal surfaces
• Generates high noise
levels.
15. ANTI CAVITY TRIM
The anti cavity trim of
control valve shall be
multi stage ,multi path
type.
ISA- RP75.23 – 1995,
“Considerations for
Evaluating Control Valve
Cavitation”,
Recommended Practice,
June 1995
The High FL Factor
( pressure recovery
factor) shall be 0.98 or
better.
18. CONTROL VALVES WITH ANTI CAVITY TRIM
IN THERMAL POWER PLANTS 500 MW
CEP /BFP Min recirculation valve
Excess dump control
Condenser for SD flash tank
HP/LP heater alternate drain to drain flash
tank.
D M normal/emergency makeup to hotwell.
Low load feed water control valve.
S H/ R H/PRDS/HPBP temperature (spray)
control valve
19. BODY/TRIM MATERIAL
SEVERE FLASHING/CAVITATION
SERVICES
BODY MATERIALS- Alloy steel as per ASTM – A217 GR WC 9
TRIM MATERIAL-- 440 C series SS
LOW FLASHING/CAVITATION SERVICES
BODY MATERIALS--Alloy steel as per ASTM A – 217 GR WC 6
TRIM MATERIAL- 17-4 PH SS
CONDENSATE & DM SERVICES
BODY MATERIALS--316SS for condensate service below 275 deg C
and above 275 deg C – ALLOY STEEL A217 GR WC 6
and 316 SS for DM WATER makeup etc
TRIM MATERIAL -316SS stellited with stellited facedguide
posts and bushings.
20. Boiler startup valve for
supercritical boiler
Once through boilers require a
minimum evaporator flow for cooling
of boiler tubes during startup .
Recirculation of the water from the
separator back to the feedwater tank
the start up is operating
continuously at high differential
pressure while boiler load is below
30%.
21. Severe services control Valves
SEVERE FLASHING/CAVITATION
SERVICES
low load and full load feed water control, HP and LP
heaters emergency drains, Deaerator overflow drain to
Hotwell, CRH flow to Deaerator, Spray control valve (SH,
RH, HPBP), RH block valve etc.
LOW FLASHING/CAVITATION SERVICES
HP heaters & LP heaters normal drain control, drain
cooler normal level control, gland steam cooler minimum
flow etc.
22. CONTROL VALVE SEAT LEAKAGE
CLASSIFICATION (ANSI/FCI 70-2-1991)
S.N LEAKAGE CLASS MAX LEAKAGE
ALLOWABLE
1 I ---
2 II 0.5 % of rated capacity
3 III 0.1 % of rated capacity
4 IV 0.01 % OF RATED
CAPACITY
5 V 0.0005 ml per minute
of water per inch of
orifice per psi
differential
23. LEAKAGE CLASS OF VALVES
Control Valves
with leakage rate
as per leakage
Class-V to
increase cycle
efficiency of plant
and safety of
equipments
Control Valves with
leakage Class-V
1. .SH/RH spray control,
2. . Heavy oil pressuring & control
system,
3. . HP/LP heater emergency level
control,
4. .CEPs/BFP minimum flow
5. .Emergency make up to
condensate,
6. . GSC minimum flow,
7. .Dearator drain to condenser
hotwell,
8. .condensate spill to condensate
reserve tank control
9. . heavy oil heating,
10. . condenser normal make-up
11. . valve gland sealing supplying
pressure control
12. . HFO, LDO shut-off valve,
13. PRDS spray valve
24. FAIL TO SAFE DESIGN
Valve shall close if
signal fails :
SH/RH spray valve
HP/LP HEATERS normal
drains
Valve shall open if
signal fails
CEP/BFP recirculation
valve.
HP/LP HEATERS
emergency drain to flash
tank .
25. NOISE
Control valve induced
noise shall be limited to
85 db at 1 mtr from
valve surface under
actual operating
condition .
The noise abetment shall
be achieved by valve
body and trim design or
by use of silencers.
Noise calculation shall be
as per ISA-75-17-1989.
VALVE with Cage-Style
Noise Abatement
27. END PREPARATION
Valve body ends shall be either butt
welded/socket welded, flanged .
The welded ends wherever required shall be
butt welded type as per ANSI B 16.25 for
control valves of sizes 65 mm and above.
For valves size 50 mm and below welded ends
shall be socket welded as per ANSI B 16.11
Flanged ends wherever required shall be of
ANSI pressure-temperature class equal to or
greater than that of control valve body.
28. VALVE ACTUATORS
The HP and LP Bypass,
turbine inlet control valves
shall be with electro-hydraulic
actuators and all
other control valves shall
be furnished with
pneumatic actuators.
proper selection and
sizing of valve actuators in
accordance with the
pressure drop and
maximum shut off
pressure and leakage class
requirements.
The valve actuators shall
be capable of operating at
60 deg. C continuously.
30. PERFORMANCE OF VALVE
i) linearity :1% of FS .
ii)Hysterisis :1% of FS.
iii)Sensitivity :0.5% of span.
iv)Accuracy : 2% of span.
31. CONTROL VALVE ACCESSORIES
Positioner,
Air filter regulator,
Air lock relay,
Position limit switch,
Position transmitter,
Solenoid valve,
E/P converter,
Junction box,
Hand wheel,
Local position indicator,
Electro pneumatic positioner ,
Volume booster,
Fail freeze type IP Converter etc. as per the
requirements.
32. SMART POSITIONER
smart digital
microprocessor based
valve positioners and
compatibility for
remote calibration &
superimposed HART
signal on input signal
4-20 m Amp &
connected with hart
management system.
34. TESTS
i) Non destructive test - ANSI B-16.34
ii) Hydrostatic shell test - ANSI B 16.34
iii) Valve seat leakage- ANSI- B 16.34.
iv) Functional test: The fully assembled
valves including actuators control
devices and accessories shall be
functionally tested .
v) CV test: CV test - ISA 75.02
35. LIST OF CONTROL VALVES IN 500
MW THERMAL POWER PLANT
1. D/A Pegging from Aux.
Steam Header
2. D/A Pegging from CRH Line
3. Main Condensate Control
4. CEP A/B/C Minimum
Recirculation
5. GSC min. flow recirculation
6. Excess Dump Control
7. Condensate for SD F/T
8. Condensate for Valve Gland
Sealing
9. HPH ‐7A/7B Normal Drain to HPH
10. HPH-7A/7B Alt.Drain to HP
Drain F/T
11. HPH‐6A/6B Normal Drain to
Deaerator
12. HPH‐6A/6B Alt. Drain to HP
Drain F/T
13. LPH‐3 Normal Drain to LPH‐2
14. LPH‐3 Alt. Drain to LP Drain F/T
15. LPH‐2 Normal Drain to LPH‐1
16. LPH‐2 Alt. Drain to LP Drain F/T
17. Deaerator Overflow
18. HPH‐8A/8B Normal Drain to
HPH‐7A/7B
19. HPH‐8A/8B Alt. Drain to HP
Drain F/T
20. LPH‐4 Normal Drain to LPH‐3
21. LPH‐4 Alt. Drain to LP Drain F/T
22. DM Normal Makeup to Hotwell
23. Emergency MU to Hotwell
24. Low Load Feed Control
25 SUPER HEATER SPRAY
26 REHEATER SPRAY
27. PRDS SPRAY
