20
DRAG ® T HE V ALVE D OCTOR ® S OLUTION
DRAG®
T H E V A L V E D O C T O R ® S O L U T I O N
The World Leader in Severe Service Control Valves
CCI designed, built and patented the fi rst DRAG® control valve in 1967,
answering the need for a valve capable of handling high-pressure
liquids and gases such as water, oil, steam, natural gas, petroleum
products and chemicals. DRAG® technology is considered one of the
landmark innovations in the history of the severe service control valve
industry. Following that invention, CCI has continued to develop and
introduce advanced product technology that has revolutionized the
industry.
CCI’s industry leadership is the result of a proven record that focuses
on performance. The knowledge gained from solving customer control
valve performance problems generates high standards for quality that
infl uence every step of the production process and extend into lifetime
support of the valves installed in your plant.
Many valve manufacturers claim to offer control valves for all
service conditions, but few can provide the complete performance
compatibility needed for severe service applications. CCI DRAG® control
valves are designed specifi cally to meet your individual application
needs. Whatever your severe service application, there is only one
intelligent choice: CCI’s DRAG® control valves.
CCI’s Proven Experience
CCI DRAG® control valves have been used for more than 40 years to
solve severe service control problems, continually serving the needs of
the fossil power, nuclear power, oil and gas, petrochemical, combined
heat and power, and pulp and paper industries.
The Valve Doctor® Approach
CCI’s dedicated team of technology specialists focuses on solving
control valve problems around the globe. CCI’s expertise extends
beyond control valve design to actuation, noise reduction, system
piping and system operation. The Valve Doctor® utilizes his expertise
to provide comprehensive solutions that enhance plant operation and
result in signifi cant operational and maintenance savings. DRAG®
technology continues to play a pivotal role in providing these solutions!
Premium solutions based on DRAG® innovation2D
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CCI severe service control valves feature premium DRAG® velocity control for precise, measurable performance.
Since 1961, CCI has provided a unique combination of engineering experience and global resources with one goal: to exceed customer expectations.
A typical CCI DRAG® disk stack features varying numbers of pressure-reducing stages to ensure superior control.
Improved plant performance
Increased MW output and reduce leakage costs
Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.
Higher reliability
Lower noise.
Better control.
Longer intervals between maintenance
Decreased maintenance costs
Reduced system costs
Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership
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Improved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performanceImproved plant performance
Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage Increased MW output and reduced leakage
Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.
Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.
Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.
Safer plant operating conditions.Safer plant operating conditions.Safer plant operating conditions.
Higher reliabilityHigher reliabilityHigher reliabilityHigher reliabilityHigher reliability
Lower noise.Lower noise.Lower noise.Lower noise.Lower noise.Lower noise.Lower noise.Lower noise.Lower noise.
Better control.Better control.Better control.Better control.Better control.
Longer intervals between maintenanceLonger intervals between maintenanceLonger intervals between maintenanceLonger intervals between maintenanceLonger intervals between maintenanceLonger intervals between maintenanceLonger intervals between maintenanceLonger intervals between maintenanceLonger intervals between maintenance
Decreased maintenance costsDecreased maintenance costsDecreased maintenance costsDecreased maintenance costsDecreased maintenance costs
Reduced system costs. Reduced system costs. Reduced system costs. Reduced system costs. Reduced system costs. Reduced system costs. Reduced system costs.
Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership
Lower cost of ownership Lower cost of ownership Lower cost of ownership
Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership
Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership
Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership
Lower cost of ownership Lower cost of ownership Lower cost of ownership Lower cost of ownership
Lower cost of ownership Lower cost of ownership Lower cost of ownership
Improved plant performance
Increased MW output and reduced leakage costs
Safer plant operating conditions
Higher reliability
Lower noise
Better control
Longer intervals between maintenance
Decreased maintenance costs
Reduced system costs
Lower cost of ownership
3The benefi ts of CCI DRAG® control valves
4
Oil, Gas and Petrochemical
Production, transmission and processing, including
LNG and petrochemicals:
Production chokes
Separator-level control
Gas lift/injection
Injection pump recycle
Overboard dump
Gas regulator
Surge relief
Gas injection/withdrawal
Metering stations (active/monitor)
Compressor recycle/anti-surge
Hot gas bypass
Emergency depressuring/gas to fl are
Amine letdown
Expander bypass (JT valve)
Vent to atmoshphere
Feedwater regulator
Feedwater pump recirculation
Spraywater
Steam header pressure control
Power Generation
Fossil and nuclear power plants, cogeneration
(CHP) facilities and other industries handling
high-pressure water or steam:
Reheat and superheat attemperator spray
Main and booster feedpump recirculation
Startup and main feedwater regulation
Deaerator-level control
Condensate booster pump recirculation
Atmospheric steam dump and steam venting
Turbine bypass
Turbine bypass spray
Sootblower control
Once-through boiler startup (base-loaded and cycling units)
System startup: B&W, CE, FW and licensees
Auxiliary steam
Turbine seal pressure control
High-level heater drains
HP coolant injection (HPCI)
Reactor core isolation cooling (RCIC)
Core spray
Residual heat removal (RHR)
Steam generator blowdown
Pressurizer PORV
CVCS letdown
Sampling
Pump test loops
The Choice is Simple
When you need a complete solution to the
demanding conditions of severe service control,
there’s only one choice: a custom-engineered
DRAG® application solution.
Proven technology for critical applications
CCI DRAG® valves have been used in severe service applications worldwide. Years of research and experience in numerous
applications have proven the superiority of the DRAG® valve in critical applications.
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Symptoms of Poor Velocity Control:
5
The Need for Velocity Control
High fl uid velocity through valve trim is a principal source of system
control problems. System control is lost due to valves damaged by the
effects of cavitation, erosion, abrasion and vibration, which can quickly
destroy a valve and disrupt system operation.
Even before damaging the valve, excessive noise, severe vibration, poor
process control and product degradation can limit a facility’s ability to
operate at maximum capacity and thereby reduce output.
CCI has pioneered the effort to develop and apply the velocity control
principle in control valves to offer total system control solutions
for many different applications. Thousands of satisfi ed customers
worldwide have benefi ted from CCI’s solutions. Velocity control criteria
as published by ISA has become the industry standard in solving control
valve problems.
Since all plants must start up and shut down, good plant control must
be available for a wide range of plant loads. CCI provides control over
a full range of valve capacity by ensuring that velocity control features
are in place for the entire valve travel. By designing DRAG® disks
throughout the travel to meet the unique requirements imposed by the
plant transients, CCI’s solutions allow the automatic control systems to
function without manual control stops to work around sensitive plant
conditions.
A single-stage pressure drop valve with poor control presents problems like cavitation, erosion, noise and vibration.
The velocity control principle: multi-stage pressure drop provides control and eliminates cavitation, erosion, noise and vibration problems.
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• Unplanned shutdown
• Lost production
• High maintenance
• Reduced effi ciency
• Manual control required
• Noise
• Trim and body wear
• Pipe vibration
• Leakage
• Pipe erosion
The uncontrolled velocity challenge
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The Velocity Control Challenge
Until CCI introduced the DRAG® valve, the design of control valves for
handling high pressure drop liquids, gases or steam had changed little.
Even today, despite other makers’ widespread attempts to copy the CCI
DRAG® solution in their modifi ed trim valves, process fl uids still fl ow
through some version of a single orifi ce or multiple area orifi ces. Fluid
velocity through each orifi ce is a function of the valve pressure drop or
required process differential head.
Fluid in the valve reaches its maximum velocity just slightly
downstream of the valve trim’s orifi ce in the vena contracta or
minimum fl owing area (see Figure 1). These high velocities produce
cavitation, erosion and abrasion, which can quickly destroy the valve.
Even before damaging the valve, excessive noise, severe vibration,
poor process control and product degradation are observed in many
applications without velocity control.
Interestingly, these high velocities are unwanted side effects of pressure
reduction through the valve and are not treated as a design criteria by
other valve manufacturers until it’s too late. Many attempts to resolve
the side effects simply treat the symptoms rather than the real cause of
the problem.
In general, poor valve performance in severe service applications is
primarily due to excessive fl uid velocity. Even using harder materials
in the valves to offset erosion from cavitation, or using pipe-lagging
or downstream diffusers, can only marginally offset valve failure from
uncontrolled velocity. Velocity must be controlled at all valve settings
to maintain valve performance and reliability. Problems resulting
from high velocity affect plant performance and output, resulting in
effi ciency loss, unit load limitations, unscheduled plant shutdowns and
damage to other equipment.
V2
V1
V2
V2 V1
= 2gh
>
Figure 1: Single-stage pressure drop
The evidence: high-velocity erosion damage on a single- stage cage and valve internals is obvious.
CCI pioneers a solution
7DRAG® technology provides velocity control
DRAG® Solution to High Velocities
DRAG® velocity control valves from CCI addressed the problems
created by high velocity a generation ago. DRAG® valves prevent the
development of high fl uid velocities at all valve settings. At the same
time, they satisfy the true purpose of a fi nal control element: to
effectively control system pressure and fl ow rate over the valve’s full
stroke. Here’s how the DRAG® valve accomplishes what the others can
only approach:
The DRAG® trim divides fl ow into many streams to minimize the mass
and energy levels (Figure 2). Each fl ow passage consists of a specifi c
number of right-angle turns to form a tortuous path (Figure 3) in which
each turn reduces the pressure of the fl owing medium by more than one
velocity head.
The number of turns, N, needed to dissipate the maximum expected
differential head across the trim, as illustrated in Figure 4, is found by
changing the equation from:
V2 (orifi ce) =
to a new equation:
V2 (DRAG®) element =
The number of turns, N, is selected to ensure a specifi c fl uid energy level
exiting the channel. Applying this principle to the DRAG® valve’s disk
stack and plug is shown in Figure 5. The disk has several fl ow channels,
each channel comprising multiple right-angle turns (Figure 6). Thus
DRAG® technology fully controls velocity in each passage on every disk
in the stack, and the valve can operate at a controlled, predetermined
velocity over its full service range.
To achieve enough capacity for the valve, CCI’s solutions add disks to
provide the necessary fl ow cross-section. This technology is in stark
contrast to valves using multiple-orifi ce-modifi ed trims. Each orifi ce
converts potential energy to kinetic energy, but with a startling increase
in velocity. Therefore, multiple-orifi ce solutions do not provide the
protection that the DRAG®-type trim provides.
In the DRAG® trim, the resistance, number and area of the individual
fl ow passages are custom matched to your specifi c application, and exit
velocities are managed to eliminate cavitation and erosion in liquid
service and vibration and noise in gas service.
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V1 V2=
V1
V2
V2 = 2gh/N
N Turns
V1 V2=
V1
V2
V1 V2=
V1
V2
V2 = 2gh
Figure 2: Multi-path pressure reduction
Figure 3: Right-angle tortuous path
Figure 4: Multi-stage pressure reduction
Figure 6: Multi-path, multi-stage DRAG® disk
Figure 5: DRAG® disk stack and plug
2gh
2gh/N
8 Cavitation — uncontrolled velocity
The Cavitation Challenge
When liquid pressure is reduced to its vapor pressure or lower, fl ashing
and bubble formation occur. In most control valves (Figure 7), fl uid
enters at pressure P1 and velocity V1. As the fl uid moves through the
reduced area of the valve trim, it accelerates to velocity VVC as its static
pressure drops suddenly to PVC – a level at or below the liquid’s vapor
pressure PV. At this point, the liquid boils. Any valve using a single or
multiple-orifi ce trim will cause this problem because of its uncontrolled
velocities in the areas of each “vena contracta,” the narrowest central
fl ow region of a jet of fl uid fl ow.
As the fl uid moves out of the throat of the valve, pressure recovery
begins, converting kinetic energy back to potential energy. Full recovery
to downstream pressure is indicated at P2 and velocity V2. When
the recovery pressure exceeds the fl uid’s vapor pressure PV, collapse
or implosion of the just-formed bubbles takes place, resulting in
cavitation. The energy thus released causes local surface stresses greater
than 200,000 psi (1400 MPa), which can consume even hardened trim
rapidly.
Symptoms of Cavitation
n Noise when liquid-handling valves modulate or shut off
n Valve components showing “pitting” damage
n Poor process control with the valve
Cavitation is the formation and subsequent collapse of microscopic vapor bubbles that can destroy trim.
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Figure 7: Inter-stage cavitation damage from insuffi cient staging
P1
V1
Pv
Pvc
inlet velocity
Vvc
Vvc
Vvc
inlet pressure
Pvc
V2 outlet velocity
Pvccavitation bubbles form here
vapor pressure
P2 outlet pressurebubbles collapse, cavitation occurs
Seat ring damage caused by cavitation results in leakage that can harm downstream equipment.
9
The DRAG® Solution to Cavitation
The DRAG® valve eliminates the destructive effects brought about by
uncontrolled fl uids in today’s processes. DRAG® technology does this by
fi rst splitting the fl ow into many small channels so that, if a gas bubble is
formed, it is very small and does not have the energy necessary to cause
stresses that would result in material failure. Secondly, DRAG® maintains
the fl uid velocity at minimum levels so that local pressures are unlikely
to drop below the vapor pressure of the fl uid. Thus none of the adverse
effects of bubble collapse can harm the valve as in other valve designs.
In addition to many years of successfully applying the DRAG® design
principles to control valve cavitation, CCI has conducted independent
tests in accordance with ISA 75.23 and verifi ed the practice. In every
possible combination of test conditions, the testing confi rmed the
DRAG® design principles and the technology’s ability to solve the most
diffi cult industry problems of fl uid fl ow control.
In general, the damaging effects of cavitation are a typical signal that
fl uid velocities are not being controlled. As previously mentioned,
using harder materials, pipe-lagging or downstream orifi ces can only
marginally offset valve failure from cavitation damage. High fl uid
velocity and insuffi cient staging (shown in Figure 7) will result in inter-
stage cavitation damage, reducing the effectiveness of the valve as a fl ow
modulating device and exposing the trim to damage, which leads to a
leaking valve. The solution to cavitation, therefore, is the DRAG® velocity
control valve, as illustrated in Figure 8.
Fluid velocity requirements, based on the vapor pressure of the fl uid (at
design temperature), is governed by the following equation:
English Metric
DRAG® — the cavitation solution D
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CCI’s multi-path, multi-stage trim designs are characterized to provide optimal valve performance at all fl ow conditions across the full stroke of the valve plug. V = 4637 (P2 - Pv)/ or V = 1000 (P2 - Pv)/
Service Conditions Fluid Velocity at Trim Exit
Continuous service single phase fl uid
100 ft/s 30 m/s
Cavitating & multi-phase fl uid 75 ft/s 23 m/s
Vibration-sensitive systems 40 ft/s 12 m/s
Table 1: Recommendation for Fluid Velocity to Control Cavitation*
Figure 8: The DRAG® solution eliminates cavitation.
P1
V1
Pv
inlet velocity
pressure
V2 outlet velocity
P2 outlet pressure
vapor pressure
* Based on information presented in the publication “Control Valves - Practical Guides for Measurement and Control” edited by Guy Broden , Jr. and Paul G. Friedman, 1998 edition, published by ISA and other sources.
10 Noise and vibration — uncontrolled velocity
A competitor’s body and trim that failed to withstand severe service conditions show signs of damage that result in poor performance and control.
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With the expertise of a CCI Valve Doctor®, our DRAG® valves are designed to your performance specifi cations and offer the ultimate solution to noise and vibration problems in severe service applications.
The Noise and Vibration Challenge
Modern plants are subject to many complex and strict regulations
dictating the allowable noise level for either the worker or for the plant
neighbors. Occasionally, a system will experience signifi cant piping
vibration that may eventually lead to a failure. Such vibration can also
cause component damage and, in many cases, the vibration is a safety
concern for both plant personnel and expensive equipment essential to
plant operation.
Frequently, the cause of vibration is a valve that has not been properly
selected for the application. The excessive fl uid velocities and energy
levels force uncontrolled pipe motion, which results in failure of pipes
and supports and damage to downstream components.
Noise and vibration are pervasive in applications involving throttling or
venting of compressible gases. For applications where noise is signifi cant,
sonic vibrations not only create hazardous health areas, but may also
pose a threat to the reliability of equipment and system operation. Even
if lagging, dampening or enclosing the noisy valve successfully controls
audible noise leaks, the potential for costly damage and valve failure
still exists. A plant may meet hearing safety requirements by insulating
the valve; however, unless the source of the noise is eliminated, the
risk of signifi cant damage to the valve and process remains. In addition,
noise propagates through the process piping and often contributes to
problems with other components in the system. Eliminating the source
and mechanism of noise is the only way to mitigate these risks.
Even more signifi cant than audible noise are the problems associated
with high vibration levels. Signifi cant vibration in a valve can
quickly lead to failure of the valve components (cage, plug, stem and
accessories) and process components, the eventual failure of pipes and
supports, and damage to downstream equipment. In extreme cases,
many control valves with signifi cant vibration problems often cause
system trips and result in costly effi ciency and production losses.
The DRAG® Solution to Noise and Vibration
In an effort to eliminate the sources of system vibration, CCI
encourages the process industries to adhere to ISA guidelines for valve
trim exit kinetic energy levels. The right-angle tortuous path trim
approach used in the DRAG® technology achieves the required low
energy levels. The right-angle turns drop the fl uid velocity to levels that
provide the expected control. Figure 9 illustrates actual fi eld results
of DRAG® technology. This fi gure shows vibration before and after
application of the DRAG® design. There is usually a 90% reduction
in the peak vibration level of the valve or piping component with the
application of DRAG®.
CCI can provide control valve systems that will ensure the noise levels
remain below the specifi ed requirements. The DRAG® valve approach is
to prevent the creation of noise as opposed to trying to muffl e it once
it is produced. CCI uses the prediction technology that forms the basis
of the IEC and ISA noise prediction standards. Noise is controlled by
making sure that the trim exit jets leaving the disk stack do not induce
excessive acoustic levels inside the pipe. Subsequently, the noise passing
through the pipe wall and sensed in the vicinity of the valve is lower
than the specifi ed levels.
DRAG® technology mitigates the excessive sonic vibrations created
within the valve by controlling the source of the noise, as demonstrated
in the following formula:
11DRAG® — the noise and vibration solution
DRAG® valves like this 28-inch (700 mm) multi-stage, pneumatic-controlled device have been installed in over 2,000 plants around the world to solve vibration and noise problems. D
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W= sound power
= fl uid density
d = characteristic dimension
U = fl uid velocity
C = velocity of sound fi eld
d2 U6
C3W
Figure 9: Stem vibration velocity for a conventional valve before retrofi t (blue line) and after retrofi t with DRAG® trim (red line)*
Table 2: Recommendation for Fluid Kinetic Energy (Velocity Head)
at trim Exit **
Service Condition Kinetic Energy (Velocity Head)
Intermittent Duty 150 psi 1030 kPa
Continuous Duty 70 psi 480 kPa
Ste
m V
ibra
tio
n V
elo
city
(mm
/s, 0
-pk)
Hertz
50
40
30
20
10
00 100 200 300 400 500
Conventional valveCCI
DRAG®
valvefull open
* “Multi -Stage Valve Trim Retrofi ts Eliminate Damaging Vibration”, J. R. Arnold, H.L. Miller, and R. E. Katz, Power-Gen 96 International, Orlando, Florida, Book IV, pg. 102-110, PennWell Conferences & Exhibitions, Houston, Texas, December, 1996.
** Based on information presented in the publication “Control Valves - Practical Guides for Measurement and Control” edited by Guy Broden , Jr. and Paul G. Friedman, 1998 edition, published by ISA and other sources.
Note: KE = V2
2gC
12 Erosion — uncontrolled velocity
The Erosion Challenge
Erosion of the valve trim can be caused by the washing action of a fl uid
or abrasion from particles entrained in the fl uid. The erosion effect
is most severe at high pressures and high concentrations of entrained
material. Even very pure water can be extremely erosive.
While clean dry gases usually are not a cause for concern, throttling
even clean superheated steam can cause severe problems, as illustrated
in Figure 10. Consider the following example: superheated steam at P1
(inlet pressure) of 600 psia (4 MPa) and T1 of 600°F (300°C) entering
a conventional or modifi ed-trim valve is let down to 50 psia (0.3 MPa).
The low pressure and high velocity inherent in fl ow through these valve
trims allow the steam to expand isentropically or polytropically to
point P2. At this point, with velocity at its peak, the steam develops a
moisture content between 12% and 20%. The resulting water droplets,
traveling at maximum velocity, will rapidly erode the trim and damage
the valve body. Pressure recovery is completed in the outlet and the
temperature reaches equilibrium, resulting in superheated steam
leaving the valve at P3 (outlet pressure) of 50 psia (0.3 MPa) and T3
of 515°F (270°C). However, while the valve has achieved its pressure
drop, continuous formation of wet, high-velocity steam will soon result
in severe trim damage. The same holds true in a gas handling service
where hydrate (ice crystals) formed under similar circumstances can
clog the conventional trim in a short time.
Erosion by solids/sand is particularly tough on control valves. Materials
that are readily available are quickly consumed by the sand-blasting
effect of entrained solids. Controlling the velocity and the use of
erosion-resistant materials adds signifi cantly to the life of the valve
components handling these fl uids.
As trim erodes, the valve’s CV changes and fl ow becomes diffi cult to
control, inducing other symptoms like increased vibration and related
high noise levels. Any time control is compromised, the risks soar. Lack
of control results in a shortened life for the valve that threatens plant
performance and reliability. Moreover, it means increased expense for
the plant operator.
Erosion by a fl uid can alter the landscape of valve components over time, affecting the quality of operation.
Erosion damage to a competitor’s valve plug caused by high fl uid velocity results in poor shutoff.
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One damaged part can shut a plant down; a CCI DRAG® valve can prevent this unnecessary downtime and give you peace of mind.
13
The DRAG® Solution to Erosion
The traditional approach to problems such as erosion include continual
maintenance, brute force or both. The brute force strategy involves
using harder materials where erosion is a problem, which covers up
the symptoms without addressing the root cause. The rate of erosion
varies as a third to fi fth-power function of fl uid velocity (V3 to V5). For
example, if the fl uid velocity can be reduced by a factor of two, then the
erosion rate will be reduced by a factor ranging between 8 and 32. To
eliminate erosion, it is essential that the fl uid velocity be maintained at
manageable levels. The DRAG® design controls velocities throughout the
disk so that pressure recovery does not take place.
For erosion problems that result from abrasion, the DRAG® trim operates
at a controlled velocity. The inlet/outlet and trim velocities are low, so
the steam expansion through the valve is isenthalpic – going from
point P1-T1 directly to point P3-T3 (see Figure 10). Steam through the
DRAG® valve never has a chance to develop destructive moisture. In gas
applications, controlled velocity minimizes the formation of hydrate,
thus preventing the trim from clogging.
CCI combines the velocity control principle and higher erosion-resistant
material to solve erosion resulting from solids like sand. Choke valve
applications use a multi-stage DRAG® disk stack produced from tungsten
carbide for substantially longer life compared to traditional solutions.
DRAG® — the erosion solution D
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Figure 10: The low pressures and high fl uid velocities inherent in conventional valve trim (single-stage and multi-stage) result in erosion by abrasion, even in clean superheated steam, as water droplets are allowed to form.
Isenthalpic Flow
Entropy
Cons
tant
Pre
ssur
eEn
thal
py
ConstantMoisture, %
P1
P2
P3
P2
SaturationLine
Multi-stage Polytropic
Single-stage Isentropic
DRAG R
Tungsten carbide DRAG® disks provide proven erosion prevention.
14 Leakage — uncontrolled velocity
The Leakage Challenge
Leakage through control valves can signifi cantly reduce plant effi ciency
and result in higher overall operational and maintenance costs. This
frequently means that millions of dollars are lost every year. This issue
is overlooked by many operators who do not realize that a valve may
still offer acceptable control while allowing signifi cant leakage when
fully closed. In reality, the leakage past most control valves results in
lost fuel, heat or system capacity, which directly impacts the economic
viability of the process. In fact, the cost of leakage in a severe service
control valve is always far greater than the price of the valve. In extreme
cases, an entire plant may be shut down because of a single leaking
valve.
The costs of leakage through a control valve are signifi cant and are often
manifested in the following ways:
n Unscheduled plant shutdowns
n Increased maintenance schedules to replace damaged valve and
system components
n System effi ciency losses resulting in increased fuel and power
consumption
n Heat rate losses and unit load limitations
n Control system oscillations or outright loss of control
Symptoms of Leakage
n High temperature in the downstream pipe for a normally
closed valve
n Loss of process control, even when valve is fully closed
n Steam or gas leaks through vents
n Inability to hold the pressure inside the condenser
n Noise produced by valve even when closed
In the extreme case, a power plant shutdown may be unavoidable because of a single leaking valve.
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Plant managers and engineers rely on CCI’s DRAG® technology for reliable performance to keep their facilities running trouble-free.
15CCI technology — the leakage solution
The DRAG® Solution to Leakage
Controlling leakage through a severe service control valve requires
a combination of technologies and a dynamic understanding of the
behavior of the fl uid as it passes through the valve. CCI customers place
a premium on tight shutoff because it translates directly into operational
cost savings. CCI engineers realize that tight valve shutoff is not only
a function of operational closing forces, but also requires control of
fl uid velocities through the valve seating area. DRAG® technology limits
the velocity of the fl uid as it enters the seating area and minimizes the
erosive forces that would otherwise compromise the valve’s ability to
effectively control leakage.
In addition to controlling destructive fl uid velocities, CCI utilizes both
high actuation forces and uniquely designed seals and seat to maintain
repeatable tight shutoff.
By combining the advantages of DRAG® with CCI’s advanced actuation,
sealing and seating technology, CCI severe service control valves provide
repeatable tight shutoff and reliable operation to assure customers that
the costs associated with system leakage are truly being controlled.
Exceptional Shutoff — Repeatable Class V (or better)
DRAG® severe service control valves offer exceptional shutoff
performance to withstand long periods of closure at high pressure
differentials. CCI uses a uniquely designed seat that, when combined
with CCI’s high actuator force, delivers tight shutoff each and every time.
The high actuator force coins (leaves a circumferential impression into)
the valve seat ring. The coining erases micro scratches caused by fi ne
debris in the fl uid, providing reliable and repeatable long-term shutoff.
In applications that need tight shutoff, CCI provides Class V or MSS-SP-
61 (equivalent to a block valve) closure.
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Leakage ClassSeat Load Requirements
Pounds per Linear Inch
kgf per Linear mm
Class IV 300 5.4
Class V 500 8.9
MSS-SP-61 1000 17.9
Table 3: Recommendation for Seat Load Requirements in Control Valves *
* Based on information presented in the publication “Control Valves - Practical Guides for Measurement and Control” edited by Guy Broden , Jr. and Paul G. Friedman, 1998 edition, published by ISA and other sources.
To ensure absolutely tight shutoff, CCI provides a DRAG® valve with pressurized seating as illustrated above.
Inlet
Outlet
A CCI DRAG® valve equipped with RHP™seating technology establishes a higher standard of valves for critical gas applications.
16 DRAG® technology offers unequalled performance
CCI’s Total Solution
Many valve manufacturers have recognized that velocity is the real
problem contributing to valve failure. Some try to contain the effects
of uncontrolled velocity or shift the problem into a more tolerable area.
Others have attempted to imitate the technology behind CCI’s DRAG®
valve solutions. However, only CCI offers the Valve Doctor® solution.
Customized for Better Flow Control
To maintain performance, velocity through the valve must be
controlled at all times. Capacity can be varied for each of the disks in
the DRAG® disk stack for superior velocity control. In addition, CCI’s
DRAG® solutions match the fl uid fl ow capacity to the system design
requirements to guarantee stable control. CCI’s unique capability to
vary the number of pressure-reducing stages throughout the valve’s
operating range allows for maximum performance.
DRAG® disk stacks also have pressure equalizing ring grooves so that
localized pressure from each disk’s outlet is equalized around the plug
(see Figure 11). This eliminates radial forces on the plug that might
otherwise cause binding, galling, radial vibration, or buffeting. In
addition, DRAG® trim offers a wide range of fl ow characteristics, and
the design can be characterized for all combinations of inlet and outlet
pressures.
Better Flow Control with Fewer Valves
DRAG® trim can be linear or characterized to provide a single, high-
rangeability valve in lieu of a more costly two-valve solution. When
necessary, the valve trim can contain labyrinth grooves to reduce the
annular fl ow between plug and disk stack (see Figure 12). This results in
a signifi cant improvement in the minimum controllable fl ow capacity
of the valve. When labyrinth grooves are utilized, DRAG® valves can
provide throttling rangeability in excess of 300:1. In new system designs,
this can eliminate the need for smaller parallel startup valves, saving
the piping and installation costs of these valves. In existing installations,
this cuts out unstable transfer points as well as the maintenance costs
associated with multiple valves.
Better Flow Control with Longer Strokes
Many manufacturers fi t the capacity and operating characteristics of
their valves to stroke lengths permitted by the actuation systems they
choose. This results in poor valve control and instability of the system.
As an example, if a valve provided by another supplier has Cv (capacity)
of 1,000 in a linear characterized trim, the actuator is likely to allow
only a travel of three inches. This is a Cv change of approximately 42
per each 1/8-inch of travel. In a DRAG® valve of the same capacity,
the stroke length would be 12 inches. This results in a Cv change of
approximately 10 per 1/8-inch of travel. The benefi t to plant operation
is a fi ner degree of control per percentage of position change, resulting
in extremely stable process control.
DR
AG
®
CCI DRAG® trim is available for globe, angle and rotary-style valve designs to create the optimal solution for customers.
Figure 12: DRAG® disk stacks have labyrinth grooves and velocity-reducing right-angle turns.
Figure 11: DRAG® disk stacks have pressure equalizing ring (PER) grooves.
17DRAG® valve features and advantages D
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G®
Benefi ts DRAG® Competition
1 Provides the Valve Doctor® Solution: CCI works
with plant operators to improve plant performance,
reliability and output with DRAG®.
2 Improves Plant Performance: CCI’s DRAG® valve
operates without effi ciency losses from valve leakage.
3 Prevents Cavitation Damage: CCI supplies up to 40
pressure-reducing stages (based on pressure drop and
fl uid conditions) to limit trim exit velocity, preventing
the damaging effects of cavitation.
4 Eliminates Erosion Damage: By controlling fl uid
velocities and providing tight shutoff, CCI DRAG® valves
eliminate erosion.
5 Low Operating Costs: Application-specifi c design
considerations like pressurized seat, plug, snap-acting
relay and custom-engineered designs ensure reliable
and repeatable performance.
6 Reduces System Costs: DRAG® valves do not require
back pressure or anti-fl ashing devices that can be
expensive and unreliable.
7 Reduces Costly Maintenance Cycles: DRAG® valves
are designed specifi cally to provide longer intervals
between maintenance and allow easy access to all
components.
8 Avoids Plant Shutdowns: CCI’s DRAG® valves are
designed specifi cally to handle the severe service
of nuclear power, fossil power, and oil and gas
applications.
18
Product Range Specifi cationsDRAG® control valves are available in a wide range of sizes, pressure classes, materials and confi gurations; typical ranges are shown below:
Velocity Controlling Stages
Up to 60, special designs available
Sizes 1/4 in. to 48 in. (6 mm. to 1220 mm.)
Pressure Ratings ANSI 150 to 4500; PED CL 300 to CL4500
DIN 10 to 400; API 10,000
Fluid
Temperature Range
-250°F to 1100°F
-155°C to 590°C
Body Style Globe, angle, “Z” body, rotary
Connection Type Buttweld to ASME B16.10; Socket Weld to AMSE B16.11; Flanged to ASME B16.5 MSS SP-44 and API 605; Special ends including clamped-joint hub confi guration
Seat Design Metallic or soft seat
Bonnet Style Bolted bonnet, metal, gasket seal body-to-bonnet joint, or pressure seal
Guiding Disk stack
Plug Design Unbalanced, balanced, pressurized seat
Characteristic Linear, equal %, quick open or custom design
Rangeability Designed to meet application needs; minimum of 30:1; over 300:1 for larger valves
Body Material Carbon steel, chrome-moly steel, stainless steel, duplex stainless steel
Bolting: Ferritic, austentic
Trim Material Disk Stack: 410, 316, or 316L stainless steel; Inconel 718; chrome-moly alloy steel; duplex stainless steel; or tungsten carbide Plug/Seat Ring: 410, 316, or 316L stainless steel; Inconel 718; 17-4PH; chrome-moly alloy steel; duplex stainless steel; or tungsten carbide (hardfaced when required)Packing/Seals: tefl on, graphite, InconelGaskets: graphite/stainless
Shutoff Capabilities Unbalanced Plug: Soft Seat- ANSI Class VI, Metal Seat- ANSI Class V, MSS-SP-61Balanced Plug: Soft Seat- ASME Class VI, Metal Seat- ANSI Class IV or VPressurized Seat Plug: Metal Seat - MSS-SP-61
CCI’s severe service valve technology for LNG applications reduces overall cost and improves performance and reliability.
Flexible specifi cations for your needsD
RA
G®
The CCI Steamjet™ valve features DRAG®’s multi-path, multi-stage design to deliver superior performance in turbine bypass applications.
Custom designs are available to meet your Cv and piping requirements. Please contact a CCI representative for details.
19
Parts
When valves need a spare part, those from the original manufacturer
work best. With the original drawings, specifi cations and equipment,
CCI can make the right replacement part for any valve to meet your
specifi c needs and application requirements. These parts are made from
the right materials, by qualifi ed machinists, with N-stamp qualifi cation
when needed. All of CCI’s spare parts meet the original industry
standards for which the valves were designed: API, ANSI or ASME.
Field Service
When you need a valve expert at your side, our fully trained and
experienced fi eld service technicians are the right answer. Whether it’s
a routine maintenance check or an emergency repair, our team has the
experience, tools and access to all information about the valves we built
for you to ensure that your valves will continue performing the way you
expect. When your conditions demand it, our people can completely
rebuild a control valve in line at your site and recalibrate it before
returning it to service. They’ll even help sort out your spares inventory.
Rebuilds
Our factory-trained specialists handle complete rebuild procedures,
including full disassembly and cleaning, welding, overlay, and
modifi cation or fabrication of needed parts; part matching for tight
sealing; reassembly; leak testing; painting; and return shipment — and
these services apply to the smallest or the biggest DRAG® severe service
valve.
Global Strength of Customer Service
CCI is committed to making each of our valves stay healthy over its
lifetime. Aftermarket specialists are proactive, contacting our customer
base and making necessary recommendations for appropriate and timely
maintenance. By implementing long-term management programs, CCI
proves its commitment to delivering the highest-quality performance
and reliability along with its dedication to achieving complete customer
satisfaction.
Boost plant output with DRAG® control valves
CCI will supply the right spare parts, built to original specifi cations, so your valve will perform like new.
DR
AG
®
Whether it’s troubleshooting, critical calibration or an emergency repair, CCI’s expert factory and fi eld service technicians have the knowledge, tools, parts and drawings to do the job right.
CCI World Headquarters—CaliforniaTelephone: 949 858 1877Fax: 949 858-187822591 Avenida EmpresaRancho Santa Margarita,California 92688 USA
CCI Austria(Spectris Components GmbH)Telephone: 43 1 869 27 40 Fax: 43 1 865 36 03Carlbergergasse 38/Pf.19AT-1233 ViennaAustria
CCI ChinaTelephone: 86 10 6501 0350 Fax: 86 10 6501 0286567/569 Offi ce TowerPoly Plaza14 Dongzhimen South Avenue Beijing 100027China
CCI FK(Fluid Kinetics)Telephone: 805 644 5587 Fax: 805 644 10802368 Eastman Avenue, Suite 8VenturaCalifornia 93003USA
CCI Italy(STI)Telephone: 39 035 29289Fax: 39 035 2928246Via G. Pascoli 10A-B24020 Gorle, BergamoItaly
CCI sales and service locations worldwide.
CCI JapanTelephone: 81 726 41 7197Fax: 81 726 41 7198194-2, ShukunoshoIbaraki-City, Osaka 567-0051Japan
CCI KoreaTelephone: 82 31 980 9800Fax: 82 31 985 055226-17, Pungmu-DongGimpo City, Kyunggi-Do 415-070Republic of Korea
CCI Sweden(BTG Valves)Telephone: 46 533 689 600Fax: 46 533 689 601Box 603SE-661 29 Säffl eSweden
CCI Switzerland (Sulzer Valves)Telephone: 41 52 262 11 66Fax: 41 52 262 01 65Im Link II, Postfach 65CH-8404 WinterthurSwitzerland
DRAG is a registered trademark of CCI.©2003 CCI 451 9/03 15K
Contact us at:[email protected]
Visit us online at:www.ccivalve.com
For sales and service near you, please visit www.ccivalve.com Throughout the world, companies rely on CCI to solve their severe service control valve problems. CCI has provided DRAG® solutions for these and other industry applications for more than 40 years.
