my SYSTEM - Singer Valve

my SYSTEM - Singer Valve
my SYSTEM
A guide to common applications
in water distribution systems
WWW.SINGERVALVE.COM
This short guide is intended to offer guidance
on some of the common problems, applications
and questions that arise from using automatic
control valves in water systems.
It is not intended to replace a full technical
catalogue so you will need to refer to that for
complete details, but this will certainly give
you some insight into the types of questions a
valve manufacturer may ask you and allow you
to have a better understanding of some of the
more common applications.
INDEX
Lowering the pressure in my System. . . . . . . . . . . . . . 1
Starting a pump in my System. . . . . . . . . . . . . . . . . . . 6
Combatting surge in my System. . . . . . . . . . . . . . . . . 13
Controlling tank levels in my System . . . . . . . . . . . . 17
Measuring flow with a valve in my System. . . . . . . . 22
Controlling flow in my System . . . . . . . . . . . . . . . . . . 25
Controlling back pressure in my System. . . . . . . . . . 28
TOPIC ONE
LOWERING THE PRESSURE
IN MY SYSTEM
If pressure feeding into a zone needs to be lowered the
traditional method employed is to install a pressure reducing
valve. This is a valve that will limit the outlet pressure of a
valve to a preset pressure regardless of the flow rate and the
inlet pressure.
WHAT YOU NEED TO KNOW
The location of this valve needs to be in an accessible area – typically
in a valve vault, as they will require occasional maintenance.
In order to size this valve you will need to know normal inlet
pressure, outlet pressure required, and normal flow rates
(minimum and maximum).
CAUTIONS
If the inlet pressure to outlet pressure ratio is greater than a 3:1
range there is a real possibility that cavitation will occur. That will
require one of two things:
a) Use two control valves in series and lower the pressure gradually over two stages
b) Use a control valve with anti-cavitation trim installed
1
High pressure
supply main
Smaller PR valve
for low flow, if required
Lower relatively steady
pressure supply to
users
Main Valve
Model 106-PR
or Model 206-PR
Manual by-pass line
Note: The smaller PR valve by-passing the main valve helps
control low flows and provides service during maintenance.
It should be set 3 - 5 psi / 0.2 - 0.35 bar higher than the larger
valve.
2
COMMON QUESTIONS
What if I have two valves feeding into the same zone?
The valves will certainly work but the issue will be ensuring that
they both open together. This is something that has to be done
during commissioning and will require two people, one at each
valve. They will need to communicate with each other to ensure
that both valves open together and this will typically involve a slight
adjustment to one of the reducing pilots.
Can my valve be installed in a situation where the chamber is
underwater occasionally?
While this is not ideal, in a pressure-reducing valve situation the
valve will happily continue to operate underwater. If this is a
regular occurrence we would suggest using a full stainless steel
pilot system.
Why is my valve size smaller than the main line size?
Valves are sized for 20 ft. /s (6m/s) velocity through the seat area
for continuous service. We like to see these valves operating in the
20-80% range of their stroke so we can also increase velocity
through the very short distance of the control valve than you
would normally size your distribution lines for. For this reason it
is common to have a control valve maybe one size smaller than
the actual line it sits in. (For this reason the reduced port valve is a
great option as it has connecting flanges the size of the main line
but internals of a smaller valve.)
3
Will my valve handle the entire flow range?
Typically not, this is why you will frequently see a smaller reducing
valve installed in parallel to the larger valve. This is there to handle
the low flows that the larger valve cannot handle. If you utilize a
control valve with the rolling diaphragm technology this low flow
rate will not be an issue as that type of control valve can regulate
down to extremely low flows and bypass valves are not required.
Why do I have different pressure set points on larger and
smaller reducing valves in a station?
In order for the smaller valve to take control during times of low
flow, this valve will be set about 5 psi higher than the larger valve.
This ensures that when the pressure downstream starts to drop,
this is the first valve that will open. (Remember it is downstream
pressure operating on the reducing pilot that keeps it closed
so when downstream pressure drops lower than spring setting
pressure, the pilot will open, in turn allowing the mail valve to
open.) If the small valve cannot maintain the pressure because flow
demand increases, the pressure will drop in the small downstream
system, thereby allowing the larger main valve pilot system to open
allowing main valve to now take flow.
What if the upstream pressure drops below the pressure
setting of the pilot?
The pressure-reducing pilot is set by the force of a spring in the
top of the reducing pilot. As a normally open pilot, this means the
spring is always trying to keep the pilot open. As the reducing pilot
senses the downstream pressure, if the pressure is greater than
the spring setting, the pilot closes. When this pressure sensed is
lower than set point the pilot opens and this releases the pressure
from the bonnet of the main valve and the valve will go wide open.
Should the upstream pressure rise, the pilot will start to regulate
again to maintain the setpoint.
4
RECOMMENDATIONS
•
Installing air release valves ahead of reducing valves is always recommended to eliminate any chance of air in the pilot system.
In-line strainers will certainly help to eliminate the items that frequently get flushed down water lines and eventually get
trapped in the control valves. It is much easier to remove a
strainer lid and clean out debris than it is to remove a pilot
system and control valve bonnet.
•
If there is the risk of somebody downstream of the reducing valve
having the ability to shut off the entire flow quickly (maybe
feeding into an industrial complex, line ends with a fire
hydrant etc.), then there is the risk that the valve could be in
an open position when somebody closes the flow. This results in high pressure passing through the valve and getting trapped downstream. A solution to combat this is to have the reducing
valve installed with downstream surge control that assists the valve in closing quickly if the pressure downstream of the valve raises a few psi higher than the normal set point.
•
An alternative to the downstream surge control would be to
install a pressure relief control valve, but that will depend on the location and the ability to discharge the water safely if the relief valve opens.
• In order to set this valve in the field it would really be
advantageous to have at least an isolating valve on the outlet side
of the valve.
• An outlet pressure gauge will also be required to set the valve.
5
TOPIC TWO
STARTING A PUMP
IN MY SYSTEM
Whenever a pump is started, the sudden increase in flow
and pressure can create pressure waves into the system that
can cause a lot of noise and damage. As this is not desirable,
engineers will frequently utilize methods to slowly ramp up
the pump speed either by using something called a “soft
start” - where the voltage or current is temporarily reduced
in a three-phase motor to give a slow pump start or variable
frequency drives – where the pump speed can be adjusted to
give a much slower start to the system.
However, both of these options can be expensive and often
traditional constant speed pumps are still used. This creates
the problem of surges at startup. A common answer to this is
to install a pump control valve. This allows the pump to start
up against a closed valve that is slowly opening as the pump
gains speed. This allows the system to gradually increase in
pressure. At the time to shut the pump off, the valve is allowed
to start closing before we turn off the pump motor and only
when the valve is almost closed does the pump actually turn
off. This is what we call an In-Line Pump Control Valve. There
is a second type of Pump Control Valve, named a Bypass Pump
Control Valve – see explanation of this after this section.
6
Isolation Valve
Motor
Starter
Panel
Singer model
106-BPC
Booster Pump
Control
Valve
Singer model
106-RPS
Pressure Relief
Booster Pump
7
IN-LINE PUMP CONTROL
WHAT YOU NEED TO KNOW
Typically this valve is going to be located very close to the pump so is
usually in some kind of pump house. It will require electrical power
for the solenoid valve, either AC or DC and will also require wiring
back to the pump control panel for a limit switch that gives the
position of the valve stem so we know when to turn off the pump
just before the valve is closed.
These valves are typically the same size as the main discharge line as
even during operation, this valve will be experiencing full flow so we
do not want to incur any more pressure loss than is necessary.
You will need to know the pump flow rate and the pressure that the
pump will be operating at. This is used to determine the valve rating
and the correct solenoid that is used in the pilot system.
You will also need to determine voltage required for the solenoid.
CAUTIONS
Determine ahead of time if you are using this valve just for starting
and stopping the pump or if you may require the valve to perform
a throttling function also. (This requires two different valve body
types.) See Common Question 2 below.
8
COMMON QUESTIONS
What if I have more than one pump feeding into a header?
You will require a pump control valve for each pump.
Can a pump control valve also be used to control flow rate
or pressure?
Yes. However, if you are intending to have this valve throttle we
do need to know this ahead of time as the valve is supplied in
two options. One utilizes what we call a PG body and this is more
like a typical control valve and allows for throttling. The alternate
is a PT style body. This is where we use a body style that has two
independent chambers in the cover. One to drive valve closed, one
to drive it open. This is our preferred pump control body but cannot
be used in regulating situations. It does however have a linear
operating curve so flow is proportional to the valve lift (e.g., 50%
open valve = 50% of flow).
The main valve body is available with an optional internal drop
check that will close the main valve in the event of no flow through
the valve. This will help to eliminate potential surges.
Is the pump shut off point adjustable?
The pump shut off point can be set by adjusting a small collar on
the valve stem that is used to trip the limit switch. This can be field
set and changed if required.
9
RECOMMENDATIONS
•
Remember that an in-line pump control valve always sees flow so
there will be a small pressure drop across the valve even when it is wide open. Select a valve that gives you the lowest pressure
drop. (For this reason this type of valve is usually same size as
pipe size.)
BYPASS PUMP CONTROL
The bypass type valve performs the same function as the inline pump control, in that it allows a slower start to the system
but rather than the valve sitting in the main line and opening
slowly, the valve sits on a bypass (like a relief valve) and is wide
open when the pump is started. As the pump reaches speed
the valve is slowly closing so the main pump header reaches
pressure slowly before it can overcome the static pressure in
the system, holding the check valve closed. Switching off the
pump is a reversal of this process. The valve starts to open and
the main header slowly drops in pressure, eliminating check
valve slam, and just before this valve is wide open, the pump is
switched off.
These valves are very useful in eliminating the in-rush of air
when a pump starts and also for removing sand/silt that you
may get from a traditional bore hole pump on start up.
10
WHAT YOU NEED TO KNOW
Typically this valve is going to be located very close to the pump
so is usually in some kind of pump house. It will require electrical
power for the solenoid valve, either AC or DC and will also require
wiring back to the pump control panel for a limit switch that gives
the position of the valve stem so we know when to turn off the
pump just before the valve is open.
Because these valves only operate when the pump is starting and
stopping they are sized with much greater velocities than an in-line
valve and are therefore typically smaller in size.
You will need to know the pump flow rate and the pressure that
the pump will be operating at. We will use this along with the static
pressure to determine suitability and the valve rating and also the
correct solenoid that is used in the pilot system.
You will also need to determine voltage required for the solenoid.
The static pressure in the system.
CAUTIONS
These valves discharge water during start up and shut down so you
will need somewhere to discharge this. Either back into a bore hole
or to a drain.
The system will need to have an in-line check valve downstream of
the connection for this valve.
11
COMMON QUESTIONS
Will I need this type of valve if I also have an in-line pump
control valve?
No. This valve is used when you do not have another type of pump
control valve.
What static pressure do I need in my system for this valve to be
able to operate?
We like to see at least 20 psi (138 Kpa).
RECOMMENDATIONS
•
These valves will be a less costly alternative to an in-line pump control valve, but if you have nowhere to discharge the water
then it is an issue. This can be a problem in areas where freezing occurs as outside drains will freeze.
•
A very good alternative if you do not need to add additional
functions to a pump control valve as this valve is only open during starting and stopping of pump so does not create a pressure drop when the system is running.
12
TOPIC THREE
COMBATTING SURGE
IN MY SYSTEM
Surge in pipelines can be catastrophic and can be caused
in several ways. Before determining a suitable method to
eliminate or mitigate surging there are a few things we need
to know.
When does the surge occur? Is this when a pump starts and
stops under normal operation? Or does this occur because
the flow is being suddenly shut off – like in the fire hydrant
situation? Is it due to a power loss?
All of these situations can create surging and there are valves
that can take care of the problem.
WHAT YOU NEED TO KNOW
First, you will need to know what your flow rates are and what your
pressure is during normal operation. What is the system static
pressure?
Secondly, what is the pipe material (yes, it does make a difference)?
How long is the pipeline? What is the pipe size? What is the
topography of the pipe?
13
TYPICAL APPLICATION
Singer Model 106-BPC
Pump Control Valve
with Internal Drop Check
Header Pipeline
Isolation Gate Valve
Booster
Pump
Connect in field
tostation header
for reliable
pressure
signal
Pump Suction Line
Singer Model 106-RPS-L&H
Surge Anticipating Relief
Valve
14
CAUTIONS
If a surge anticipating valve is recommended then you will require a
discharge for the water that will be released if a surge occurs.
Traditional surge anticipating valves do require a minimum system
static pressure of 92 ft (28m). If you do not have this pressure then
all is not lost – we do have a surge solution that will work for you.
COMMON QUESTIONS
I have three pumps feeding into a header. Do I need a surge
valve on each pump?
No, you do not. If anything, having a valve too large or having too
many will actually create more problems for you. One surge valve
on the combined header from the pumps would be sufficient.
Won’t a relief valve take care of surges?
Sadly, a pilot-operated relief valve will not open fast enough to take
care of a surge scenario, because a relief pilot only opens when it
senses the higher pressure, when the pressure surge wave arrives
at the valve which is just too late. That is why you do need a true
surge anticipating valve that will already be opening before the
surge wave reaches the valve.
Will a surge tank system eliminate the need for these valves?
Yes, but at a much larger capital cost and the added expense of ongoing maintenance.
15
RECOMMENDATIONS
•
First, no valve company is ever going to do a complete surge analysis for you. At best we calculate what the maximum surge
you could expect to see over the longest distance of the pipeline,
but that does not take into account other lines feeding into it or
size changes, etc., so if you really want to know the surges you
could see we recommend having an engineering company
conduct a real surge analysis on your system.
• If ever you see surge valve sizes that are close to the size of the
main line, be cautious. Oversizing of these valves can be as much of a headache as under sizing.
•
This surge anticipating valve is mounted in a tee, downstream
of the pump check valve(s) and a sensing line has to be provided
that is connected from the valve to a connection on the main
pump header.
•
If the static pressure is under 40 Psi (275 kpa) we would
recommend a Surge Anticipating on Rate of Rise Control Valve.
This is a very unique valve that actually measures the rapid rate
of pressure rise in a surge event and opens the valve to handle
the surge wave. This valve cannot be oversized and is guaranteed
to always close after a surge event.
16
TOPIC FOUR
CONTROLLING TANK
LEVELS IN MY SYSTEM
There are several solutions to maintaining the level in a tank.
It really depends on whether you want the tank to maintain a
set level or if you can allow the tank level to drop before the
tank refills. Control valves to maintain levels fall into three
categories:
1) Altitude valves – traditionally used on larger storage tanks
and in areas where freezing can occur so you cannot have
exposed pilot tubing or a float in the tank.
2) Float valves – smaller tanks, up to 4 m (13 ft) and areas
where there will be no freezing. Typically used on tanks inside
buildings.
3) Electrically operated valves. These valves rely on a signal
from the top of the tank (level probe or ultrasonic), to actuate a
solenoid on the control valve to open and close the valve.
17
TYPICAL APPLICATION
Sensing connected to
drain line or the reservoir
(completed by others).
Sensing line minimum
recommended size is
3/4 in / 20 mm. Slope to
avoid air pockets.
Non-adjustable
drawdown
Drain
Reservoir
tank
Distribution
to users
Provide connection to
drain for displaced water
from bonnet
Higher pressure supply
18
Singer 106-A-2, one-way
flow altitude control
valve, with a manual
by-pass
WHAT YOU NEED TO KNOW
What is the pipe size, inlet operating pressure and flow rate
required?
What is the height of the high water level in the tank above the
centerline of the inlet pipe?
Where will the valve be located? Ground level?
Is this in a location that will see freezing?
Will the same valve fill the tank and also let water out of the tank?
Do you want to maintain a set level in the tank at all times or can
you allow the tank to empty and then refill? If so, how many feet
(meters) can the water level drop before you want the valve to refill
the tank?
CAUTIONS
If an altitude valve is being used remember that it will need a
sensing point. This should be at least ¾ inches (20 mm) and ideally
situated on a static line connected to the bottom of the tank
or drain of reservoir. If there is no static line then the next best
situation would be the outlet line from the tank. The connection
should also be at the same elevation as the altitude pilot.
If electronic valves are used there has to be a signal to the valve
controller from the tank. This can either be from a pressure
transmitter, conductance probes, or a non-contacting system like
ultrasonic or radar. Remember, if the tank is in a location that
experiences freezing, ice will form on the top and will give a false
reading. The electronic version also requires power on site.
19
COMMON QUESTIONS
When my tank is filling it draws the pressure in the system
down. How can I stop this?
This is very common and a simple solution is to add a sustaining
feature to the level control valve. This ensures that the tank will
fill but will always ensure that there is a preset minimum pressure
maintained in the supply system. The tank will not fill as quickly
when the valve is throttling but at least you will still have pressure in
the system.
Is there a maximum tank height that I can use a float valve on?
If the valve is mounted within 13 ft (4 m) of height difference
between the float and the valve it will be fine. However, on really
high tanks that would mean the float valve could be mounted very
high above the ground, which may not be ideal for maintenance
and operation. That is where an altitude valve or electrically
operated valve has the advantage.
20
RECOMMENDATIONS
• The choice to use float valves versus altitude valves or electronic valves can be broken down this way:
- If it is in a freezing location, the pilot lines will freeze so a float
valve is not practical and ice forming on the surface will impede
top down measurements so an altitude valve is the best choice.
- If the tank is less than 13 ft (4 m) in non-freezing climates, then
a float valve is a good choice. Above that height, then an
altitude valve.
- If the tank is located in a non-freezing environment, and the
location has power then the solenoid option is a good choice
as it also gives the ability to control the fill rate of the tank.
- If there is a chance that the inlet to the altitude valve will have a lower pressure than the head of water in the tank produces,
we recommend adding a check feature to the altitude valve to prevent flow reversal.
21
TOPIC FIVE
MEASURING FLOW WITH
A VALVE IN MY SYSTEM
Control valves can actually be used
to measure the flow in your system!
However, traditionally flow meters
would be used and commonly
in municipal systems these are
electromagnetic types. Depending on
the manufacturer and installation
these can be very accurate
and cost effective. But, what
happens if you have to retrofit
a flow meter and do not have
the straight run space that
these flow meters require? This is where
adding a flow meter into a control valve can start
to make good sense.
WHAT YOU NEED TO KNOW
What are the minimum and maximum flows that you are
likely to see?
What is the pressure in the line?
What is the pipe material?
What are the installation details? Conventional magnetic flow meters
require five pipe diameters upstream and two downstream.
22
Singer Valve recently introduced a control valve with a built in, single
point insertion, magnetic flowmeter. This has proven to be a very cost
effective method of having a flow signal from a control valve that may
also be controlling another variable, i.e., pressure, level, etc.
CAUTIONS
Magnetic flow meters are prone to “noise.” That is electrical
interference due to poor grounding or motors that may be close by.
You cannot always do too much about the motors but you can
take care of grounding. It is always advisable to install grounding
rings (stainless steel plates that sit between flanges that you attach
a ground wire to). These will ensure that the flow meter is well
grounded.
Also try and keep wiring between the flow meter and the convertor
to a minimum.
SPECIAL NOTE: Don’t try and shorten this wire yourself as adding
joints into this cable just makes matters worse as far as noise is
concerned.
Not all flow meters are created equal. Unless you are only ever going
to see maximum flow rate, make sure you specify a meter that lists a
percentage of rate or reading for accuracy, not full scale.
COMMON QUESTIONS
How many straight runs do I need ahead of my valve with an
insertion flow meter?
Ideally three pipe diameters. However, it depends on what is
upstream. If it is a wide open gate valve, this can be installed right
up to the control valve. An open butterfly valve with the stem
vertical will require one pipe diameter, but if the stem is horizontal,
three pipe diameters.
23
Can I install a valve directly to the outlet of my control valve?
This is not ideal but a wide open gate valve will be OK. Butterfly
valves have to be checked to ensure the disc will open into the valve
without binding.
How accurate will this flow meter be?
2% of reading is what the flow meter manufacturer will guarantee
based on their lab testing. It typically is much better than this but
that is the figure that we use.
Remember, all magnetic flow meters are actually reading velocity
and then calculating volume flow, so they all have a low velocity cut
off point where the water is just moving too slowly to accurately
measure. This is 0.3 ft./s or 0.09 m/s.
RECOMMENDATIONS
•
A full line size magnetic flow meter is always going to provide the best accuracy, but will require more space for install. An insertion
magnetic flow meter is a useful recommendation where space is not available.
• Always install grounding rings. This really ensures we get a good
signal from the flow meter sensor to the convertor.
•Maximum distance between the insertion probe and convertor
is 200 ft. (61m). Order the correct length at time of ordering and
only get as much as you need. Avoid running this cable near
electric motors or any other electrical interference. (It is better to
mount the convertor close to the probe and run the 4-20 mA
signal wire if any distance has to be reached.)
24
TOPIC SIX
CONTROLLING FLOW
IN MY SYSTEM
Control valves make excellent flow limiting valves. What we
mean is that they will allow flow up to a preset value and then
if the demand tries to exceed that flow rate the valve will
throttle down to ensure that the flow rate remains at the set
point. Very useful in applications where you can only accept
a certain flow, or you want to restrict a user to a set flow or
where you possibly want to guarantee you never over pump
and risk penalties!
WHAT YOU NEED TO KNOW
What is the pipe size and maximum flow rate required?
What is the minimum and maximum pressure in the pipeline?
CAUTIONS
This valve does use an orifice plate to give the control pilot the
differential pressure that is calculated to control the flow. Because
of that it is important to have your flow requirements sorted out
beforehand. (Typically the orifices are sized to give a low pressure
drop close to the low end of the spring range of the pilot.) Because
the differential pressure is proportional to the square of the flow,
requiring flow adjustments will require pressure setting adjustments
and that may be a problem (depending on the pilot range). The
alternative would be to get a new orifice plate.
Turndown (or range-ability) is typically 2:1.
25
STORAGE TANK
Singer Valve model 106-RF
or Model 206-RF
Isolation valve
Standard paddle style orifice plate
-install between downstream flanges and connect pilot sensing to downstream tap in pipeline
- completed in field by others
26
COMMON QUESTIONS
Do I need any straight runs before this control valve?
No. This valve can be installed with other valves, strainers, elbows,
tees, etc., upstream.
Can I install the orifice plate against the outlet of the
control valve?
Yes, however, ideally you are better to install this downstream to get
a more accurate reading. Tests have shown that five pipe diameters
downstream are ideal but this is not always practical.
RECOMMENDATIONS
•
If full flow control is required (as opposed to flow limiting) then a dual solenoid control valve should be used instead of this valve.
This will allow for full flow range adjustments automatically without the need for an orifice plate.
27
TOPIC SEVEN
CONTROLLING BACK
PRESSURE IN MY SYSTEM
Back pressure or sustaining valves are used in systems to
protect the upstream of the valve from experiencing low
pressure due to high demand downstream of the valve. A
pilot is set to the lowest pressure you require upstream of the
valve, so as long as pressure is greater than this setting the
valve remains wide open. As soon as inlet pressure drops down
to the pilot setting the main valve starts to throttle to ensure
that the upstream pressure never falls below that set point,
regardless of downstream demand. This is a common valve for
such applications as protection of a sensitive user upstream,
reservoir filling and for keeping pumps on their pump curve.
WHAT YOU NEED TO KNOW
What is the pipeline size, flow rates and operating pressure?
What is the sustaining pressure you want to maintain?
CAUTIONS
Because this valve is only concerned with valve inlet pressure, it
has no concern for what is happening downstream. It will even
close fully to protect the upstream pressure so caution must be
used to ensure that this situation would not be dangerous for the
downstream users.
28
Critical User
Singer Model 106-RPS
or 206-RPS Pressure
Sustaining Valve
Residential
29
COMMON QUESTIONS
Can I combine this valve with another hydraulic function?
Yes, certainly. It is very common to see this valve pilot system
paired with a pressure reducing valve so you have a sustaining
valve that as long as the inlet pressure is high above the sustaining
setting will act as a reducing valve, but should inlet pressure drop,
the sustaining feature takes control. It is also common to see this
function installed on altitude valves for reservoir filling.
RECOMMENDATIONS
• In order to set this valve in the field it would really be
advantageous to have at least an isolating valve on the inlet
side of the valve.
• An inlet pressure gauge will also be required to set the valve.
30
my SYSTEM in water distribution systems
A guide to common applications
AUTHORS: MARK GIMSON & ALEJANDRO DUQUE
ABOUT SINGER VALVE
Singer Valve designs and manufactures automatic control valves
for the global water industry. Since 1957, its pilot operated
diaphragm control valves have been installed on virtually
every continent around the world. Whether it is water loss
management in Southeast Asia, water conservation concerns in
Saudi Arabia or urban distribution demands in the United States,
Singer provides water management solutions to governments,
cities, companies and contractors around the world.
WWW.SINGERVALVE.COM
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