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Liquid Nitrogen Distribution System


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Title: Liquid Nitrogen Distribution System

Liquid Nitrogen Distribution System
  • This tutorial is intended to familiarize EOS
    personnel with the operation of the Liquid
    Nitrogen Distribution System (LNDS)
  • Contents
  • 1. System Description
  • 2. Manual Control Panel
  • 3. Remote Control
  • 4. Alarm Response

System Description
  • The APS has installed a Liquid Nitrogen
    Distribution System (LNDS). This system
    consists of four modules A - D. Each module is
    supplied by a 3000 gallon liquid nitrogen dewar.
    These dewars are located in the open gas yards
    between 431/432, 433/434, 435/436, 438. The
    system is operated at approximately 40-psi
    pressure and is always kept full under normal
    operating conditions. The lines are vacuum
    jacketed for insulation purposes and do not show
    evidence of the cryogenic liquid inside. Piping
    is marked to indicate that the line contains
    liquid nitrogen.  

System Relief Valve
Shut Off Valve
3000 Gal. Dewar
Vacuum Jacketed Transfer Line

Pneumatic Dewar Valve
System Description Graphical Representation
Each module has a temperature sensor at its
center and each end. There are a total of 35
individual drop lines supplying LN2 to each of
the Insertion Device (ID) beamlines.
Mechanical keep full valve Electrical keep full
valve Temperature sensor located here
Mechanical keep full valve Electrical keep full
valve Temperature sensor located here
Temperature sensor located here
Interconnect valve
Main Feed line
User Drop Line
User Drop Valves
Dewar Valve
3000 Gallon Storage Dewar
System Description Graphical Representation
System Description Interconnect Valves
The modules are joined by pneumatic interconnect
valves. This allows an alternative source of LN2
for a Module should its own 3000 gallon dewar run
low. The interconnect valves are between Modules
A-B, B-C, C-D
Interconnect valve
System Description Dewar and Drop Valves
  • A pair of manual and pneumatic valves connect the
    3000 gallon dewar supply to the distribution line
    circling the storage ring mezzanine. Each truck
    lock also contains an LN2 fill station for
    experimental dewars. The fill stations are
    isolated from the main dewar by a manual shut off

Manual shut off valve for fill stations
Manual isolation valve for LNDS
Pneumatic Dewar valve for LNDS
Pneumatic User Drop valve
Compressed Air Line for pneumatic valve operation
  • The LNDS supplies liquid nitrogen each ID
    beamline. The User Drop valve is a pneumatic
    valve used to control the flow of LN2 to the
    beamline. Components and connections to each
    drop vary with user need.

System Description Keep Full System
The lines are kept full via mechanical float Keep
Full valves (one on either side of each module)
that vent boil off gas thus keeping liquid in the
line. As a back up, electrical keep full valves
are adjacent to the mechanical valves.
Temperature sensor Monitors line temperature to
determine if liquid is present.
Mechanical float keep full valve Vents gas to
keep liquid in the line.
Electrical keep full valve (used only as a
User Drop Valve
User Drop Line
Distribution Line
System Description Pneumatic Valve Position
  • The pneumatic valves have two limit switches used
    to communicate their position (open or closed) to
    the programmable logic controllers (PLCs) that
    monitor the system. A 0 100 position
    indicator can be used to visually indicate if a
    valve is opened or closed.

Position Indicator
Open Limit Switch
100 (open)
0 (closed)
Close Limit Switch
Shown OPEN
Manual Control Panel
  • Each module has a manual control panel located in
    a rack on the storage ring mezzanine. These
    controls are just downstream of the cross over
    piping from each truck lock area to the LN2
    distribution line circling the storage ring
    mezzanine. These racks are designated
  • 7-ID-AR-RR02
  • 15-ID-AR-RR02
  • 23-ID-AR-RR02
  • 34-ID-AR-RR02

Manual Control Panel Valves
  • All pneumatic valves for a module can be operated
    from its control panel. All valves capable of
    being controlled have a three-position toggle
    switch with positions labeled
  • Each valve can be opened or closed by placing
    the switch in the appropriate position. Valve
    position is indicated on the panel by either a
    green (open) or red (closed) LED.
  • Only those valves whose toggle switches have
    been placed in the AUTO position can be remotely
    operated. Remote operation can be controlled by
    the touch panel screen or via an EPICS control
    screen run on a PC or UNIX workstation.
  • Operation in manual mode is restricted by the
    LNDS System Manager.

Manual Control Panel 24VDC Power Supplies
  • Each module has a PLC (programmable logic
    controller). It is powered by a 24VDC power
    supply. The voltage and current meters are on
    the left hand side of the control panel.
  • A second 24VDC power supply provides power to the
    valve solenoids, position limit switches, etc.
    The voltage and current meters are on the right
    hand side of the control panel.
  • The voltage for both should read 20 VDC to 24VDC.
    The current will vary depending upon the devices

Controls Power Supply Voltage and Current
Field Device Power Supply Voltage and Current
Manual Control Panel LOVE Controllers
  • Modules A, B, and C each have three thermocouples
    which monitor the temperature throughout their
    distribution lines the D module has four. They
    are located at either end of each module and at
    its center. The fourth thermocouple for Module D
    measures the temperature at the very end of the
  • LOVE controllers on the control panel monitor and
    display the thermocouple temperature readings.
    These readings are used to indicate that there is
    liquid nitrogen within the line. If the reading
    is 155 C or colder, liquid nitrogen is present.
  • The temperature at each electronic Keep Full (KF)
    valve is monitored and will read -60 C if there
    is liquid in the main line. Alarm points are set
    to report if the system is warming up.
  • LOVE controllers on the control panel also
    display the pressure and level for its 3000
    gallon dewar. Dewar pressures range from 30 - 40
    psi. Dewar levels are displayed in Inches of
    H20 and are scaled from zero (completely empty)
    to 100 (full). Alarm points are set at 17 inches
    of H20 to report low levels.

1 - Upstream line temperature 2 - Center line
temperature 3 - Downstream line temperature
Dewar Pressure (PSI) Dewar Level (In of H20)
1 - Upstream KF temperature 2 - Downstream KF
Manual Control Panel Touch Screen Display
  • A touch screen display located at the top of the
    Manual Control Panel is the primary control
    device for any LNDS module.
  • Three different screens display all relevant
    information regarding the system. Normally, a
    graphical representation of the module is
    displayed. This STATUS SCREEN provides the same
    information as the LEDs on the control panel and
    values as displayed on the LOVE controllers. It
    does not contain any control functions.

Manual Control Panel Touch Screen
  • By touching the area marked GO TO ADMIN SCREEN,
    a new screen is displayed which requires a
    password. (The System Manager and designee use
    this screen to set the administrative

Pressing GO TO ADMIN SCREEN yields touch Pad
Type the correct password, press ENT and then
press GOTO ADMIN SCREEN for access.
Manual Control Panel Touch Screen Display
  • When the correct password is entered, a screen
    appears that allows administrative selection of
    which valves can be controlled via the touch
    screen and/or EPICS.
  • If the ENABLE DEWAR is not granted, the Dewar
    valve cannot be remotely controlled.
  • If GLOBAL ENABLE is not given, no valves in the
    module can be remotely controlled.
  • Individual valves can be remotely controlled when
    the proper permit is granted by pressing the
    ENABLE VALVE OPERATION buttons. Permits are
    shown by a green indicator light.

By touching the area marked GO TO OPERATIONS
SCREEN, the operation screen appears.
Manual Control Panel Touch Screen Display
  • The User Drop valves can be operated from the
    OPERATIONS screen provided that the switch on the
    control panel controlling the valve is in the
    AUTO position and that ENABLE VALVE OPERATION
    permit has been granted by the LNDS System
    Manager to allow remote operation of that valve.
    Remote control of these valves via EPICS requires
    that the same conditions be met.

Remote Control EPICS
Click here for LNDS_Top.adl
  • Remote control and monitoring of the LNDS is
    achieved through EPICS display screens.
  • XFD-Display.adl is the main control screen used
    by the Floor Coordinators. From this screen
    there is a button used to access LNDS_Top.adl.

Remote Control EPICS
  • The LNDS_Top.adl screen uses EPICS process
    variables (PVs) to display the status of all four
    modules. Green, yellow and red are used to
    denote the status of valves, pressures,
    temperatures and level readings.

Open User Drop valves Open Keep Full valves Open
Dewar valves Closed Interconnect Valves
Interconnect Valve
User Drop Valves
Closed User Drop valves Closed Keep Full
valves Closed Dewar valves Open Interconnect
Temperature readings
Unknown condition or Fault -Temperature out of
range -Pressure too high/low -Dewar level too
Dewar Valve
Dewar Pressure
Dewar Level
Use Rate for each module
Average Use Rate setting
LNDS_Module.adl control screens
  • Usage Rate / 10 Min intervals are shown at the
    bottom. A FC has the ability to set a normal
    use rate to compare to and to trigger an alarm
    when it is exceeded.

Remote Control EPICSUse Rates
  • Abnormally high use rates can be detected when
    their value exceeds the estimated consumption (in
    IN of H20) set by the floor coordinator. An
    overly large use rate can imply a leak in the
    distribution line.
  • Values of a use rate lt 0.3 are attributable to
    normal fluctuations.
  • Values of a use rate gt 0.3 and lt 0.5 imply that 1
    user is drawing LN2 from the module.
  • Values of a use rate gt 0.5 and lt 0.9 imply that 2
    users are drawing LN2 from the module.
  • Values of a use rate gt 1.0 and lt 1.4 imply that 3
    users are drawing LN2 from the module.
  • Values of a use rate gt 1.5 and lt 1.9 imply that 4
    users are drawing LN2 from the module.
  • Because of the nature of the users draw of LN2
    it is unlikely that one would observe use rates
    greater than (0.5 Number of Users allowed to
    open their Drop Valve). Consequently, alarm
    points are set depending upon the number of users
    on a module.

Implies 1 2 beamlines drawing LN2 from the
Conservatively set for 4 beamlines connected to
this LNDS module.
Remote Control EPICSAlarm Conditions
  • Dewar pressure out of range (lt28 or gt75)
  • Dewar level low (lt18)
  • Line temperature warm (gt-155 C)
  • Use rate out of range. (gtEST. IOW)

When these ranges are exceeded, the EPICS PVs
display the fault condition in red. Also, an
email page will be sent to the 0101 pager and the
LNDS System Manager.
Module A, Dewar Level Low alarm
Remote Control EPICS Valve Control
  • LNDS_ModuleX.adl (XA, B, C, or D) are the EPICS
    control screens each module. They represent the
    system graphically and are the displays from
    which the pneumatic valves can be controlled
    remotely. REMEMBER the only valves that can be
    controlled remotely are those whose manual switch
    is in AUTO and had been allowed administratively
    to be operated remotely.

Keep Full valve (Normally closed)
Interconnect valve (Normally closed)
User Drop valves
Dewar Valve
Remote Control EPICS Access Status
  • ACCESS STATUS is used to allow or deny remote
    accessing of the control PVs used by EPICS. It
    has three states User, System Manager, and No
    Control. Users can control their individual drop
    valve via their own computer network. The FC is
    provided with the ability to override the user
    control if system problems warrant. Remember,
    though, valve operation from EPICS can be
    over-ridden via the manual control panel at any
    time. Any valve switched out of the AUTO
    position into the OPEN or CLOSED position is no
    longer controlled through EPICS.

NOTE When Access Status is changed, Control
Access to ALL modules is changed.
Click to change Access Status
Remote Control PLC monitoring control
  • Along with the EPICS PVs, the PLCs monitor the
    readings from the LNDS sensors. The PLCs have
    been programmed to automatically close valves in
    order to protect the system from damage. EPICS
    alarm points are set higher than the values at
    which the PLCs will act. The reason for this is
    to allow the Floor Coordinator time to react to
    the situation and take precautionary steps to
    isolate the problem.
  • The PLC for the individual modules are programmed
    to take the following actions
  • Close Dewar valve if the Dewar Pressure is gt 85
  • Close Dewar valve if the Dewar Pressure is lt 20
  • Close All User Drop valves if the Distribution
    Line Temperature is gt -150 C
  • These conditions can be overridden via the
    manual controls. They should not be overridden
    without first contacting the LNDS System Manager
    or their designee.

Remote Control Data Verification
  • There are times when the information displayed on
    EPICS does not seem to be consistent with normal
    operations of the LNDS. For example, a
    temperature reading has been observed as
  • TS-C3 - 200
  • The actual temperature of liquid nitrogen is
    -196 C, so this reading should be considered
    suspect. Readings like this sometimes occur when
    there are network problems. If there is ever a
    question regarding the validity of the
    information on the EPICS screens, the Manual
    Control Panel should be checked directly.

Alarm Response
The EPICS controls software is programmed to
alarm if certain PVs report values outside of the
expected operational range. If an alarm occurs
the LNDS_Top.adl screen should be consulted for
an overview of the system. On occasion alarms
are caused by problems with the EPICS PV
gateways. Regardless, floor coordinators should
always determine the cause of any LNDS alarm.
  • If any TEMPERATURE reading is in alarm it is
    possible that there is insufficient liquid within
    the distribution line for that module.
  • If any PRESSURE reading is in alarm it is
    possible that there is too little or too much
    pressure within the system to operate properly.
  • If any DEWAR LEVEL reading is in alarm this means
    that there is insufficient liquid in the 3000
    gallon dewar for that module.

Alarm Response Temperature
The temperature readings fluctuate throughout the
day. If a temperature reading is higher than
-155 C, the EPICS software will put a red box
around the alarming PV on the LNDS_Top.adl
screen. It will also send out an email page.
For example LNDS ALARM DTEMP3 -154.0
(01/20 0015)
In this example, the temperature reading TS-D3
temporarily spiked at 0015 hrs and triggered an
alarm, sending out an email page to 0101 and the
LNDS System Manager. When the temperature
reading dropped below -155 C the box around the
corresponding PV changed from red to green.
Alarm Response Temperature
If any distribution line temperature reading
within a module is higher than -155 C it could
mean that there is insufficient liquid within the
line. Record the Dewar valve position, the Dewar
Pressure, and the Dewar level in the Floor
Coordinator shift log.
If Dewar Valve Open Dewar
Pressure 28 psi lt (Reading) lt 75 psi Dewar
Level gt17 Inches of H20 Temperature in
alarm for more than 5 minutes Then Close the
Dewar Valve for the module and open the
Interconnect valve for the adjacent module with
the greater Dewar Level.
As shown in the previous slide, the system can
revert to normal operating temperatures within a
few minutes. Remember, if the temperature rises
above -150 C the PLC will automatically close
all of the User Drop valves. If this occurs,
close the Dewar valve and open the appropriate
interconnect valve IMMEDIATELY. If the
conditions above are not met, contact the LNDS
System Manager.
Alarm Response Pressure
The EPICS controls software is set to alarm in an
overpressure or underpressure situation. If the
system alarms, check the Dewar valve position,
the Dewar Pressure, and the Dewar level.
Open Dewar Pressure (Reading) gt 75
psi Dewar Level gt17 Inches of
H20 Then Close the Dewar Valve for the module
and open the Interconnect valve for
the adjacent module with the greater Dewar
Open Dewar Pressure (Reading) lt 24
psi Dewar Level gt17 Inches of
H20 Then Close the Dewar Valve for the module
and open the Interconnect valve for
the adjacent module with the greater Dewar
Pressure values can drop appreciably ( lt28 psi )
when several Users are drawing liquid nitrogen
from the system at the same time. If you notice
the pressure dropping consult the Usage rate and
see that the pressure returns to normal operating
conditions after 10-20 minutes.
Alarm Response Dewar Level
The EPICS controls software is set to alarm if
the Dewar Level drops below 17 inches of H20. If
the Dewar level in a module alarms, close the
Dewar valve, and open the interconnect valve of
the adjacent module which has the greater
level. The LNDS is on a three day per week fill
schedule Mondays, Wednesdays, and Fridays. The
liquid nitrogen deliveries typically occur before
12 noon. Since each of the 3000 gallon Dewars
will report a low level alarm at 17 inches of
liquid, this means that each Dewar only has
roughly 80 inches of liquid for use. During peak
consumption the LNDS loses 25 inches of liquid
per Dewar per day.
Fill to 100 inches of liquid 24 hours 75
inches of liquid 24 hours 50 inches of
liquid 24 hours 25 inches of liquid ALARM
17 inches of liquid
Consider an 800 a.m. Friday morning fill. At
800 a.m. Monday morning there will be roughly 25
inches of liquid left in a particular module. If
this is the case for all of the modules, there is
insufficient liquid in the system to last one
more day. A fill of the entire system is
required by roughly noon, otherwise an emergency
delivery needs to be initiated. If you suspect
that the LNDS is running low, contact the LNDS
System Manager.
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