1. SNO+ Cover Gas Bag Fabrication and System
Instrumentation, Scintillator Plant
Construction and UI Involvement
September 8, 2013
By Jennifer Mauel
Queen's University Physics Department
1
2. Table of Contents
Section 1: The Cover Gas System
Introduction.................................................................................................................................4
1.1 Cover Gas Bags.......................................................................................................................4
Bag Pressure Tests...........................................................................................................4
Bag Fabrication................................................................................................................7
Bag Boxes.........................................................................................................................9
1.2 Instrumentation.....................................................................................................................9
Laser Distance Sensors....................................................................................................9
Calibration............................................................................................................9
` Reproducibility/Stability Test.............................................................................10
Webcams.......................................................................................................................11
Oxygen Monitors...........................................................................................................11
NTRON Microx Inline ZR....................................................................................12
Calibration, Sensitivity and LAB Compatibility Tests.............................13
Radon Emanation..................................................................................14
Presens OIM Pst6-D12/L20................................................................................15
Vacuum Pump................................................................................................................15
Valves.............................................................................................................................16
Section 2: Scintillator Plant Construction..............................................................................................17
2.1 Leak-checking......................................................................................................................17
2.2 Scintillator Plant Construction.............................................................................................29
Section 3: Lower Universal Interface Leak-Checking............................................................................32
2
3. List of Figures
Figure 1: Bag fitting connects to u-tube manometer and compressed air supply. Laser distance
sensor sits underneath the bag belly.......................................................................................................5
Figure 2: Rotary hand-held heat sealer...................................................................................................7
Figure 3: Helium leak-checker with sniffer probe...................................................................................7
Figure 4: Pre-rubberizing in the negative pressure room.…...................................................................8
Figure 5: Post-rubberizing in the negative pressure room......................................................................8
Figure 6: Cover gas bag in one of the custom-designed boxes...............................................................9
Figure 7 Laser distance sensor circuit...................................................................................................10
Figure 8: Laser distance sensor calibration set-up................................................................................10
Figure 9: Potential webcams for monitoring the cover gas bags..........................................................11
Figure 10: Typical in-line set up of NTRON oxygen analyser.................................................................12
Figure 11: Leak-testing the zirconia probe mounting and ¼” cross.....................................................13
Figure 12: Calibration, sensitivity testing and LAB compatibility testing..............................................14
Figure 13: The Pfeiffer Vacuum MVP 006 diaphragm pump................................................................15
Figure 14: Graph of pumping speed vs. pressure.................................................................................16
Figure 15: Positions of the various manual valves in the Cover Gas System (design is preliminary)...17
Figure 16: Locations (from left to right) of vessels V-23, E-101 and E-307..........................................18
Figure 17: Location of E-304 in Scintillator Plant..................................................................................19
Figure 18: Diagram of E-307..................................................................................................................20
Figure 19: Diagram of V-23....................................................................................................................21
Figure 20: Diagram of E-101..................................................................................................................22
Figure 21: Diagram of E-304..................................................................................................................23
Figure 22: Pumping down E-101 with a bellows pump........................................................................28
Figure 23: Pumping down E-101 with a bellows pump........................................................................29
Figure 24: The Upper Utility Room........................................................................................................30
Figure 25: The Upper Utility Room........................................................................................................31
Figure 26: The Upper Utility Room........................................................................................................31
Figure 27: The temporary door and walls in the Utility Room..............................................................32
Figure 28: Example of a crack between bolts 6 and 7..........................................................................33
Figure 29: Lower UI Leak-Checking Schematic......................................................................................34
Figure 30: Graphs of the leaks found in the outer O-ring.....................................................................35
List of Tables
Tables 1.1-1.4: Trials 1-4 of the Bag Pressure Test and Laser Distance Sensor Reproducibility Test......6
Tables 2.1-2.7: Leak Checking Results for June 11, 12,18, 19, 20, 25, 26 and 27 on vessels V-23, E-
101, E-307 and E-304.......................................................................................................................24-27
Table 3.1: July 22 Inner O-ring Leak Test...............................................................................................35
Table 3.2: July 23 Outer O-Ring Leak Test.............................................................................................36
3
4. Section 1: The SNO+ Cover Gas System
To prevent radon permeating the Acrylic Vessel (AV), the detector will be sealed off from the
lab environment. The LAB Cover Gas System will enable the detector to be sealed without pressure
fluctuations damaging the AV. The system consists of flexible bags to expand and contract, an
emergency u-trap as a pressure safety device and the pipes which connect the system to the
Universal Interface (UI).
System Design:
The Cover Gas System will consist of 3 240L bags made with an aluminized laminate
material. The bags will expand and contract to compensate for pressure fluctuations in the mine
and maintain atmospheric pressure in the nitrogen cover gas. The system instrumentation includes:
• At least one oxygen monitor installed in-line to detect leaks.
• A vacuum pump to regulate the nitrogen level.
• A differential pressure transducer to monitor the difference between the cover gas pressure
and mine pressure (difference between inside and outside of the UI),
• Webcams to visually monitor the bags.
• Laser distance sensors, placed underneath the bag belly to monitor the bag volume.
• Valves:
• Connecting the bags to the UI.
• Connecting the nitrogen boil-off to the bags and the oxygen monitor.
• Connecting the vacuum pump to the bags and the oxygen monitor
• To enable different parts of the system (i.e. the bags and the oxygen monitor) to be
isolated and cleaned by pumping and purgeing with nitrogen.
• To isolate the oxygen monitor when necessary for re-calibration.
1.1 - Cover Gas Bags
In May 2013 the final material and construction method for the cover gas bags had been
determined and a small test bag had been made and leak-checked. Between May and July of 2013,
five full-size cover gas bags were fabricated, leak-tested, and pressure-tested. Follow pressure tests
in May 2013, the design of the cover gas system was modified from 4 200L bags to 3 240L bags. This
is because the bags were found during pressurizing tests to hold a greater volume of air than
originally planned for. Five bags are currently packaged and ready to be installed on site.
Bag Pressure Tests
The purpose of the Bag Pressure Tests were to determine the volume of gas that the full-size
bags could hold before becoming pressurized, as well as the maximum pressure that the bags could
tolerate. The bags needed to withstand a pressure of 0.3psi or greater, as the Emergency U-tube
System will be activated if the cover gas pressure reaches this pressure.
To test the bag volume, a full-size bag was connected to a compressed air supply and U-tube
manometer (see Fig. 1), and gradually pressurized by adding 30-50L of air at a time. In the 4 trials a
pressure build up of 0.005psi was seen at 262L, so it was concluded that 240L would be the
maximum bag volume. Results are shown in Tables 1.1-1.4. The Laser Distance Sensor, which will be
used to monitor the bag volume was also tested at this time to determine whether the voltage
4
5. readings it produced for certain distances were reproducible. Details on these results can be found
in Section 1.2.
To determine the maximum tolerable pressure, a small test-bag was connected via its fitting
to the same U-tube manometer and compressed air supply used for the volume tests. The bag was
filled with air while also being pressed down upon. The bag was found to tolerate a pressure of
0.4psi which is sufficient for the purposes of the Cover Gas System.
Figure 1: Bag fitting connects to u-tube manometer and compressed air supply. Laser distance
sensor sits underneath the bag belly.
Given the maximum allowable pressure in the bags was 0.1psi, the manometer calculation
for the maximum pressure in the bag follows1
:
P1-P2 =ρgh
where
• (P1-P2) is the maximum allowable pressure difference between the bag and the atmospheric
pressure; 0.1psi is approximately equal to 689.475729 Pa.
• ρ is the density of water, assumed to be 1000 kg/m3.
• g is the acceleration due to gravity, assumed to be 9.81 m/s2
Solving for h, the difference in height between the water level on either side of the u-tube
manometer, the change in height for the maximum allowable pressure difference of 0.1 psi was
determined to be approximately 7 cm. No error was assumed in any of the
values/constants/conversion factors, so the value of h also assumes no error.
1 Banaschewski, Kevin, Results of Covergas Bag Testing. May 16, 2013.
5
7. 100 4.75 0.434 0
150 3.90 0.317 0
200 3.67 0.288 0
210 3.58 0.278 0
240 3.345 0.252 0
Conclusions:
Since the bags did not become pressurized at 240L of gas in any of the trials it was
determined that 3 240L bags would provide sufficient pressure compensation in the Cover Gas
System. The laser sensor was also deemed to be sufficiently accurate for distance measurement as
the voltage reading consistently corresponded with the distance measured with measuring tape.
Bag Fabrication
The bag material was cut into 74”x37” rectangles (in the Target Room Clean Room). The pieces
were then heat-sealed with a hand-held rotary heat-sealer apparatus developed in the summer of
2012. The heat-sealer was moved along the desired seam of the bag very slowly 2-3 times to create
an appropriate seal.
Figure 2: Rotary hand-held heat sealer.2
Figure 3: Helium leak-checker with sniffer probe.3
2 M-Pak Systems Online, Constant Heat Roller Series. http://mpaksys.homestead.com/bgpr12.html.
3 Inficon, Helium Sniffer Leak Detector. http://products.inficon.com/en-us/nav-
products/Category/ProductGroup/pg_LeakDetectors?path=Products%2F
7
8. Once sealed the bag would be taken for leak-checking. The bag was filled with helium and a
helium probe was moved very slowly across the surface of the bag, which is known as the “sniffer”
mode on the leak-checker
If no leak was found, the bags were then painted with a black rubberizing spray paint (Plasti-
Dip brand) which helped prevent the development of pin-holes in the material. This was done in the
negative pressure Team Area in the Integrated Learning Centre for safety purposes. Each side of the
bag took a full day to spray paint. The most effective method was to spray a thin layer every half
hour throughout the work day.
Figure 4: Pre-rubberizing in the negative pressure room.
Figure 5: Post-rubberizing in the negative pressure room.
8
9. After spray painting the bags were leak-checked again. Only one of the bags was found to
have a leak after rubberizing, which was caused by a problematic fitting. The fitting was sanded
down and a new bag was made. Five bags are currently available for installation.
Bag Boxes
Boxes were designed and made for transporting the cover gas bags. The aim was to restrict
bag movement during travel as much as possible to avoid the development of pin-holes. The boxes
were customized to fit the size of the bags which were rolled up on each side and rested on a layer
of styrofoam with a hole for the fitting.
Figure 6: Cover gas bag in one of the custom-designed boxes.
1.2 - Cover Gas System Instrumentation
Laser Distance Sensors
Laser distance sensors will be installed under each cover gas bag to monitor the volume. As
the bags expand, the bag belly drops down towards the sensor proportional to the change in bag
volume. The model selected was the Baumer OADK25I7480, which supplies a voltage reading that
corresponds to changes in distance (between 10-100cm) from the sensor.
Calibration:
The distance sensor was arranged in a circuit that included a voltmeter, multimeter, a 500Ω
resistor and the laser. It was calibrated by fixing it to a ruler 1 meter away from a wall, and a piece of
9
10. cardboard was moved along the ruler. Every 10cm the voltage was read on the voltmeter.
Figure 7: Laser distance sensor circuit.
Figure 8: Laser distance sensor calibration set-up.
Reproducibility Test:
To test the reproducibility of the voltage reading for different bag volumes, the laser sensor
was fixed underneath the same bag being pressure-tested (see Section 1.). As the bag was
pressurized the distance of the belly from the laser sensor was measured with measuring tape and
the voltage reading from the sensor was recorded in Tables 2.1-2.4. The position sensor was found
to successfully produce similar voltage readings for similar distances from the bag.
10
Multimeter
500Ω Resistor
Laser
Laser Distance Sensor
Circuit
Laser Distance
Sensor
100cmRuler
Laser Distance Sensor Calibration Set-up
11. Stability Test:
To test the long-term stability of the position sensor, the device was positioned as picture in
the Fig. 8 for one month continuously. The voltage was recorded regularly and was consistently the
same number.
Webcams
A system of webcams will be installed in the Cover Gas System – one for each bag. They will
be connected to the DeltaV system for constant visual monitoring of the bags. On the
recomendation of Joey D, the Night Owl 4-Channel LTE Full D1 DVR 500GB system has been
considered. The purchase includes 4 cameras and a 4 Channel DVR with 500GB harddrive. Cost is
yet to be determined.
Figure 9: Potential webcams for monitoring the cover gas bags.4
Oxygen monitors
At least one oxygen monitor will be installed in-line in the cover gas system to monitor for
leaks. The presence of oxygen in the system is not particularly harmful in itself to the experiment,
but it would indicate a leak which would lead to radon ingress. The requirements for the oxygen
monitors were5
:
1. Ability to run in flow-through mode, for use in the sealed system.
2. The emanation of the oxygen probe and the inside of the analyzer need to meet the
Cover Gas background requirement of 650 atoms/day.
3. Sensitivity of 7ppm oxygen in cover gas.
4 Tigerdirect.com, Night Owl LTE-84500 8 Channel LTE D1 DVR - 500GB Hard Drive, 4 Cameras, Indoor/Outdoor, 30' ft
Night Vision, H.264 Compression, 240 fps, Motion Activated, PC & Mac Compatible,
http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4368615
5 Fatemighomi, Nasim, Oxygen Monitor Specification. June 2013.
11
12. Sensitivity Calculation6
:
A 1.0E-4mBarL/s leak is equivalent to 2590 radon atoms/day.
Concentration of radon in mine air = 5.7E7 atoms/m³
Concentration of oxygen = 6.4E24 atoms/m³
Conc. Radon/Conc. Oxygen = 9.28E-18 atoms Ra/atoms O2
2590 Radon atoms/day = 2.72E20 Oxygen atoms/day leak
Number of Nitrogen atoms in system n = PV/RT
= 123·1000Pa·1.25m³/(8.314Pa·m³/mol·K)/293K
= 3.8E25
Therefore, sensitivity should be 2.72E20/3.8E25 = 7 ppm Oxygen
4. Compatible with LAB vapour.
5. 4-20mA output for the DeltaV system.
6. Low leak rate for in-line mounting (less than or equal to 10E-8mBar·L/s acceptable
for Cover Gas System).
Two Oxygen monitors were found and ordered to be tested for sensitivity, compatibility with
LAB vapour and radon emanation. The monitors found include:
NTRON Microx Inline ZR
Technology: This probe is a screw-mounted zirconia cioxide sensor inside stainless-steel/aluminum
alloy housing. The ceramic zirconia cell allows oxygen ions to pass through at high temperatures,
and the movement of the ions generates an EMF which can be measured to determine oxygen
concentration. 7
Advantages: Cheap, reliable and sturdy.
Disadvantages: Operates at approximately 650°C inside the sensor (40°C outside). This is potentially
hazardous as the flash point of LAB is 120°C-140°C. Radon emanation of the housing/zirconia cell
may be a problem as well.
Cost: $1495.00
Figure 10: Typical in-line set up of NTRON oxygen analyser.8
NTRON Microx Inline ZR Tests:
Following calibration, tests will determine:
6 Fatemighomi, Nasim, Oxygen Monitor Specification. June 2013.
7 Toray Engineering Co. Ltd., The Principle of Measurement of Zirconia Oxygen Analyzers. http://www.toray-
eng.com/measuring/tec/zirconia.html.
8 NTRON, OEM Oxygen Analysers, 2013. http://www.ntron.com/microx-zirconia.asp.
12
13. – Sensitivity
– LAB compatibility
– Radon emanation
Test Design and Methodology:
A 2” pipe-tee has been welded with a ¼” pipe connection welded to one end cap and a
10mm M16x1.5mm thread tapped (for the zirconia probe mounting) on the other end cap. The tee
will be swageloked to a 1/4” cross which will connect to a helium leak-checker, helium gas supply, a
pressure gauge and a vacuum pump.
Leak-Testing the Sensor Mounting and Cross:
Figure 11: Pumping down and leak-testing the zirconia probe mounting and ¼” cross.
The cross was attached to the leak-checker and pumped down. If the pressure reading is on
the order of magnitude of 10E-3mBar, then an appropriate vacuum has been achieved and the cross
can be leak-tested. This was done by spraying each Swagelok connection and the sensor mounting
with a 2-5 second burst of helium gas.
The leak-testing was successful and no significant leak (<10E-8mBar·L/s) was found for the
sensor-mounting, which was the area of concern.
Calibration, LAB Compatibility and Sensitivity:
The device will be calibrated by pumping the tee down to vacuum level (10E-3) and
13
Helium Leak-
Checker
Pipe tee with
Oxygen Sensor
attached
Pressure Gauge
14. supplying helium gas into the system, which has a known level of oxygen (2-4ppm9
). The reason for
using helium gas (rather than nitrogen) is purely convenience, as there is a helium container in the
emanation room where tests will take place. Calibration will also determine the sensitivity of the
oxygen monitor. Since the sensor claims to have a sensitivity of 1ppm, flowing 2-4ppm oxygen (in
the helium) will indicate whether the sensor can produce a reading close to the 1ppm oxygen
concentration.
To test LAB compatibility, a small amount of LAB will be placed at an end in the pipe tee.
Running the oxygen monitor in helium gas and LAB vapour for at least one full day should determine
whether or not the device is compatible with the substance.
Following LAB tests, provided LAB has no apparent effect on the sensor, sensitivity will be re-
tested. This will further determine whether LAB damages the sensor - whether it affects the
sensitivity. Sensitivity will be tested by again supplying helium gas to the system.
Figure 12: Calibration, sensitivity testing and LAB compatibility testing.
Radon Emanation Test:
To prepare for emanation the pipe tee and cross was disconnected from the helium gas
supply and pumped down for roughly three hours. It is important to remove all helium gas from the
tee as it emanates a significant amount of radon. Some out-gassing will still occur in the stainless
steel after pumping down which will have to be taken into account for the emanation tests.
9 Modern Industrial Equipments Private Ltd., Industrial Gases. http://www.indiamart.com/modern-industrial-
equipments/industrial-gases.html.
14
Helium gas
supply
Pressure Gauge
Pipe tee with
Oxygen Sensor
attached
Vacuum Pump
LAB will go in
here
15. Emanation is currently underway.
Presens OIM PSt6
Technology: Polymer optical fibre inside a screw-mounted stainless steel fitting. A blue-green LED
light excites the oxygen sensor to emit fluorescence, and when the sensor encounters an oxygen
molecule the excess energy is transferred to the oxygen molecule which decreases or “quenches”
the fluorescence signal10
.
Advantages: Temperature during operation and radon emanation is not likely to be an issue. The
Fibox 3 LCD Trace, which is the fiber-optic oxygen transmitter, can have inputs from multiple oxygen
sensors, in case more than one is needed for the cover gas system. (The technology is very cool!)
Disadvantages: Expensive.
Cost: Probe + Transmitter = $1 308.00 + $8 542.00 = $9 850.00
No testing apparatus has been designed for the Presens monitor yet.
Vacuum Pump
A vacuum pump will be installed in the Cover Gas System in for the purpose of purging the
system with Nitrogen and regulating Nitrogen levels. The pump selected was the Pfeiffer Vacuum
MVP-006 Diaphragm Pump. It was chosen for it's small size, which gives a slow and manageable
pumping rate of 6L/min. Further properties include:
• 24 (± 10%) V DC power supply.
• G 1/8” flange (in and out) with common metric vacuum thread standard.11
(It will need
adapter for the 1/4” pipe it connects to.)
The cost of the pump was $1825.00.
Figure 13: The Pfeiffer Vacuum MVP 006 diaphragm pump.12
10 Presens Precision Sensing GmbH, The Smart Measurement Method.
http://www.presens.de/products/brochures/category/sensor-probes/brochure/oxygen-probes.html#tab-probes.
11 ANVER Corp Vacuum Fittings Explanation, 2013. http://www.anver.com/document/vacuum%20components/vacuum
%20cups/Fittings/vacuum-fittings-conversions.htm
12 Pfeiffer Vacuum, MVP 006-4, Diaphragm Pump, 24V DC. http://www.pfeiffer-vacuum.com/products/diaphragm-
pumps/mvp-006/onlinecatalog.action?detailPdoId=4223
15
16. Figure 14: Graph of pumping speed vs. pressure for the MVP 00613
.
Valves
Two kinds of valves will be installed in the cover gas system for (1) 2” piping and (2) 1/4”
piping (see Fig. 15).
(1) Three 2” Edge-welded or 3 3/8” CF flanged valves will connect the bags to the UI. The
requirements were as follows:
• All-metal (stainless steel, ultra-pure)
• 2” tube or 3 38” CF flange connection
The valve of choice is the Carten Controls HB 2000-10LV, which was the only valve found to
fit all the requirements. Due to the cost of a new model ($3 165.00), alternative options are
currently being investigated.
(2) There will also be (likely) four 1/4” VCR manual or actuated valves, positioned in front of:
• The boil-off nitrogen supply.
• The vacuum pump.
• Each bag.
• The oxygen monitor.
These valves are critical for cleaning the system, as it will be possible to isolate system
components (i.e. the bags or the oxygen monitor) to pump and purge with boil-off nitrogen. Also
when the oxygen monitor needs re-calibration, it can be isolated from the bags to perform this
operation. If there is a leak in one of the bags, then the valves going to the bags can be closed until
the leaking bag is identified. These valves are reasonably priced and available from Swagelok
company.
13 Pfeiffer Vacuum, MVP 006-4, Diaphragm Pump, 24V DC. http://www.pfeiffer-vacuum.com/products/diaphragm-
pumps/mvp-006/onlinecatalog.action?detailPdoId=4223#product-characteristic
16
17. Figure 15: Positions of the various manual valves in the Cover Gas System (design is preliminary).
Section 2: Scintillator Plant Construction
2.1 - Leak-checking
To ensure LAB purity it is important that the vessels being installed in the Scintillator Plant be
vacuum tight. The target level for the Uranium chain due to radon permeation leads to a vacuum
leak tightness requirement of 10E-6mbar·L/sec (for all phases of the experiment). Although Rn
background is less critical for the double beta decay phase, 210Pb plateout will collect as
background for the solar neutrino phase. Krypton and Argon levels require the same air leak rate.
Thus in order to achieve below target background levels, vessel fittings are required to have a leak
rate of 10E-9mbar·L/sec. Vessels and pumps require a leak rate of 10E-8mbar·L/sec 14
.
On the days that I was assigned to work with Andrew Stripay underground, I was able to
assist with helium leak-checking and torquing down the Scintillator Plant vessels to prepare them
for installation. For leak checking each vessel would be pulled under a vacuum and a small amount
of helium would be sprayed on the fitting being tested. Once helium was sprayed, the leak rate was
recorded approximately every five minutes or more frequently depending on the speed of the leak
(to prevent missing the peak leak rate). Once the peak was reached the leak rate was recorded less
frequently as the leak rate returned to acceptable levels. The vessels that were leak-tested include
V23, E-101, E-307 and E-304. The following diagrams give a visual description of each vessel and
indicate their locations n the Scintillator Plant.
14 Ford, Richard, Scintillator Process Systems. March 4, 2012.
17
2” Edge-welded
or 3 3/8” CF
1/4” VCR
34. Figure 23: Pumping down E-101 with a bellows pump.
2.2 - Scintillator Plant Construction
I was also able to contribute to the construction of the Scintillator Plant on the days I was
assigned to work in the Utility Room. My activities included:
• Covering vessels with plastic tarp and taping (to protect from drywall dust).
• Setting up temporary tarp walls and ceilings to prevent dust contamination in clean lab area.
• Vacuuming.
• Painted scaffolding.
• Disposing of spare drywall pieces.
• Rewired network cables into drywall area.
• Carrying construction materials (scaffolding, etc.) to Utility Room.
34
37. Figure 26: The Utility Room is getting a little crowded.
Figure 27: The Upper Utility Room.
37
38. Figure 28: The temporary door and walls in the Utility Room.
Section 3: Lower Universal Interface Leak-Checking
The first connection point between the AV and the calibration hardware is the Lower UI. To
ensure that no contamination from outside media permeates the detector, it is critical that the seal
between the UI and the detector is airtight. The seal consists of two fluorocarbon O-rings (a double
O-ring seal), which is the sole separation volume between the outside hardware and the detector.
The maximum allowable leak rate of the seal is 10E-8 mBar·L/s. Additionally the seal will be pumped
and purged with nitrogen gas to prevent Radon entering the air in the volume. Leak testing activities
have found that in the worst-case scenario the seal meets this criterion. More specifically, it was
found that the outer O-ring leaks significantly more than the inner O-ring. Thus, the total leak rate
of the seal was found to exceed the required value by several orders of magnitude15
.
On July 22 and 23 I assisted Benjamin Davis-Purcell in leak-testing the inside and outside of
the UI. There are six cracks between the teflon spacer pieces as there are six pieces each for the
inner and outer spacers. Bursts of helium (5 seconds at 29.5psi) were sprayed into these cracks, as
they were the optimum way to get helium past the spacers to reach the O-rings. Once the helium
was sprayed the crack was sealed with aluminum tape to ensure the helium was forced into the
15 Davis-Purcell, Benjamin, Lower UI Leak-Checking. August 30, 2013.
38
39. crack and reaching the inner or outer O-ring. At the same time helium was being blown, the leak-
checker was on and pumping the volume to vacuum. The leak rate was monitored at 15-second
intervals for 2 minutes, or longer if the leak rate was still increasing after 2 minutes. If a leak was
detected, then helium would also be sprayed nearby the crack (see Fig. 27) to determine whether it
was indeed the source of the leak. Each crack is denoted by the bolts it lies between (e.g. bolts 6/7).
The results are summarized as follows16
:
• Inner O-Ring: No leak rate increase detected.
• Outer O-Ring: - No measurable increase between bolts 18/19, 24/25, 30/31, 5/6, 7, 7/8,
8/9, 9/10, 10/11, 11/12, 13/14
- Slight increase at bolts 12/13, 36/1
- Very large increase at 6/7
Figure 29: Example of a crack between bolts 6 and 717
.
16 Davis-Purcell, Benjamin, Lower Universal Interface. August 15, 2013.
17 Davis-Purcell, Benjamin, Lower UI Leak-Checking. August 30, 2013.
39
40. Figure 30: Lower UI Leak-Checking schematic.
40
UI
Helium Leak-
checker
Leak-checker
exhaust – run
out of DCR into
SNO+ Control
Room
Pumping down
O-ring volume
Lower UI Leak-Checking Schematic
41. Figure 31: Graphs of the leaks found in the outer O-ring18
.
Table 3.1: July 22 Inner O-ring Leak Test
Bolt 6/7 12/13 18/19
Time (s) Pressure
(mBar)
Leak Rate
(mBar·L/s)
Pressure Leak Rate Pressure Leak Rate
0 3.00E-1 9.20E-7 3.20E-1 1.00E-7 3.3E-1 1.20E-7
15 3.00E-1 9.20E-7 3.20E-1 1.00E-7 3.3E-1 1.20E-7
30 3.00E-1 9.20E-7 3.20E-1 1.00E-7 3.3E-1 1.20E-7
45 3.00E-1 9.20E-7 3.20E-1 1.00E-7 3.3E-1 1.10E-7
60 3.00E-1 9.20E-7 3.20E-1 1.00E-7 3.3E-1 1.10E-7
75 3.00E-1 9.10E-7 3.20E-1 1.00E-7 3.3E-1 1.10E-7
90 3.00E-1 9.00E-7 3.20E-1 1.00E-7 3.3E-1 1.10E-7
18 Davis-Purcell, Benjamin, Lower UI Leak-Checking. August 30, 2013.
41
