1. EDM Collaboration Meeting, February 14-15, 2007 Valve Bucket-Dewar Tests Steve Williamson UIUC

2. EDM Collaboration Meeting, February 14-15, 2007 Goals of the Bucket Dewar Tests Test valve components (not complete valves)  Test concepts for seat and stem  Materials  Geometry  Develop technology for making seat and stem (e.g. polishing Teflon)  Verify that valve seat/stem design sufficiently seals LHe II  Determine required seating force  Test seal for many cycles  Test bellows for many cycles  Test LHe “hydraulic” actuator concept (?)

3. EDM Collaboration Meeting, February 14-15, 2007 How Good?  Two types of valves:  V1, V2, V4, and V5 seal “gas” of dilute 3 He in purified 4 He  Use molecular flow model: average velocity (v av ), ballistic mean free path ( ), leak time constant (  )  Assume some allowed degradation  Calculate allowed leak area (atoms hitting leak area leak out)  Evaluate conductance and flow of gas under test conditions.  V3 and V6 seal liquid He II  Max V3 leak rate determined by allowed pressure change during  m  Max V6 leak rate determined by allowed heat load during regeneration Example: Cell Isolation (V1) Valve

4. EDM Collaboration Meeting, February 14-15, 2007 Two Types of Valves 1.4.6 Volume Displacement 1.4.11.1 Volume Displacement Interconnect Plumbing 1.4.10.1 Cell Isolation (V1) Valve Actuators and Interfaces 1.4.5 Purifier 1.4.10.6 Purifier isolation (V6) Valves 1.4.1 3He Atomic Beam Source (ABS) 1.4.2 ABS Interface 1.4.3 Polarized 3He Collection System 1.4.8 Pressurizer 1.4.10.5 Purifier Control (V5) Valve 1.4.10.4 Collection Isolation (V4) Valve 1.4.10.3 Pressurizer Standoff (V3) Valve 1.4.10.2 Pressurizer Isolation (V2) Valve 1.4.11.2 Collection/ Purifier Interconnect Plumbing 1.4.11.3 Pressurizer/Cell Interconnect Plumbing Seals He II liquid Seal 3 He “gas”

5. EDM Collaboration Meeting, February 14-15, 2007 Some Limits ValveLimit Test Conditions Q m (mol/s) Q v at 300K (atm-cc/s) V1 Cell Isolation 10% drop in signal over  m =10 4 s 77 K  p = 45 Torr 6.07  10 -6 0.150 V2 Pressurizer isolation 5% drop in signal over 500 s fill time 77 K  p = 45 Torr 1.88  10 -4 4.63 V3 Pressurizer stand-off 1% drop in pressure over  m =10 4 s 0.5 K 760 Torr 4.55  10 -6 0.112 V4 Collection Isolation 3 He concentration drops by 5% during 500 s storage time 77 K  p = 45 Torr 4.79  10 -6 0.118 V5 Purifier Control Signal drops by 5% during 500 s fill time 77 K  p = 45 Torr 9.41  10 -5 2.32 V6 Purifier Isolation 1 mW heat load during regeneration 0.5 K  p = 3 Torr 6.88  10 -6 0.169 Note: these are “whistlers” (very high leak rates)

6. EDM Collaboration Meeting, February 14-15, 2007 First step: Build Bucket Dewar Valve Tester Gas Handling Circuit for valve seat testing DGH 8/13/06 to helium gas source to vacuum pump to vacuum pump to leak detector Baratron 1Baratron 2 Valve being tested Liquid helium level This is the tube that the actuator goes through This volume should be as small as possible to reduce evacuation and filling time Valve seat assembly Valve actuator Vacuum/motion feed-through Heat shields Supply tube Exhaust/actuator tube LHe level sensor

7. EDM Collaboration Meeting, February 14-15, 2007 Bucket Dewar Test Insert  Completed in early December  Used for room temp, LN2, LHe, and LHe II tests since then. Top Flange (pretty crowded) The Insert Installed in Dewar

8. EDM Collaboration Meeting, February 14-15, 2007 Valve Seat/Stem Geometry*  Benefited from experience of John Doyle’s group at Harvard.  Ball designs are insensitive to rotations – but fail if seat/ball are out of round.  Flat designs are insensitive to XY rotation, but fail if surfaces are not flat. * From notes of Nathan Brahms Harvard Choice

9. EDM Collaboration Meeting, February 14-15, 2007 More on Geometry*  Empirically, conductance (C) depends on the geometry.  Smaller r, larger F is better. (Bolted flanges can produce enormous force.)   (T) is basically constant below 77 K  Two regimes for w:  Knife-edge  Insensitive to dirt  Not very repeatable (edge deforms other surface)  Large area  Need smooth surfaces  Need higher closing force  Use soft material to deal with dirt. * From notes of Nathan Brahms w r

10. EDM Collaboration Meeting, February 14-15, 2007 Valve Materials  Valves don’t seal because of:  Surface roughness  Dirt  Two types of materials:  Hard: glass, metal, Al 2 O 3 *, Vespel, Kapton, Torlon  Often come with good surface (Kapton, glass)  Do not accommodate dirt  Soft: Teflon* (PFTE), Kel-F, PFA (fluorocarbons)  Difficult to polish  Can be deformed by closing pressure  Composite materials are out (too hard to polish). Seat Boot SoftHard SoftBiological valves. Imprint of seat on stem must not be misaligned.* HardNo hole in polished hard material. e.g. Engine valves. Fail if held open by dirt.

11. EDM Collaboration Meeting, February 14-15, 2007 Our First Shot  Torlon 5030 with Kapton gasket  Problems:  Composite material is too hard to polish (used stainless steel)  Kapton and Torlon (or steel) are both “hard” materials (dirt problem). Also tried a Teflon gasket.  A gasket seals on TWO surfaces. Use Teflon boot. Torlon 5030 piston (but initially acrylic or aluminum) Torlon 5030 outer wall and seat Torlon 5030 gasket clamp Kapton gasket Boot Seat Kapton Gasket

12. EDM Collaboration Meeting, February 14-15, 2007 Lessons  Dirt is a REAL problem. Sintered filters seem to make it worse.  Our initial w was too small. Try larger w  smaller r  If it doesn’t seal at room temperature, it won’t seal when colder.  Use simple apparatus on leak detector to check seat/boot  Allows much faster tests – no cryogenic turn-around. Seat Teflon “Boot” Load Cell Inlet to leak detector Ball Joint Screws for compression  clean room

13. EDM Collaboration Meeting, February 14-15, 2007 Polishing Teflon  Teflon is soft – tends to “gouge” when polished.  Harvard Technique  Sand by hand on granite with 400, 600, 1000, 1200, 1500 grit sandpaper.  On lathe, 1500 grit, then “plastic polish” with polishing cloth.  Hours of grad student labor.  Another technique (light-guide machining):  Diamond machine on lathe (slow feed, high RPM).  Surface is improved if Teflon is “frozen” by cooling in LN2 before machining.  Another idea:  Teflon “melts” at 327° C (begins to decompose around 350 ° C)  Use optical flat pressed against surface “cast” a flat surface. Diamond Tool

14. EDM Collaboration Meeting, February 14-15, 2007 Soft Seat, Hard Boot  Teflon tends to retain deformation after applied pressure.  After cycling, small misalignment can cause leak  Make seat out of Teflon, instead of boot.  Less sensitive to misalignment  Edges of hard material do not contact soft  No need to fabricate hole in hard material (e.g. ceramic, glass)  Smaller Teflon surface to polish  5  10 -9 Atm-cc/sec (leak detector limit) with optical flat or cast acrylic boot at room temperature.  But larger volume of Teflon can break due to thermal shock. Teflon Cold Shocked Polished Teflon

15. EDM Collaboration Meeting, February 14-15, 2007 A “Self Cleaning” Valve?  Dirt continues to be a problem.  Contributes to non-reproducibility of tests.  May originate in test assembly or vacuum system – despite good vacuum technique.  Dirt will also be a problem for the experiment.  Geometry issues  Sealing on an “edge” increases closing force per unit area  Sloping surface allows boot + gravity to move the dirt – provides a place for dirt to go.  Departure from Harvard flat-on-flat design: wear may be an issue  Room temperature tests with Teflon seat and an edge:  Ball was difficult to polish while retaining roundness.  High seating force required (>50 lbs on 3/8” diameter seat)  All suffered from “porous” Teflon (need better quality?)

16. EDM Collaboration Meeting, February 14-15, 2007 Return to Harder Materials  Use Vespel seat and boot – hard plastic  Try cone-on-chamfer (cork-in-bottle) geometry  Cones are more easily fabricated (lathe)  Self-centering (if stem can comply)  Wedge shape multiplies force (10°   6)  Reproducible over a few (<10) cycles  D=3/8”  Sealed (leak det. limit) at 10 lbs at room temp.  30 lbs required at LN2, LHe  And at LHe II with  p  500 Torr D

17. EDM Collaboration Meeting, February 14-15, 2007 What’s Next  Complete tests of large diameter Vespel valve.  D=1”  Already found to seal at 30 lbs at room temp.  Low temperature tests – to be done.  Closing force versus number of cycles – to be measured.  Hard-on-hard valve with more closely matched conical seat.  Need to understand constraints on materials from polarized 3 He relaxation studies.  Design and build complete valve test apparatus. 100 Cycle Test (0-50 lbs seating force)