1. nEDM Collaboration Meeting, May 19, 2008 Valve Progress Steve Williamson

2. nEDM Collaboration Meeting, May 19, 2008 Goal of Valve R&D  Highest priority: the completion of a “full valve test”.  Fabricate a full-sized prototype valve  Use reasonable (though not necessarily final) materials  Test it under realistic conditions  LHe II inside at ~1.7 K  Vacuum outside

3. nEDM Collaboration Meeting, May 19, 2008 Prerequisites  A valve design  A Facility for testing the valve  A dewar  A dewar insert (for vacuum and refrigeration)  A critical parts must be tested.  Valve seat and boot  Bellows assembly  Valve body  Plastic flange seals

4. nEDM Collaboration Meeting, May 19, 2008 Prototype Valve Design  Completed 2/21/08  Based on Jan’s earlier design  Some features:  Uses our tested Vespel seat/boot design  Double seal (closed and open)  Two sliding “linear bearings” maintain alignment of seat/boot.  Uses off-the-shelf Be-Cu bellows  Acrylic body and spool piece

5. nEDM Collaboration Meeting, May 19, 2008 Valve Test Apparatus  Dewar (Precision Cryogenics) Received 3/12/08  Super-insulated (no LN 2 shield)  ~50 l “belly”  Insert (Janis) received 3/12/08  100 mW cooling power at 2K  LHe throttle valve on 1K pot  6 ½” lines (1 removable)  Two motion feed-thru lines  Large internal vacuum volume  Combination was tested by Janis to verify 100 mW cooling power below 2 K  Should serve for pressurizer and valve testing for the project (i.e. WBS 1.4.9.6) Internal vacuum vessel not shown

6. nEDM Collaboration Meeting, May 19, 2008 Testing of Bellows  Use standard Miniflex type BC-100-40- 12-1 Be-Cu bellows.  Joints made with Stycast 2850FT (not welded)  Bellows was compressed 11/16” (no extension) at a rate of about 0.8 Hz.  Tests performed at 4.2 K in bucket dewar  1000 Torr Baratron monitored vacuum on interior of bellows.  Tested on leak detector after test.  Test performed twice with two different bellows.  Both bellows survived more than 500,000 cycles without failure.

7. nEDM Collaboration Meeting, May 19, 2008 Pressure-tested one Be-Cu Bellows (a side note)  Possibly use this bellows for hydraulic actuator  Performed test at room temperature  He pressure on outside, vacuum (leak detector) inside  No significant deformation/failure at 110 lbs force (~90 psi)  Serious deformation at 300 lbs (~250 psi) Vacuum sideHelium side

8. nEDM Collaboration Meeting, May 19, 2008 Valve Body  First attempt  Machine in two parts and glue.  Glued joint looked “problematic”; technicians reject the part.  Second attempt  Machine from a single block of acrylic.  Diamond machine interior  Failed leak check (near blind tapped flange holes). Holes filled and re- tapped – still leaks.  Theory: stress crack despite care  Third attempt  Machine from a single block  Use simplified shape  Yet to be leak checked, but our best candidate  Ultimately:  Cast (expensive, long lead)  Minimally machine Machining 2 nd attempt 3 rd under polarized light

9. nEDM Collaboration Meeting, May 19, 2008 Flange Seals  The design calls for “double” seals:  Acrylic-vespel-acrylic or Acrylic-copper- acrylic  Use Kapton gaskets  Use silicon-bronze screws.  Due differential thermal contraction, screws end up longer than clamped flanges  Leak  Strategy: use ceramic spacers and make acrylic as thin as practical.  Example: MaterialLength at 300 K Length at 4K Copper thermal contact0.5”0.4984” Acrylic flanges0.35”0.3458” Brass screws0.85”0.8467” Difference: (Brass – rest)0”0.0026” 1” ceramic 0.5” copper 0.35” acrylic Acrylic-acrylic-acrylic seal MaterialIntegrated CTE to 4K Ceramic (assume pyrex)-0.056% Copper-0.325% Acrylic-1.21% Brass-0.384%

10. nEDM Collaboration Meeting, May 19, 2008 Flange Seals  The design calls for “double” seals:  Acrylic-vespel-acrylic or Acrylic-copper- acrylic  Use Kapton gaskets  Use silicon-bronze screws.  Due differential thermal contraction, screws end up longer than clamped flanges  Leak  Strategy: use ceramic spacers and make acrylic as thin as practical.  Example: MaterialLength at 300 K Length at 4K Ceramic spacers1”0.9994” Copper thermal contact0.5”0.4984” Acrylic flanges0.35”0.3458” Brass screws1.85”1.8429” Difference: (Brass – rest)0”-0.0007” 1” ceramic 0.5” copper 0.35” acrylic Acrylic-acrylic-acrylic seal MaterialIntegrated CTE to 4K Ceramic (assume pyrex)-0.056% Copper-0.325% Acrylic-1.21% Brass-0.384%

11. nEDM Collaboration Meeting, May 19, 2008 Test of flange seals  Tests on smaller flanges were successful.  Test of two double seals on a simple tube  Performed in new valve test dewar.  No leaks at 77 K  Leaked at 4K

12. nEDM Collaboration Meeting, May 19, 2008 Flange Seal Leak  Could be due to change of Kapton seal design.  Holes through gasket for better force transfer  But may produce less force per unit area  Could be due to leak in exhaust line  Copper tube Stycast to acrylic  Leak check at room temperature should answer this Old Design New Design Possible leak here

13. nEDM Collaboration Meeting, May 19, 2008 Plans  Solve double flange seal problem  Probably return to bucket dewar (lower LHe cost, faster cool-down)  Try earlier gasket design  Use thin (0.2 total”) acrylic in seal region  Assemble and test with “simplified” body design and single valve seat.  Body, spool piece, and bellows assembly are already complete  Finish seat and stem (when seal design perfected)  Some small adaptations of actuator required for new dewar  Success of this valve could be considered to complete R&D project

14. nEDM Collaboration Meeting, May 19, 2008 Future Steps  Double sealing valve  Necessary if Be-Cu proves unfriendly  Requires additional alteration of actuator  2X longer travel  Spring to allow force control when retracting  “Non-pressurizing” valve  If no free surfaces, then closing valve will pressurize LHe (and squirt depolarized 3 He into the system)  Use a second set of bellows (one set extends, the other retracts) to maintain constant volume.  In-line valve  Needed above and below IV1

15. nEDM Collaboration Meeting, May 19, 2008 Another Issue  If bellows is not 3 He friendly…  With valve closed, “top” side of valve is exposed unfriendly surface  This is not fixed by double seal action.  May require “hiding” the bellows  Telescoping shield?  Polyimide flexible coating inside bellows?  Kapton bellows? “Origami” Kapton bellows We need to test more materials for 3 He depolarization.