nEDM Collaboration Meeting, November 1-3, 2007 Valve Progress Steve Williamson, UIUC

nEDM Collaboration Meeting, November 1-3, 2007 Bucket Dewar Tests  Testing of the Vespel “cork-in-bottle” seat was successfully completed.  1” diameter, 80 lbs closing force  continuous cycles  Leak rate < 3  std. cc/sec (background rate) with super-fluid He at 1.7 K  … But not without some difficulty

nEDM Collaboration Meeting, November 1-3, 2007 Testing Problems  Accidental warm-up caused leak at “press-fit” inlet connection shortly after the Annual Review.  May also have caused cold leak in Vespel (or could have been caused by new flange connection)  Re-fabricated seat and plug had bad surface due to chipped diamond tool.  Re-re-fabricated plug was slightly off-axis.  Actuator motion was impaired by lack of lubrication.  Actuator controller died due to leaky capacitor – paused final cycle test for about a day About a month of frustration Stick-slip from non- concentric plug Sticking in actuator

nEDM Collaboration Meeting, November 1-3, 2007 Postmortem after 10,000 cycles  Visual inspection: no obvious signs of wear except a light ring at seal line.

nEDM Collaboration Meeting, November 1-3, 2007 Diamond machined surface Region where surface has been scraped during closure Vespel builds up in a ridge above the seal line SEM Scans* of “Piston” SEM scan of seal line after a few hundred cycles SEM scan of seal line after >10000 cycles Note: This is NOT the same “piston” Diamond machined surface seems smoother Ridge (Vespel build- up) at seal line is narrower. * Thanks to Steve Clayton!

nEDM Collaboration Meeting, November 1-3, 2007 Another SEM Picture of Seal Line after 10,000 cycles  Ridge seems pretty sharp.  Dust particles (below line) – easy targets for focusing.

nEDM Collaboration Meeting, November 1-3, 2007 Another SEM Picture of Seat after 10,000 cycles  Below seal line, edge is rough – accumulated dirt?  Focusing is not easy. Beveled seat edge Seal edge

nEDM Collaboration Meeting, November 1-3, 2007 Plans for Bucket Dewar Testing  Try to eliminate “popping” of the cork (may or may not be an improvement).  Does not happens if tan(  ) >    is the static coefficient of friction.  For 300K Vespel,   0.35, so  must be > 19°.  At lower temperature,  may be smaller.  Our valve had  =10°.  “Cork Popping” Position Load

nEDM Collaboration Meeting, November 1-3, 2007  Try to reduce closing force.  Engineers: How Much?  Scaling the valve to 3.5 cm diameter implies closing force of 110 lbs.  Everything is easier for lower closing force  Mechanical support of valve can be less massive (lower heat load)  System for transmitting force can be less massive (lower heat load)  Valve wear should be reduced  Try materials softer than Vespel  Kel-F  Acrylic Plans for Bucket Dewar Testing Rockwell Method

nEDM Collaboration Meeting, November 1-3, 2007 K. D. May, “Advanced Valve Technology”, NASA SP-5019, 1965 Soft close-fitting tip could act as “wiper” rather than “scraper”. Plans for Bucket Dewar Testing  Try adjusting seat geometry  May contribute to lowering seating force  May improve immunity to dirt  Some Ideas:  NASA “Scrubber” design  Soft (Kel-F?) wiper on plug

nEDM Collaboration Meeting, November 1-3, 2007 Highest Priority: Full Valve Test  Goals:  Fabricate a full-sized valve  Use reasonable (though not necessarily final) materials  Test it under realistic conditions  LHe II inside at ~1.7 K  Vacuum outside  Hardware required:  Large (12” ID) dewar  Dewar insert with 1 K pot, motion feed-thru, and gas/vacuum/instrumentation lines  A valve

nEDM Collaboration Meeting, November 1-3, 2007 The Dewar  Ordered from Precision Cryogenic Systems  $8.1K  Delivery: 3-4 mo. (~Jan ’08)  Features  Super-insulated (no LN 2 shield)  ~50 l “belly”  Matched in dimensions to insert

nEDM Collaboration Meeting, November 1-3, 2007 The Insert  Ordered from Janis  $27.3k  Delivery: 3-4 mo. (~Jan ’08)  Features:  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

nEDM Collaboration Meeting, November 1-3, 2007 The Valve  Design by Bartoszek Eng. based on Jan’s earlier concept  Double seal (open and closed) using our best design. Open seal hides bellows from 3 He.  Be-Cu bellows assembly (from Mini-flex)  All Be-Cu welding to be performed by vendor  Design of assembly has iterated with vendor  Acrylic body  Current plan is to cast, then final machine.  A glued prototype is being fabricated. Open Seat Closed Seat Plug Bellows Assembly Acrylic Body Inlet Outlet

nEDM Collaboration Meeting, November 1-3, 2007 Valve Issues  Bellows assembly may have long lead time (no estimate yet)  Cast acrylic body may have long lead time.  Fall-back: glue the assembly.  Actuator must be modified: controlled force required when closing and opening.  Delay in dewar and insert  We will do plenty of room temp tests (dewar and insert may not actually be on critical path).  Fall-back: do bucket dewar tests in 3 He refrig. cryostat.  This conflicts with polarized 3 He lifetime studies.