Valve Update  Study several stem/seat geometries (Feb)  Demonstrate He II leak tight for 3/8, 1 in. diameter with modest (~ few psi) pressure difference  Vespel seat and stem – 3 He friendly?  Receive $65k supplement from NSF for ‘full valve prototype’ D. Beck, UIUC (for S. Williamson) June 7, 2007

Two Types of Valves Volume Displacement Volume Displacement Interconnect Plumbing Cell Isolation (V1) Valve Actuators and Interfaces Purifier Purifier isolation (V6) Valves He Atomic Beam Source (ABS) ABS Interface Polarized 3He Collection System Pressurizer Purifier Control (V5) Valve Collection Isolation (V4) Valve Pressurizer Standoff (V3) Valve Pressurizer Isolation (V2) Valve Collection/ Purifier Interconnect Plumbing Pressurizer/Cell Interconnect Plumbing Seals He II liquid Seal 3 He “gas”

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  V2 Pressurizer isolation 5% drop in signal over 500 s fill time 77 K  p = 45 Torr 1.88  V3 Pressurizer stand-off 1% drop in pressure over  m =10 4 s 0.5 K 760 Torr 4.55  V4 Collection Isolation 3 He concentration drops by 5% during 500 s storage time 77 K  p = 45 Torr 4.79  V5 Purifier Control Signal drops by 5% during 500 s fill time 77 K  p = 45 Torr 9.41  V6 Purifier Isolation 1 mW heat load during regeneration 0.5 K  p = 3 Torr 6.88  Note: these are “whistlers” (very high leak rates)

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

Best Results: ‘Harder’ Materials  Use Vespel seat and stem – 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

A Larger Vespel Valve  D=1”  Sealed at 30 lbs at 300 K  Sealed at 80 lbs at 1.6 K  after 200 open/close cycles Valve Temp Leak detector Inlet Pres

Can we pressurize?  Use 3 He to pressurize after introducing 4 He to valve.  Kind of expensive ($200/l STP)  Mixtures of 3 He and 4 He turn out to have an intermediate vapor pressure. 4 He 3 He 1.5E-8 atm-cc/s Valve Temp Inlet Pres Leak Det 4 He Vap Pres 3 He Vap Pres

What’s Next…  Test closing force versus number of cycles  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)

‘Full’ Valve Test  Features:  Full size prototype valve  Continuous operation at 1.5 K  Pressurization  Strategy:  Use large LN2 jacketed dewar  Use internal vacuum vessel surrounded by LHe  Use 1K pot to get to 1.5 K  2 motion feed-throughs (valve, pressurizer)  Procurement:  Order from Janis? ~$12k ~$25k