NEDM Collaboration Meeting, May 19, 2008 Valve Progress Steve Williamson.

nEDM Collaboration Meeting, May 19, 2008

Valve Progress

Steve Williamson


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


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


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


Valve Test Apparatus Dewar (Precision Cryogenics) Received

3/12/08 Super-insulated (no LN2 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


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.


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 side Helium side


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 2nd attempt

3rd under polarized light


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:

Material Length at 300 K

Length at 4K

Copper thermal contact 0.5” 0.4984”Acrylic flanges 0.35” 0.3458”

Brass screws 0.85” 0.8467”

Difference: (Brass – rest) 0” 0.0026”

1” ceramic

0.5” copper

0.35” acrylic

Acrylic-acrylic-acrylic seal

Material Integrated CTE to 4K

Ceramic (assume pyrex) -0.056%

Copper -0.325%Acrylic -1.21%

Brass -0.384%


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:

Material Length at 300 K

Length at 4K

Ceramic spacers 1” 0.9994”

Copper thermal contact 0.5” 0.4984”Acrylic flanges 0.35” 0.3458”

Brass screws 1.85” 1.8429”

Difference: (Brass – rest) 0” -0.0007”

1” ceramic

0.5” copper

0.35” acrylic

Acrylic-acrylic-acrylic seal

Material Integrated CTE to 4K

Ceramic (assume pyrex) -0.056%

Copper -0.325%Acrylic -1.21%

Brass -0.384%


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


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


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


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 3He 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


Another Issue If bellows is not 3He 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 3He depolarization.

NEDM Collaboration Meeting, May 19, 2008 Valve Progress Steve Williamson.

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Transcript of NEDM Collaboration Meeting, May 19, 2008 Valve Progress Steve Williamson.