This page contains the the Gas Seal tests
2008-07-16 O-rings

Viton o-ring material was purchased and tested.
Gas seal test is still good. (By the way, the gas seal test, started in August 2007, had shown no loss since December.)
Torque to compress o-ring (see Gas Seal page, 2007-11-22) increased from 11 inch-pounds to 12 or 13 inch-pounds. This creates an increase of ~20% in the force on the field cage inserts and should be OK with the safety factor that was built in.
2007-11-22 Torque to compress the o-ring

I measured the torque required to compress an o-ring and the yield torque for brass screws.
The o-ring is 3.55mm in a groove with 3.65mm width and 2.75mm depth. This is my standard 4-surface contact, high compression, groove.
The original measurements, 2007-11-19, were sloppy. I used the full length o-ring and counted on the bending of the cover plate to select only a section of the length. I have repeated the measurements using a 6cm length of o-ring material centered on one screw. This is the distance between screws in the outer flange. I also now explicitly discuss a safety factor.


2007-08-21 Gas seal test

The gas seal test has has been completed with the captured gas on the pad-board side of the module while the "outside of the chamber" is exposed to air, as shown in the first two figures.

I then installed the "endplate" and "module" as shown in the first two figures.

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2007-05-08 Gas seal test

The gas seal test has started with the captured gas on the pad-board side of the module while the "outside of the chamber" is exposed to air. Corrections should be made to the 0-ring slots: the outer radius at the corners was maintained at the same value as the inner radius, rather than increasing the radius by the width of the o-ring.

The 0.071inch o-ring is fitted in a 0.075inch slot, 0.057inch deep. Therefore the compression is 0.014inch. (The compression to fill the cross section of the slot would be 0.018 inch.)

Initial observation: The volume, ~275cc, was overpressured with air to 1.06 atmosphere absolute (1psi gauge). After 1.3 hours, the pressure had dropped by 0.006 atmosphere. Thus, the leak rate, at the applied overpressure, is (0.006*275cc)/(1.3hour) =~1.3cc/hour. Of course, the leak-rate-in of oxygen will depend on the partial pressure of oxygen, which is 3x the overpressure that was used in this test. So, this leak rate could be ~4cc/hour per module. This is probably not acceptable. This is an upper limit of the leak rate through the module seal; there are many other potential locations.


2007-04-10 Gas seal test

We will perform a series of tests of the gas seal design of the readout module. This shows the "readout module" that will be used for the tests. The red part is the module back-frame. The sealing surface includes an o-ring groove(1.76mm). The back-frame also includes the strong section with threaded holes (~3mm).

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Below are 5 figures showing one configuration: with the captured gas "outside the chamber" and the pad-board exposed to air. The 1st figure shows the mounting box, without the module module installed. The rim is a model of the mounting surface on the large-prototype endplate. The sealing surface is in the x-y plane and is the innermost surface in that plane. The 2nd figure shows the module in place on the mounting box. In the 3rd figure, we are looking at the bottom with the cover-plate removed. The is the inside of the captured gas volume in this configuration. The bracket is used to pull the readout module back-frame and thus compress the o-ring. The 4th figure again shows the bottom view, but with the bracket removed to expose the back of the readout module back-frame. The 5th (last) figure shows a cut-away of the assembly for this configuration.

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In a second configuration, the captured gas is on the pad-board side of the module while the "outside of the chamber" is exposed to air. This is achieved with the same parts by flipping the spacer and cover-plate to the other side of the endplate. Again, the 1st figure shows the mounting box, without the module installed. The sealing surface of the "endplate" is facing down and can not be seen. Again, the 2nd figure shows the full assembly with the module in place on the mounting box. The 3rd figure also shows the top (air side) of the assembly but with the bracket removed to expose the back of the readout module back-frame. In the 4th figure we are looking at the bottom with the cover-plate removed. The is the inside of the captured gas volume in this configuration. This exposes the readout module pad-board that will be in the gas volume. The 5th (last) figure shows a cut-away of the assembly for this configuration.

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