§1 Entry Ticket: Pre-Synchronous Session Diagnostic

Scenario: "The Tuesday Afternoon Mystery"

R1-A was used for a successful demonstration this morning. The system reached its normal base pressure of 0.05 mbar with no issues. After the demo, the system was vented (controlled vent through R1-FLT-VENT, R1-V-VENT opened slowly then closed, chamber at ~950 mbar) and left in VENTED state (both valves closed, pump off) over lunch.

This afternoon, a different operator begins roughing. The pumpdown is normal from 950 to 1 mbar (~2 minutes).

Below 1 mbar, the pumpdown slows significantly. After 30 minutes, R1-G-CH reads 0.20 mbar and is still dropping slowly.

The operator isolates the system (R1-V-ISO closed, R1-V-VENT closed, pump off) and records the following rate-of-rise data:

Additional context: The morning operator mentions that the demonstration involved placing several rubber test pieces inside the chamber — pieces that had been stored in a humid workshop area.

Entry Question 1: Gas Load Pattern

The rate of rise for each interval has been calculated below:

Examine the rate-of-rise values. Is the rate constant or decreasing over time? What gas load source does this pattern indicate — a leak or outgassing?

Your answer:

Entry Question 2: Contamination Hypothesis

Given the system history (morning demo, rubber test pieces from humid storage), what are the two most likely sources of the elevated gas load? Explain your reasoning for each.

Your answer:

Entry Question 3: Why Not a Leak?

The rate of rise is relatively high (0.10 mbar/min initially). How do you know this is NOT a real leak, despite the elevated rate? What specific evidence from the data supports your conclusion?

Your answer:

Entry Question 4: Vent Filter Check

The system was vented through R1-FLT-VENT this morning. If the extended pumpdown were caused by particulate contamination from a degraded vent filter, how would the pumpdown behaviour be expected to differ from what is being observed? Name one distinguishing feature.

Your answer:

Entry Question 5: Escalation Note

Write a 3-sentence escalation note for the shift supervisor summarising: (1) what was observed, (2) what the evidence indicates, and (3) what additional information would help clarify the situation. Use specific readings and component IDs.

Your answer:

§2 Worked Example: Entry Ticket Model Answer

Entry Question 1 — Model Answer

The rate decreases from 0.10 to 0.016 mbar/min over 10 minutes. This is a concave curve — the classic outgassing (desorption) pattern. The gas load source is surface-related: water desorption and/or material outgassing, not a real leak.

Entry Question 2 — Model Answer

Source 1: Water desorption from rubber test pieces. Rubber stored in a humid workshop will have absorbed significant water vapour. When placed in vacuum, this water slowly releases (outgasses), creating a large gas load in the 1–0.01 mbar range. Rubber is particularly problematic because it has high permeability and absorbs water readily.

Source 2: General surface water re-adsorption. The chamber was vented and left at atmosphere over lunch (~2 hours). During this time, water vapour from the ambient air re-adsorbed onto all internal surfaces. This is normal but adds to the total gas load for the afternoon pumpdown.

Entry Question 3 — Model Answer

Despite the high initial rate (0.10 mbar/min), this is NOT a real leak because the rate is decreasing — from 0.10 to 0.016 mbar/min over 10 minutes. A real leak produces a constant rate because atmosphere is an unlimited gas source.

The decreasing rate is the definitive evidence: the gas source is being depleted (surface desorption), not replenished (leak from atmosphere). The shape of the curve, not the initial magnitude, is the diagnostic key.

Entry Question 4 — Model Answer

If particulate contamination from a degraded vent filter were the primary cause, the extended pumpdown would likely show different characteristics: the system might show relatively normal pumpdown on the first cycle, with the particle-related effects (increased surface area for water adsorption) becoming apparent primarily after venting and re-pumping. Additionally, particles would introduce a risk of virtual leaks (trapped gas pockets) that would produce identical rate-of-rise patterns across repeated cycles — unlike true outgassing, which improves with each cycle. The current pattern (no particles reported, first pumpdown of the afternoon showing extended time) is more consistent with water/outgassing contamination than particulate contamination.

Entry Question 5 — Model Answer

"R1-A pumpdown stalled at 0.20 mbar after 30 minutes of roughing — normal base is 0.05 mbar. Rate-of-rise test shows decreasing rate (0.10 → 0.016 mbar/min over 10 min), consistent with elevated outgassing rather than a leak.

Likely cause: water and material outgassing from humid-stored rubber test pieces placed in the chamber this morning. Additional information needed: confirmation of whether rubber test pieces are still in the chamber, and whether an extended pump-down cycle reduces the base pressure toward 0.05 mbar."

§3 Worked Example: Situation Report

Scenario Context (Facilitator-Provided During Synchronous Session)

R1-A has been running for two hours. It initially reached 0.08 mbar (slightly above normal). Over the last 30 minutes in ROUGHING state, R1-G-CH has been gradually rising from 0.08 to 0.15 mbar while the pump continues running.

Model Situation Report

System: R1-A State: ROUGHING (R1-V-ISO open, R1-V-VENT closed, R1-P-RP running) Time: 14:30

Observation: R1-G-CH has risen from 0.08 mbar to 0.15 mbar over 30 minutes during active roughing. Pump is running and sounds normal. R1-G-BX reads ~950 mbar.

Interpretation: Pressure rising during active pumping means gas load is increasing — the pump can no longer maintain the initial base pressure. This is not normal during steady-state roughing. Possible causes: (1) developing leak at a seal (gas ingress increasing over time as the seal degrades or shifts); (2) thermal outgassing from a component that is warming up during extended operation; (3) pump oil backstreaming increasing at sustained low pressure.

Unknowns → Evidence Needed:

1. UNKNOWN: Is the pressure rise constant or accelerating? → Record R1-G-CH every 5 minutes for the next 20 minutes to characterise the trend.
2. UNKNOWN: Is this a leak or an outgassing/contamination source? → Isolate the system and perform a rate-of-rise test to check for constant vs decreasing rate.
3. UNKNOWN: Has anything changed in the pump exhaust? → Check R1-FLT-EXH for unusual odour or oil discharge that might indicate pump issues.

Escalation: "R1-G-CH rising during active roughing — 0.08 → 0.15 mbar over 30 min. Pump running normally.

A rate-of-rise test after isolation would help determine whether the gas source is a developing leak or thermal outgassing. Will report findings after test."

§4 Worked Example: Evidence Brief

Scenario Context

Following the situation report above, the operator isolates R1-A. Rate-of-rise test results:

Model Evidence Brief

System: R1-A State during test: ISOLATED (R1-V-ISO closed, R1-V-VENT closed, R1-P-RP off) Test: Rate-of-rise, 10-minute duration

State Call: ISOLATED — both valves closed, pump off. Confirmed by valve positions.

Observed Evidence:

• Rate of rise: 0.12 mbar/min constant across all intervals (1, 3, 5, 10 minutes)
• No decrease in rate over the full 10-minute test
• Starting pressure: 0.15 mbar

Plausibility Check: Constant rate is NOT consistent with outgassing (which should decrease). Constant rate IS consistent with a real leak — atmosphere providing a steady gas source at 0.12 mbar/min.

Hypotheses (ranked):

1. Real leak (most likely) — constant rate from unlimited atmospheric source. Possible locations: R1-V-ISO seat (valve was recently operated), chamber O-ring (sealing surface), any flanged connection.
2. Unusual constant outgassing source (less likely) — a large contamination source could produce a near-constant rate early in the test, but the absolute constancy over 10 minutes argues against this.

Discriminator Evidence:

• Repeat the rate-of-rise test after re-pumping. If the rate is identical → leak confirmed (recharging between cycles). If the rate decreases on the second test → contamination more likely.
• Check recent maintenance history: were any seals disturbed or replaced?

UNKNOWN → Evidence Needed:

1. Leak location — need physical inspection of seal surfaces, potentially helium leak testing
2. Whether the leak developed gradually or suddenly — need operational log review
3. Whether pump performance is contributing — need to verify pump ultimate pressure independently

Escalation Note: "Rate-of-rise test confirms constant gas ingress at 0.12 mbar/min — consistent with a real leak, not outgassing. The most likely leak locations are R1-V-ISO seal and the chamber O-ring. Additional information needed: physical inspection of seal surfaces and potentially helium leak testing to confirm the leak location."

§5 Worked Example: Sector Lens Output

Scenario Context

Using the leak scenario from §4, the student applies the General Industrial sector lens.

Model Sector Lens Output

Base scenario: R1-A real leak at 0.12 mbar/min, identified through rate-of-rise test.

Sector: General Industrial

Sector Lens Application:

In a general industrial vacuum setting (e.g., vacuum packaging, degassing, drying), this leak rate would mean:

• Process impact: Depending on the target pressure, a 0.12 mbar/min leak may prevent the system from reaching process specification. For processes requiring pressures below ~1 mbar, this leak would cause the system to stall above target.
• Production consequence: Products processed under these conditions may not meet quality specifications — e.g., incomplete degassing, inadequate moisture removal, or poor seal quality in vacuum packaging.
• Maintenance priority: In a production environment, this would typically be classified as a priority maintenance issue — not an emergency shutdown, but a scheduled repair before the next production run.

Escalation (sector-specific): "Leak rate of 0.12 mbar/min identified on R1-A. In a general industrial vacuum application, this would prevent the system from meeting typical process specifications below 1 mbar.

Additional information needed: leak location confirmation through physical inspection or helium leak testing. Product quality is at risk if the system is used in this condition."

§6 Reading List

Use these references to deepen your understanding of the concepts covered in Module 2. They're organized by topic and include page numbers for quick navigation.

How to Use This List:

• Start with Milne, Chapter 2 for a narrative introduction to surface interactions and outgassing
• Read Varian, Chapters 2–3 for the clearest explanation of gas sources and leak detection — this is the most directly relevant resource for Module 2
• Reference Pfeiffer, Sections 4.1–4.3 when you need precise definitions or diagrams of leak types and RGA operation
• Browse the KJLC/ORNL deck, slides 250–320 for visual reinforcement of outgassing data and material properties

KJLC/ORNL Deck — Slide Guide for Module 2:

End of Assessment Content — Module 2