Module 2 Scenario Cards: Influences on Real Vacuum Systems

Module: M02 — Influences on Real Vacuum Systems Rig Configuration: R1-A (Simple Single-Pump Roughing Rig) Cards: SC-M02-01 through SC-M02-03

R1-A Component Reference

Component ID	Name	Type
R1-CH	Chamber	Volume
R1-P-RP	Roughing Pump	Pump
R1-V-VENT	Vent Valve	Valve
R1-V-ISO	Isolation Valve	Valve
R1-G-CH	Chamber Gauge (Pirani)	Gauge
R1-G-BX	Barometric Reference	Indicator
R1-FLT-VENT	Vent Filter (sintered metal)	Filter
R1-FLT-EXH	Exhaust Filter (oil mist)	Filter
R1-L-FL	Foreline	Line
R1-L-VENT	Vent Line	Line
R1-L-EXH	Exhaust Line	Line

SC-M02-01: The Slow Climb — Outgassing or Leak?

Clue: Compare the current reading to what you would expect. Is the system behaving normally for its state?

Guide: Check R1-G-CH against the expected base pressure. If the reading is higher than expected, consider: how long has the system been pumping? Was anything changed recently? What could introduce additional gas load?

Module: M02 Rig Config: R1-A Competency: M02-COMP-02 Indicators Assessed: M02-IND-02.01, M02-IND-02.03

System State

State Name: ISOLATED One-line description: R1-A has been roughed down and isolated. The chamber pressure is rising slowly. Is this normal outgassing or a real leak?

Valve Positions

Valve ID	Valve Name	Position	Why
R1-V-VENT	Vent Valve	CLOSED	System is isolated — no venting path active.
R1-V-ISO	Isolation Valve	CLOSED	System is isolated — chamber disconnected from pump.

Gauge Readings

Gauge ID	Gauge Name	Reading	Unit	What It Tells You
R1-G-CH	Chamber Pirani	See time series below	mbar	Pressure is rising after isolation — the question is how it's rising.
R1-G-BX	Barometric Reference	~950	mbar	Atmospheric baseline — confirms altitude-corrected reference.

Rate-of-Rise Data

Time after isolation	R1-G-CH (mbar)	Rise since last reading	Rate (mbar/min)
0 min	0.08	—	—
1 min	0.20	0.12	0.12
2 min	0.29	0.09	0.09
5 min	0.44	0.15	0.05
10 min	0.56	0.12	0.024

Pump Status

Pump ID	Pump Name	Status	Notes
R1-P-RP	Roughing Pump	OFF	Pump was turned off at time of isolation.

Media Placeholder

[Media: SC-M02-01 Rate-of-Rise Chart]

Line graph plotting R1-G-CH vs time from the data table above
Curve should be visibly concave (bending toward horizontal)
Annotations showing the decreasing rate at each interval
Colour-coded (gauge reading in yellow)
Priority: P2-STRONGLY RECOMMENDED

Student Prompt

The following rate-of-rise data was recorded for R1-A after a routine pumpdown and isolation.

1. Recognise: What pattern is present in the rate-of-rise data? Is the rate constant, increasing, or decreasing? 2. Interpret: Based on this pattern, what is the most likely source of the gas load? Is this normal behaviour or a problem? 3. Communicate: Write a one-sentence status note summarising your finding, suitable for a shift handover log. 4. Escalate: Does this finding require escalation? If so, what specific information should be included?

Teaching Points (Facilitator Notes)

Expected student observations:

Rate of rise decreases over time: 0.12 → 0.09 → 0.05 → 0.024 mbar/min
The curve is concave — bending toward horizontal
This is the classic outgassing pattern

Key learning moments:

The distinction between "pressure is rising" (which is alarming if you don't know better) and "rate of rise is decreasing" (which is normal)
Students should be able to articulate why outgassing decreases: diffusion-limited process, "easy" gas desorbs first, deeper molecules take longer
The rate values (0.02–0.12 mbar/min) are within normal outgassing range — no escalation needed

Model status note: "R1-A rate-of-rise test after isolation at 0.08 mbar: pressure rose to 0.56 mbar over 10 minutes. Rate decreased from 0.12 to 0.024 mbar/min — consistent with normal outgassing. No action required."

Common student errors:

Concluding "there's a leak" because pressure is rising (ignoring the decreasing rate)
Failing to include numerical evidence in their status note
Not distinguishing between the pattern (decreasing) and the magnitude (the specific numbers)

SC-M02-02: The Chamber That Won't Pump Down — Contamination

Clue: Look at the rate-of-rise pattern. Is it constant or decreasing? This is your primary diagnostic tool.

Guide: A constant rate = leak (unlimited atmospheric source). A decreasing rate = outgassing (finite surface source). Calculate the rate for each interval and compare.

Step by step

R-I-C-E pattern: Recognise the rate trend. Interpret based on source type (leak vs outgassing). Communicate specific numbers and what they mean. Escalate with a recommendation for the next test.

Module: M02 Rig Config: R1-A Competency: M02-COMP-01, M02-COMP-02 Indicators Assessed: M02-IND-01.02, M02-IND-02.02, M02-IND-02.03

System State

State Name: ROUGHING (stalled) One-line description: R1-A is being roughed but the pressure has stalled well above the system's normal base pressure. The pump is running normally.

Background Information (Provided to Students)

R1-A was used yesterday for a demonstration. During the demo, the chamber was opened multiple times.

A visiting technician handled internal fixtures without gloves. The system was left in VENTED state (both valves closed, pump off, chamber at atmosphere) overnight.

This morning, the operator begins roughing. The pump sounds normal.

R1-G-BX reads ~950 mbar. But the pumpdown doesn't look right.

Valve Positions

Valve ID	Valve Name	Position	Why
R1-V-VENT	Vent Valve	CLOSED	Roughing — vent path closed to prevent air ingress.
R1-V-ISO	Isolation Valve	OPEN	Roughing — chamber connected to pump through foreline.

Gauge Readings

Gauge ID	Gauge Name	Reading	Unit	What It Tells You
R1-G-CH	Chamber Pirani	0.35 (stalled)	mbar	Pressure dropped normally from 950 to ~1 mbar, then slowed dramatically. After 30 minutes, it has stalled at 0.35 mbar. Normal base pressure for this system is 0.05 mbar.
R1-G-BX	Barometric Reference	~950	mbar	Atmospheric baseline normal.

Pump Status

Pump ID	Pump Name	Status	Notes
R1-P-RP	Roughing Pump	ON — running normally	No unusual noise, vibration, or exhaust odour. Pump sounds and behaves as expected.

Pumpdown Comparison

Phase	Expected Time	Today's Time	Notes
950 → 100 mbar	~30 seconds	~30 seconds	Normal — bulk gas removed as expected
100 → 1 mbar	~2 minutes	~2 minutes	Normal — viscous flow regime
1 → 0.1 mbar	~5 minutes	20+ minutes and stalled at 0.35 mbar	Abnormal — extended pumpdown, stalled above normal base

Media Placeholder

[Media: SC-M02-02 Pumpdown Curve Comparison]

Two curves: "normal pumpdown" reaching 0.05 mbar, and "today's pumpdown" stalling at 0.35 mbar
Both start identically at 950 mbar; diverge below ~1 mbar
Annotate the "contamination plateau" where today's curve flattens
X-axis: time (minutes). Y-axis: pressure (mbar, log scale)
Priority: P2-STRONGLY RECOMMENDED

Student Prompt

The following pumpdown data was recorded this morning for R1-A.

1. Recognise: Compare today's pumpdown to the expected performance. Where does the pumpdown deviate from normal? 2. Interpret: Given the system history (multiple chamber openings, ungloved handling), what contamination sources might explain the elevated base pressure? Name at least two. 3. Communicate: Write a 3-sentence escalation note: (1) what was observed, (2) what the evidence indicates, and (3) what additional information is needed to confirm the diagnosis. Use specific readings and component IDs. 4. Escalate: What additional information would help distinguish between possible explanations? Identify at least one specific observation that would narrow the diagnosis.

Teaching Points (Facilitator Notes)

Expected student observations:

Pumpdown is normal above 1 mbar (bulk gas removal is unaffected by surface contamination)
Pumpdown stalls at 0.35 mbar — well above the normal base of 0.05 mbar
The pump is running normally (this rules out pump failure)

Key learning moments:

Contamination increases gas load, not pump performance — the pump is working fine, but it's fighting a higher gas load than usual
Ungloved handling deposits fingerprint oils (hydrocarbon contamination)
Multiple chamber openings increase surface water (re-adsorption from humid air)
The stall point (0.35 mbar) represents a new equilibrium: gas load from contamination equals pump throughput at that pressure

Model escalation note: "R1-A pumpdown stalled at 0.35 mbar after 30 minutes — normal base is 0.05 mbar. Pump running normally (no unusual noise or exhaust). System was opened multiple times yesterday and internal surfaces were handled without gloves.

Evidence indicates hydrocarbon contamination from fingerprints and elevated water load from repeated venting. Additional information needed: whether pump-down cycling reduces the base pressure, or whether chamber cleaning is required to address hydrocarbon contamination."

Common student errors:

Blaming the pump ("the pump must be failing") without evidence
Not connecting the system history (ungloved handling) to the symptom (elevated base pressure)
Suggesting "check for leaks" without first considering contamination — the pumpdown profile (normal above 1 mbar, stalled below) is more consistent with contamination than a leak

SC-M02-03: The Post-Vent Particle Problem

Clue: This scenario involves a contamination event. Think about what was introduced and how it would affect the system.

Guide: Contamination sources release gas molecules over time. Consider: what material was introduced? How was it stored? Was moisture involved? How would this appear in a rate-of-rise test?

Module: M02 Rig Config: R1-A Competency: M02-COMP-01, M02-COMP-02 Indicators Assessed: M02-IND-01.02, M02-IND-02.02

System State

State Name: VENTED (at-rest) → then ROUGHING One-line description: After a controlled vent, particles are found inside the R1-A chamber. The next pumpdown shows unusual gauge behaviour.

Background Information (Provided to Students)

R1-A was used for a routine pumpdown earlier today. The system reached its normal base pressure of 0.05 mbar with no issues. It was then vented using the standard procedure (R1-V-ISO closed, R1-V-VENT opened slowly, pressure allowed to rise to ~950 mbar, then R1-V-VENT closed).

When the chamber was opened to remove a sample, the operator noticed fine dust particles on the sample surface and inside the chamber — particles that were not there when the sample was loaded.

The operator closes the chamber, and begins a new roughing cycle. During this pumpdown, R1-G-CH behaves normally from 950 → 1 mbar, but takes longer than usual to drop from 1 → 0.1 mbar.

Valve Positions (During Investigation Roughing)

Valve ID	Valve Name	Position	Why
R1-V-VENT	Vent Valve	CLOSED	Roughing — vent path sealed.
R1-V-ISO	Isolation Valve	OPEN	Roughing — chamber connected to pump.

Gauge Readings

Gauge ID	Gauge Name	Reading	Unit	What It Tells You
R1-G-CH	Chamber Pirani	Slow drop from 1 → 0.1 mbar (taking ~12 min vs normal ~5 min)	mbar	Pumpdown extended in the range where surface effects dominate.
R1-G-BX	Barometric Reference	~950	mbar	Atmospheric baseline normal.

Pump Status

Pump ID	Pump Name	Status	Notes
R1-P-RP	Roughing Pump	ON — running normally	Pump performance is unchanged from the earlier (successful) pumpdown.

Key Evidence

Particles visible inside chamber and on sample surface after venting
Previous pumpdown (before vent) was normal — no contamination
Particles appeared after the controlled vent
Extended pumpdown in the 1–0.1 mbar range on subsequent roughing

Student Prompt

The operator has reported particles inside the R1-A chamber. The following evidence is available for review.

1. Recognise: When did the particles most likely enter the chamber? What evidence supports your conclusion? 2. Interpret: The vent filter (R1-FLT-VENT) is supposed to prevent particulate contamination during venting. What might explain why particles got through? Name at least two possible explanations. 3. Communicate: Why is the pumpdown extended in the 1–0.1 mbar range after this contamination event? What is the connection between particles and pump-down performance? 4. Escalate: Write a 3-sentence observation summary: (1) what was observed, (2) what the evidence indicates, and (3) what additional information is needed before the system is used again.

Teaching Points (Facilitator Notes)

Expected student observations:

Particles entered during venting — the chamber was clean before the vent, contaminated after
The vent filter is the protective barrier; if particles got through, the filter may be compromised
Extended pumpdown below 1 mbar suggests increased surface gas load from the particles (more surface area for water and gas adsorption)

Key learning moments:

Vent filter function: R1-FLT-VENT captures airborne particles during controlled venting. If the filter is degraded, damaged, or bypassed, particles enter the chamber with the incoming air.
Why particles affect pumpdown: Particulate contamination adds surface area inside the chamber. Each particle adsorbs water and gas. More surface area means more surface desorption, which means a higher gas load in the 1–0.1 mbar range. The pumpdown isn't stalled (it eventually reaches base) but it's extended.
Possible filter issues:
Filter element degraded or saturated (sintered metal clogged or damaged)
Vent valve was opened too quickly (turbulence bypassed the filter)
Filter connection is loose (air bypassing the filter element)
Someone vented by cracking a flange instead of using the vent line (completely bypassing R1-FLT-VENT)

Model escalation note: "Particulate contamination observed inside R1-A chamber after controlled vent. Particles were not present before venting. Evidence indicates a possible issue with R1-FLT-VENT (damage or degradation) or that venting may not have been performed through the vent line.

Additional information needed: inspection of R1-FLT-VENT condition and confirmation of the vent procedure used. Chamber and sample should be cleaned before next use."

Common student errors:

Not connecting the vent event to the particle appearance (assuming particles were "already there")
Not considering how particles affect gas load (particles are often dismissed as a cleanliness issue rather than a vacuum performance issue)
Suggesting "replace the pump" when the pump is performing normally — the problem is contamination, not pump failure

End of Scenario Cards — Module 2