Module 6 Scenario Cards: Pumping Principles & Pumping Behaviour
Module: M06 — Pumping Principles & Pumping Behaviour Rig Configuration: R1-A (Simple Single-Pump Roughing Rig) Cards: SC-M06-01 through SC-M06-03
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-M06-01: Pump Won't Reach Base Pressure — Multi-Module Diagnostic
Module: M06 Rig Config: R1-A Competency: M06-COMP-01, M06-COMP-02 Indicators Assessed: M06-IND-01.04, M06-IND-02.01, M06-IND-02.04 Cross-Module Knowledge: M02 (rate-of-rise interpretation, gas load sources), M03 (conductance, effective pumping speed), M04 (seal condition, O-ring failure modes), M05 (isolation points, valve function)
System State
State Name: ROUGHING (stalled) One-line description: R1-A has been roughing for 40 minutes. The viscous flow phase was normal, but the system has stalled at 0.18 mbar — well above the normal base pressure of 0.05 mbar. Multiple pieces of evidence have been collected to guide diagnosis.
Background Information (Provided to Students)
R1-A has been in regular service for six months and has been performing within specification until this week. The system reached 0.05 mbar consistently every day last month. This morning, the operator starts a routine pump-down from VENTED state (~950 mbar).
The viscous flow phase (950 to 1 mbar) completes in the normal ~90 seconds. Below 1 mbar, the pump-down slows and the system stalls at 0.18 mbar after 40 minutes of continuous pumping. The operator stops and collects evidence systematically.
No maintenance has been performed recently. No changes have been made to the chamber, foreline, or any connections. The workshop conditions are normal (not unusually humid).
Valve Positions (During Investigation)
| Valve ID | Valve Name | Position | Why |
|---|---|---|---|
| R1-V-VENT | Vent Valve | CLOSED | System is being roughed; vent path sealed. |
| R1-V-ISO | Isolation Valve | See test sequence below | Opened for roughing, closed for rate-of-rise test. |
Evidence Package (Provided to Students)
Evidence 1 — Pump-Down Data:
| Time from start | R1-G-CH (mbar) | Notes |
|---|---|---|
| 0 min | 950 | Start from VENTED state |
| 1.5 min | 1.0 | Viscous flow phase — normal |
| 5 min | 0.45 | Slower than expected below 1 mbar |
| 10 min | 0.28 | Still dropping but slowly |
| 20 min | 0.20 | Nearly stalled |
| 40 min | 0.18 | Stalled — no further progress |
Evidence 2 — Rate-of-Rise Test (R1-V-ISO closed at 0.18 mbar):
| Time after isolation | R1-G-CH (mbar) | Rate (mbar/min) |
|---|---|---|
| 0 min | 0.18 | — |
| 1 min | 0.22 | 0.040 |
| 3 min | 0.30 | 0.040 |
| 5 min | 0.38 | 0.040 |
| 10 min | 0.58 | 0.040 |
Evidence 3 — Pump Independent Test: R1-P-RP disconnected from foreline and tested at its own inlet: reaches 0.009 mbar in 5 minutes. Within rated specification.
Evidence 4 — Visual Inspection:
- R1-FLT-EXH exhaust: clean, no visible oil mist
- Oil sight glass: oil level correct, colour clear amber
- Pump sound: normal, no unusual noise or vibration
- Pump body temperature: warm, consistent with normal operation
- Foreline connections: all clamps tight, no visible damage
- Chamber flange: bolts appear tight, no visible gaps
Evidence 5 — System History:
- Chamber last opened 3 weeks ago for a demonstration (nothing placed inside)
- All O-rings replaced 4 months ago during scheduled maintenance
- Foreline is original specification (25 mm bore, 0.6 m, straight)
- No process gases have been used — system pumps air only
Pump Status
| Pump ID | Pump Name | Status | Notes |
|---|---|---|---|
| R1-P-RP | Roughing Pump | ON (during roughing) / OFF (during RoR test) | Pump is healthy — reaches 0.009 mbar independently. All visual checks normal. |
Media Placeholder
[Media: SC-M06-01 Evidence Dashboard]
- Split view: pump-down curve (stalling at 0.18 mbar) alongside rate-of-rise plot (constant 0.040 mbar/min)
- Callout comparing today's pump-down to the reference curve
- Annotation: "Pump verified at 0.009 mbar — pump is not the problem"
- Priority: P2-STRONGLY RECOMMENDED
Student Prompt
The lead technician is investigating the R1-A performance problem. All five evidence packages are available above.
1. Recognise: List every piece of evidence and state what each one tells you. Separate what is KNOWN from what is SUSPECTED. Pay specific attention to the rate-of-rise pattern — what does a constant rate mean? 2. Interpret: Three hypotheses are proposed: - Hypothesis A: The pump is failing and needs replacement. - Hypothesis B: The foreline conductance has degraded, limiting effective pumping speed. - Hypothesis C: A seal has developed a leak, allowing atmospheric gas to enter the chamber.
For each hypothesis, state whether the evidence supports, contradicts, or is neutral — and cite the specific evidence item. Rank the hypotheses from most to least likely. 3. Communicate: A colleague suggests: "We should just buy a bigger pump — 20 m³/h instead of 5 m³/h — that will overpower whatever the problem is." Write a 3-4 sentence response explaining why this suggestion does not address the root cause. Explain the relationship between gas load, effective pumping speed, and base pressure to support your argument. 4. Escalate: Write an escalation note (4-5 sentences) for the maintenance supervisor. Include: what was observed, what the evidence points to, what has been ruled out, and what questions remain unanswered. Include at least 3 UNKNOWN items that require further evidence to resolve.
Teaching Points (Facilitator Notes)
Expected student observations:
- Viscous flow phase is normal — rules out gross system problems (major leak, pump failure, massive conductance restriction)
- Molecular flow phase is severely degraded — problem is in the molecular flow regime
- Rate-of-rise: constant at 0.040 mbar/min — this is a REAL LEAK signature (M02). The rate does not decrease, meaning the gas source is non-depleting (atmospheric ingress)
- Pump independent test: 0.009 mbar — pump is healthy, eliminating Hypothesis A
- Foreline is original specification — no geometry change, and the viscous phase is normal, making Hypothesis B unlikely
- All visual checks normal — no obvious mechanical failure visible
Hypothesis evaluation:
| Hypothesis | Verdict | Key Evidence |
|---|---|---|
| A: Pump failure | Eliminated | Pump reaches 0.009 mbar independently (Evidence 3). All visual pump checks normal (Evidence 4). |
| B: Foreline conductance | Unlikely | Foreline is original spec (Evidence 5). Viscous flow phase is normal (Evidence 1) — a conductance restriction would also slow the viscous phase. |
| C: Seal leak | Supported (leading) | Constant rate-of-rise at 0.040 mbar/min (Evidence 2) is the definitive signature of atmospheric gas entering the chamber. O-rings are 4 months old — compression set is possible but early. |
Key learning moments:
- "Bigger pump" fallacy: This directly tests the Week 6 rubric. A bigger pump (higher S_eff) would lower the steady-state base pressure (P = Q/S = 0.040 × V_chamber / S_eff in mbar), but the leak still exists. Atmospheric contaminants (water, oxygen) continue entering. In a process application, the contamination would ruin product regardless of the pressure reading. The fix is to eliminate Q (fix the leak), not to increase S.
- Constant rate is the discriminator: Students must demonstrate that they understand the M02 rate-of-rise interpretation. Constant = leak. Decreasing = outgassing. This is the foundational diagnostic skill applied in a pump-context scenario.
- Pump health checks matter: Even when the pump is not the problem, the systematic pump health assessment (sound, oil, exhaust, temperature) is valuable — it provides evidence to RULE OUT pump-related causes confidently.
Model escalation note: "R1-A is stalling at 0.18 mbar (normal base: 0.05 mbar). Viscous flow phase is normal (950 to 1 mbar in 90 seconds). R1-P-RP reaches 0.009 mbar independently — pump is within spec.
Rate-of-rise test shows a constant rate of 0.040 mbar/min, consistent with a real atmospheric leak. All visual checks (oil, exhaust filter, connections, pump sound) are normal. Leading hypothesis: a seal on the chamber boundary (R1-V-ISO seat, R1-V-VENT seat, or chamber flange O-ring) has developed a leak.
UNKNOWN: (1) Which specific seal is leaking — sequential isolation tests with each valve would help localise the zone. (2) Whether the 4-month-old O-rings show visible compression set or damage — removal and visual inspection would provide this information. (3) Whether the leak is in the valve seat or the flange connection — a localised helium spray test (if available) would help discriminate."
Common student errors:
- Proposing pump replacement despite the independent pump test ruling it out
- Accepting the "bigger pump" suggestion without recognising the contamination issue
- Failing to identify the constant rate-of-rise as a leak (instead calling it "outgassing")
- Not using specific evidence item numbers when evaluating hypotheses
- Writing an escalation note that declares root cause without acknowledging the three unknowns
- Including operating steps (how to perform the isolation test) rather than observational reasoning
SC-M06-02: Backstreaming Symptoms — Elevated Base Pressure with Hydrocarbon Indicators
Module: M06 Rig Config: R1-A Competency: M06-COMP-02 Indicators Assessed: M06-IND-02.01, M06-IND-02.03, M06-IND-02.04 Cross-Module Knowledge: M02 (contamination sources, outgassing vs leak), M03 (molecular flow behaviour), M04 (material contamination), M05 (isolation valve function)
System State
State Name: ISOLATED (post-investigation) One-line description: R1-A has been pumping at low pressure for extended periods over the past two weeks. The base pressure has gradually risen, and a thin-film coating specialist who inspected the chamber interior reports finding an oily residue on the chamber walls. The system has no foreline trap.
Background Information (Provided to Students)
R1-A has been used for daily pump-down demonstrations for two weeks. The daily routine has been: start from VENTED state, pump down to base pressure, leave the pump running at base pressure for 2-3 hours while demonstrating gauge behaviour to students, then vent and shut down.
At the start of the two-week period, the base pressure was 0.05 mbar — normal. By the end of the first week, the base pressure had crept up to 0.07 mbar.
By the end of the second week, it reads 0.10 mbar. The pump-down time has also increased: 8 minutes initially, now 12 minutes.
A thin-film coating specialist visiting the facility inspects the chamber interior (during a vented state) and reports: "There is a faint oily film on the chamber walls. It looks like hydrocarbon contamination — I've seen this before on systems with backstreaming problems."
The maintenance technician collects additional evidence.
Valve Positions (During Rate-of-Rise Test)
| Valve ID | Valve Name | Position | Why |
|---|---|---|---|
| R1-V-VENT | Vent Valve | CLOSED | System is isolated for rate-of-rise testing. |
| R1-V-ISO | Isolation Valve | CLOSED | System is isolated — chamber disconnected from pump. |
Evidence Package (Provided to Students)
Evidence 1 — Base Pressure Trend:
| Day | Base Pressure (mbar) | Pump-Down Time (min) | Daily Pump Time at Base (hours) |
|---|---|---|---|
| Day 1 | 0.05 | 8 | 2.5 |
| Day 5 | 0.06 | 9 | 3.0 |
| Day 8 | 0.07 | 10 | 2.5 |
| Day 10 | 0.09 | 11 | 3.0 |
| Day 14 | 0.10 | 12 | 2.0 |
Evidence 2 — Rate-of-Rise Test (Day 14, isolated at 0.10 mbar):
| Time after isolation | R1-G-CH (mbar) | Rate (mbar/min) |
|---|---|---|
| 0 min | 0.10 | — |
| 1 min | 0.13 | 0.030 |
| 3 min | 0.17 | 0.020 |
| 5 min | 0.20 | 0.015 |
| 10 min | 0.25 | 0.010 |
Evidence 3 — Pump Independent Test: R1-P-RP reaches 0.008 mbar at its own inlet. Within specification.
Evidence 4 — Visual Observations:
- Chamber interior: faint oily film on walls, reported by thin-film coating specialist as "hydrocarbon contamination consistent with pump oil backstreaming"
- R1-FLT-EXH: clean exhaust, no visible oil mist
- Pump oil: clear amber, correct level
- Pump sound and temperature: normal
- R1-V-ISO: no visible damage; the valve has been open for extended periods daily during pump-down demonstrations
Evidence 5 — System Configuration:
- R1-A does not have a foreline trap between R1-V-ISO and R1-P-RP
- R1-V-ISO has been open for 2-3 hours daily while the pump runs at base pressure
- No gas ballast has been used
- The workshop is well-ventilated and climate-controlled
Pump Status
| Pump ID | Pump Name | Status | Notes |
|---|---|---|---|
| R1-P-RP | Roughing Pump | OFF (during investigation) | Pump is healthy — reaches 0.008 mbar independently. Oil condition normal. |
Media Placeholder
[Media: SC-M06-02 Backstreaming Mechanism Diagram]
- Cross-section showing foreline between pump and chamber with R1-V-ISO open
- Arrows showing normal gas flow direction (chamber → pump) alongside reverse oil vapour migration (pump → chamber)
- Annotation: "At low pressure with minimal gas flow, oil vapour drifts freely toward the chamber"
- Callout showing oily residue depositing on chamber walls
- Priority: P2-STRONGLY RECOMMENDED
Student Prompt
The maintenance technician has collected the evidence above. A thin-film coating specialist has identified what appears to be hydrocarbon contamination inside the chamber.
1. Recognise: Describe the trend in the evidence. What has changed over the two-week period, and what has stayed the same? What is the significance of the rate-of-rise pattern — decreasing rate, not constant? 2. Interpret: The oily film on the chamber walls is the key new evidence. Explain the mechanism by which pump oil can reach the chamber interior, even though gas is flowing in the opposite direction during pumping. Why is this problem worst when the pump runs at low pressure for extended periods? Connect this to at least two M02 concepts. 3. Communicate: Write a 3-4 sentence explanation for the visiting thin-film coating specialist that describes: (a) why R1-A is susceptible to this problem, and (b) what types of measures are known to control or prevent backstreaming in general. Use generic descriptions rather than specific product names. 4. Escalate: The facility manager asks: "Is this a health and safety concern or just a performance issue?" Provide a structured answer that addresses both the performance consequences and any safety or contamination implications. Include at least 3 UNKNOWN items.
Teaching Points (Facilitator Notes)
Expected student observations:
- Gradual degradation over two weeks — not a sudden failure
- Both base pressure and pump-down time are worsening in parallel
- Rate-of-rise: DECREASING (0.030 to 0.010 mbar/min) — this is an outgassing pattern, not a leak
- The outgassing source is the oily film itself — hydrocarbons deposited on the chamber walls slowly evaporate under vacuum
- Pump is healthy (0.008 mbar independently) — this is not a pump mechanical failure
- R1-FLT-EXH is clean — the problem is not on the exhaust side but on the inlet/foreline side
Key learning moments:
- Backstreaming mechanism: At base pressure (~0.05 mbar), the gas throughput through the foreline is very low. In molecular flow, there is no bulk gas "wind" to push oil vapour back toward the pump. Oil vapour molecules from the hot pump can randomly migrate through the foreline and into the chamber. With R1-V-ISO open for 2-3 hours daily, the oil vapour has ample time to reach the chamber and deposit on the cooler walls.
- The oily film IS the gas load: The deposited oil creates a new outgassing source on the chamber walls. Under vacuum, the hydrocarbon film slowly evaporates, contributing to the gas load. This is why the base pressure has risen and the pump-down time has increased — the chamber now has an additional gas load source that was not present when the system was clean.
- Decreasing rate-of-rise confirms outgassing: The oily film is a finite (though slowly replenished) gas source. Under vacuum, the volatiles evaporate — hence the decreasing rate. This distinguishes backstreaming contamination from a seal leak (which would be constant).
- M02 connections: (1) Backstreaming is a contamination source identified in M02 Lesson 4. (2) The hydrocarbon film creates surface outgassing (M02 gas load source). (3) The chamber surfaces are now contaminated — the base pressure equation shows P_base = Q_total / S_eff, and Q_total has increased because of the new oil-sourced gas load.
- Control measures: (a) Close R1-V-ISO when extended pumping at base pressure is not needed — isolation prevents further vapour migration. (b) Install a foreline trap between R1-V-ISO and R1-P-RP — the trap intercepts oil vapour before it reaches the chamber. (c) Use gas ballast — increases gas flow through the pump, sweeping oil vapour toward the exhaust. (d) Consider replacing R1-P-RP with a scroll pump — oil-free operation eliminates backstreaming entirely.
Model explanation for the thin-film specialist: "R1-A uses an oil-sealed rotary vane pump (R1-P-RP) with no foreline trap between the pump and the chamber. When the system runs at base pressure for 2-3 hours daily with R1-V-ISO open, oil vapour from the pump migrates backward through the foreline into the chamber — there is insufficient gas flow to oppose this at low pressure.
The deposited oil is the hydrocarbon film you identified. Control options include closing the isolation valve during extended idle periods, installing a foreline trap to intercept the vapour, using gas ballast to increase exhaust-ward flow, or replacing the pump with an oil-free type."
Health and safety answer: "Both. Performance: the oily film increases the chamber's gas load, raising base pressure and extending pump-down times — this will worsen if not addressed.
Safety: the oily film itself is not an acute hazard inside a sealed chamber, but it represents pump oil contamination of a workspace. If this were a process chamber (thin-film coating, semiconductor), the hydrocarbon contamination would be a serious quality problem.
The oil mist hazard is handled by R1-FLT-EXH on the exhaust side and is not related to backstreaming. UNKNOWN: (1) The exact composition of the oily film — is it pump oil or a breakdown product? (2) Whether the contamination has affected any internal seals or gauge accuracy. (3) Whether cleaning the chamber walls (solvent wipe) would restore normal base pressure, or whether deeper cleaning (bake-out) is required."
Common student errors:
- Confusing backstreaming (oil going toward the chamber through the foreline) with exhaust oil mist (oil going out through R1-FLT-EXH) — these are opposite directions
- Identifying the problem as a leak because the base pressure rose (the rate-of-rise clearly shows outgassing, not a leak)
- Not connecting the oily film to the elevated gas load — treating the contamination and the base pressure rise as separate problems
- Suggesting pump replacement without mentioning simpler control measures (valve isolation, foreline trap)
- Including operating steps ("close the valve, then open the vent") instead of diagnostic observations and interpretations
SC-M06-03: Pump Behaviour Change — Noise, Vibration & Exhaust Observation
Module: M06 Rig Config: R1-A Competency: M06-COMP-02 Indicators Assessed: M06-IND-02.02, M06-IND-02.04 Cross-Module Knowledge: M02 (rate-of-rise for context), M04 (oil condition assessment), M05 (system state interpretation)
System State
State Name: ROUGHING (with abnormal pump symptoms) One-line description: R1-A is being roughed. The pump (R1-P-RP) has developed multiple abnormal symptoms: a new rattling noise, increased vibration, visible oil mist at the R1-FLT-EXH exhaust, and a stronger-than-usual exhaust odour. The system is still reaching a base pressure, but it is degraded.
Background Information (Provided to Students)
R1-A has been in daily use for nine months. The pump (R1-P-RP) was last serviced (oil change and general inspection) six months ago. For the past three days, the operator has noticed progressive changes in the pump's behaviour during pump-down.
Day 1: A faint rattling noise, barely noticeable. System reached 0.06 mbar (slightly above the normal 0.05 mbar).
Day 2: The rattling is louder and more consistent. The operator also notices the pump body feels hotter than usual. System reached 0.09 mbar.
Day 3 (today): The rattling is clearly audible from 2 metres away. The pump body is noticeably hot — too uncomfortable to hold a hand on for more than a few seconds.
The operator detects a faint oily/burnt smell near the exhaust and can see a slight haze of oil mist at the R1-FLT-EXH exhaust outlet. The system reaches 0.15 mbar after 20 minutes and appears to be stalling.
The operator stops the pump-down and collects evidence.
Valve Positions (During Investigation)
| Valve ID | Valve Name | Position | Why |
|---|---|---|---|
| R1-V-VENT | Vent Valve | CLOSED | System was being roughed. |
| R1-V-ISO | Isolation Valve | CLOSED | Operator isolated the chamber for investigation. |
Evidence Package (Provided to Students)
Evidence 1 — Three-Day Trend:
| Day | Base Pressure (mbar) | Pump-Down Time to Base | Noise | Body Temp | Exhaust | Oil Condition |
|---|---|---|---|---|---|---|
| Day 1 | 0.06 | 9 min | Faint rattle | Normal warm | Clean | Clear amber |
| Day 2 | 0.09 | 13 min | Louder rattle | Hotter than usual | Clean | Slightly darker |
| Day 3 | 0.15 (stalling) | >20 min, stalled | Loud rattle at 2m | Too hot to touch | Visible oil mist, burnt smell | Noticeably dark |
Evidence 2 — Rate-of-Rise Test (Day 3, isolated at 0.15 mbar):
| Time after isolation | R1-G-CH (mbar) | Rate (mbar/min) |
|---|---|---|
| 0 min | 0.15 | — |
| 1 min | 0.17 | 0.020 |
| 3 min | 0.20 | 0.015 |
| 5 min | 0.22 | 0.010 |
| 10 min | 0.25 | 0.006 |
Evidence 3 — Pump Independent Test (Day 3): R1-P-RP tested at its own inlet: reaches 0.05 mbar (previously reached 0.009 mbar during last service check). The pump's own performance has degraded.
Evidence 4 — Visual Observations (Day 3):
- Oil mist visible at R1-FLT-EXH exhaust outlet — this was never visible before
- Oil in sight glass: dark, possibly slightly foamy
- Exhaust has a burnt/acrid odour that is new
- Pump body temperature: significantly elevated compared to normal
- Vibration can be felt through the bench surface when pump is running
- No visible external oil leaks from the pump
Evidence 5 — System History:
- Pump oil changed 6 months ago (manufacturer recommendation: 6-12 months depending on use)
- Pump has been running 4-6 hours per day, 5 days per week for 9 months
- No process gases — air only
- No previous pump problems noted in the maintenance log
Pump Status
| Pump ID | Pump Name | Status | Notes |
|---|---|---|---|
| R1-P-RP | Roughing Pump | OFF (during investigation) | Pump has degraded — now reaches 0.05 mbar independently (previously 0.009 mbar). Multiple abnormal symptoms present. |
Media Placeholder
[Media: SC-M06-03 Pump Health Assessment Checklist]
- Visual diagram of R1-P-RP with annotated observation points
- Callouts at: oil sight glass (dark oil), exhaust outlet (visible mist), body surface (temperature), mounting base (vibration), inlet connection (gas path to foreline)
- Traffic-light indicators: green (Day 1 levels), amber (Day 2), red (Day 3)
- Priority: P2-STRONGLY RECOMMENDED
Student Prompt
The operator has been tracking R1-P-RP's behaviour over three days. Today the pump is showing clearly abnormal symptoms.
1. Recognise: Document the three-day progression of symptoms. For each observable (noise, temperature, exhaust, oil condition, base pressure), describe how it has changed from Day 1 to Day 3. What is the overall pattern — sudden failure or progressive degradation? 2. Interpret: The rate-of-rise test (Evidence 2) shows a decreasing rate. The pump independent test (Evidence 3) shows the pump now reaches 0.05 mbar instead of its previous 0.009 mbar. How do these two pieces of evidence relate? What does the gap between the pump's current performance (0.05 mbar) and the system stall (0.15 mbar) indicate — is the pump the only problem, or is something else contributing? 3. Communicate: The maintenance supervisor needs to be informed that R1-P-RP requires attention. Write a structured observation report (5-6 sentences) that documents what was observed, when the changes started, how they have progressed, and what the current status is. Do NOT diagnose the internal pump failure — that is the maintenance technician's role. The report should communicate the external evidence only. 4. Escalate: The supervisor asks: "Can we keep running the pump until the scheduled maintenance next month?" What does the evidence indicate about the viability of this proposal? Consider: (a) the trend direction (is it getting worse?), (b) safety implications of the current symptoms, and (c) what could happen if the pump is run to failure. Include at least 3 UNKNOWN items.
Teaching Points (Facilitator Notes)
Expected student observations:
- Progressive degradation over 3 days: Every observable has worsened. This is not a single event — something inside the pump is deteriorating.
- Noise progression: Faint rattle → louder → clearly audible at 2 m. Indicates a mechanical source that is worsening (worn bearing, damaged vane, loose component).
- Temperature increase: Normal warm → hotter than usual → too hot to touch. The pump is generating more heat — likely because internal friction has increased (worn parts), or the pump is working harder due to degraded internal sealing.
- Oil degradation: Clear amber → slightly darker → noticeably dark. The oil is either thermally degrading (overheating), accumulating wear particles (mechanical damage), or both.
- Exhaust changes: Clean → clean → visible oil mist + burnt smell. R1-FLT-EXH is either saturated (due to increased oil carry-over from the degraded pump) or the pump is generating more oil mist than normal.
- Base pressure degradation: 0.06 → 0.09 → 0.15 mbar (stalling). The pump's own performance has dropped from 0.009 to 0.05 mbar (Evidence 3), but the system stalls at 0.15 mbar — worse than the pump alone.
Key learning moments:
- The gap between pump performance and system performance: The pump now reaches 0.05 mbar independently (degraded but functional). The system stalls at 0.15 mbar — three times worse. This gap tells you that the pump degradation is compounded by something else. Most likely: (1) the degraded pump oil is backstreaming more (darker, degraded oil has higher vapour pressure), adding gas load to the chamber, and/or (2) the increased exhaust back-pressure from R1-FLT-EXH saturation is further reducing effective pumping. The system is experiencing multiple cascading effects from a single root cause (pump wear).
- Rate-of-rise is outgassing, not a leak: The decreasing rate (0.020 to 0.006 mbar/min) tells the student this is NOT a seal leak — the gas source depletes. The source is likely the chamber surfaces, which are now receiving more backstreaming oil due to the pump's degraded condition. The outgassing is elevated compared to a clean chamber.
- Safety considerations: Running a pump to failure risks: (a) oil overheating and potential fire/smoke, (b) catastrophic mechanical failure (broken vane fragments), (c) oil spill from seal failure, (d) complete loss of system availability. The visible oil mist at the exhaust is already a health concern — the operator is being exposed to oil aerosol that R1-FLT-EXH is no longer fully capturing.
- Escalation discipline: The student should document symptoms without diagnosing pump internals. The internal cause (worn vanes? bearing failure? damaged seals?) is for qualified maintenance — the student's job is to communicate the external evidence pattern clearly enough that maintenance can prioritise and plan.
Model observation report: "R1-P-RP has shown progressive degradation over the past three days. Day 1: faint rattling noise appeared, base pressure slightly elevated to 0.06 mbar (normal: 0.05 mbar). Day 2: rattling louder, pump body noticeably hotter than normal, oil slightly darker, base pressure 0.09 mbar.
Day 3 (today): rattling clearly audible from 2 metres, pump body too hot to touch, oil visibly dark, visible oil mist at R1-FLT-EXH exhaust (previously always clean), and a burnt odour from the exhaust.
System stalled at 0.15 mbar after 20 minutes. Pump independent test shows 0.05 mbar (previously 0.009 mbar at last service). All symptoms are worsening — the trend indicates an accelerating mechanical or oil-related issue inside the pump."
Response to "keep running until scheduled maintenance": "The evidence does not support continued operation until next month. The three-day trend shows accelerating degradation — every observable is worsening, not stabilising. The visible oil mist at the exhaust means R1-FLT-EXH is no longer fully protecting the workspace — this is both a health concern (operator inhalation) and an environmental concern.
If the pump is run to failure, the consequences could include: sudden loss of vacuum capability (unplanned downtime), catastrophic mechanical failure (potential safety hazard), or oil overheating (fire/smoke risk in extreme cases).
UNKNOWN: (1) The internal cause of the rattling — is it a worn bearing, damaged vane, or loose component? The progression rate depends on the specific failure mode. (2) Whether the dark oil contains metal wear particles — an oil sample analysis would reveal this. (3) Whether R1-FLT-EXH needs replacement (saturated from increased oil carry-over) or whether the pump itself is generating abnormally high oil mist. The trend data indicates that earlier inspection would reduce the risk of unplanned failure."
Common student errors:
- Diagnosing the internal pump failure ("the vanes are worn" or "the bearings have failed") — students do not have access to pump internals and should not speculate beyond the external evidence
- Recommending the pump continue running because "it still reaches a base pressure" — ignoring the trend and safety implications
- Not connecting the visible oil mist to R1-FLT-EXH performance — the mist means the filter is overwhelmed, which is diagnostically significant
- Treating each symptom (noise, heat, oil, exhaust) independently rather than recognising them as a correlated cluster pointing to a single progressing internal problem
- Including operating procedures ("shut down the pump by closing the valve and pressing the stop button") rather than observational evidence and diagnostic reasoning
End of Scenario Cards — Module 6