Module 6 Workbook: Pumping Principles & Pumping Behaviour (Capstone)
Estimated Completion Time: 45-60 minutes
Part A: Knowledge Check (20 marks)
Short-answer questions testing recall from Module 6 async learning content. 2 marks each. 10 questions.
A1. State the three functions that oil serves in an oil-sealed rotary vane vacuum pump. Explain which of these functions is most important for the pump's ability to achieve low pressure.
(2 marks)
A2. Identify the pump type that operates by transferring momentum to individual gas molecules using high-speed rotating blades. State what flow regime this pump operates in and explain why it requires a backing pump.
(2 marks)
A3. Describe the function of R1-FLT-EXH on R1-A. State what type of contaminant it captures, where it is located in the gas path, and what it protects.
(2 marks)
A4. Explain the key difference between oil-sealed and oil-free roughing pumps. Describe one advantage and one limitation of each type, with reference to a vacuum application where the distinction between them matters.
(2 marks)
A5. On R1-A, the pump reaches 0.009 mbar at its own inlet during an independent test. However, the system stalls at 0.20 mbar.
All visual pump health checks (oil condition, exhaust, sound, temperature) are normal. Explain what this gap between pump capability and system performance indicates. State whether the pump is the cause of the problem.
(2 marks)
A6. On a multi-pump system, a turbomolecular pump is backed by a rotary vane pump. Explain why the turbomolecular pump's performance depends on the backing pump maintaining adequate exhaust pressure. Describe what happens to the system if the backing pump's oil becomes contaminated and its ultimate pressure degrades.
(2 marks)
A7. R1-P-RP has been running at base pressure (~0.05 mbar) for several hours with R1-V-ISO open. The system has no foreline trap. Describe the mechanism by which pump oil can migrate toward the chamber under these conditions.
Explain why this migration is more significant at low pressure with minimal gas flow than during the initial pump-down from atmospheric pressure.
(2 marks)
A8. R1-A's pump oil appears milky and cloudy instead of the normal clear amber. The system has been used in a high-humidity workshop with frequent pump-down and venting cycles. Explain the most likely cause of the oil condition and describe how it affects the pump's vacuum performance.
(2 marks)
A9. A rate-of-rise test on R1-A shows a constant rate of 0.04 mbar/min. The pump reaches 0.009 mbar independently. A colleague proposes replacing R1-P-RP with a larger pump (higher pumping speed) to solve the elevated base pressure.
Explain why the larger pump does not address the underlying problem, despite the fact that increased effective pumping speed lowers the steady-state base pressure for a given gas load.
(2 marks)
A10. R1-P-RP shows the following three-day progression: Day 1 — faint rattle, base pressure 0.06 mbar. Day 2 — louder rattle, pump body hotter than normal, oil slightly darker, base pressure 0.09 mbar. Day 3 — rattle audible from 2 metres, pump too hot to touch, oil visibly dark, visible oil mist at R1-FLT-EXH exhaust, base pressure 0.15 mbar and stalling.
An independent pump test on Day 3 shows R1-P-RP reaches 0.05 mbar (previously 0.009 mbar). Explain what the progressive nature of these symptoms indicates about the type of problem. Describe why the gap between the pump's independent performance (0.05 mbar) and the system stall (0.15 mbar) suggests that additional effects are compounding the pump degradation.
(2 marks)
Part B1: System Diagnostic — Single-Mechanism Scenario (10 marks)
A focused diagnostic scenario requiring interpretation of trend data and contamination evidence on a single system. 5 marks each. 2 questions.
Scenario: Gradual Performance Degradation on R1-A
R1-A has been used for daily pump-down demonstrations for two weeks. The daily routine has been: start from VENTED state (~950 mbar), 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. The base pressure has gradually risen over the period:
| 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 |
On Day 14, the system is isolated (R1-V-ISO closed, R1-V-VENT closed, pump off) and a rate-of-rise test is performed:
| Time after isolation | R1-G-CH (mbar) | Rate of rise (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 |
Additional evidence:
- R1-P-RP reaches 0.008 mbar at its own inlet — within specification
- R1-FLT-EXH exhaust is clean — no visible oil mist
- Pump oil: clear amber, correct level
- Pump sound and temperature: normal
- A visiting specialist inspects the chamber interior (during a vented state) and reports a faint oily film on the chamber walls, described as hydrocarbon contamination
- 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
B1-Q1. Examine the two-week base pressure trend and the rate-of-rise data. Classify the rate-of-rise pattern (constant, increasing, or decreasing) and state what type of gas source this pattern indicates.
Explain why the pump independent test result is important for interpreting the data. Describe what the gradual nature of the degradation (worsening over two weeks, not sudden) tells you about the type of problem. (5 marks)
B1-Q2. The oily film on the chamber walls has been identified as hydrocarbon contamination. Based on R1-A's configuration (oil-sealed rotary vane pump, no foreline trap, R1-V-ISO open for extended periods at low pressure), explain the mechanism by which this contamination reached the chamber interior.
Describe how the deposited oil film acts as a gas load source that contributes to the elevated base pressure. Identify at least two measures that are known to control or prevent this type of contamination in general terms. (5 marks)
Part B2: System Diagnostic — Multi-Evidence Capstone Scenario (10 marks)
A complex multi-factor scenario requiring systematic hypothesis evaluation and integration of concepts from multiple modules. 5 marks each. 2 questions.
Scenario: R1-A Stalls at 0.18 mbar — Multi-Module Diagnostic
R1-A has been in regular service for six months and has been reaching 0.05 mbar consistently every day. This morning, the operator starts a routine pump-down from VENTED state (~950 mbar).
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 |
Rate-of-rise test (R1-V-ISO closed at 0.18 mbar, R1-V-VENT closed, pump off):
| 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 |
Additional evidence:
- R1-P-RP tested independently at its own inlet: reaches 0.009 mbar in 5 minutes — within specification
- 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
- Foreline is original specification (25 mm bore, 0.6 m, straight)
- No maintenance has been performed recently
- All O-rings replaced 4 months ago during scheduled maintenance
- Chamber last opened 3 weeks ago for a demonstration (nothing placed inside)
B2-Q1. Three hypotheses are proposed for the performance degradation:
- 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. Cite the specific evidence for each evaluation. Rank the hypotheses from most likely to least likely. (5 marks)
B2-Q2. The constant rate-of-rise of 0.040 mbar/min has been identified as the signature of a real leak. A colleague suggests: "A larger pump with more pumping speed would lower the base pressure and solve the problem." Explain why this suggestion does not address the root cause — consider what would happen to the contaminant species entering the chamber even if the numerical pressure reading improved. Then, explain how the isolation points on R1-A (R1-V-ISO and R1-V-VENT) divide the system into distinct zones, and describe what information rate-of-rise data collected from different isolation configurations would reveal about the location of the leak. (5 marks)
Part C: Practical Reflection (10 marks)
Connects learning to real-world application. Open-ended. 5 marks each. 2 questions.
C1. Describe a situation where the concepts from this module — pump types and their trade-offs, pump health assessment, backstreaming, effective pumping speed, the "bigger pump" fallacy, oil condition monitoring, or systematic multi-factor diagnosis — would matter in a vacuum-related setting. This could be:
- (a) from your current or previous workplace,
- (b) from a lab session you have experienced, or
- (c) a realistic scenario you can envision in an industry that uses vacuum systems (such as semiconductor fabrication, thin-film coating, or research labs).
Explain what someone in that role would understand differently about system performance or troubleshooting with the knowledge from this module. Be specific — reference at least one concept by name. (5 marks)
C2. What was the most surprising or counterintuitive idea you encountered in this module? Why did it challenge your expectations?
If you have workplace experience, describe how this changes your understanding of something you have observed on the job. If you are new to vacuum technology, describe how this concept changes the way you would think about how vacuum systems are maintained, diagnosed, or protected from contamination. (5 marks)
Marking Summary
| Part | Available | Achieved |
|---|---|---|
| A: Knowledge Check | 20 | |
| B1: Single-Mechanism Diagnostic | 10 | |
| B2: Multi-Evidence Capstone Diagnostic | 10 | |
| C: Practical Reflection | 10 | |
| Total | 50 |
Assessor: ________________________________ Date: ________________________________ Comments: ________________________________________________________________________
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