Correct: B) To remove bulk atmospheric gas from the chamber, reducing pressure from atmosphere (~950 mbar) to the rough vacuum range (~10^-2 to 10^-3 mbar)

Correct: C) Turbomolecular pumps operate by transferring momentum to individual molecules — at atmospheric pressure the gas is too dense, and the high gas load can mechanically damage the high-speed rotor blades

Correct: B) An off-centre rotor with spring-loaded vanes that slide against the stator wall, trapping gas in crescent-shaped volumes sealed by oil

Correct: C) Two interleaving spiral-shaped scrolls — one fixed, one orbiting — that create gas pockets moving from the outer edge to the centre

The scroll pump uses the relative motion between two spiral elements to trap and compress gas. As the orbiting scroll moves, crescent-shaped pockets form at the outer edge, migrate inward, shrink in volume (compressing the gas), and exhaust at the centre. There is no oil in the gas path — scroll pumps are oil-free. This eliminates backstreaming and exhaust oil mist concerns entirely, which is why scroll pumps are chosen for clean applications like semiconductor processing and analytical instruments.

Correct: B) False

False. Diaphragm pumps have a limited ultimate pressure — typically around 1 to 10 mbar — because the flexible membrane cannot create the tight sealing that oil provides in a rotary vane pump. Rotary vane pumps reach approximately 10^-3 mbar (single-stage) or 10^-4 mbar (two-stage). Diaphragm pumps are chosen when cleanliness is the priority and only modest vacuum levels are needed — they are completely oil-free with very clean exhaust, making them suitable as backing pumps for small turbo pumps or for analytical instrument applications.

Correct: C) It uses high-speed rotating blades (20,000–90,000 RPM) to transfer momentum to individual gas molecules, operating in the molecular flow regime

The turbomolecular pump operates on a fundamentally different principle than positive displacement roughing pumps. Roughing pumps (rotary vane, scroll, diaphragm) trap volumes of gas and mechanically compress them. The turbo pump instead uses angled rotor blades spinning at extreme speed to "bat" individual molecules toward the exhaust through a series of rotor-stator stages. This molecular momentum transfer principle only works at low pressures where gas is in the molecular flow regime — individual molecules interacting with blades rather than a dense fluid resisting them.

Correct: C) Sealing the gaps between the rotor, vanes, and stator (preventing gas from leaking past); lubricating the sliding vane contacts; and removing heat from the compression process

The oil in a rotary vane pump is not just a lubricant — it is a critical functional element. Without oil, gas would leak past the vanes during compression, dramatically reducing the pump's ability to achieve low pressure. The oil film between the vane tips and the stator wall provides the gas-tight seal that makes the pump effective. The lubrication and cooling functions are secondary but essential for mechanical longevity. This triple role of the oil is also why oil contamination and loss are serious — they directly affect pump performance.

Correct: C) The roughing pump becomes the backing pump — it maintains low pressure at the turbo pump's exhaust so the turbo can maintain its compression ratio

A turbo pump compresses gas from its inlet (high vacuum) to its exhaust (rough vacuum). If the exhaust pressure rises too high, the turbo pump's compression ratio is insufficient and it cannot maintain vacuum. The roughing pump, now acting as the backing pump, continuously removes gas from the turbo's exhaust to keep it at an acceptable pressure (typically 0.1–1 mbar). If the backing pump fails, the turbo pump overloads and the system loses vacuum. This is why the pumping sequence is a chain — each pump depends on the next.

Correct: B) The volume of gas a pump can process per unit time at the pump inlet, measured in L/s or m³/h

Pumping speed describes volume throughput at the inlet — it tells you how much gas the pump can handle. A pump rated at 10 L/s processes 10 litres of gas per second at whatever pressure exists at its inlet. Critically, pumping speed at the pump inlet is not the same as effective pumping speed at the chamber — Module 3 taught you that conductance losses in the foreline reduce the speed actually delivered to the chamber. A 10 L/s pump connected through a restrictive foreline might only deliver 3 L/s of effective pumping at the chamber.

Correct: C) The pressure at which the pump's throughput equals the gas load from the pump's own internal sources — at this point the pump is fighting its own outgassing and internal leakage

Every pump generates some gas load internally — oil vapour, outgassing from internal surfaces, and small leaks past internal seals. At ultimate pressure, the pump's rate of gas removal exactly equals the rate of gas entering from these internal sources. The pump is running but making no further progress. This sets the absolute floor for system performance, although in practice the system's base pressure is usually limited by chamber gas load (M02) and conductance (M03) rather than the pump's ultimate pressure.

Correct: B) The pump body becomes hot during operation (60–80 degrees C is normal) — contact with the pump surface can cause burns

Compressing gas generates heat, and the pump body absorbs this thermal energy during operation. A rotary vane pump running at normal operating temperature (60–80 degrees C) is uncomfortably hot to touch. If the pump is overheating — due to blocked cooling, degraded oil, or excessive gas load — the body temperature may be significantly higher. Burns from hot pump surfaces are a real workplace hazard. Other pump hazards include oil exposure (skin contact, inhalation of oil mist) and moving parts (belts, rotating shafts).

Correct: A) True

True. When R1-P-RP compresses gas, the sealing oil gets aerosolised into fine droplets that are carried with the exhaust. Without R1-FLT-EXH, this oil mist would be released into the workshop — creating inhalation hazards, depositing oil on nearby surfaces, and contributing to environmental contamination. R1-FLT-EXH is a coalescing filter that captures the oil aerosol and returns the collected oil to the pump reservoir. Clean gas exits to atmosphere. A blocked or saturated R1-FLT-EXH is a maintenance issue — it increases exhaust back-pressure, which can degrade pump performance.

Correct: C) Pump oil vapour migrating backward through the foreline toward the chamber — contaminating chamber surfaces with hydrocarbon molecules

Backstreaming is oil vapour moving in the opposite direction to normal gas flow — from the pump toward the chamber. At very low pressures with minimal gas flow through the foreline, there is no "wind" to push oil vapour back toward the pump. The vapour can drift freely through the foreline and deposit on chamber surfaces as a hydrocarbon film. This is a contamination problem, not a leak — the base pressure may only be slightly elevated, but the chamber surfaces become coated with pump oil. Control methods include foreline traps, gas ballast, valve isolation, and using oil-free pumps.

Correct: C) Document the observation (when the noise started, what it sounds like, whether it changes with pump-down phase), compare to previous normal behaviour, and escalate to maintenance — a new grinding noise indicates potential mechanical wear that should be investigated before it worsens

A change in pump sound is diagnostic information. The fact that the pump still reaches base pressure does not mean the problem can be ignored — mechanical wear is progressive. Today's grinding noise becomes next month's bearing failure or vane damage if not investigated. The correct approach follows the observation-comparison-documentation-escalation framework: note specifically what changed, when, and under what conditions. Then escalate to someone qualified to investigate the pump internals. You don't need to diagnose the cause — you need to recognise the symptom and communicate it clearly.

Correct: C) R1-FLT-EXH is saturated or partially blocked — the increased exhaust back-pressure is reducing the pump's effective throughput, and oil is bypassing the filter element

The visible oil mist is the critical clue. Under normal conditions, R1-FLT-EXH captures all exhaust oil aerosol — you should never see oil mist at the exhaust outlet. Visible mist means the filter element is no longer performing properly: either saturated (full of collected oil that is not draining back) or damaged (oil passing around the element). A blocked filter also increases exhaust back-pressure, which reduces the pump's ability to move gas — explaining the longer pump-down. The pump itself is fine (0.03 mbar independently), and the rate-of-rise test rules out a leak. The foreline would not cause visible oil mist at the exhaust.