Module 1

Practice Quiz

Vacuum Fundamentals & System Orientation

Module 1 — Practice Quiz (Formative)

15 questions

Question 1 — Definition of Vacuum

A vacuum is best described as:

  1. A space with absolutely no gas molecules inside it
  2. A region where the pressure is below the surrounding atmospheric pressure
  3. Any sealed container connected to a pump
  4. A space where the pressure is exactly zero
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Correct: B) A region where the pressure is below the surrounding atmospheric pressure

Question 2 — Atmospheric Pressure at Selkirk

At Selkirk College (530 m elevation), the typical atmospheric pressure is approximately:

  1. 1013 mbar
  2. 760 mbar
  3. 950 mbar
  4. 500 mbar
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Correct: C) 950 mbar

Question 3 — Absolute vs Gauge Pressure

What is the key difference between absolute pressure and gauge pressure?

  1. Absolute pressure is always higher than gauge pressure
  2. Gauge pressure is used in vacuum work because it is more accurate
  3. Absolute pressure is measured from zero (perfect vacuum), while gauge pressure is measured relative to the local atmosphere
  4. They are different names for the same measurement
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Correct: C) Absolute pressure is measured from zero (perfect vacuum), while gauge pressure is measured relative to the local atmosphere

Question 4 — Pressure Units

Which three pressure units are most commonly used in vacuum technology?

  1. PSI, bar, atm
  2. mbar, Torr, Pascal (Pa)
  3. kPa, PSI, mmHg
  4. bar, inHg, atm
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Correct: B) mbar, Torr, Pascal (Pa)

The three primary units in vacuum technology are millibar (mbar), Torr, and Pascal (Pa). This course uses mbar as the default. The conversion is: 1 atm ≈ 1013 mbar ≈ 760 Torr ≈ 101,325 Pa.

Question 5 — Pressure Ranges

A chamber reads 0.5 mbar on its gauge. What vacuum pressure range is this in?

  1. Atmosphere
  2. Rough vacuum
  3. Medium vacuum
  4. High vacuum
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Correct: C) Medium vacuum

Rough vacuum extends from atmospheric pressure down to about 1 mbar. Medium vacuum covers approximately 1 mbar down to 10-3 mbar. High vacuum covers 10-3 down to 10-7 mbar. At 0.5 mbar, the chamber is in the medium vacuum range — below rough vacuum but well above high vacuum.

Question 6 — Gas Behaviour

Statement: "A vacuum pump works by pulling gas molecules out of the chamber."

  1. True
  2. False
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Correct: B) False

This is one of the most common misconceptions. A vacuum pump does not "pull" gas — it creates a region of lower pressure. The higher-pressure atmosphere then pushes gas molecules from the chamber through the pump, just as water flows downhill due to a pressure difference. The pump removes gas molecules that reach it and exhausts them to atmosphere, maintaining the pressure gradient.

Question 7 — Viscous vs Molecular Flow

At atmospheric pressure, gas molecules inside a chamber behave most like:

  1. People in a packed stadium — constantly bumping into each other and barely able to move freely
  2. People in an empty parking lot — moving freely without encountering anyone
  3. Water flowing through a narrow pipe
  4. Dust particles floating in still air
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Correct: A) People in a packed stadium — constantly bumping into each other and barely able to move freely

At atmospheric pressure, the mean free path (average distance a molecule travels before hitting another molecule) is extremely short — molecules collide constantly, like people in a packed stadium. This is viscous flow. As pressure drops to below about 10-2 mbar, the mean free path becomes longer than the chamber dimensions, and molecules travel freely across the space without collisions — molecular flow, like an empty parking lot.

Question 8 — Component Identification

On the R1-A training rig, what does the component ID "R1-V-ISO" refer to?

  1. Rig 1, Vent, Isolation line
  2. Rig 1, Valve, Isolation
  3. Rig 1, Volume, Isolated chamber
  4. Rig 1, Valve, Inlet/Supply/Output
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Correct: B) Rig 1, Valve, Isolation

The naming convention is [System]-[Type]-[Name]. R1 = Rig 1. V = Valve. ISO = Isolation. So R1-V-ISO is the isolation valve on Rig 1 — the valve that connects or disconnects the chamber from the roughing pump through the foreline.

Question 9 — Component Purpose

What is the purpose of the barometric reference gauge (R1-G-BX) on the R1-A rig?

  1. It measures the pressure inside the vacuum chamber
  2. It controls the vent valve opening speed
  3. It shows the current local atmospheric pressure, providing a reference point for comparing chamber gauge readings
  4. It measures the pump exhaust pressure
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Correct: C) It shows the current local atmospheric pressure, providing a reference point for comparing chamber gauge readings

The barometric reference (R1-G-BX) reads the current local atmospheric pressure (~950 mbar at Selkirk). It does not measure the chamber. Its value is that you can compare R1-G-CH (chamber gauge) against R1-G-BX to determine the system state. When both read the same value, the chamber is at atmosphere. When they differ significantly, the chamber is under vacuum.

Question 10 — System State Identification

On the R1-A rig, R1-G-CH reads 950 mbar, R1-G-BX reads 950 mbar, both valves are closed, and the pump is off. What state is the system in?

  1. ROUGHING
  2. ISOLATED
  3. VENTED
  4. CONTROLLED VENT
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Correct: C) VENTED

When the chamber gauge matches the barometric reference (~950 mbar), the chamber is at atmospheric pressure. Both valves are closed and the pump is off — the system is at rest. This is the VENTED state, the default resting condition of the R1-A rig.

Question 11 — System State Identification

On the R1-A, the pump is running, R1-V-ISO is open, R1-V-VENT is closed, and R1-G-CH reads 25 mbar and dropping. What state is the system in?

  1. ROUGHING
  2. VENTED
  3. ISOLATED
  4. CONTROLLED VENT
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Correct: A) ROUGHING

The pump is on, the isolation valve is open (connecting the chamber to the pump), the vent valve is closed (preventing atmospheric air from entering), and the chamber pressure is dropping. This is the ROUGHING state — the pump is actively removing gas from the chamber.

Question 12 — Gas Flow Path

During a pump-down on the R1-A, gas travels from the chamber to atmosphere. What is the correct flow path?

  1. R1-CH → R1-V-VENT → R1-FLT-VENT → ATM
  2. R1-CH → R1-P-RP → R1-V-ISO → ATM
  3. R1-CH → R1-V-ISO → R1-L-FL → R1-P-RP → R1-FLT-EXH → R1-L-EXH → ATM
  4. R1-CH → R1-FLT-EXH → R1-P-RP → R1-V-ISO → ATM
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Correct: C) R1-CH → R1-V-ISO → R1-L-FL → R1-P-RP → R1-FLT-EXH → R1-L-EXH → ATM

During roughing, gas flows from the chamber through the open isolation valve (R1-V-ISO), along the foreline (R1-L-FL), through the roughing pump (R1-P-RP), through the exhaust oil mist filter (R1-FLT-EXH), along the exhaust line (R1-L-EXH), and out to atmosphere. The vent path is blocked because R1-V-VENT is closed.

Question 13 — Rate of Rise

The R1-A chamber has been pumped down and then isolated (both valves closed). Over 10 minutes, the chamber gauge reading rises from 2 mbar to 2.5 mbar. What is the most likely explanation?

  1. The pump has malfunctioned
  2. There is a large leak — the system needs immediate repair
  3. Normal outgassing from the chamber walls and internal surfaces
  4. The vent valve has been accidentally opened
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Correct: C) Normal outgassing from the chamber walls and internal surfaces

A slow pressure rise of 0.05 mbar/minute after isolation is typical of outgassing — gas molecules releasing from the chamber walls, O-ring seals, and internal surfaces. A real leak would show a much faster rise (10+ mbar/minute). Outgassing is normal behaviour, not a fault. The rate of rise is the diagnostic clue — it tells you whether you are seeing normal behaviour or a genuine problem.

Question 14 — Vent Filter Purpose

Why does the R1-A rig have a vent filter (R1-FLT-VENT) on the vent line?

  1. It removes oil from the pump exhaust
  2. It reduces the speed of pump-down
  3. It prevents dust and particles from being drawn into the chamber when atmospheric air enters during venting
  4. It measures the purity of the incoming air
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Correct: C) It prevents dust and particles from being drawn into the chamber when atmospheric air enters during venting

When the vent valve opens to bring the chamber back to atmospheric pressure, air rushes in. Without a filter, dust particles and contaminants in the ambient air would be carried into the chamber. The sintered metal vent filter catches these particles, protecting the chamber's internal surfaces. The exhaust filter (R1-FLT-EXH) has a different job — it catches oil mist from the pump exhaust.

Question 15 — Schematic Reading

On a vacuum system schematic, you see the isolation valve symbol shown in the open position and the vent valve symbol shown in the closed position. The pump symbol indicates the pump is running. Without seeing any gauge readings, what can you determine about the system?

  1. The system is vented to atmosphere
  2. The system is in an isolated hold
  3. The system is likely in a roughing (pump-down) state
  4. Nothing — you need gauge readings to determine the state
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Correct: C) The system is likely in a roughing (pump-down) state

Valve positions and pump status alone give you strong evidence. Isolation valve open + vent valve closed + pump running = the classic ROUGHING configuration. The pump is pulling gas from the chamber through the open isolation valve, and the closed vent valve prevents atmospheric air from entering. Gauge readings would confirm and quantify, but the valve positions and pump status already tell the story.