Correct: B) Stainless steel — because of its low outgassing, corrosion resistance, and ability to withstand bake-out temperatures

Correct: C) The porous aluminium oxide layer on the surface traps water vapour, which desorbs slowly under vacuum

Correct: C) Gasket material for CF (ConFlat) flanges, where it deforms under compression to create a metal-to-metal seal

Correct: C) When compressed in its groove, the elastic material pushes outward against both sealing surfaces, creating a gas-tight barrier maintained by the elastic restoring force

An elastomer O-ring works by elastic compression. When two flanges are brought together, the O-ring is squeezed into its groove and deforms. The compressed rubber exerts a restoring force that pushes outward against both mating surfaces, creating a continuous gas-tight barrier. As long as the O-ring remains compressed and undamaged, the seal holds. This is fundamentally different from a metal seal, which relies on permanent (plastic) deformation rather than elastic recovery.

Correct: C) Metal seals rely on plastic deformation of a copper gasket by knife edges, creating a permanent seal; elastomer seals rely on elastic compression and are reusable

The CF seal works by driving precision knife edges into a soft copper gasket. The copper permanently deforms (plastic deformation) — it does not spring back. This creates an extremely tight seal with zero permeation and negligible outgassing. The trade-off is that the gasket must be replaced every time the joint is opened (single-use). Elastomer O-rings, by contrast, rely on elastic recovery and can be reused many times.

Correct: B) A centering ring holding an O-ring, secured by a single clamp

KF flanges are the "quick connect" of vacuum technology. Two flat flanges meet face-to-face with a centering ring (a metal carrier holding an O-ring) between them. A single clamp — hinged or wing-nut style — squeezes the flanges together, compressing the O-ring. Assembly takes seconds, not minutes. On R1-A, KF-style fittings are likely used on the foreline connections (R1-L-FL) between the isolation valve and the roughing pump.

Correct: C) Large-diameter connections are needed to provide high conductance for efficient gas flow

ISO flanges serve the same vacuum range as KF (rough to moderate high vacuum, elastomer-sealed) but are available in much larger sizes (DN63 and above). Large-diameter flanges provide high conductance — the wide opening allows gas to flow freely between the chamber and pump without restriction. Recall from Module 3 that conductance scales dramatically with diameter. ISO flanges are the solution when large pumping ports are needed. For UHV performance, CF flanges are required, regardless of size.

Correct: A) True

True. Elastomer seals (used in KF and ISO flanges) cannot survive bake-out temperatures above approximately 150-200 degrees C — they would soften, outgas heavily, or decompose. Additionally, elastomer permeation and outgassing prevent reaching UHV pressures. CF flanges with copper gaskets survive bake-out to 450 degrees C and provide the zero-permeation seal needed for UHV performance. This is why you see CF flanges on research instruments and semiconductor tools that require very low base pressures.

Correct: B) It holds the O-ring centred between the two flanges and sets the correct gap for proper O-ring compression

The centering ring is a metal carrier that holds the O-ring in position and ensures the correct flange-to-flange gap. Without it, the O-ring could shift off-centre (creating an uneven seal) or the flanges could close too far (over-compressing the O-ring) or not far enough (under-compressing it). The centering ring is a simple but critical piece of hardware that makes KF assembly reliable and repeatable.

Correct: C) Allow movement between connected components — for vibration isolation, alignment adjustment, or thermal expansion compensation — while maintaining vacuum integrity

Bellows are corrugated metal tubes (usually stainless steel) that can flex, compress, or extend while maintaining a vacuum-tight seal. Common uses include isolating a chamber from pump vibration, allowing slight misalignment between components during assembly, and accommodating thermal expansion when a system is heated or cooled. Without bellows, rigid connections between components could stress flanges and seals when anything shifts.

Correct: B) The plastic outgasses heavily under vacuum — releasing trapped water, solvents, and volatile compounds — adding a large gas load that the pump must work against

Most plastics have high outgassing rates compared to metals. They absorb water, solvents, and atmospheric gases during manufacturing and storage, then release these molecules slowly under vacuum. This creates a persistent gas load that raises the base pressure and extends pump-down time. This is why the Module 4 rule of thumb applies: if a material is soft, flexible, or porous, it probably outgasses significantly. Hard, dense, polished metal surfaces outgas least.

Correct: B) False

False. In a rough vacuum system operating above approximately 0.01 mbar, permeation through elastomer seals is negligible compared to other gas load sources (surface water desorption, outgassing from materials, and any minor leaks). Elastomer permeation becomes a limiting factor only in high-vacuum and ultra-high-vacuum systems where the target base pressure is very low (below 10^-7 mbar). On R1-A, the Viton O-rings on R1-V-ISO and R1-V-VENT are perfectly adequate — permeation is not the performance-limiting factor at rough-vacuum pressures.

Correct: C) Its outgassing rate — how much gas the material releases under vacuum

Outgassing rate is the single most important factor for vacuum compatibility. A material that is mechanically strong, chemically inert, and aesthetically pleasing is still unsuitable for vacuum if it releases excessive gas under low pressure. "Vacuum-compatible" is primarily a statement about gas behaviour, not mechanical strength. A block of wood could withstand atmospheric pressure on a vacuum chamber — but its outgassing of water, terpenes, and volatile organics would be catastrophic for vacuum performance.

Correct: B) Compression set — the O-ring has permanently deformed and may no longer exert sufficient sealing force, leading to a gradual leak

Compression set occurs when an elastomer is held under compression for an extended period and loses its ability to spring back. The O-ring takes on a permanent flat shape and can no longer exert the elastic restoring force needed to maintain a seal. The diagnostic signature is a gradual deterioration in vacuum performance over time — a system that once sealed well begins to show slow, worsening leak rates. This is an age-related failure mode, distinct from sudden failures like cuts or chemical attack.

Correct: C) The adapter introduces a restriction — gas flow is limited by the smaller KF25 bore, which may reduce effective pumping speed at the chamber

Every adapter or transition in a vacuum system is limited by its smallest internal dimension. A KF25-to-KF40 adapter allows the physical connection, but gas must still flow through the KF25-sized bore. This restriction reduces conductance compared to a full KF40 connection. Recall from Module 3 that conductance scales dramatically with diameter — so this apparently minor adapter could meaningfully reduce effective pumping speed at the chamber, especially in the molecular flow regime where conductance depends entirely on geometry.