Pump Type Comparison Matrix

Module 06 — Pumping Systems & Maintenance  |  VacTech Fundamentals

Pump Type Operating Range Typical Speed Clean / Dry? Maintenance Best For
Roughing
Rotary Vane 		atm → 10−3 mbar 2 – 50 L/s Oil-sealed Oil changes (quarterly to annually); vane replacement; exhaust filter/mist eliminator service General roughing; backing turbo pumps; robust workhorse for industrial vacuum
Roughing
Scroll 		atm → 10−2 mbar 2 – 30 L/s Dry Tip seal replacement (~10,000 hours); periodic scroll cleaning Clean roughing & backing; semiconductor fab; analytical instruments; oil-free requirement
Roughing
Diaphragm 		atm → 10 mbar 0.5 – 5 L/s Dry Diaphragm replacement (~10,000 hours); valve plate inspection Corrosive gas handling; backing scroll or turbo; chemistry labs; small analytical systems
High-Vac
Turbomolecular 		10−2 → 10−10 mbar 50 – 3,000 L/s Dry Bearing service (grease: ~20,000 hrs; magnetic: ~60,000 hrs); rotor balance check High vacuum & UHV; analytical instruments; thin-film deposition; research chambers
High-Vac
Cryopump 		10−3 → 10−12 mbar 500 – 10,000 L/s Clean Regeneration cycle (warm-up & pump-out, every few weeks to months depending on gas load) UHV; clean environments; semiconductor; very high water vapour pumping speed

Selection Guidelines

  • Oil-sealed vs. dry: Oil-sealed rotary vane pumps risk backstreaming oil vapour into the chamber. Use a foreline trap or switch to dry pumps (scroll, diaphragm) for clean applications.
  • Turbo pumps need a backing pump: Turbomolecular pumps cannot exhaust to atmosphere. They require a roughing pump (scroll or rotary vane) on their foreline to maintain exhaust pressure below ~10 mbar.
  • Cryopumps are capture pumps: They trap gas on cold surfaces rather than transferring it. They must be regenerated periodically (warmed up) to release accumulated gas. They are not suitable for continuous high-gas-load processes.
  • Compression ratio matters: Turbo pumps have excellent compression ratios for heavy molecules (N2, Ar) but poor compression for light gases (H2, He). For hydrogen-dominated outgassing, consider supplementary pumping (e.g., titanium sublimation pump).
  • Selkirk atmospheric pressure: ~950 mbar. Factor this into pump-down time calculations.
ANT-M06-003  |  VacTech Fundamentals — Selkirk College  |  Print-friendly reference card