Choosing between a dry scroll pump and an oil-sealed rotary vane pump is the most common primary-vacuum decision in a research or analytical lab. Both reach similar ultimate pressures; the real differences are contamination, maintenance, and cost of ownership. Here is the practical comparison, model-agnostic first, then with typical examples.
How they differ mechanically
A rotary vane pump compresses gas with sliding vanes in an oil-sealed stator — the oil seals, lubricates, and cools, and inevitably back-streams a small amount of vapour toward the inlet. A scroll pump compresses gas between two nested spiral scrolls sealed by a PTFE tip seal — no oil anywhere in the vacuum path.
Head-to-head
| Criterion | Dry scroll (e.g. Edwards nXDS) | Oil-sealed rotary vane (e.g. Edwards RV, Pfeiffer Duo) |
|---|---|---|
| Ultimate pressure | ~10-2–10-3 mbar class | ~10-3 mbar class (two-stage), often slightly deeper |
| Contamination | Oil-free vacuum path — clean for MS, cryostats, gloveboxes | Oil back-streaming; needs foreline trap for clean work |
| Vapour handling | Good with gas ballast; condensables tolerated | Oil emulsifies with solvents/water — frequent oil changes |
| Routine maintenance | Tip seal every 1–2 years; no oil, no disposal | Oil checks/changes several times a year in solvent duty |
| Noise / vibration | Low; lab-friendly | Moderate; oil mist filter recommended indoors |
| Purchase price | Higher upfront | Lower upfront |
| 5-year cost of ownership | Often lower in clean labs (no oil, less labour) | Oil, filters, labour, disposal accumulate |
Choose a scroll pump when…
- The vacuum must be hydrocarbon-free: mass spectrometers, load locks, cryogenics, glovebox regeneration, anything feeding a turbo on an analytical system.
- The pump lives in the lab with people: lower noise, no oil mist, no oil handling.
- You want minimal scheduled maintenance and predictable consumable cost (one tip seal kit).
Choose a rotary vane pump when…
- Budget is tight and the process tolerates (or already assumes) oil — freeze dryers, rotary evaporators, schlenk lines with traps.
- You pump heavy, continuous gas loads at higher inlet pressures, where oil-sealed pumps shrug off duty that wears tip seals quickly.
- The pump sits in a plant room where oil mist and noise are non-issues.
The refurbished angle
Because scroll pumps carry a higher list price, the refurbished market discount is proportionally larger — a bench-tested nXDS with a fresh tip seal typically lands near the price of a new rotary vane pump, removing the main argument for accepting oil in a clean lab. Whichever you choose, insist on a documented ultimate-pressure test, not just “powers on.”
PLC North carries tested Edwards and Pfeiffer scroll and rotary vane pumps, each shipped with a measured base-pressure report. Not sure which suits your chamber volume and gas load? Contact us and we will size it with you.