MACHINE FAMILY
Dry (Oil-Free) Screw Compressors
Large flow, dirty gas, no oil in the compression space.
Two synchronous rotors running without oil in the gas path, with timing gears and shaft seals outside the compression space. Tolerates dirty gas, polymers and liquid carry-over that would destroy a diaphragm or a reciprocating machine.
The envelope
| Recommended discharge pressure | ≤ 45 bar(g) |
|---|---|
| Differential pressure | ≤ 15 bar |
| Suction flow window | 300–100,000 m³/h |
| Per-stage ratio / stages | 4.5:1 per stage · at most 2 stages on one crankshaft |
| Oil-free | Available / by design |
| Sealing | Shaft seals only — the compression space itself is oil-free (labyrinth / carbon-ring / mechanical seals, often with a buffer gas) |
| Wetted materials | Carbon steel, Cast iron / ductile iron, Stainless steel 316L, Duplex 2205, 13Cr martensitic stainless |
| Design standards | API 619 (rotary-type positive-displacement compressors) where specified |
Where it is used
- Flare gas, refinery off-gas and other dirty or polymerising streams
- Low-pressure, large-flow hydrogen
- Continuous duties where contamination would wreck a piston or a diaphragm
Where it stops
- 45 bar(g) discharge ceiling — above it, the family leaves the table
- The limit most often forgotten: differential pressure ≤ 15 bar; above it the duty goes to review, not exclusion
- Suction flow below 300 m³/h is too small for the frame
The 45 bar(g) and 15 bar differential limits are published by international makers; Chinese institutes have delivered machines beyond the differential limit, which is why exceeding it routes to review rather than refusal.
Related reading
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