About & Methodology

What this tool does, where the numbers come from, and — more usefully — what it refuses to do.

1. What it is

GasCompressorSelect is a deterministic pre-selection rule engine for positive-displacement process gas compressors: diaphragm, reciprocating (piston), dry screw, oil-injected screw, plus liquid-ring and Roots machines as boundary cases. You enter a gas and a duty point; it returns a machine type, a staging estimate, gas-path materials and an RFQ-ready specification sheet.

It exists because the first three days of a compressor enquiry are usually spent asking a manufacturer to explain things a catalogue could have said. The answer you get here is deliberately a starting frame for a quotation request, not a substitute for a manufacturer's engineering judgement.

2. Why there is no AI answering you

The recommendation you receive is produced by the same code every time, from a knowledge base you can read. Three reasons:

Reproducibility. Two engineers entering the same duty get the same answer, today and next year — and we can show you exactly which constraint produced it.
Auditability. Every recommendation carries an "elimination record": every machine type it considered and, for the ones it rejected, the specific reason. You can check our reasoning against your own experience instead of taking it on trust.
Responsibility. A plausible-sounding wrong compressor specification is a safety and budget problem. We prefer an honest "this needs an engineer" to a confident guess.

3. Where the envelopes come from

Machine envelopes were calibrated from published product data of twelve international manufacturers (including Hofer / NEA, PDC Machines, Howden, Burckhardt, Kobelco, Nash and Aerzen) and cross-checked against Chinese manufacturers (including ZDHS, Hengjiu, Tiangao, Himile, Shenyang Yuanda, Kobelco Wuxi, CSSC 711 Institute, Moon-Tech, Hanbell, Kenflo, Zhanggu and Changgu).

The recommended envelope follows the Chinese supplier pool, not the industry extreme. Where an international builder advertises 1,000 bar or 3,000 bar capability but our supplier pool has no evidence of delivering it, we do not recommend it: we confirm the duty with you and pass it to a manufacturer's engineering team. Recommending a machine nobody in our network can build produces nothing but wasted RFQ rounds — for you and for them.

Where sources disagree we either state the disagreement or take the conservative figure. The purpose of the tool is to save you a bad quotation round, not to win an argument about who does the biggest machine.

4. What the engine actually calculates

Pressure ratio and differential pressure from absolute pressures. You can enter bar(a) or bar(g); the engine converts before doing anything else.
Capacity conversion. Screw, liquid-ring and Roots envelopes are published as inlet volume at suction conditions, while diaphragm and reciprocating envelopes are published in normal cubic metres. Your standard flow is converted to inlet volume with the ideal-gas relation, and the tool tells you when that conversion is getting thin (above about 10 bar(a) suction, real-gas effects stop being negligible).
Staging. Not a guess: it solves for the smallest number of stages that keeps the peak stage discharge temperature inside the limit, subject to each machine's per-stage ratio capability and a four-stage ceiling per crank train.
Discharge temperature. Estimated adiabatically with intercooling assumed between stages. Three different models are declared in the knowledge base, because the adiabatic relation is simply false for an oil-flooded screw or a liquid-ring machine — those machines control temperature with the injected liquid, and the report says so rather than printing a number we would have to take back.

5. Boundaries we do not cross

The following get no automatic recommendation. To be exact about who does what: we read the enquiry, confirm we received it within 24 hours and forward it to compressor manufacturers. The sizing, staging confirmation, material selection and quotation belong to the manufacturer's engineering team — we have no engineers on staff, and we do not promise another company's response time.

Capacity stated in actual m³/h — converting it needs suction conditions and a compressibility factor; doing it approximately would move you across machine envelopes.
Pyrophoric gases (silane, phosphine, arsine), which cannot be reduced to a routine specification.
Duties where the estimated discharge temperature cannot be brought under its limit within four stages.
Gases carrying solids, deep suction vacuum, or a differential pressure below about 0.3 bar (that is a blower purchase, not a compressor purchase).
Centrifugal and axial territory — very large flows, or a large continuous flow of a very light gas at a mild pressure ratio. When your duty belongs to that world we tell you who plays in it, and we do not pretend our supplier pool does.
Any duty where no machine type in our catalogue survives — you get the full elimination list instead of something bent into shape.

6. Business model, stated plainly

This tool is free because it is supported by Chinese manufacturing partners. If you ask us to, we forward your inquiry to compressor manufacturers so they can quote. We do not rank suppliers for money, we do not take commission on a sale, and we do not claim to have audited anyone. Supplier verification is listed as a checklist precisely because it is your job, not ours.

See the Privacy Policy for what happens to your contact details.

7. Known limitations

No real-gas compressibility correction, and no polytropic efficiency — staging and discharge temperature are screening estimates.
No gas mixtures beyond the fixed compositions stated in the knowledge base (biogas is modelled as 60/40 methane/CO₂; natural gas as pipeline-quality methane).
No manufacturer model numbers, and no price bands at all. We looked at the publicly available cost data for this class of equipment and did not find anything we trust enough to print: what is published is either vendor marketing copy or market-research teaser figures with no method behind them, and neither covers the full machine range. The cost of a machine swerves on gas composition, materials, certification scope and driver selection far more than any honest band would capture — so the report stops where a quotation starts.

Knowledge base v0.1.0 · Last updated September 2026.