Diaphragm vs Piston vs Screw Compressors: A Comparison Table

Our tool recommends three machine families by default — diaphragm, reciprocating (piston) and screw — plus liquid ring and Roots as boundary machines. It names the family before it asks about anything else.

The table below is the whole decision in one view. The column most comparison tables leave out is the last one: what happens outside each envelope, because in a process gas duty that is where the cost lands.

Read it together with the decision order that follows, and you can place your own duty point instead of collecting quotes to find out.

The comparison table

One line on centrifugal and axial machines: they are not in this table. A dynamic machine is the right family for large continuous flow at a low pressure ratio, and those duties are normally packaged projects bought by engineering and procurement contractors. That is a different selection question from the one this table answers, which is positive-displacement selection by gas, pressure, differential pressure, flow and phase.

In what order does the tool eliminate families?

The decision sequence matters more than the table. Ours runs in this order, and each step can end the conversation:

1. Gas properties first. A pyrophoric gas — silane, phosphine, arsine — sends the enquiry straight to a human, before pressure is even considered. A purity-critical gas rules out oil-injected machines regardless of how well they fit the pressure and flow. A wet corrosive gas pushes towards liquid ring.
2. Discharge pressure. Above 45 bar (650 psi), dry screw is out. Above 50 barg (725 psi), oil-injected screw is out. Above 75 bar (1,090 psi), only reciprocating and diaphragm remain. Above 400 bar (5,800 psi), only diaphragm, up to 900 bar (13,050 psi). Above 900 bar, an engineering review.
3. Differential pressure. For dry screw machines the constraint is not the discharge pressure but the difference across the machine: 15 bar (218 psi). This is the most underrated number in the category, and it is the reason a duty that looks comfortable at 45 barg can still be the wrong fit.
4. Flow. Below 300 m³/h suction, screw machines drop out. Above 100,000 m³/h, the duty has left the positive-displacement window entirely and the answer is an honest decline, not a stretch.
5. Phase and contaminants. Liquid droplets or solids in the gas rule diaphragm and reciprocating machines out; dirty, polymerising or liquid-carrying gas points at screw or liquid ring.
6. Last, the constraints that got dropped along the way. A non-lubricated requirement that was set aside two branches earlier is re-applied at the end. If it conflicts with the machine that survived, the duty goes to a human.

How do the recommended ranges compare with what manufacturers publish?

The recommended column tracks documented production rather than the highest figure manufacturers publish for each family. The two are not the same question, and a buyer who has seen a 1,000 bar catalogue entry deserves both columns side by side.

The two columns answer different questions. The published figure is what a manufacturer can build and will quote for a specific duty. The recommended figure is the range this tool returns an automatic answer for.

On diaphragm machines the two columns now sit close together, and the reason is documented production. High-pressure hydrogen diaphragm machines are in series production in China to 70 MPa (700 bar), with 90 MPa (13,050 psi) machines delivered — including a five-machine set at 22, 45 and 90 MPa for a Foshan integrated station in July 2026 — and published ceilings at 100 MPa (14,500 psi). The recommended window follows those deliveries to 900 bar; only the 900–1,000 bar band goes to an engineering review. On the reciprocating side the gap is narrower than it looks: domestic evidence now reaches 40–50 MPa (400–500 bar, 5,800–7,250 psi — Himile, Shanghai Dalong, Shenyang Yuanda), while European manufacturers publish to 1,000 bar (14,500 psi) for the same family. The recommended window follows the domestic evidence to 400 bar.

The practical consequence is that many duty points end in a handover rather than a report. A handover carries the duty point and the specific boundary it hit, which is a better outcome than a confident answer that cannot be built.

Which constraint do buyers most often forget?

Discharge temperature is estimated in our tool as T2 = T1 × pressure ratio^((k−1)/k), with the isentropic exponent k taken from the gas data. Above 135°C (275°F) the duty goes to a human rather than being solved with an invented intercooling arrangement. For polymerising gases such as vinyl chloride the limit is 100°C (212°F).

The 135°C figure is a safety limit, not a capability limit, and our data set applies it with a per-family margin: dry screw machines are treated with 45°C of headroom, reciprocating machines with 15°C, and diaphragm and Roots machines with none.

The practical point is that discharge temperature is what most often decides how many stages a duty needs, and stage count is exactly the thing we refuse to guess. A single crankshaft carries at most four stages in our reference data. Above four, the answer is a human, not a fifth stage.

When does this go to a human?

These are the boundaries as the tool applies them:

• Discharge pressure above 900 bar — the 900–1,000 bar band is an engineering review; above 1,000 bar is bespoke design
• Suction flow above 100,000 m³/h — outside the positive-displacement window
• A flow figure entered in actual m³/h
• Estimated discharge temperature above 135°C (275°F), or above 100°C (212°F) for vinyl chloride
• Pyrophoric or highly toxic specialty gases
• Obvious solids or heavy liquid mist in the gas
• Low molecular weight combined with very large continuous flow — a dynamic machine's duty
• More than four stages, or a ratio combination no single family in the table covers
• A gas that is not in the library
• Radioactive gas service

What people assume, and what the table says

Questions we get about the comparison

Why does your table stop at lower pressures than the manufacturers publish? Because the recommended column is a screening range, not a ceiling on what the industry builds. The diaphragm window runs to 900 bar (13,050 psi), following documented Chinese production — series machines to 70 MPa and 90 MPa machines delivered; above 900 bar every duty is an engineering review. The published maxima for every family are set out in the table above.

Can I substitute a centrifugal machine to save cost? We do not recommend dynamic machines, and cost is not part of our output. If your duty is large continuous flow at low pressure ratio, the physics of a dynamic machine may suit it — but that is a different selection question from the one this table answers.

Why is differential pressure an issue for screw machines and not for the others? Because for a dry screw machine the differential across the rotors drives deflection and the resulting internal leakage, so the constraint is structural rather than a pressure-vessel rating. The full reasoning and its source are in the data set, and it is why 15 bar (218 psi) is a handover trigger rather than a hard exclusion.

Does a bigger pressure ratio always mean more stages? It usually means more stages, but we do not calculate the stage count. Above four stages on a single crankshaft the duty goes to a human, and the intercooling arrangement is designed there rather than here.

What is the difference between API 618 and API 619 here? They cover different machine families. API 618 is the reciprocating process compressor standard, API 619 the rotary positive-displacement one. Our table follows those scopes.

What this article does not cover

Note that power, efficiency, cylinder configuration, intercooling design and the final material call are all outside this article. It covers machine-family selection by gas, pressure, differential pressure, flow and phase — plus the boundaries at which the tool hands the duty to a human.

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