Compressor Selection

Quick pick (TL;DR)

High flow, low–moderate pressure ratio → centrifugal (smooth, low maintenance, needs anti-surge).
Low flow, high ratio → reciprocating (high pressure, pulsation & valves).
Moderate flow, oil-flooded duty → screw.
Very high flow → axial.
Estimate gas power from the adiabatic relation, keep the ratio per stage ≲ 3.5–4 (else add stages with intercooling), and provide anti-surge control on centrifugals.

Step 1 — Choose the type

Type	Flow / ratio	Notes
Centrifugal	High flow / moderate	Needs anti-surge
Reciprocating	Low flow / high ratio	Pulsation
Screw	Moderate	Robust
Axial	Very high flow	Big duties

Step 2 — Worked gas power

Gas 0.5 m³/s, ratio 3

Adiabatic gas power P = (k/(k−1)) · (P1·Q1/η) · [(P2/P1)^((k−1)/k) − 1] Given P1 = 100 kPa , Q1 = 0.5 m³/s P2/P1 = 3 , k = 1.3 , η = 0.75 Step 1 — Exponent (k−1)/k = 0.3/1.3 = 0.2308 3^0.2308 − 1 = 1.289 − 1 = 0.289 Step 2 — Multiply k/(k−1) = 1.3/0.3 = 4.333 P1·Q1/η = 100×0.5/0.75 = 66.7 kW P = 4.333 × 66.7 × 0.289 = 83.4 kW Step 3 — Stage check ratio 3 ≤ ~4/stage → 1 stage OK Answer → centrifugal, 1 stage, ~83 kW gas power

Power scales with the ratio term; keep ratio/stage < ~4 (else add stages + intercooling).

Step 3 — Control & protection

Centrifugal needs anti-surge control.
VFD/IGV vs clearance pockets.
Recip: pulsation dampeners; dry-gas seals.

Gas power calculator

Adiabatic gas power & stage check

P = (k/(k−1))·(P1·Q1/η)·[(P2/P1)^((k−1)/k) − 1].

Inlet P1 (kPa a)

Discharge P2 (kPa a)

Inlet flow Q1 (m³/s)

Efficiency

Single-stage adiabatic estimate — above ratio ~4 add stages + intercooling.

Common mistakes

Centrifugal at low flow/high ratio.
Single stage with ratio > ~4.
No anti-surge / pulsation study.

Requisition & datasheet

Gas, flow, P1/P2, ratio, T, k.
Type, stages, power, control.

Frequently asked questions

What should I know about Compressor Selection?

High flow, low–moderate pressure ratio → centrifugal (smooth, low maintenance, needs anti-surge). Low flow, high ratio → reciprocating (high pressure, pulsation & valves). Moderate flow, oil-flooded duty → screw. Very high flow → axial. Estimate gas power from the adiabatic relation, keep the ratio per stage ≲ 3.5–4 (else add stages with intercooling), and provide anti-surge control on centrifugals.

Which standards or codes apply?

API 617 (centrifugal & axial), API 618 (reciprocating), API 619 (screw), API 11P / ISO 13631 (packaged), ASME PTC 10 (performance).

Standards — API 617/618/619; ISO 13631; ASME PTC 10.