Screw Compressor Sizing Calculator

Compressor Configuration

Compressor Type

Gas Type

Capacity Control Method

Gas Properties

Gas Specific Gravity (Air = 1.0)

Molecular Weight

lb/mol

Specific Heat Ratio (k = Cp/Cv)

Natural gas: 1.26-1.31 | Air: 1.40 | Refrigerant: 1.1-1.2

Operating Conditions

Inlet Pressure

psig

Discharge Pressure

psig

Inlet Temperature

°F

Flow Rate

ACFM = actual cubic feet per minute at inlet conditions

Compressibility & Altitude

Z-Factor at Inlet

Z-Factor at Discharge

Site Altitude

Affects atmospheric pressure (14.7 psia at sea level)

Understanding Screw Compressor Sizing

Oil-Flooded Screw
Oil injected into compression chamber provides sealing, cooling, and lubrication. Single-stage ratio up to 10-15:1. Discharge temp limited to ~250°F. Requires oil separation downstream.

Dry (Oil-Free) Screw
Timing gears prevent rotor contact. No oil in gas stream. Single-stage ratio limited to 4-5:1. Higher discharge temps (350-400°F). Used where oil contamination is unacceptable.

Typical Applications:
Gas gathering and boosting (500-12,000 ACFM), vapor recovery, fuel gas compression, refrigerant compression, process gas boosting, wellhead gas compression, and landfill gas applications.

📚 Learn the Theory

Understand screw compressor design, oil-flooded vs dry operation, API 619, rotor profiles, and applications in gas gathering

Read Engineering Guide →

Results

Brake Horsepower

BHP

Motor HP (NEMA) -

Pressure Ratio -

Stages Required -

Discharge Temperature -

Adiabatic Efficiency -

Volumetric Efficiency -

Specific Power -

Inlet ACFM -

Standard SCFM -

Standard MMSCFD -

Rotor Estimate
Male Rotor Dia: - in
Speed: - RPM

Key Formulas

BHP = W_ad / (η_ad × η_mech)

W_ad = Adiabatic power (HP)

η_ad = Adiabatic efficiency (70-82% flooded, 65-78% dry)

η_mech = Mechanical efficiency (~95%)

T2 = T1 × r^(k-1)/k (adiabatic)

r = P2/P1 (pressure ratio, absolute)

Standards & References

API 619
Rotary-Type Positive Displacement Compressors
CAGI
Compressed Air & Gas Institute Performance Standards
GPSA Engineering Data Book
Section 13: Compressors & Expanders
API 614
Lubrication, Shaft-Sealing and Oil-Control Systems

Engineering Notes

Oil-flooded max ratio: 10-15:1 single stage (oil cooling limits discharge temp)
Dry max ratio: 4-5:1 single stage (thermal limits)
Discharge temp limit: 250°F oil-flooded, 350-400°F dry
Flow range: Typically 500-12,000 ACFM (screw optimal range)
Oil separation: Oil-flooded requires coalescing separator downstream (residual <3 ppm)
Tip speed: Male rotor typically 20-80 m/s depending on size

Quick Reference — Typical Screw Compressor Data

500 ACFM, 3:1 ratio, oil-flooded → ~75 BHP
2000 ACFM, 3:1 ratio, oil-flooded → ~280 BHP
5000 ACFM, 4:1 ratio, oil-flooded → ~900 BHP
1000 ACFM, 3:1 ratio, dry → ~175 BHP
Oil/gas ratio: 2-5 gal/min per 100 ACFM

Frequently Asked Questions

What is the maximum compression ratio for a screw compressor?

Oil-flooded screw compressors can achieve single-stage ratios of 10-15:1 due to oil cooling. Dry (oil-free) screw compressors are limited to 4-5:1 per stage. Higher overall ratios require two-stage compression with intercooling.

What is the difference between oil-flooded and dry screw compressors?

Oil-flooded screw compressors inject oil into the compression chamber for sealing, cooling, and lubrication, achieving lower discharge temperatures and higher compression ratios. Dry screw compressors use timing gears to prevent rotor contact, producing oil-free gas but with lower efficiency and pressure ratio limits.

When should I use a screw compressor instead of reciprocating?

Choose screw compressors when you need continuous flow (500-12,000 ACFM), can tolerate lower efficiency, want simpler operation with fewer moving parts, or need to handle dirty/wet gas. Reciprocating compressors are preferred when efficiency is critical, flow is variable, or very high pressure ratios are needed.

What API standard covers screw compressors?

API 619 (Rotary-Type Positive Displacement Compressors for Petroleum, Chemical, and Gas Industry Services) covers screw compressors. CAGI (Compressed Air and Gas Institute) also provides performance testing and rating standards.