The pressure ratio defines the technical distinction between blowers and air compressors. Correct equipment selection prevents energy waste. It supports regulatory compliance.
Defining Equipment by Pressure Ratio
The American Society of Mechanical Engineers (ASME) categorises air-moving equipment by pressure ratio. The pressure ratio is the discharge pressure divided by the suction pressure.
- Fans operate with a pressure ratio up to 1.11.
- Blowers operate with a pressure ratio between 1.11 and 1.20.
- Air compressors operate with a pressure ratio exceeding 1.20.
Blowers deliver high air volumes at low pressures, typically 0.1 to 1.0 bar(g), depending on technology. Air compressors provide higher pressures, typically ranging from 4 to 13 bar. Using an air compressor for low-pressure tasks creates immediate energy inefficiency.
Mechanical Architecture and Efficiency
Mechanical design determines efficiency and pressure stability. Equipment is classified into positive displacement or dynamic technologies.
Positive Displacement: Lobe vs Screw
Positive displacement machines trap a fixed air volume within a casing.
- Rotary Lobe Blowers: The Atlas Copco ZL series uses two intermeshing lobes. These units lack internal compression. Because there is no internal compression, pressure only rises once air meets downstream resistance. This results in lower thermodynamic efficiency compared to internally compressing machines. This process is isochoric compression.
- Rotary Screw Blowers: The Atlas Copco ZS series utilises helical rotors. These rotors compress air internally. This adiabatic compression is up to 30% more efficient than lobe technology.
Dynamic Technology: Centrifugal and Turbo
Dynamic machines transfer kinetic energy to the air using high-speed impellers.
- Turbo Blowers: The Atlas Copco ZB series features direct-drive permanent magnet motors. Many models use magnetic bearings to eliminate friction. These units provide steady airflow for high-volume processes.
- Centrifugal Blowers: The ZM multistage range employs multiple impellers to meet specific pressure targets. These machines suit harsh environments and fluctuating demands.
The Economic Cost of Throttling
Industrial facilities often use 7-bar air compressors for tasks requiring 1 bar. This practice is commonly referred to as throttling. It is economically inefficient.
Throttling regulated air from 7 bar down to 1 bar wastes the energy used during initial compression. Every 0.14 bar (2 psi) increase in unnecessary pressure raises energy costs by 1%. This metric quantifies the cost of over-pressurising a compressed air system. Switching to Low Pressure Blowers for low-pressure applications often delivers 40% energy savings.
Application-Driven Selection Logic
Pressure and flow requirements dictate the appropriate technology choice.
| Application | Required Pressure | Recommended Technology |
| Wastewater Aeration | 0.5 – 0.9 bar | ZS Screw or ZB Turbo Blower |
| Dilute Phase Conveying | < 1.0 bar | ZL Lobe or ZS Screw Blower |
| Dense Phase Conveying | 1.0 – 4.0 bar | ZE/ZA Low-Pressure Compressor |
| Pneumatic Tools | 6.0 – 7.0 bar | GA Rotary Screw Compressor |
| Air Knives (Drying) | 0.1 – 0.3 bar | High-Speed Centrifugal Blower |
centrifugal compressors share dynamic principles with turbo blowers. They are ideal for high-flow industrial roles. The Difference Between CFM and PSI determines correct system sizing.
UK Regulatory Context: PSSR 2000
The Pressure Systems Safety Regulations 2000 (PSSR) create legal obligations for UK owners and operators. These regulations prevent injuries from stored energy hazards.
PSSR applies to systems containing air at pressures exceeding 0.5 bar above atmospheric. This threshold includes almost all industrial blowers and air compressors. A Written Scheme of Examination (WSE) is mandatory if the safe working pressure (bar) multiplied by the internal volume (litres) exceeds 250. J Ll Leach provides competent persons to manage WSE documentation.
Digital Control and Monitoring
Atlas Copco equipment utilises integrated control systems to optimise Specific Power.
- Elektronikon Controllers: These units manage motor speed to match real-time demand.
- SMARTLINK: This remote monitoring platform identifies system anomalies.
SMARTLINK supports predictive maintenance and air leak surveys. These tools identify pressure drops. They prevent uncontrolled energy loss. Consistent monitoring ensures the system maintains its original efficiency ratings.
Summary of Technical Differences
- Pressure Range: Blowers operate up to 1.5 bar; compressors operate from 4 bar to 13+ bar.
- Energy Efficiency: Screw blowers reduce energy consumption by 30% compared to lobe blowers.
- Legal Compliance: Systems above 0.5 bar require a maintenance plan and a WSE under PSSR 2000.
- Volumetric Flow: Blowers deliver higher air volumes at a lower Specific Power cost.
J Ll Leach is a Premier Distributor for Atlas Copco. We supply and maintain high-efficiency systems from depots in Stoke-on-Trent, Birmingham, and Shrewsbury.
An energy audit identifies whether a blower can replace a high-pressure compressor.