Compressor

Compressor

A compressor is a machine that generates force by compressing gas or vapor, producing compressed air for industrial applications. The compressor increases aeriform body pressure through a mechanical procedure, delivering air at pressures necessary for multiple purposes across bottling and manufacturing operations.

Compressed air is atmospheric air reduced in volume and stored in pressure-resistant tanks or used immediately. As the fourth form of energy used in industry, compressed air offers unique characteristics: unlike gas, water, and electricity supplied by external companies, it is generated on-site directly by the user, with quality and production costs depending entirely on internal systems.

How Compressors Work

The air compressor operating principle involves several key components:

• Motor — drives the compression mechanism
• Air inlet valve — allows atmospheric air entry
• Air outlet valve — releases compressed air
• Storage tank — holds compressed air for use

Air is sucked into the machine, compressed by internal components according to the specific technology, and pushed into the tank. When maximum pressure is reached, the cycle completes and the compressor stops, restarting when pressure drops below a predefined threshold.

Compressor Selection Criteria

Choosing the correct compressor requires evaluating several parameters:

Flow Rate

Flow rate indicates the air volume the compressor delivers to power multiple devices simultaneously. This value is expressed in:

• Liters per second (l/s)
• Cubic meters per hour (m³/h)
• Normal cubic meters per hour (Nm³/h) — standardized reference conditions

The normal cubic meter (Nm³) refers to dry air at 0°C (273 K), barometric pressure of 101,325 Pa (1.01325 bar), at sea level altitude. This convention allows universal comparison between different systems. Normal flow rate must be converted to effective flow rate based on actual operating conditions before selecting equipment.

Recommended practice: select a compressor offering approximately 30% safety margin above estimated requirements.

Pressure

Operating pressure depends on the industrial equipment or pneumatic circuit being powered, expressed in bar or pascal (Pa):

• Single-stage compressors — maximum 10 bar
• Multistage compressors — up to 400 bar

Power and Storage

Compressor power depends on desired air flow and outlet pressure. The compressed air reservoir must be correctly sized to avoid constant engine stress, allowing the motor to start according to demand without continuous operation.

Types of Compressors

Two main categories exist: volumetric (positive displacement) compressors and centrifugal (dynamic) compressors. Most industrial compressors are volumetric machines achieving compression by reducing air volume.

Piston Compressors

Piston compressors offer economical solutions for non-continuous use:

Considerations for piston compressors:

• Generally the most economical option among compressor types
• May expel some oil with compressed air — filtration systems required for clean air applications
• Relatively noisy operation may affect nearby workers
• Best suited for intermittent use rather than continuous operation

Screw Compressors

Screw compressors use helical screws instead of pistons and represent the most common model in industrial applications:

Key advantages of screw compressors:

• Considerable flow rate and high compression ratio even in single-stage configuration
• 100% duty cycle — capable of continuous operation
• Variable speed models (with inverters) adapt rotation speed to demand, optimizing energy consumption
• More compact than equivalent-performance piston models

Vane Compressors

Vane compressors use sliding foils in an eccentric rotor to achieve compression. Characteristics include:

• Good energy efficiency
• Lower rotation speed than screw compressors at equivalent pressure and flow
• Reduced component wear and maintenance requirements
• Common in printing, wood processing, and packaging industries
• Oil-free models available for energy and medical sectors

Centrifugal (Dynamic) Compressors

Centrifugal compressors draw air through paddle wheel movement, similar to automotive turbochargers. These machines serve applications requiring high flow rates and sustained pressure without interruption:

• Flow rates up to 500,000 m³/h
• Pressures up to 200 bar
• Integrated reducer for optimal engine speed regulation
• Primary use in energy sector and chemical industry

Oil-Free Compressors

Oil-free compressors compress air without oil in the compression chamber, eliminating contamination risk and special filtration requirements. These models provide clean air essential for:

• Bottling operations — product safety and quality
• Electronics industry — semiconductor production
• Pharmaceutical and chemical industries — contamination-free processes
• Medical sector — sterile air requirements
• Food processing — hygiene compliance
• Automotive assembly — finishing operations

Oil-free compressors must satisfy ISO 8573-1 Class 0 standard, guaranteeing total absence of oil. Higher classes define maximum permissible oil quantities, requiring additional air dryers for proper air quality.

Cooling Systems

Air-Cooled Compressors

Air-cooled compressors use forced ventilation containing approximately 100% of consumed motor energy as heat within the compressor unit. These systems are widely available and simpler to install.

Water-Cooled Compressors

Water-cooled compressors place modest demands on room ventilation, as cooling water absorbs approximately 90% of motor energy as heat. Better cooling in intercoolers and aftercoolers increases efficiency and water vapor condensation.

Three water cooling configurations exist:

Air Treatment Equipment

Dryers

Atmospheric air contains water vapor that increases during compression heating. As compressed air expands and cools, saturated vapor transforms into condensate requiring separation. Dryers eliminate remaining water vapor that would compromise equipment function.

Refrigeration dryers exploit the relationship between temperature reduction and humidity condensation. Efficiency is expressed as Pressure Dew Point (PDP) — the condensation temperature at pressure above atmospheric. Limitation: cannot operate below 0°C PDP (condensate would freeze).

Adsorption dryers use hygroscopic materials to absorb moisture, achieving dew points down to -70°C. Essential for:

• External piping installations
• Environments below refrigeration dryer dew point
• Food and pharmaceutical critical applications

Filtration

Atmospheric air entering compressors contains fine dust and impurities, plus oil particles from lubrication systems and water aerosols. Air purity classes are defined by ISO 8573-1:2010, specifying maximum contaminant content for each class.

Filter systems typically combine multiple elements:

• Particle filters — remove solid contaminants
• De-oiling filters — eliminate oil mists
• Coalescing filters — capture water and oil aerosols
• Activated carbon filters — remove vapors and odors
• Sterile filters — eliminate microorganisms for food, pharmaceutical, and cosmetic industries

Condensate Drains

Condensate contains emulsified oil particles, dust, and impurities requiring drainage from collection points. Three drain types exist:

• Float drains — valve opens when liquid exceeds threshold, closes before air escapes
• Electronic drains — valve controlled by electronic level sensor
• Timed drains — solenoid valve opens at preset intervals with adjustable timing

Environmental note: Condensate discharge into sewers risks significant fines. As a compressed air waste product, condensate contains hydrocarbons, sulfur dioxide, copper, lead, iron, and other harmful substances.

Compressed Air Storage

Compressed air tanks are typically constructed from carbon steel with external epoxy powder coating for corrosion resistance. Available in vertical (most common) or horizontal configurations, tanks must be sized according to:

• Compressor capacity
• Regulation system requirements
• Expected consumption including peak demands

Tanks maintain constant system pressure, compensating for consumption peaks exceeding compressor capacity. Installation should be near the compressor in a cool environment, allowing access to condensate drain and safety valve.

Safety Valves

Safety valves prevent maximum permissible pressure from being exceeded, functioning even if upstream safety devices fail. Types include:

• Free exhaust — direct pressure release
• Conveyed exhaust — connectable to discharge piping
• High-pressure specific — designed for elevated pressure systems

Key sizing parameters: calibration pressure (opening threshold), discharge flow rate, and operating temperature. Conformity declaration accompanies all safety valves.

Compressor Room Requirements

The compressor room houses most compressed air network components and must meet specific requirements for optimal performance. Centralized installation is generally preferable, ensuring:

• Better operating economy
• Improved network design
• Easier use and maintenance
• Protection against unauthorized access
• Proper noise control
• Controlled ventilation

Installation Considerations

Essential compressor room specifications:

• Floor space — sufficient for current equipment plus future expansion
• Clear height — adequate for lifting electric motors or heavy components
• Floor drain — condensate management from compressor, aftercooler, reservoir, dryers
• Load-bearing capacity — level floor supporting equipment weight
• Lifting equipment — crane or forklift access for heavy components
• Anti-vibration — pads for centrifugal compressors transmitting vibrations

Ventilation Requirements

All compressor room units produce heat requiring extraction through ventilation:

• Air-cooled compressors — nearly 100% of motor energy appears as heat in ventilation air
• Water-cooled compressors — approximately 10% of motor energy in ventilation air

Ventilation specifications:

• Air intake from outside, preferably without long ducts
• Suction opening positioned low but protected from snow
• Ventilation fans high on end wall, air inlet on opposite wall
• Air velocity at inlet opening maximum 4 m/s
• Protection against explosive, corrosive dust and substances

Heat recovery represents an efficient alternative to simple extraction, utilizing waste energy for facility heating.

Outdoor Installation

When indoor facilities are unavailable, compressors may be installed outdoors under canopy, addressing:

• Freeze risk — condensate pockets and drains
• Weather protection — rain and snow at air inlet and ventilation openings
• Solid base — asphalt, concrete slab, or leveled cobblestone
• Contamination risk — dust, flammable, or aggressive substances
• Security — protection against unauthorized access