How to Choose a Used High-Pressure Compressor for PET Blowing

Choose a used high-pressure compressor for PET blowing by matching delivered airflow, operating pressure and air quality to the blower's actual requirement. Confirm cooling, air treatment, control arrangements and mechanical condition before comparing price. A “40 bar” description alone does not establish sufficient capacity.

This guide covers used high-pressure compressor systems for PET bottle production, including complete packages and booster installations.

1. Establish the blower's air requirement

Obtain consumption data for the exact blower configuration and intended bottle. Supply:

  • Blower: manufacturer, model, generation, installed options and air-recovery arrangement.
  • Production: bottle volume and design, required output, production schedule and format range.
  • Air demand: high- and low-pressure requirements, minimum pressure at the machine, flow reference conditions and consumption profile.
  • Air quality: specified particle, moisture, oil and any microbiological requirements at the point of use.
  • Site: altitude, ambient conditions, electrical supply, available cooling, existing air system and intended redundancy.


Do not size a compressor from bottle volume and bottles per hour alone. Blowing pressure, process, air recovery and other users affect demand. If consumption data is unavailable, obtain a model-specific estimate and identify its assumptions before confirming compressor selection.

For the machine itself, see our PET stretch blow moulding buying guide.

2. Compare airflow on the same reference basis

Free air delivery and normal flow

Free air delivery (FAD) expresses delivered air as an equivalent volume at stated inlet or free-air reference conditions. Normal flow uses specified normal reference conditions. Neither should be confused with the smaller physical volume occupied by air in a pressurised pipe.

Ask for the reference pressure, temperature and moisture basis behind figures in m³/h, Nm³/h, m³/min or litres per second. Two values should not be treated as equivalent simply because both use cubic metres per hour.

On an identical reference basis, 750 m³/h equals 12.5 m³/min or approximately 208.3 litres per second. This unit conversion does not convert normal flow to FAD, or free-air volume to compressed discharge volume.

Delivered flow at the required pressure

Request verified delivered flow at the proposed operating pressure and site conditions. Distinguish it from piston displacement, nominal swept volume or a model's capacity at another pressure.

For illustration, if documented high-pressure demand is 600 m³/h and a project-specific 15% operating allowance is agreed, the initial requirement is 690 m³/h on the same reference basis. The allowance is an example, not a universal sizing rule. Assess leakage, treatment losses or purge air, other consumers and future production separately.

A receiver can buffer short demand peaks, but it cannot compensate indefinitely for inadequate compressor output. Size storage and controls against the demand profile rather than average flow alone.

3. Match pressure and compressor configuration

Establish the minimum pressure needed at the blower under production conditions. Allow for pressure losses through treatment equipment, receivers and pipework, while keeping operation within the documented ratings of every component.

Distinguish gauge pressure, commonly written bar(g), from absolute pressure, bar(a). Confirm the basis when reviewing data or performing calculations. A maximum design or allowable pressure is not the same as the normal operating setpoint.

Do not assume every PET bottle requires 40 bar blowing pressure. Use the blower manufacturer's process requirement for the bottle, and verify compressor performance at the selected supply pressure.

Full compression systems and boosters

A complete compressor may take atmospheric air through its compression stages to the required pressure. A booster requires an existing supply at specified inlet conditions.

For a booster, confirm minimum inlet pressure, inlet flow capacity, inlet air quality and temperature, and the effect on the upstream plant. Compare the combined power and treatment needs of both stages; a booster sold on its own is not a complete atmospheric-air-to-blowing-air installation.

4. Confirm air quality and treatment

Oil-free compression is commonly used for PET blowing, but the complete supply must meet the defined point-of-use specification. An oil-free label does not establish acceptable moisture, particles or microbiological quality throughout the downstream network.

Check the certification and stated scope for the exact compressor model where relevant. Oil-free compression does not necessarily mean that the drive mechanism contains no lubricating oil; review the manufacturer's design and maintenance requirements.

Specify drying by the required pressure dew point at defined operating conditions. Pressure dew point and atmospheric dew point are different measures. Verify dryer capacity at the actual pressure, inlet temperature, ambient conditions and required flow.

Confirm that aftercooling, separators, drains, filters and dryer are included and correctly rated for the high-pressure installation. A low-pressure dryer should not be assumed suitable for a high-pressure circuit. Assess air quality after treatment and distribution, where it is needed by the process.

5. Assess cooling and installation

Identify whether the compressor is water-cooled or air-cooled and use its installation documentation to establish requirements. For water-cooled equipment, confirm cooling-water temperature, flow, quality and pressure, heat rejection and the required cooling tower, chiller or other heat-removal system.

A tower included with a used compressor must still be assessed for the new site's conditions and operating duty. Air-cooled equipment requires sufficient ventilation and a suitable route for removing heat.

Check electrical supply, motor starting, connected load, service clearance, floor and foundation requirements, vibration isolation, noise and access for maintenance. Include any missing auxiliary equipment in the installation scope.

Have the receiver, pipework, valves and protection arrangements assessed for the intended pressure and installation. Obtain equipment identification, pressure documentation and inspection records for review by the competent installation specialist.

6. Inspect condition, hours and maintenance

Review total running hours and load hours separately, together with service history. Definitions vary by controller, so establish what each counter records and whether components or controls have been replaced.

Low load hours do not establish condition on their own. Consider starts, unloaded operation, storage, cooling-water condition and maintenance intervals. Ask for the scope and date of any overhaul, including which components were inspected or replaced.

Where possible, inspect the compressor under load. Record delivery pressure, measured flow where available, electrical input, temperatures, vibration, alarms and the treatment equipment's operation. Nameplate power and a short running video do not establish delivered capacity or efficiency.

For reciprocating equipment, a qualified inspection should cover relevant valves, rings, cylinders, bearings, sealing and cooling components. Inspect intercoolers, aftercoolers, drains and control systems, and assess the dryer and cooling installation as part of the package.

For dismantled or long-idle equipment, establish preservation measures, completeness and recommissioning work. Confirm spare-parts and service availability for the exact model and generation.

7. Compare operating cost and supply scope

Compare electrical input and delivered airflow at the same pressure and reference conditions. Use consistent boundaries: compressor-only consumption differs from a complete system including dryer, pumps and cooling equipment.

For illustration, 120 kW of measured input at 750 m³/h of delivered flow gives 0.16 kWh per delivered cubic metre on that flow basis. This is a calculation example, not a performance claim for a particular machine. Compare both full-load performance and operation across the expected demand range.

Consider control strategy, unloaded energy, maintenance, treatment pressure losses, cooling costs, leakage and production redundancy. An oversized machine with unsuitable controls can operate inefficiently at low demand.

Obtain an itemised supply list covering the compressor, motor, control cabinet, air treatment, receiver, cooling equipment, pipework, spares and documentation. Include repairs, transport, installation and commissioning in the total project cost.

Frequently asked questions

What size compressor do I need for my PET blower?

Start with the blower's high-pressure consumption at the intended bottle, output and process settings. Confirm the flow reference basis, supply pressure, air recovery, treatment losses and required margin before selecting a compressor.

Does a 40 bar compressor suit every PET blowing machine?

No. It must deliver sufficient air at the required pressure and quality, with compatible controls and utilities. Some applications use a lower blowing pressure, while other constraints may rule out a particular compressor.

Are 750 m³/h and 750 Nm³/h the same?

Not necessarily. The first figure needs its reference conditions identified; the second refers to a stated normal basis. Establish the pressure, temperature and moisture references before comparing or converting them.

Does oil-free mean that no dryer or filters are required?

No. Drying, filtration and other treatment depend on the specified air quality, site conditions and distribution system. Confirm performance at the point of use.

Is a larger air receiver a substitute for a larger compressor?

No. A receiver can buffer intermittent demand within the permitted pressure range, but sustained consumption must be met by adequate compressor and treatment capacity.

Discuss your compressed-air requirement

Send PETmachinery your blower model, bottle formats, required output, documented air consumption and pressure, site conditions and available utilities. Include existing compressor details, budget and target installation date.

Email sales@petmachinery.com to discuss suitable options, or browse our used high-pressure compressor systems. Capacity, condition and technical suitability are assessed for each enquiry.

For related machinery, read our guide to choosing used PET and beverage production equipment.

Technical references

Manufacturer resources provide background on compression, airflow and treatment. Verify specifications against the particular used installation and intended operating conditions.