Rotary Screw Air Compressors

Electric rotary screw compressor series documented in the catalogue

The normal-air electric catalogue documents three relevant configuration paths for this page: fixed-speed LG, variable-speed EB/BPLG and Ⅱ-coded two-stage configurations in both families. The original model key identifies Ⅱ as second-stage compression. The clean specification tables above select confirmed rows from the fixed-speed, variable-speed and two-stage tables so that a small 6 bar example is not used to represent the whole documented range.

Across the cited normal-air tables, confirmed rows cover 5–18 bar (0.5–1.8 MPa), 7.5–560 kW motor power and 0.8–110 m³/min nominal flow. These are catalogue entries, not a single operating envelope for every model: pressure, nominal flow and motor power must be read together from one row. The manual also lists YLG / YLGⅡ electric mobile arrangements; use the electric mobile image as a configuration reference only, not as proof of a particular listed model.

• LG fixed-speed family: compare a fixed-speed package where the measured plant load is a stable base duty.
• EB/BPLG variable-speed family: compare variable-speed control where demand changes materially during operation and the usable control range fits the measured profile.
• Ⅱ-coded rows: the manual identifies the Ⅱ designation as two-stage compression; fixed-speed LGⅡ and variable-speed EB/BPLGⅡ examples are shown separately in the catalogue table.
• The normal-air manual describes its compressor series as micro-oil screw compressors; it does not identify an oil-free compressor model for this page.

Choose a configuration before requesting a model quotation

A fixed-speed package is commonly evaluated for a stable base load, while a variable-speed package may be evaluated where demand changes materially during a shift. These are comparison categories, not claims about a universal energy result. A variable-speed drive still has a usable operating range, minimum speed, motor limits and control response that must be confirmed. A fixed-speed unit can also operate in a sequenced multi-machine system, where several machines share base and trim duties.

The motor-power values in the catalogue tables are motor rated power; they are not package electrical input. Ask the supplier to state package-specific input power and delivered flow at the proposed discharge pressure, including the test method, reference conditions and whether power is full-load, part-load, unloaded or standby. Avoid comparing energy numbers taken at different pressures, flow bases, ambient conditions or unloaded states.

Ask the supplier to explain the control sequence at low demand, during rapid peaks and when one package is unavailable. Check how inlet modulation, start-stop, load-unload or speed control affects delivered flow and power. Review pressure-band settings and whether a local controller, plant master controller or building management system will be the decision-maker.

Specify the package, pressure, flow and treatment as one system

Rotary screw packages may use an oil-injected compression process or an oil-free compression process. In an oil-injected arrangement, the fluid can support sealing and cooling inside the compression stage, followed by separation and treatment. In an oil-free arrangement, the compression process is designed without oil introduced into the compression chamber, but the complete installation can still have contamination sources in ambient intake air, piping, seals, coolers, condensate or downstream equipment.

Select the compression process after defining the end-use quality requirement. Food, pharmaceutical, electronics, paint and instrument-air users should identify the applicable contamination limits, sampling method and point of measurement instead of treating “oil-free” as a blanket product or process guarantee. ISO 8573-1 is a classification framework for contaminants and purity classes; the relevant class, test evidence and treatment train must be specified for the application. A component certificate does not by itself approve the complete assembly or prove point-of-use quality.

Begin with the pressure required at the consuming equipment, then add only the losses and control margin that are justified by the installation design. Do not raise compressor pressure simply to compensate for an unknown restriction. State whether pressure is gauge or absolute, and identify the normal, minimum and peak values. The catalogue flow values on this page retain the manual’s nominal m³/min designation; they are not stated as FAD. Values using different reference bases are not directly interchangeable.

Air quality should be written as an end-use requirement, not as a marketing adjective. Identify particles, water and oil limits, pressure dew point, filtration location and the required verification method. Treatment may include aftercooling, separators, filters, dryers, drains and point-of-use equipment. The compressor outlet, storage vessel outlet and point of use can have different conditions. Include the most demanding user without assuming that the entire plant needs the same treatment if a segregated branch is technically acceptable.

An aftercooler can reduce discharge temperature and allow condensate separation, but it does not replace a dryer when the process requires a defined pressure dew point. Filters must be selected for the contaminant and flow duty, and their pressure drop and drain arrangement should be included in the review. Automatic drains, condensate handling and discharge routing need local environmental and safety checks.

A receiver can buffer short demand changes, reduce rapid control cycling and provide a stable measurement location, but its useful role depends on demand shape, pressure band and control logic. It is not a substitute for adequate compressor capacity or a cure for distribution losses. Confirm vessel code, inspection, relief protection, isolation and drain requirements for the installation jurisdiction.

Where a rotary screw compressor fits

A screw package is often considered when a plant has a steady base load, repeated shifts or many pneumatic users operating at the same time. Its positive-displacement rotors deliver a continuous stream rather than the discrete strokes associated with a reciprocating machine. That does not make every screw package the right choice: a small, intermittent demand may be better served by a different arrangement, while an installation with large short peaks may need storage, sequencing or a supplementary machine.

The correct comparison is the complete system at the required operating point. Review actual demand over a representative production period, including unloaded or idle time, start-up events, leaks and future expansion. A nominal motor size is not a substitute for flow data. CAGI describes standardized data sheets as a way to compare relevant compressor performance information, while noting that energy is a major life-cycle cost consideration.

• Appropriate starting point: recurring plant demand with a defined pressure band and enough operating hours to justify a packaged rotary solution.
• Use caution when demand is highly intermittent, unusually low, rapidly changing or dominated by short peaks.
• Do not infer suitability from the compressor family name alone; verify flow, pressure, control range and air quality together.

Plan installation, cooling and maintenance before ordering

Reserve access for filters, separators, coolers, belts or couplings where applicable, oil or condensate service, electrical equipment and lifting or replacement. Confirm the floor, foundation, vibration limits, intake location and discharge routing. An air-cooled package adds heat to the room; a water-cooled package adds water-side requirements. Intake air should be clean enough for the chosen process, and the room should prevent recirculation of hot exhaust air into the compressor inlet.

The distribution design should separate production requirements from local equipment preferences. Check pipe size, branch arrangement, isolation points, ring-main strategy, elevation changes, drains and point-of-use regulators. Measure or estimate pressure drop across the full route at the specified flow, including dryers, filters, valves and flexible connections. For multiple compressors, document sequencing, common receiver location and the effect of an isolated machine on minimum plant pressure.

Maintenance requirements depend on the compressor design, OEM instructions, ambient conditions, operating hours, load profile and the condition of intake and treatment components. A quotation should identify service access, consumables, inspection points, instrumentation and the records needed to maintain warranty or compliance. Do not use a universal service interval or predicted lifespan without the specific manual and duty assumptions.

Compare more than purchase price. Request a clear separation of full-load, part-load, unloaded and standby power where relevant, plus the assumptions behind any annual energy estimate. CAGI’s verification program explains that published rotary-compressor data sheets are intended to support comparison and that performance testing uses specified methods; participation and verification must still be checked for the exact quoted model. Include energy, treatment consumables, condensate disposal, planned service, downtime exposure and replacement strategy in the lifecycle review.