SL+ Series Oil-Free Screw Air Compressors

Many plants need only 0.3~0.4MPa at the point of use, yet still run compressors set to 0.7MPa or higher. The surplus pressure is simply dumped through a reducing valve — the machine draws the same power, but the air is not put to work. This kind of pressure waste is one of the most easily overlooked energy drains in a compressor room.

The Fusheng SL+ series low-pressure screw air compressor is built specifically for low-pressure duty. Aimed at delivering low pressure with high volume, it produces the same air delivery for less energy — an average saving of 30% against the pressure waste of a conventional compressor. The series runs at 0.3/0.4MPa working pressure, with air delivery of 10~46m³/min and power from 37~185kW.

Wasted Pressure Is Wasted Electricity

Compressor energy consumption is directly related to discharge pressure: set the pressure higher and more work is needed to compress the same volume of gas. If the site really needs only 0.4MPa but is supplied by a machine set to 0.8MPa, the extra pressure is neither used by the equipment nor recoverable — it is simply absorbed by the reducing valve.

Bringing discharge pressure down to what is actually required is the most direct way to save energy at low pressure. But simply turning a conventional model down does not work — its rotor profile and airend parameters are designed for higher pressures, and running it at low pressure usually moves it away from its efficient range. An airend purpose-built for low pressure is optimised for that duty from the design stage, which is what makes higher air delivery possible for the same energy input.

A Low-Pressure Airend: More Air for Less Energy

At the heart of the SL+ series is an energy-efficient airend designed for low-pressure duty. Because the target pressure is lower, the airend works under more favourable compression conditions and converts more of the input power into useful air delivery. That is what designing for low pressure and high volume means — meeting the process requirement while cutting unnecessary compression work.

For users, the test is clear: if the whole air system works steadily at 0.3~0.4MPa but is fed by high-pressure machines, switching to a low-pressure model usually delivers the most direct return. Conversely, if high-pressure demand genuinely exists on site, process requirements should not be sacrificed for the sake of saving energy.

High-Efficiency and Standard: Choosing Between the Two Lines

The specification table shows at least two product lines in the SL+ series:

• The high-efficiency line: models from SL37A-3 through SL160A-3, discharge pressure 0.3MPa, air-cooled, aimed at applications with a narrow pressure requirement and a focus on higher efficiency;
• The standard line: models from SL30A upward, discharge pressure covering 0.35/0.4/0.45MPa, with a choice of air or water cooling — more flexible pressure settings and a broader fit.

Both target low-pressure duty, and the difference lies mainly in pressure points and configuration. Where the pressure requirement is single and efficiency is the priority, the high-efficiency line is the first choice; where several pressure settings are needed, or site cooling conditions are unusual, the standard line fits better.

Before Converting to Low Pressure, Audit Your Air Pressure

The return from a low-pressure model comes from compressing only what is needed, but that depends on knowing the real pressure demand on site. Before converting or selecting new equipment, an audit is worth carrying out:

• Record the rated working pressure of each major air-consuming device and identify the one with the highest requirement;
• Check the actual pressure at the end of the piping network to confirm whether undersized pipe or excessive length is causing pressure drop;
• Separate devices that use air continuously from those that use it occasionally, so a few units do not push up the pressure for the whole station;
• Assess pressure loss in the existing air storage and treatment stages to see whether there is room for improvement.

An audit often reveals that only a few devices genuinely need high pressure, and that a local booster or a dedicated unit can serve them — without running the entire station at the highest pressure.

Technical Specifications

Industries and Applications

• Processes that run steadily at 0.3~0.4MPa air pressure;
• Pneumatic conveying and blow-off duties that call for low pressure and high volume;
• Textiles, chemical fibre and similar industries where low pressure and high volume dominate;
• Compressor rooms with an existing high-pressure supply that needs re-optimising around actual pressure demand.

Selection Advice

1. Confirm the real air pressure requirement first: base the decision on the pressure demanded by the most demanding device rather than on the parameters of the old model;
2. Recalculate air delivery once pressure comes down: at low pressure the same power can produce more air, so the model may be smaller than expected;
3. Choose the cooling method by site conditions: consider water cooling where circulating water is available and power is high, otherwise air cooling is simpler;
4. Factor in piping pressure loss: longer and narrower pipe means lower pressure at the point of use, and this should be calculated as part of selection.

Conclusion

The logic of saving energy at low pressure is simple: do not compress pressure you do not need. The SL+ series replaces a conventional airend with one built for low pressure, trading less energy for the same air delivery, and then uses high-efficiency and standard lines to cover different pressure points and configurations. In low-pressure applications, choosing the right pressure level is often more effective than buying a more expensive machine.