FPM+-T Two-Stage Oil-Cooled PM VSD Screw Air Compressors

The energy consumption of compressed air comes down to one thing: compressing the gas to the target pressure. In single-stage compression, the entire pressure ratio is applied to a single pair of rotors in one step. The compression process heats up quickly, the single-stage pressure ratio is high, and the gas that flows back between the rotors (internal leakage) increases accordingly, which limits efficiency. The higher the power, the more pronounced this problem becomes.

The ESSENCE FPM+-T two-stage oil-cooled PM VSD screw air compressor tackles this problem through staged compression. It covers three models — FPM+55A/W-*T, FPM+75A/W-*T and FPM+90A/W-*T — with power from 55 to 90 kW, a working pressure of 0.7–1.25 MPa and air delivery of 3.76–20.80 m³/min, using PM VSD starting and coupling drive.

Two-Stage Compression: Splitting One Compression Step into Two

Two-stage compression means dividing the compression of air into two stages and cooling the air between them. The benefits can be broken down into three points:

• Lower pressure ratio per stage: each stage handles a smaller pressure difference, so the load on the rotors is more balanced;
• Interstage cooling: the hot compressed gas is cooled before it enters the second stage, so the second stage draws in cooler air and the compression process stays closer to isothermal;
• Less internal leakage: with a lower pressure ratio per stage, the gas flowing back between the rotors is reduced, and effective air delivery improves.

In other words, two-stage compression is not an extra step added for its own sake; it does the same job in a gentler way, recovering the efficiency that would otherwise be lost to high temperatures and backflow.

Oil-Cooled PM Motor: Addressing Heat Sensitivity Up Front

The FPM+-T uses PM VSD starting and an oil-cooled design. Permanent magnet motors are sensitive to temperature, and prolonged exposure to high heat can affect both their efficiency and their reliability. Oil cooling keeps the motor's temperature rise within a reasonable range, so the advantages of PM drive hold up during long, continuous operation.

Combined with VSD control, the unit's speed follows air demand: when demand drops, speed and energy consumption fall; when demand rises, speed increases to keep pace with the air required, avoiding the unloaded waste of a fixed-speed machine's load/unload mode.

Dimensions and Weight: What to Sort Out Before Installation

Unlike smaller units, models above 55 kW need to be planned for at the installation stage. The three FPM+-T models have net weights of 2350 kg, 2520 kg and 2950 kg, with overall dimensions (L × W × H) of 2250 × 1344 × 1694 mm, 2250 × 1344 × 1694 mm and 2300 × 1450 × 1750 mm respectively.

This means floor load capacity, access routes and lifting conditions all need to be confirmed before purchase. The three models occupy similar floor space, but the 90 kW model is slightly larger in length, width, height and weight, so the layout should be calculated for the actual model rather than estimated from the smallest in the series. These details, which seem unrelated to performance, are often exactly what determines whether the equipment can be installed smoothly.

Three Models, One Tight Power Ladder

The FPM+-T comes in three power steps — 55, 75 and 90 kW — as the models FPM+55A/W-*T, FPM+75A/W-*T and FPM+90A/W-*T. At 0.8 MPa, for example, the three models deliver 4.80–12.00, 6.60–16.50 and 8.00–20.00 m³/min respectively, with fairly even steps between adjacent ratings.

This focused line-up targets a clearly defined operating range: the 55–90 kW band is exactly where the main compressors of many mid-sized factory air stations sit. Rather than spreading out a long list of models, it makes more sense to make each power point solid within this band — a common approach for two-stage compressors.

Technical Specifications

Taking the 90 kW model as an example, air delivery is 8.32–20.80 m³/min at 0.7 MPa, 8.00–20.00 m³/min at 0.8 MPa, 6.76–16.90 m³/min at 1.0 MPa and 5.84–14.60 m³/min at 1.25 MPa. Air delivery still drops as pressure rises, and the selection logic is the same as for single-stage models: settle the pressure first, then the air delivery.

Who It Suits

• Mid-to-large plants running long, continuous shifts: differences in energy efficiency keep compounding over long operating hours;
• Sites where electricity is a large share of cost and energy-saving targets are explicit: two-stage compression and VSD control both act on running costs;
• Production lines with pronounced swings in air demand: PM VSD makes air supply follow demand;
• New-build or retrofit projects with room to plan installation properly: the weight and dimensions of the unit need to be built into the layout at an early stage.

Selection Advice

1. Confirm the pressure level first: air delivery varies noticeably across the 0.7–1.25 MPa range, so take the value that matches actual demand;
2. Check the installation conditions: confirm floor load capacity, access routes and the lifting plan in advance;
3. Assess the VSD payoff: the larger the swings in air demand, the more VSD control pays off;
4. Include air treatment and piping in the overall design: the outlet is G2 or square flange DN80, and pipe sizing should match the unit.

Conclusion

The value of two-stage compression is not one more line on a specification sheet, but that it reduces energy losses at the level of the compression principle itself. For mid-to-large units in the 55–90 kW band that run continuously year-round, this efficiency saved at the source is more direct than any remedy applied after the fact.

For equipment that runs continuously over the long term, every kilowatt-hour saved adds up to a significant difference over time — which is reason enough to understand the principle clearly when selecting a model.