Pressure dips are what block pneumatic conveying lines — and over-pressure is what quietly wastes your power. Every extra 1 bar above real demand adds roughly 8% to energy consumption, so the safe zone is narrow. A screw air compressor for pneumatic conveying has one job: hold steady flow at a stable pressure so cement, flour, pellets or resin powder never settles out of suspension inside the pipe. Get one spec wrong and a single blockage can stop a 24/7 line for hours while operators purge and restart the system.

A conveying line is a variable-demand load. The rotary valve feeds product in pulses, bends and risers shift the back pressure, and every silo vent changes the resistance the compressor sees. A fixed-speed screw unit reacts by loading, unloading or venting through its relief valve, and each pressure swing lets solids drop out of the air stream. A ten-minute pressure dip becomes a two-hour blockage. The answer is not always a bigger machine — it is a compressor matched to the conveying pressure band and duty cycle.

The Six Specs That Keep Product Moving

These six numbers decide whether a conveying line runs all night or plugs at 2 a.m.

• Flow at delivery pressure: ask for m³/min (or CFM) at the working bar, not free-air CFM. A machine that only hits its rating at 7 bar will starve a line running at 2.5 bar.
• Pressure band: spec how tight the pressure must stay. Overshooting by 1 bar costs about 8% more energy; undershooting drops solids out of suspension.
• Specific power: compare kW per m³/min, not nameplate kW. This is the number that decides your lifetime electricity bill.
• VSD turndown: a variable-speed drive lets the compressor follow demand instead of idling, which removes unloaded running and the pressure swings that cause blockages.
• Pressure dew point: wet air makes hygroscopic powders clump. A refrigerated dryer that holds a stable pressure dew point keeps material flowing.
• Ambient rating: machines designed for 52°C operation keep running when a 40°C-rated unit trips in a hot, dusty conveying area.

Compare Specific Power Before You Compare Price

Specific power is the cleanest way to compare machines. On a 37 kW class unit, a single-stage screw can run around 7.3 kW per m³/min, while a two-stage machine in the same size sits near 6.5 kW per m³/min. The gap widens at 90 kW, where a two-stage vertical configuration can reach about 5.9 kW per m³/min. That difference lands directly on the electricity meter: the same output costs less per cubic meter of air, hour after hour.

Pressure setting is where the quiet money leaks. Because every 1 kg of pressure adds about 8% to power draw, a compressor set one bar above the conveying requirement pays an 8% energy tax every hour it runs. Lock the pressure band first, then let a permanent-magnet motor with VSD control follow real demand. Together, two-stage compression, a PM motor and intelligent VSD control can cut 20–50% of energy use versus an old fixed-speed single-stage unit.

What Buyers Get Wrong

• Quoting free-air CFM instead of flow at delivery pressure, then wondering why the line starves.
• Skipping the dryer and letting hygroscopic powder bridge and clog.
• Oversizing the compressor and letting it run unloaded, which still burns power.
• Ignoring ambient temperature and watching the machine trip in a hot, dusty silo room.

Match the Compressor to the Line

Start from the main rotary screw air compressor page, then compare variable speed and two-stage options before you commit to a size. Send us your air consumption in m³/min at working pressure, the powder type, line length and number of bends, and we will size a unit that holds pressure without paying the 8%-per-bar energy tax.