A conical screw compressor is an offshoot of the conventional screw compressor. In a typical screw compressor, two meshing helical screws or rotors are mounted side-by-side in a housing. The rotors spin in opposite directions and draw air into the cavities between them. Volume decreases as air progresses along the rotors and compresses air, which is discharged at the outlet.
A conical screw compressor, in contrast, consists of the male (inner) screw revolving inside the female (outer) screw. Vert Rotors of Edinburgh, Scotland developed the first unit in 2013 and subsequently patented the design. The company also developed the proprietary mathematical algorithms and software used to generate the precision conical screws profiles, and it manufactures the screws with CNC machines capable of holding geometrical tolerances within ± 5 µm.
A conical compressor does not have clearance between the male and female screws and the housing, because the female screw acts like a housing. This significantly reduces the leakage path for the gas and even a small (sub-1 kW) conical compressor remains highly efficient. As air travels along the rotors, the volume of the chamber reduces, increasing the pressure. Air is then ejected at the discharge end of the device at a higher pressure.
The technology displays low noise and vibration characteristics and is capable of continuous operation. Versus conventional piston compressors that can operate at noise levels around 100dB(A), conical compressors run significantly quieter, as low as 62 dB(A).
The conical compressor is highly compact (because one screw sits inside the other), yet powerful. It produces two to three times higher pressure in a single stage, compared to competing products, and is capable of 20:1 pressure ratios. And a Vert conical compressor reportedly has double the efficiency of an equivalent scroll compressor, and double the single-stage pressure capability of a twin-screw compressor.
Conical screw compressors vary in size. Vert Rotors has built and tested a range of designs, from a tiny 20 W screw compressor, which fits in the palm of a hand, to a large 10 kW machine producing 75 m3/h (44 cfm). This is a major difference from traditional twin-screw compressors, which cannot be smaller than 2.2 kW. Even the smallest conical screw compressors successfully produce high pressure of 16 to 22 bar in a single stage.
The company is applying the technology in a number of products. For example, a small 0.8-kW conical screw is 50% more efficient at 8 barg than alternative low-vibration scroll compressors of the same capacity. The Nautilus is a quiet “desktop” compressor for up to 300 psi pressure. And the new 1.6 kW A150 unit is rated at 10 bar and 150 lpm. Vert also produces custom designs, including a low-vibration/low-noise “super-compressor” which is said to be 200% more powerful and 89% lighter than others on the market, designed to improve satellite propulsion.