Quiet, convenient, high-quality stainless steel units for the professional drying of hollow spaces and insulation layers following water ingress or damp damage, using blowing and sucking operation. The unit can be used as a pressure of vacuum pump for conveying air and non-explosive gases as well as gas-air mixtures. The built-in compressor is air-cooled, meaning it is 100% oil-free. The aluminium fan wheel rotates inside a die-cast casing with a side-channel. Air is sucked in, and propelled by the fan wheel and side channel on a spiral course, accelerating several times, until it reaches high pressure and exits through the pressure channel. Perfectly suited for combined operation with AERIAL adsorption dryers and VDT water separators.