Abstract: A method uses a high density compressed liquefied gas in cleaning applications in a closed recycle system to achieve effective and economical cleaning without using any high pressure generating device. The closed recycle system can include a pressure cleaning vessel provided with a plurality of nozzles for pre-cleaning, atmospheric containers for expanding compressed liquid, sound wave generators and an agitator. The system can also include a pressure recovery vessel provided at a lower portion than the pressure cleaning vessel and having a detachable drain cylinder suspended from under the pressure recovery vessel and also having a temperature regulator for receiving contaminated liquid that has been pre-cleaned from a pressure cleaning room.