Gas Gathering compressor is compulsory for each gas well. The compressor in this application is used to collect the gas from one well or several wells to boost and transport to downstream gas treatment plant. Since in most of the cases the compressors are located at or near wellhead and there might be no availability of civil utility such as power supply, instrument air or drain pit and furthermore heavy condensate is also contained in the gas, thus a specific solution is made for this application to satisfy the site and gas condition. Furthermore, while time goes on year by year, the gas pressure shall deplete, therefore a specific configuration is designed especially for this case.