Design Features of a Small Oilfree, Reciprocating, High Pressure Compressor

The paper describes the design concept of a small, oilfree, reciprocating high pressure compressor which was particularly developed for NGV-applications (NGV = Natural Gas for Vehicles). It is field proven in several thousand installations in various parts of the world. The compressor head is also used in a small hermetically sealed compression unit for technical gases like N2, Air, Ar, He, H2, C02, etc .. The compressor compresses the gas from atmospheric pressure to 200 bar. New design solutions for the valves, drive mechanism and high pressure seal are described and discussed. INTRODUCTION The compressor introduced in this paper is the result of several years of intensive development and testing. The compressor was particularly designed for NGV-applications where the gas is taken from the mains at about 20 mbar g and compressed to 200 bar (3'000 psi) into the high-pressure tank fitted in the Natural Gas-driven vehicle. The refueling normally takes several hours until the appropriate fill pressure is reached and the compressor shuts down automatically. This application is field proven in several thousand NGV-installations. The heart of the device is a four-stage, oilfree, high pressure compressor head which in modified versions can also be used for the compression of a variety of technical gases like N2, Air, Ar, He, Hz, C02, etc .. Fig.l shows a cross section of the compressor unit for technical gases using the same basic compressor design as for NGV. The main features of the compressor are: compact design hermetically sealed quiet, low vibration oilfree compression wide operating temperature range ~40°C/~40°C easy serviceable/long service intervals suitable for large scale production These features are the result of a variety of new design solutions like: fully balanced scotch yoke drive with linear needle bearings small multiple plastic plate valves in all four stages clearance seal in the high pressure stage integrated interstage connections