Multistage gas compressor and its control method

The piston compressor for compressing gas and air has a gas supply and discharge pipe (6,7). To compensate a time-changeable mass or volume flow through the pipes there are compensation means (10) which are regulated in dependence on the gas pressure detected by the sensor (8) so that the gas exit pressure is kept substantially constant. A mechanical, electronic, pneumatic or hydraulic regulator (9) can be used to regulate the volume of the pre-compressor (10) used as compensation means. Independent claim describes method for regulating the compensation by adjusting the flow in dependence on the gas pressure detected by the sensor.