Compressor control system and method for controlling the same

A method for controlling a compressor installation having at least one lubricated screw-type compressor connected to a pressure vessel and being driven by an electric motor having continuously adjustable speed settings, said compressor connected to a gas inlet conduit, a gas outlet conduit having an an outlet valve, and a return conduit having a closing valve, said method comprising the steps of:

• compressing gas supplied by said gas inlet from a lower pressure to a higher, predetermined pressure valve by said compressor;
• regulating the speed of the electric motor of said compressor as a function of compression pressure, said motor speed decreasing as said pressure in said pressure vessel approaches a predetermined pressure value, said motor stopping when the pressure in said pressure value reaches said predetermined pressure value;
• and
• regulating the transport of the lubricating agent through the return conduit with a control valve having a calibrated opening and being controlled by a control device, wherein as the number of revolutions of the compressor drops below a predetermined number of revolutions, said control valve is urged into a position that restricts the flow of the lubricating agent through said calibrated opening, said control value releasing flow restriction of the lubricating agent when said number of revolutions exceed said predetermined number of revolutions.