Patent ID: 7107973

Claim:
A method of supplying compressed air to a system, said method comprising the steps of: (a) driving a first compressor by a power source shaft to compress air; (b) driving a second compressor by the power source shaft to compress air; (c) operating the compressors at least partially in series so that at least some air that is compressed by the first compressor is further compressed by the second compressor and then supplied to the system; and (d) operating the compressors at least partially in parallel so that at least a portion of air is compressed by the first compressor and at least another portion of air is compressed by the second compressor and the at least a portion and at least another portion of compressed air are supplied to the system without passing through the other compressor, said driving steps of (a) and (b) each being performed so that both compressors are continuously operated by the power source shaft at a substantially constant relative speed to the power source shaft speed during the operating steps of (c) and (d).