A device (10) for circulating sealing gas for mechanical dry seals (11) of a centrifugal compressor (13) at times when the machine is stationary and pressurized; the device comprises a sealed reciprocating compressor (12), which includes a piston (14) slidable in a cylinder (16), and the piston (14) is moved by a magnetic coupling to an external magnetic element (20) which moves along the said cylinder (16).