A pumping apparatus comprising: i) a first reversible volumetric gear pump comprising: - a first pair of toothed wheels; - a first housing compartment for housing the first pair of toothed wheels; ii) a second reversible volumetric gear pump comprising: - a second pair of toothed wheels; the first volumetric pump drawing in rotation the second volumetric pump; - a second housing compartment for housing the second pair of wheels; characterised in that it comprises: * a first channel that places in fluid connection a first zone of the first compartment and a first zone of the second compartment; * a second channel that places in fluid connection a second zone of the first compartment and a second zone of the second compartment; * means for opening/closing the first and the second channel (13, 23); * an outer casing comprising a first, a second, a third and a fourth opening (14, 15, 24, 25) intended to allow the fluid communication of the pumping apparatus with the outside; * means used to block the third and fourth openings (24, 25); in a first operating configuration: said first zone of the first compartment and said first zone of the second compartment defining a suction of the first and of the second pump (1, 2), respectively, said second zone of the first compartment and said second zone of the second compartment defining a delivery of the first and of the second pump (1, 2), respectively, said means for opening/closing the first and the second channel (13, 23) blocking the second channel and allowing the fluid communication of the first zone of the first compartment and of the first zone of the second compartment through the first channel; the first opening being crossed by the inflowing operating fluid directed towards the first zone of the first compartment and to the first zone of the second compartment; the second opening being crossed by the outflowing operating fluid coming from the second zone of the first compartment, the third opening being blocked, the fourth opening being crossed by the outflowing fluid coming from the second zone of the second pump; in a second operating configuration: said second zone of the first compartment and said second zone of the second compartment defining a suction of the first and of the second pump (1, 2), respectively, said first zone of the first compartment and said first zone of the second compartment defining a delivery of the first and of the second pump (1, 2), respectively, said means for opening/closing the first and second channel (13, 23) blocking the first channel and allowing the fluid communication between the second zone of the first compartment and the second zone of the second compartment through the second channel; the first opening being crossed by the outflowing operating fluid coming from the first zone of the first compartment, the second opening being crossed by the inflowing fluid directed towards the second zone of the first compartment and towards the second zone of the second compartment; the third opening being crossed by the outflowing fluid coming from the first zone of the second compartment; the fourth opening being blocked; in the second operating configuration the rotation direction of the first and of the second pair (11, 21) of wheels being opposite to that assumed in the first operating configuration. i) a first reversible volumetric gear pump comprising: - a first pair of toothed wheels; - a first housing compartment for housing the first pair of toothed wheels; - a first pair of toothed wheels; - a first housing compartment for housing the first pair of toothed wheels; ii) a second reversible volumetric gear pump comprising: - a second pair of toothed wheels; the first volumetric pump drawing in rotation the second volumetric pump; - a second housing compartment for housing the second pair of wheels; - a second pair of toothed wheels; the first volumetric pump drawing in rotation the second volumetric pump; - a second housing compartment for housing the second pair of wheels; * a first channel that places in fluid connection a first zone of the first compartment and a first zone of the second compartment; * a second channel that places in fluid connection a second zone of the first compartment and a second zone of the second compartment; * means for opening/closing the first and the second channel (13, 23); * an outer casing comprising a first, a second, a third and a fourth opening (14, 15, 24, 25) intended to allow the fluid communication of the pumping apparatus with the outside; * means used to block the third and fourth openings (24, 25);