A collector circuit and associated circulation process, for intercepting and selectively diverting, at least partially, a fluid flow continuously flowing in a fluid circulation system, for drilling rigs. The collector includes a first sub-circuit with a first duct, with a first valve, and a second duct with a second valve; and; a second sub-circuit; The first sub-circuit, depending on the operating configurations of the first valve and the second valve, is adapted to allow the transit of the fluid flow in the first duct, and selectively divert fluid flow towards the second duct. The second sub-circuit is fluid-dynamically connected to the second duct of the first sub-circuit for receiving fluid flow, diverted by the first sub-circuit, and directing it towards a first outlet of the second sub-circuit. The second sub-circuit and the first sub-circuit are independent, and the second sub-circuit is removable from the collector circuit.
