A ring conduit (1) carries fluid from a storage vessel (2) via a pump (3) and a valve (4) to the feed point (17) and one or more user branch conduits (5-8) are introduced in the circuit. Excess fluid is fed back again to the storage vessel (2) via a first or a second back flow conduit (1,6 16'). The ring conduit (1) is connected via two further valves both to the storage vessel and to the pump. USE/ADVANTAGE - To clean pipe conduits. The cleaning bodies remain continuously in the conduit system without reversal of direction, no special cleaning fluid is required, the system does not have to be opened, and there is no emission of solvent vapour into the atmosphere.