Self-cleaning centrifugal separator having a main piston valve defining one side of the separating chamber and connected to at least one auxiliary piston valve

In a centrifugal seprator constructed for intermittent discharge of sludge, comprising:

• a rotatably mounted separator drum having an upper end member and a lower end member, and at least one sludge discharge passageway disposed at the radially outward periphery of the drum, one of said end members comprising a main piston valve movable axially to open and close the sludge discharge passageway for desludging, a closing chamber disposed in the drum outwardly of the main piston valve for receiving and discharging control fluid for, respectively, forcing the main piston valve to the closed position and relieving force for initiating the moving of the main piston valve to its open position under the influence of material filling the drum, means for supplying fluid to the closing chamber and means for discharging fluid therefrom,
• the improvement which comprises:
• an auxiliary piston valve mounted in the drum and on the main piston valve and disposed axially outwardly of the main piston valve, a partition ring mounted in the drum and separating a portion of the auxiliary piston valve from the main piston valve, the auxiliary piston valve being axially moveable in the drum so that an auxiliary piston valve closing chamber is provided on the axially outward side of the auxiliary piston valve and an auxiliary piston valve opening chamber is provided on the axially inward side of the auxiliary piston valve, and means for supplying control fluids to the auxiliary piston valve closing and opening chamber for, respectively, exerting a closing and opening force on the auxiliary piston valve, the mounting of the auxiliary piston valve on the main piston valve being such that said closing and opening forces on the auxiliary piston valve are transmitted to the main piston valve and add to the influence of the control fluid of the closing chamber of the main piston valve.