Automatic three stage centrifugal sludge separator

In an automatic, three stage, sludge discharging centrifugal separator for separating a primary liquid into sludge, heavy liquid and light liquid components, and including a primary liquid inlet (19), a plurality of nested separator plates (15), a light liquid outlet (1), a heavy liquid outlet (2), sludge outlet means (48), generally cylindrical casing means (44, 45) surrounding and defining said inlet and outlets, a valve cylinder (50) slidable on said casing means between a raised position at which said sludge outlet means are closed and a lowered position at which said sludge outlet means not open, a first expandable pressure chamber (32) for raising said valve cylinder, a second expandable pressure chamber (31) for lowering said valve cylinder, means (17) defining a heavy liquid discharge passage (27) between said casing means and said separator plates, and drive means (52, 53) for rotating all of the above structure, the improvements characterized by:

• a. a first reservoir (24) for heavy liquid,
• b. first passage means (66, 65, 35, 61) communicating between said reservoir and said second pressure chamber,
• c. piston means (36) slidably mounted in said casing means and including valve means (38, 39) controlling said first passage means,
• d. a heavy liquid level sensing chamber (30),
• e. a first operating chamber (33) for said piston means, and
• f. overflow passage means (69, 22, 21) communicating between said sensing chamber and said first operating chamber, whereby when the sludge accumulates in the casing means to a predetermined level it blocks the heavy liquid discharge passage, the heavy liquid level builds up in the sensing chamber and flows through the overflow passage means into the first operating chamber, the piston means is moved to open the valve means, heavy liquid flows from the first reservoir into the second pressure chamber, the valve cylinder is lowered, and the sludge outlet means are opened.