Mixproof valves can be either double or single seated. A double-seated mixproof valve has two independent seals separating the two liquids and a drainage chamber between. This chamber must be open to atmosphere to ensure full mixproof safety in case either of the two seals should leak. When a double-seated mixproof valve is activated, the chamber between the upper and lower body is closed and then the valve opens to connect the upper and lower pipelines. When the valve is closed, first the upper plug seals and then the leakage chamber is opened to atmosphere. This gives very small product losses during operation.
The single-seat mixproof valve has one seat and two seals, but on the same plug. The area between the two seals is open to atmosphere. This leakage drain chamber is closed by small shut-off valves before the single-seat mixproof valve is activated. An external CIP line is connected to the drainage line via the small valves for cleaning.
