Vacuum filters are simple and reliable machines and therefore have gained wide acceptance in the chemical, food and pharmaceutical industries.
Some of the very old museum like filters are illustrated on the
The filtration areas for standard machines are:
The various types of vacuum filters may be grouped as follows:
There are two concepts in layout design:
Generally industrial vacuum pumps such as the liquid-ring or the rotating-vanes type operate at a vacuum of 500-600 mmHg. Hence in barometric leg layouts the filter is mounted 8-9 meters above ground level to ensure that the liquid level in the leg will not flood the filtrate receiver. This applies to liquids with a specific gravity of 1 however for heavier liquids the filter elevation with regard to the ground level may be lowered. Barometric leg layouts require therefore a structure for the filter but the advantage is that the filtrate pump operates under a positive suction head. On the other hand, floor mounted layouts require a receiver mounted filtrate pumps of special low NPSH design to effectively deliver the filtrate under the full vacuum on the suction side. The scheme below also shows a floor mounted layout with a partitioned receiver and two one-way flaps that open and close by solenoid controlled air balancing pipe. However, although this design uses a conventional positive suction head pump, it is rarely used owing to the moving parts of the receiver and the risk of vacuum leakages from the flap seals.
The block diagram for a typical filter station and its components may look like this:
The advantages and disadvantages of vacuum filtration compared to other separation methods are: