These filters are used where we need fine filtration in less space. This filter operates on the principle of vacuum. Pressure difference is created across the filter media to increase the flow rates through it. There are various types of vacuum filters:

Hydraulic Vacuum Filter

Construction:

Hydraulic Vacuum Filter From 100 LPM to 6000 LPM It's a tank with the conveyor running inside. Filter paper is placed below the conveyor. There are vacuum chambers below filter paper that are connected to the suction of the pump. Construction of vacuum chamber is that very high velocities are maintained to avoid any accumulation over the period. Pump creates the pressure difference across the filter paper. Maximum pressure difference across the filter paper reaches up to -0.8 bar. I.e. 600mm of Hg. Paper moves with the help of sludge accumulated on the filter paper.

Advantages:

Very large volume of sludge can be handled because of its peculiar construction. Very large flow can be handled in smaller area because of large pressure difference across the filter paper as compared to gravity filter. Fine filtration is possible. Very fine filter paper could be used because of large pressure difference across the filter paper. Conveyor itself acts as a storage tank. It does not need separate tank.

Pneumatic Vacuum Filter

Construction:

Pneumatic Vacuum Filter From 800 LPM onwards. It's ONLY a conveyor. Filter paper is placed above the conveyor. vacuum blower creates the pressure difference across the filter paper. Maximum pressure difference across the filter paper reaches up to -0.4 bar. i.e. 300mm of Hg. Paper moves with the help conveyor, sludge accumulated on the filter paper & weight of the fluid. Conveyor carries the filter paper. There is a tray below the conveyor to collect & pass the fluid to tank.

Advantages:

Not very large volume of sludge can be handled. Comparatively smaller flow is handled because of less pressure difference across the filter paper as compared to hydraulic vacuum filter. It could be used for granular sludge as well as the longitudinal longer size particles because all the material is collected & carried by filter paper.

Drum Type Vacuum Filter

The stainless steel wedge wire drums are provided in the conveyor. Suction of the pumps is directly connected to the drums & vacuum is created across the wedge wire screen. Fluid levels are needs to be maintained above the drums to avoid air leakage.

These are very widely used in Sugar syrup filtration.


Merits Of Vacuum Filter Over Conventional Gravity Filter

Fine filtration is possible. Finer filter paper is used because of high pressure difference across the filter paper. Requires less space as compared to paper band filter for the same flow rate. Very high sludge handling capacity. Less paper consumption because of high pressure difference across the paper filter which results in good cake filtration. Totally enclosed fully automatic system. No daily maintenance, which reduces the manpower. Trouble free operation. High viscous fluids can be easily handled.