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Vacu-Matic: Principles

Hoffman Vacumatic Filters are flatbed vacuum units.

A continuous metal conveyor belt supports the disposable media, while a heavy-duty Hoffman exhauster creates a vacuum beneath the media. As liquid increases and, at a preset limit, a vacuum switch causes the belt (and media) to be indexed. As media is newly exposed, it can be pre-coated by dirty liquid prior to entering the vacuum chamber.


The Vacu-Matic relies on the flow of air to perform three major functions. First, air is used to dry the cake prior to sludge removal. This minimizes loss of process liquids and reduces sludge disposal costs. Second, using the optional air skimmer, air flow is directed by the exhauster discharge over the liquid pool to skim away floating contaminants. Third, air passing the filter chamber aerates the cleaned liquid. This is particularly important in the case of coolants to control bacterial growth and resulting coolant rancidity.

Vacu-Matic: Hi-Flo-Matic Operation

The filter feed pump supplies the Vacu-Matic with process fluid from the dirty tank. This liquid is pumped to the distributor and evenly apportioned across the filter bed pool. The bed consists of a flat wire belt supporting the filter media. A Hoffman exhauster produces vacuum in the chamber beneath the filter bed, drawing the liquid through the media and the built up deposit of solids (filter cake).

When the pressure drop across the filter cake/media reaches a given limit, an electrical switch is closed. This indexes the media and, as a result, discharges spent media and dried filter cake into the disposal container. At the same time, clean media is drawn onto the filter bed. Both the vacuum in the chamber and the liquid level drop due to the inrush of liquid through this fresh media. This sudden flow builds the filter cake back to a functional level. The clean liquid passing through the fliter cake and media drains into the clean liquid compartment of the holding tank. A “water leg” is maintained in the clean overflow pipe to sustain a vacuum in the filter.

Where excessive floating solids or tramp oil exist in the incoming liquid, discharge air from the vacuum producer can operate an optional air skimmer. This moves floating materials toward the dirty end for removal as media is indexed. Should the filter bed become flooded due to mechanical malfunction or unexpected impurities in the process, the liquid level is reduced via the overflow slot connected to the side gutter. This is connected to an overflow drain pipe dumping into the dirty compartment of the holding tank.


Following are just some of the applications in which the Hoffamn Vacu-Matic filter has been used with great success:

  • Grinding Applications
  • Hot & Cold Rolling
  • Wire Drawing
  • Machining Coolants
  • Caustic Washes
  • Continuous Casting
  • Mill Waste Filtration
  • Phosphatizing
  • Paint Booth Filtration
  • Clarifier Underflow
  • Can Body Production
  • Food Waste
  • Wet Scrubbers
  • Parts Washing

Click here to view the vacu-matic filter sizing specifications

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