Filter presses are used to remove liquid from sludge, slurries and other waste streams. They work by applying pressure to squeeze liquid out through a filter medium, leaving behind a filter cake of dewatered solids.

There are two main types of filter presses: hydraulic presses and plate and frame presses. Both use alternating filter plates and cloths, but hydraulic presses use hydraulic cylinders to apply pressure while plate and frame presses use mechanical screw mechanisms.

How Hydraulic Filter Presses Work

Hydraulic filter press consist of:

  • Vertical or horizontal filter plates – Made of thick metal that clamp together.
  • Filter cloths or membranes – Provide the filtering surface between plates.
  • Hydraulic cylinders – Provide the squeezing force to press the plates together. High pressure hydraulic oil in the cylinders pushes the plates closed.
  • Accumulators – Buffer vessels that store hydraulic oil under high pressure.
  • Piping and valves – Circulate and control the flow of hydraulic oil.
  • Control panel – Automates and monitors the press cycle.

During operation, the filter cloths are assembled between the plates with the sludge or liquid waste. The press closes as hydraulic oil under high pressure is pumped into the cylinders, forcing the plates together. This squeezes liquid out of the cloths while retaining the solids. The liquid is drained out and the filter cake discharged once pressing is complete.

Benefits Of Hydraulic Filter Presses:

  • High Plate Pressures – Hydraulic cylinders can generate very high pressures of up to 4,000 PSI, resulting in more efficient dewatering.
  • Continuous Operation – Hydraulic systems allow for non-stop pressing cycles for continuous throughput.
  • Automated Control – Fully automated sequence and cycle management for hands-free operation.
  • Quick Closing – Hydraulic cylinders can close plates very quickly for fast cycle times.
  • Easy Maintenance – Simple design with few potential failure points and easy access for service.
  • Gentler Compression – Hydraulic presses can apply pressure more slowly and evenly on heat-sensitive materials.

Uses Of Hydraulic Filter Presses:

  • Municipal wastewater treatment – Dewatering of sludge from primary and secondary clarifiers.
  • Industrial wastewater – Filtration of oily wastewater, chemical sludge, mining slurry and other industrial waste streams.
  • Food processing – Removal of liquid from fruit and vegetable pulps, paste and juice production.
  • Chemical manufacturing – Filtration of liquid residues, slurries and byproducts.
  • Pharmaceuticals – Recovering process water from wet cake residues.

Plate and frame presses use a crankshaft or screw mechanism to turn wedge-shaped clamping pieces that force the filter plates together. They generate lower pressures compared to hydraulic presses, resulting in:

  • Lower dewatering efficiency – Produces filter cakes with higher moisture content.
  • Slower cycle times – Due to lower clamping force, plate and frame presses take longer to close fully.
  • More manual operation – Require more user intervention to adjust pressure and start/stop cycles.
  • Potentially lower cost – Since hydraulic systems are more expensive initially.