Filter Press Basics

Plate and Frame Filters- Plate and Frame was the original design, and is still used in some applications. The plate has a series of channels or pips creating high and low points. A cloth or paper filter media sits on top of the plate and filtrate passes through in the drainage area around the low points. The frame creates the empty space necessary for two plates to have a chamber between them. Cake accumulates within the chamber.

Recessed Filter Plates- Recessed filter plates eliminate the need for frames. The plate’s border is thicker than the high points of the drainage area, creating half of the chamber. The plate it touches creates the other half.

CGR: Caulked Gasketed Recessed Filter Plates- CGR plates are a recessed plate that has filter media caulked into place, normally in an octagonal configuration. It seal feed and drain holes with o-rings.

Here is a list of various configurations for filter media.

Drape Over cloth- Twice the length of a plate, a Drape Over Cloth sits on top of the plate and lays down each side. It can be held in place by small nubs, or “dog ears”.

Drape Over Paper- If the cake has a tendency to blind the filter media after one batch, a filter paper can be draped on top of the cloth. When the Filter Press opens to discharge, the paper is thrown out with the cake.

Duplex Cloth- Two separate cloths, each the size of a plate’s single face, are sewn to a gusset that covers the feed hole that runs through a plate. The top and side edges of the cloth either have grommets or Velcro to secure both sides of the cloth to the plate.

CGR Cloth- This Duplex Cloth is shaped to fit in the grooves of a CGR Plate. There is a rope sewn into the cloth’s border that gets caulked into each side of the plate.

Partially Formed Cakes Could Indicate Plugged Drainholes

As filtrate passes through the filter cloth it collects on the plate panel and drains into outlet holes on the corner(s) of the panel. The outlet holes have a channel that goes into the adjacent corner eye. The channel runs between the packing surfaces. Another function of the system is to allow the cake to be dried “blown down” by compressed air. The manifold piping at the end of the press can be valved to let air into the even-numbered plates pushing the liquid thru the cloth/cake/cloth out the odd-numbered plates. Sometimes particles of precoat and bodyfeed pass through the filter cloth and become trapped within the drainage channels plugging or partially blocking them. It can be easy to overlook, since you can’t see into the channels unaided.

Inconsistency Will Direct Your Troubleshooting

The plug likely occurs after a filter cloth tear or if the filter media is too permeable for the precoat and body feed used. The best time to check is when you notice a chamber has not formed a dry, firm cake as it usually does. If some chambers in the filter pack form great cakes and others form wet partial cakes, this could indicate which plates are plugged.