Filter Press Basics

The Filter Press is one of the oldest filtration technologies still in use today. It was first developed in the mid 1800's. Unlike vacuum filters, which operate continually, the Filter Press and many other pressure filters run in batches. After a batch of slurry has run through the filter, and the filtrate drained out, it must shut down, open the filter pack, and discharge the solid cake.

The components of a filter press include the frame or skeleton and the filter pack. The filter pack consists of plates, sometimes frames, and filter media.

Frame Components

Stationary Head- The side of the frame without the closure system has a head that aligns with the filter pack. It is also known as the fixed head. It has a feed hole for the slurry to enter and drain hole for filtrate to exit.

Follower Head- The hydraulic ram pushes the follower head, or thrust head against the filter pack. There are no feed or drain holes on this head.

Closure System- A hydraulic ram is used to press the plates together and hold the filter together during operation. It creates a positive seal and prevents leaks.

Sidebars- The filter press plates rest on sidebars to keep alignment and bear weight.

Pump- Necessary to create the pressure which drives the process, it is usually a positive displacement pump or a centrifugal feed pump.

Extra Features- Newer models can include additional components like plate shifters, spray bars, and automatic cake dischargers.

Types of Plates

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.

Diaphragm Filter Plates- A recessed filter plate with a diaphragm. When solid cake has bridged its chamber, touching both plates, water is pumped into the diaphragm which swells. This swelling decreases the amount of space available, further dewatering the cake. Diaphragm plates are sometimes staggered with recessed filter plates, so that only one side of any given chamber will swell.

Industrial Filter Media

While cotton was the main filter media, in the 1960's synthetic fibers created better performing and longer lasting press cloths. National Filter Media  has a wide variety of fibers, and weave types.

Here is a list of configurations for 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 cake has a tendency to blind 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 side of the cloth to the plate.

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

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