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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.
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. Please contact Shane in the link on the Navbar if you would like to ensure that the cloth your filter uses is the best one for your application.
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.
Filter Press Wear Parts
National Filter Media can supply the following wear parts for any make or model:
- Plate and Frame Cloths (Drape over cloths)
- Recessed Press Cloths
- Plate and Frame Papers (drape over papers)
- Custom manufactured cloth
- Caulking hammer kit
- Caulking cord
- CGR Cloths
National Filter Media’s Filter Press Specialist, Dave Sperry created this thorough troubleshooting guide.
- Duplex cloths are seeing premature failure. Either the rubber neck for the feed hole tears the seam or the cloth gusset inhibits flow. NFM’s Two-Ply Hypalon Barrel Neck solves both issues.
- Caulking in CGR cloths with a mallet and dog bone is time consuming and tiring. NFM’s caulking hammer makes installation a breeze.
Filter Press with Recessed Plates Creating a Partially Formed Cake?
Check out this article if your recessed plate filter press has some chambers that either have wet cakes or chambers that won’t fill or dewater. This has been a problem in industries ranging from wine to antifreeze reclamation. This is likelier to occur if precoat and bodyfeed are used to aid in cake formation.
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.
Count on NFM to Fix Your Recessed Plate Filter Press!
Why is this bypass occurring? Contact Shane and he’ll put your local NFM territory manager in touch with you. We’ll dig in to the specifics of your process to ensure that both your body feed selection and the filter media are the best choice.
Contact A Technical Expert
Call us today to learn how our expertise can provide you with the filtration solution you’ve been looking for. We’ll build a relationship with you that will last well beyond the sale, providing you with unparalleled customer service and technical filtration expertise.