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We have seen what are the fundamental parts that make up a plate filter press, and among these is the plate pack.
There are, as you have undoubtedly seen, various types and models of filter plates depending essentially on the sector we are in and the results we want to achieve in terms of dehydration and cycle time.
The first system historically used is the so-called ‘plates and frames‘ system.
The filter press using this type of plate is thus made up of a set of alternating solid elements (plates) and hollow elements (frames).
Between each plate and the adjoining frame are placed filter cloths or washable boards that form chambers into which the turbid suspension to be filtered is fed.
Assembly is achieved by pushing the pack consisting of frames, cloths and plates against a fixed end plate (called a fixed header) with a movable plate (called a movable header).
At the corners of each plate and frame or on special appendages arranged externally to them are holes which in the assembly form the turbid suspension feed channel, the wash water feed channel, the filtrate discharge channel and, if necessary, the wash water discharge channel.
Probably the most commonly used model is the recessed plate (or recessed), which is an evolution of the plate-and-frame system.
The frame seen in the previous point is integrated inside the plate, significantly improving the stability of the plate. This allows the use of recessed filter plates with much higher filtration pressure levels
The chamber filter plates are designed and constructed to allow the filtrate to be discharged either through traditional taps or through 1-2-3-4 manifolds (depending on the configuration) cut into the filter plates themselves and/or according to customer requirements.
The feed hole can be cut either in the standard position or in other dimensions
The recessed plate variant, where it is necessary to avoid drips during the filtration phase, is the so-called CGR, or leak free, or Gasket plates.
This model of chamber filter plate is made with ‘calafatate‘ cloth and with a perimeter O-ring seal applied. The latter allows for a good fit between the matched plates and enables optimal sealing during filtration.
Such plates are most often used in the pharmaceutical sector when it is very important to avoid drips or leaks.
The use of this technology instead of standard chamber plates generates higher productivity with shorter filtration cycles, higher cake dewatering and more efficient cake washing.
There are also membrane plates, when it is necessary to shorten the cycle time or when it is necessary to maximise the percentage points of dryness in the cake.
This is because the membrane has a real mechanical squeezing action on the cake (squeezing) which is carried out by inflating the membrane inside the plate with air or better still water.
Membrane plates can be coupled all together (Full Membrane) or next to a plate called a Companion.
The ‘FULL MEMBRANE‘ plate pack consists of membrane plates coupled together. The rubber membranes are fixed at the perimeter by means of a suitable channel, while at the feed hole, they are secured by means of steel flanges.
The optimal functioning of the membranes occurs during the squeezing phase of the cake due to pressure with air or water (recommended) under the membranes. Through special ducts in the plate body, the pressurised air or water expands the membranes, allowing them to further press the product to be filtered. Finally, the liquid obtained from pressing passes through the drainage holes at the corners, in communication with the outermost collectors.
The “MIXED MEMBRANE PACK” or “MIXED MEMBRANE PACK” is made up of a complete membrane plate and a plate that is combined called a Companion. This assembly is often used in special filtration processes with washing and/or drying stages. The operating procedure, however, is identical to the plates with the FULL MEMBRANE system.
