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One of the distinguishing features of a high-performance filter press – other options being equal – is the filtrate discharge system.
The filtrate discharge in filter presses is precisely the way in which the filtered liquid is conveyed and collected.
Lo scarico del filtrato nelle filtropresse è appunto il modo con cui il liquido filtrato viene convogliato e raccolto.
The first system, and also the most economical, is the bottom side discharge, or also called gutter discharge (which is normally open).
With this type of drain, the filtrate exits from the bottom of the plate (from both sides or just one side depending on the model) and through a bend is conveyed into an open tray used precisely for collecting the filtrate.
In some cases, downstream of the bend there is also an exclusion tap that serves to intercept the wire in case it is broken (you can see the turbid-coloured filtrate discharge indicating that cloth has broken).
With this solution it is true that it is possible to immediately identify which cloth is damaged, but it is also true that I do not exploit the filter press to its full potential.
With the drain in closed manifold and flood valve (also known as drain valve) I can in fact increase the efficiency of filtration.
When there is no explicit need to use the side drain, it would be better to avoid it, because by installing the tap at the bottom of the plate, during the first stages of filtration the filtrate comes out from below without first filling the chamber completely.
The solution with a flood valve is different: with a suitable valve we cause flooding of the plate pack:
This option provides for a filtrate discharge in a common closed manifold: the 4 outlet holes (or 2 in smaller machines) of the filtrate are combined in one manifold. A valve (called a flood valve) is placed in one of the ducts in the lower part, the opening of which is controlled by a PLC. This opening occurs when the pressure usually reaches 3/4 bar. Before 3/4 bar, the filtrate only flows out of the 2 upper holes, so that the filling of the filtration chamber is ensured. By doing so, the pre-ring is properly formed, which greatly aids the final separation of the cake.
Once 3 bar pressure is reached, the valve is actuated and the filtrate can flow out of all 4 holes.
Needless to say, the increase in filtration efficiency with this device is tangible, moreover, again for better filling of the plate pack I have a distribution of pressures inside the plates that is significantly better