Rotating leaf filters

Direct sluicing of all parts of the leaf is also obtained in some filters by the use of moving sluices (Fig. 14). 

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The rotating leaf filter (Figure 13) is particularly adapted for installations where the cake is very difficult to remove by sluicing. It is designed so that the leaves can be rotated with the sluice sprays on, allowing the entire area of the leaf to receive the full force of the sluice jet. If it is undesirable to mix the entire cake with sluice liquid, the bulk of the cake can be vibrated off the leaves first and removed from the filter shell, after which the remaining cake can be sluiced off. 

Horizontal Vessel, Horizontal Leaf Filters. These filters consist of a horizontal cylindrical vessel with an opening at one end (Fig. 19). A stack of rectangular horizontal trays is mounted inside the vessel the trays can usuaUy be withdrawn for cake discharge, either individuaUy or in the whole assembly. The latter case requires a suitable carriage. One alternative design aUows the tray assembly to be rotated through 90° so that the cake can faU off into the bottom part, designed in the shape of a hopper and fitted with a screw conveyor. 

Vacuum filters include the nulschc filter, enclosed agitated vacuum fillers, the vacuum leaf filter, the tipping pan filter, horizontal rotating pan filters, horizontal belt vacuum fillers, rotary vacuum drum lilters. and rotary vacuum disk filters. 

Vacuum Filters, Continuous Type.— Vacuum leaf filters which dipped into a tank or basin of the material to be filtered were the predecessors in point of time of the continuous rotating vacuum filters of today, practically the only type of continuous vacuum filter which exists today. The old leaf type of vacuum filter was intermittent in operation and one of two sets of operations were necessary with them (omitting for brevity the washing operations). In one set the leaves were stationary and after the tank or basin was filled suction was applied and a cake of the proper thickness accumulated. It was then necessary to run off the balance of the material in the tank or basin, reverse the air current and blow off and wash out the cake which had accumulated. After this was done fresh material was allowed to enter and the cycle of operations was repeated- In the other set of operations and better from a mechanical point of view the filter leaves with their accumulated cake were removed by machinery and after the cake was dropped the leaves could be returned to the tank for further solid accunaulation. 

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