Filter presses separate solids from liquid in a slurry. They consist of a frame, a moving cylinder and a pack of plates that when pressed together form a series of chambers into which the slurry to be separated is pumped. The liquid in the slurry passes through filter cloths attached to the plates, while the solids are captured on the cloth. At the end of a filtration cycle, the plates open to discharge the solids in cake form.
Filter presses can be designed with several different types of plate opening systems, including:
- Standard opening
- Fast opening
- Instantaneous opening
- Pack opening
Manual plate opening systems require an operator to move the plates into the opening position to release the solid cakes.
Standard automatic plate shifting systems feature a mechanism that allows the opening of one plate at a time to release the solid cakes at the end of a filtration cycle.
When the filtration cycle has been completed, the hydraulic cylinder retracts and the mechanism moves one plate into the open position, allowing the solid cake to be discharged. Then, the mechanism moves the next plate into the open position, allowing that cake to fall. This process continues until all the plates have been moved into the open position and all the cakes have been discharged.
The standard automatic plate opening system offers greater access between the plates, allowing for faster cloth changes and ease of maintenance. It is ideal for thicker feed sludges and for incorporating an automatic cloth washing feature.
Fast opening plate shifting systems allow the filter plates to be opened one at a time in quick succession. At the end of a filtration cycle, the hydraulic cylinder retracts and the plate shifting device automatically moves the first plate into the open position, which allows the solid cake to be discharged. Then, the device quickly moves the next plate into the open position, until all the plates have been opened to release the cakes.
This fast opening system is similar to the standard opening system, only it opens the plates about three times quicker. Also similar to the standard opening system, the fast opening system allows for greater access for maintenance activities and for incorporating an automatic cloth washing feature.
Instantaneous plate transport systems allow all the filter plates to start to open when the hydraulic cylinder retracts. With this type of system, all the plates are connected with a chain. When the hydraulic cylinder retracts at the end of a filtration cycle, all the plates start to open to release the solid cakes.
This type of opening mechanism is ideal for smaller capacities. However, the type of opening system is largely dependent on the application, and the instantaneous transport system has been incorporated into some larger filter presses.
Instantaneous pack plate transport system allows for the opening of plates by packs of 10 plates. With this type of system, 10 plates are connected on a chain. When the hydraulic cylinder retracts at the end of a filtration cycle, the first pack of plates begins to open, one after the other. When the mechanism reaches the next pack of plates, these plate open, pressing the plates in the previous pack back together.
This type of opening system is ideal for small capacities or for applications requiring a small footprint, as the pack opening system reduces the space needed for all the plate to be open at once.
The best filter press plate opening system for an application depends on the material being dewatered. Slower opening systems are better for tougher or thicker sludges, as it allows more time for the cake to be released. Instantaneous and pack opening systems have smaller gaps between the filter plates when in the open position, so these have limited maintenance access.
In addition, certain opening systems allow for a plate shaking step to take place immediate after the cake is released to help remove any residue left on the cloth.
Testing the feed material and considering the overall goals of the application will factor heavily into determining the best filter press plate opening system (and/or if the plate shaking step is necessary) for an application.