The air blowdown procedure is an important procedure to ensure dry filter cake. It is the most effective way to purge air out of the cake and any residual moisture in the filter press. This process is very similar to wringing out a sponge. The core air blowdown procedure outlined below has become the industry standard.
Once the diaphragm pump has dead-headed at the maximum feed pressure of 100 PSI, the Filter Press is full. Simply turn off the pump, and it is time to operate the air blowdown. Close the three ball valves on the outlet manifold, and close the center feed inlet ball valve.
The next step is to open the air blowdown valve and adjust the Air Regulator to about 35 – 45 PSI. As the air that enters the filter press through the upper left-hand corner of the manifold, the air is forced through the entire filter press. Because of the porting denoted by the one button or the three button plate, the air enters into the sludge chamber via the upper left-hand corner of the three button plates and exits via the bottom right-hand corner of the one button plates. This is why it is Imperative to Maintain the 1-3-1 Sequence of the plates. This process will push excess water out through the outlet manifold in parallel to each sludge chamber. This process allows for a better cake release and a drier filter cake.
Once the sludge blowdown process is complete, the filter press is ready to be opened so that the plates can be cleaned. Watch the video below to see a visual explanation of the process.
An older and obsolete way to doing the blowdown procedure was by using the Tee inline of the center feed pipe assembly and push air into the Filter Press to dry the cake. This method will push air into the same path as the slurry path.
The air passes through each chamber in series, but all air must pass through chamber one, before entering chamber two, then to chamber three, and so on. This method will do an excellent job of drying the sludge cake in the center feed pipe and the first few chambers, but is much less effected in drying the chambers at the end of the plate stack.
It is recommend to use the method described in above for the best results to dry the sludge.
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