Typical Met-Chem Filter Press Operation Overview
Before the operator can begin filling the filter press, it should be confirmed that the plates are in the 1-3-1-3 button alignment. (This alignment is critical in the air blow-down process.) The unit then, needs to be completely closed and all valves should be in the appropriate position. This is accomplished by pushing all them in place by extending the hydraulic cylinder and attaining the recommended PSI. (4000 for automatic and 6500 for manual)
The incoming solution enters into the filter press via a diaphragm pump that is plumbed to the center feed pipe. When the plates are closed, the sludge accumulates in the cavity between the plates. The filtered water exits through the filter cloth and works its way through the stack alternating between the left upper and lower corners and right upper and lower corners, due to the porting differences on the on button and three button plates.
As the filter press fills, it is recommended to begin the feed at 25 PSI and to gradually amp up the pressure at steady intervals (25, 50, 75) to the maximum pressure of 100 PSI. Upon initial filling of the filter press, the pump will thrust at quick intervals. Conversely, as the press fills, the diaphragm pump will slow down significantly. The easiest way to tell that the press is full is, to listen to the diaphragm pump once it hits 100 PSI. It will dramatically reduce to 30 second to 1 minute intervals between thrusts or it may deadhead (stop) altogether. This is your indicator that the cycle is complete. Cycle time can vary from as little as 30 minutes to over 4 hours depending up on what is being filtered. When the filter press is full, all of the chambers will be filled with sludge.
Once the press is full, it is time to operate the air blow-down. When the three ball valves on the outlet manifold are closed, and the inlet center feed ball valve is closed, the air that enters the filter press via the small ball valve on the upper left hand corner of the manifold is forced through the 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 process will push excess water out through the outlet manifold. This process allows for a better cake release and a drier filter cake. Think of this a wringing out the sponge. This is why it is imperative to maintain the 1-3-1-3 alignment of the plates.
Once the sludge-blown-down process is complete, the filter press is ready to be opened so that the plates can be cleaned. To open the automatic filter press, reverse the air valve on the automatic hydraulic pump to allow the cylinder to slowly pull open the steel pusher plate. On the smaller manual units, release the ram pressure by simply opening the release valve and the pusher plate will retract via an internal return spring.
Now that the plates are released, pull apart the plates one by one. Most of the sludge will fall into the sludge dumpster on its own. A sludge spatula is provided on new Filter Presses to aide in the sludge removal. Sometimes it is necessary to scrape the residual sludge from the cloths. However, care should be taken to ensure that the cloths are intact and the o-ring and o-ring sealing surfaces are in position and free from obstructions.
Once all plates are clean, the filter press is ready to be closed hydraulically. The three outlet manifold ball valves should be opened, the center feed pipe should be opened and the pump is ready to be switched to the on position. Once the diaphragm pump is reset to 25 PSI, the unit is ready to resume the next fill cycle.