First of all, it should be pointed out, even if it may seem trivial and superfluous, that the acid washing of the cloth is performed when there is no sludge inside the volume of the machine. It is therefore an out-of-cycle phase and it is usually the user who decides (intervening from the HMI) after how many cycles or hours of use he wants to carry out the acid washing (based on the level of incrustations reached by the cloths).

This wash works by flooding; Once the moment has been decided in which to carry out the acid washing of the cloths, the machine will close the plate pack, through the hydraulic cylinder mounted in the rear fixed head, under pressure.
At this point, through special automatic valves usually placed in the line of the lower filtered discharge pipes, hydrochloric acid is introduced into the volume of the machine. Filling of the filter press ends when the acid starts to flow out of the upper filtered discharge manifolds. The filling signal of the machine can be obtained through a level probe or through a timer inside the PLC.

Now all the automatic valves remain closed allowing the acid to interact with the filter cloths, scraping them.
The acid is made to react with the cloths for a time that can be established and adjusted using the appropriate parameter in the HMI.
Once the end of the acid washing has been established, the acid discharge valve is opened and, by gravity, the acid flows out of the machine.
Depending on the type of process to be performed, the acid can be re-sent to the same tank from which it was taken, or sent to a second tank from which it will then have to be refined and reused.