What is the working principle of a diaphragm press filter, which is an enhanced filter press with an added elastic membrane, achieving squeezing and filtering?

The main difference between diaphragm press filters and ordinary box press filters is the addition of a semi-automatic diaphragm press filter—a composite rubber plate-type elastic membrane diaphragm—between the filter plates and filter cloth. During operation, upon completion of the feed, a high-pressure fluid medium can be injected between the filter plate and the diaphragm.

At this point, the entire diaphragm will swell and compress the filter cake, thereby achieving further dewatering of the filter cake, known as squeezing filtration. Initially, it involves positive pressure dewatering, also referred to as pulp feeding dewatering, where a certain number of filter plates are tightly arranged in a row under strong mechanical force, forming spaces between the filter plate surfaces.

The filter chamber receives the filtered material under strong positive pressure. Upon entering the chamber, the solid particles of the filtered material are retained by the filtering medium (such as filter cloth) to form a filter cake, while the liquid portion passes through the filtering medium and is discharged from the chamber, achieving the purpose of solid-liquid separation. As the positive pressure increases,

The separation of solid and liquid is more complete, but considering energy and cost, an excessively high positive pressure is not cost-effective.

After pulp dewatering, a pressure filter equipped with a rubber squeezing membrane compresses the medium (such as air or water) into the back of the squeezing membrane, pushing it to further dewater the squeezing filter cake, which is called squeezing dewatering. After pulp dewatering or squeezing dewatering, compressed air enters the filter chamber on one side of the filter cake.

Filter cakes remove liquid moisture from the other side of the filter cake through the filter cloth and out of the filter chamber, a process called air-drying. If both sides of the filter chamber are lined with filter cloth, the liquid can uniformly pass through both sides of the filter cloth and exit the filter chamber, achieving double-sided dehydration of the filter chamber. After dehydration is complete, the filter plate is released.

Mechanical pressing force is used to gradually separate the filter plates individually, and then the filter chamber is opened to unload the cake, completing a primary work cycle. Depending on the properties of the filtering material, the press filter can be set for feeding slurry dewatering, squeezing dewatering, blowing dewatering, or single/double-sided dewatering, with the aim of significantly reducing the moisture content of the filter cake.