ntroduction to the operating principle of diaphragm filter press

The diaphragm filter press is a type of filter press that features an elastic membrane between the filter plate and the filter cloth. During use, after the feeding process is completed, high-pressure fluid or gas medium can be injected into the diaphragm plate, causing the diaphragm to expand and compress the filter cake. This process, commonly known as filter pressing, enhances solid-liquid separation efficiency.

The membrane filter press has been widely used in various industries requiring solid-liquid separation. It is considered an upgraded alternative to the ordinary box filter press due to its higher processing efficiency, lower moisture content in the filter cake, and better adaptability to different materials.

The key difference between the diaphragm filter press and the ordinary box filter press is the addition of two layers of elastic membranes on both sides of the filter plate (with composite rubber membranes being a single integrated structure). During operation, after feeding is completed, a high-pressure fluid medium can be injected into the diaphragm plate.

When used for sludge and sewage treatment, the moisture content of the filter cake can be reduced to below 60%. Compared to traditional box filter presses, the solid content can be doubled, significantly reducing transportation costs. The filter cake can even be directly incinerated in power plants, achieving resource utilization by converting sludge into usable material and wastewater into purified water. This makes it an effective replacement for the traditional box filter press.

Operating Principle of the Diaphragm Filter Press

The process starts with positive pressure dehydration, also known as slurry dehydration. In this phase:

A series of filter plates are tightly arranged under strong mechanical force, forming sealed filtration chambers.

The slurry (material to be filtered) is pumped into the filter chambers under high pressure.

The solid particles in the slurry are trapped by the filter medium (such as filter cloth), forming a filter cake.

The liquid portion is expelled through the filter cloth and discharged.

As positive pressure increases, solid-liquid separation becomes more efficient.

Squeeze Dehydration Process

After initial slurry dehydration, the filter press—equipped with a rubber squeeze membrane—performs secondary dehydration:

A compressed medium (such as gas or water) enters behind the squeeze membrane, pushing it forward to further compress the filter cake, removing additional moisture.

Air Drying (Wind Dehydration)

Once the slurry is dehydrated or squeezed, the system can perform air drying:

Compressed air is introduced into one side of the filter cake.

The air passes through the filter cake, carrying moisture from the opposite side out through the filter cloth.

If both sides of the filter chamber are covered with filter cloth, the liquid is evenly discharged from both sides, ensuring maximum dehydration efficiency.

After dehydration, the mechanical pressure on the filter plates is released, and the plates are gradually pulled apart to discharge the filter cake.

Depending on the characteristics of the material, the filter press can be equipped with different filtration methods, such as:
✔ Slurry feeding
✔ Membrane squeezing
✔ Air drying (single or double-sided blowing)

The ultimate goal is to minimize the moisture content of the filter cake, optimizing efficiency and reducing post-processing costs.