Precoat: What It Is and How to Apply in a Filter Press

Often the effectiveness of an industrial filter press is judged based on the clarity of the liquid exiting the filter. Of course, for many industrial processes the flow rate, or how fast the liquid can be filtered, is critical as well. An ideal system filters a maximum amount of impurities while at the same time providing minimum restrictions on flow. Adding a precoat to filtration equipment can greatly improve the clarity of the output without sacrificing flow rate. It can also help prolong the life of the filter cloth.

What is Filter Press Precoat?

Precoat material is any porous substance that allows liquid to pass through. Common precoat materials are diatomaceous earth, perlite and cellulose. The viscosity of the liquid and the size of the impurities will determine how coarse or fine a precoat should be. The substance should be fine enough to mix with water but not so fine as to be impassable. It is the gaps within the substance that will provide much of the actual filtration.

For example, perlite is milled as lightweight bubble structures of various grades to produce specific flow characteristics. These structures utilize jagged interlocking structures to create billions of microscopic channels between particles to produce ideal flow rates across a variety of applications.

Perlite can be used as a filter aid for filter press precoat
Perlite is a lightweight filter aid and utilizes billions of microscopic channels between particles

How is Precoat Applied?

The precoat substance is usually mixed with water to form a slurry. That slurry is then passed through the actual filter medium until the water is clear and the precoat forms a filter cake on top of the filter cloth. The cake becomes the first point for input. Before the liquid to be purified hits any other filter press parts, it passes through the cake where the microscopic nooks and crannies between the precoat trap irregular particles while allowing the liquid to pass.

M.W. Watermark - Cellulose can be used as a filter press precoat
Cellulose can be used as a filter press precoat

How Does Precoat Benefit Filtration?

Precoat provides numerous benefits to the filtration process. Aside from improving the clarity of the filtrate by adding an extra filtration layer, it significantly prolongs the life of the filter cloths. Without a precoat, the impurities removed from the liquid can bind directly to the filter medium. This can blind or damage the filter medium and require cleaning or replacement sooner rather than later.

A precoat captures these impurities and creates a cake that breaks away cleanly from the filter cloth. An easier cake release can reduce the amount of filter cloth cleaning required, thus potentially reducing manpower requirements and increasing productivity.

M.W. Watermark - Along with other benefits, precoat allows for the filter cake to break away cleanly from the filter cloth
Along with other benefits, precoat allows for the filter cake to break away cleanly from the filter cloth

M.W. Watermark can recommend the best precoat option for your filter press application. Contact us to learn more.

About M.W. Watermark

M.W. WATERMARK wants to make a difference. We are passionate about the world’s water. We are innovative, focused on customer service and always try to exceed expectations. We are an environmentally conscious company with people who are energized, encouraged and inspired to make a difference on our planet by helping to keep our shared, finite water supply clean and usable for generations to come. We build amazing, custom water and wastewater treatment equipment. Together, we can make a difference.

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Precoat: What It Is and How to Apply in a Filter Press