Filter Cloths 101 & FAQ
M.W. Watermark manufactures all of our filter cloths in our facility in Holland, Michigan, U.S.A.
By manufacturing cloths in-house, we are able to utilize our laser-cutting tables and experienced sewing staff to provide fast turnaround times and ship direct – all while maintaining a quality product and the best service for our customers.
Watch the videos below to learn more about our filter cloth manufacturing processes. (Scroll to bottom of page for “how-to” videos on cloth installation).
The Role of Filter Cloths and Cake
It can be easy to look past the cloth’s true role in a process, believing that the cloth does the filtering, when in reality most of the filtering gets done by the cake itself forming in the recessed chamber. Understanding this, it becomes easier to improve the press operation and to adjust to problems and changes.
Filter cloths are the front line of a filtering process, serving as the the foundation needed to build a filter cake.
Learn More on Our Blog…
“Filter Cloths for Large Filter Presses: Mining and Energy Industry Spotlight” – Read more.
“Precoat: What It Is and How to Apply in a Filter Press” – Read more.
“A Filter Press Is a Depth Filter: The Role of Filter Cloths and Cake in the Dewatering Process” – Read more.
“How Filter Cloth Media Selection Affects Performance” – Read more.
“How to Know When to Replace Your Filter Cloths” – Read more.
“Options for Cleaning Your Filter Cloths” – Read more.
Filter Cloth 101: Terms
When a cloth’s porosity is hindered, and the cloth no longer allows the filtrate to flow.
These fibers are single, smooth extrusions and have high strength. “Mono” cloths have excellent cake release characteristics and resistance to blinding. This style has low particle retention. To provide a layman’s visual, this material is very similar to fishing line, and has higher tensile strength.
Multi-filament or “Spun” Fibers
Compared to the “Mono” fiber above being similar to fishing line, “Multi-filament” threads, think “yarn”. The fibers vary in size, but are grouped together in a single strand. The main benefit of multi-filament fibers is better particle retention.
This blend of both types of fibers is extremely popular, as it encompasses benefits from both types of thread, in particular, strength from the mono- fiber, and particle capture from the multi-fiber.
CGR vs. NG
“CGR” is an acronym for “Caulked, Gasketed, Recessed chamber.” CGR plates should provide a virtually leak-proof filter press. Cloths for these plates are octagon shaped, with a caulking rope or cord sewn into the edge of the cloth. “NG” means “Non-Gasketed.” The NG cloth is faster and simpler to install, though the trade off is that occasionally some dripping can happen when using NG cloths.
A latex coating can be added to the edges of an NG cloth to help prevent leaks.
“Cubic Feet per Minute” is the measure of flow or air permeability of the cloth media.
The most common are plain, twill, and satin.
- Twill Weave adds a diagonal rib or line to the weave, adding strength at the expense of a little stability. Cake release is average.
- Satin Weave is popular for its excellent cake release and excellent resistance to blinding.
- Plain Weave is average in strength, cake release, and stability.
Filter Cloth Materials
Filter cloths come in many different materials including polypropylene, polyester, cotton, nylon, felt, and many other materials. The most common filter material:
- Polypropylene: Polypropylene is the most common material. It has strong resistance to acid and alkali alike. A satin finish added to the fiber can allow for easy cake release. “PP” is a top choice for a wide range of applications, and is by far the most popular material. Latex borders can be applied to a non-gasketed cloth to provide a better seal under pressure.
- Nylon: This durable fiber is often chosen for its long life in the face of abrasives. Though higher in cost, nylon blends offer such durability that the higher cost can be justified by longer service life.
- Polyester: Often chosen when sustained operating temperatures are over 180 degrees, or when oxidizing agents are present.
Filter Press Cloth FAQ
Q: What is the micron rating of this cloth?
A: Cloth does not have a micron rating. Cloth air permeability, or porosity, is measured using the Frazier Air Permeability scale. The unit of measure is cubic foot per minute, or CFM, which is a cloth permeability measurement. The ranges of CFM are wide, and are determined by the thread counts and weight of a fabric.
Q: How can I make the installation of gasketed cloths faster?
A: Depending on your press operation, changing cloths can be labor intensive and difficult, and often the down-time is problematic. One solution is to purchase a cloth air hammer (P/N 4000-0235, $242.00 ea) which greatly speeds the filter cloth installation.
Another solution is to get additional plates to “swap out” between cycles, so you can replace cloths in the extra plates while the press still runs at full capacity.
A third solution is to send plates with old cloths to M.W. Watermark, and have our experienced staff clean the plates, change the cloths & gaskets, and ship them back. Usually this service can be done within 2-3 days in our facility.
Q: My cloths are wearing out at the center feed neck/corner feed. What can I do?
A: You can ask for either a latex reinforced cloth, or in an extreme case a rubber barrel neck to protect against wear in those areas.
Q: How can you test a new cloth for our application?
A: First, contact our process experts for a recommendation. Once a cloth type is selected, we recommend that you run a test on a shortened stack in your press. This can be done by moving the “end plate” to cut off the stack so that just the test cloths are used. To protect the plate at the end of the stack, use a back-up plate to support the tail plate. Take care to monitor the pressure, as it will fill fast, and run the press with the shortened stack. You should see results quickly.
Q: Can I clean the cloths with a pressure sprayer?
A: You can, if care is taken to not get too close with the spray tip, or use the sprayer in anything other than a “fan” spray pattern. Keeping spray pressure under 1000 PSI is recommended as well.
Q: Can we clean cloths with chemical cleaners?
A: Polypropylene cloths can handle both caustic and acidic solutions. Nylon, polyester and felt cloths need special consideration and may be damaged from these chemicals. Contact M.W. Watermark about your specific situation.
Q: How can I extend my filter cloth life?
A: Filter cloth life is shortened by chemicals, mechanical wear, abrasion, and blinding. We can help to determine whether your cloths are being attacked by your process chemicals. Mechanical wear can be reduced by using a more durable cloth. Blinding often comes from “slamming” sludge into the press. Consider an Auto Feed Pump Control System, or an AFPCS to automatically and gradually increase pressures. “Pre-coating” a press with DE or similar products can also add substantial life to cloths. The coating protects against wear and minimizes blinding.
M.W. Watermark offers:
- Gasketed (CGR) and non-gasketed (NG) cloths
- Hook-and-loop material and latex additions to improve sealing on non-gasketed cloths
- Custom patterns and styles
- Fast lead times: Many standard cloths are stocked for quick shipping
- Filter cloth removal and installation
Visit our Filter Cloths main webpage to learn more and download our Filter Cloths Product Guide.
Need accessories for your filter press, including spatulas, cloth installation tools or bulk bags? Download our Aftermarket Accessories Sheet.