Vacuum Filtration FAQ

In typical Liquid-Solid Separation applications, when should Vacuum Filtration be used and when should Pressure Filtration be employed?

If continuous separation is required, vacuum filters are preferred to batch-type pressure filters. Large Particle Size Distributions favor Vacuum Filtration while fine Particle Size Distributions favor Pressure Filtration. If the Cake Resistance Value is low, vacuum filtration will perform well. If the Cake Resistance Value is high, pressure filtration will work best.

If the process has significant variability in terms of PSD (Particle Size Distribution), TSS (Total Suspended Solids), and SG (Specific Gravity), then vacuum filter will be troublesome. Pressure filters are more forgiving with upstream changes.

If achieving low cake moisture is essential, pressure filters will outperform vacuum filters, in most cases.

Read our Filter Press FAQs or Belt Filter Press FAQs to learn more about pressure filtration.

Particle Size Distribution (PSD), Total Suspended Solids (TSS), and Specific Gravity (SG)  are the three primary process variables that dictate which type of vacuum filter will work best.

If cake washing is required, Horizontal Belt Vacuum Filters are preferred with a high wash to solids ratio. Rotary Drum Vacuum Filters are preferred with a low-medium wash to solids ratio. Disc Vacuum Filters are not used in cake washing applications.

In all cases, we recommend first checking the liquid ring vacuum pump seal water so it is at the correct flow, pressure, and temperature.

In a Rotary Drum Vacuum Filter, increasing drum speed, increasing vat level, or increasing feed pump can increase production rate.

In a Horizonal Belt Vacuum Filter, increasing belt speed or increasing feed pump will increase production rate.

In a Disc Vacuum Filter, increasing disc speed, increasing vat level, or increasing feed pump will increase the production rate.

The upper limit of the production rate for each machine is the rising cake resistance value at thicker cakes.

The Micronics Engineered Filtration Group has an In-House Vacuum Filtration Lab that can help you optimize filtration in your process. Contact us to learn more about how our filtration experts can help you optimize your process.

A trade off exists between drying/dewatering time and cake formation time. You can achieve a lower moisture filter cake by adjusting the settings of manual filtrate control valves to place more vacuum on the dry zone than on the cake form zone. Slowing the speed offers more dry time.

Reducing cake thickness will reduce the cake resistance value and result in a lower moisture filter cake.

There are a few ways to determine if the filter cloth on a vacuum filter is blinded and needs replacement. If the cake is not uniform, or is thick in sections but thin or non-existent in other sections, it may be blinded. Similarly, if the filter cloth will not form a consistent filter cake it may be blinded.

A cloth may also be blinded if pressure washing of the filter cloth does not regenerate its permeability. Visually impaired filter cloth with small holes or a filmy appearance also indicates the cloth is blinded.

If your cloth is blinded and you need new filter cloth, please contact us so a filtration expert can assist you. We are experts in helping you extend the lifetime of your filter cloth as well as ensuring you are using the right filter cloth for your process requirements and operating conditions.

There are a few ways to improve the quality of filter cake discharge.

  1. Adjust the discharge assembly doctor blade closer to the filter cloth, to within 1/8 inch.
  2. Increase discharge assembly cloth wash flow and pressure, and possibly temperature.
  3. Pressure washing the filter cloth may improve the quality of filter cake discharge but should be employed on durable fabrics only.
  4. Increasing the vacuum air flow to the dry/dewatering zone may improve the quality of filter cake discharge. Increase the cake thickness until it results in too high a cake resistance value.

To improve cake washing, we recommend that you first verify that all cake wash bar nozzles are not plugged, and the cake wash flow and pressure are correct. Additionally, verify that the fan-pattern nozzles are in fact overlapping. Controlling the cake’s thickness optimizes the cake wash acceptance rate.

To improve cake washing, you might consider adding an additional cake wash zone or spray bar to the machine.

Increasing the temperature of the cake wash solute is another tool to improve cake washing. We recommend using “hot” water for cake washing, i.e., demineralized or RO Permeate or low conductivity wash water, at high temperatures. Our technical experts are happy to work with you to further optimize your cake washing.

The Micronics Engineered Filtration Group offers Replacement Parts for Vacuum Filters, including spray bars, nozzles, scraper blades, and more.

Contact Our Experts

Micronics Is Your Trusted Partner for Total Engineered Filtration Solutions. We offer end-to-end solutions from Filter Media to Industry-Leading Filtration Equipment, to Spare Parts & Accessories, to On-Site Field Services and In-House Laboratory Services. Whether for your Filter Press, Belt Press, Leaf Filter, Vacuum Filter, or Baghouse, you can count on Micronics’ deep industry and applications knowledge for the right engineered filtration solution to meet your needs. We look forward to working with your team.

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