Zwag Filters (ANFD)

All-In-One Operation

The ZWAG filter has every tool needed for ultimate batch control and flexible operation — pressure and vacuum rated, agitation, replaceable filter media, temperature measurement and control, and contained discharge.

Fully Contained Solution

The fully contained and automated system protects operators and the environment. Spent cake containing hazardous substances can be efficiently and safely collected for disposal.

Custom Built to Exact Requirements

Agitated Nutsche filter dryers (ANFD) come in a wide range of sizes from 0.1m2 to 6m2 in surface area, and 50L to 12,000L in volume. Available in a variety of metals, ranging from Stainless-Steel to Hastelloy.

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Simplify Filtration with Steri Rentals!

Experience the simplicity of filtration firsthand with our rental filters. Operating Steri filters is a seamless process, yielding pure and exceptional results. We maintain a stock of ZWAG filter rentals, available in various sizes up to 0.5m2, with Hastelloy construction for added durability.

Our smaller ZWAG filters come skid-mounted, ensuring swift and effortless installation. Whether you’re engaged in laboratory work, pilot processes, or short-term production runs, these filters are perfect for your needs. Renting a unit from us is a cost-effective solution, that can be up and running within just a few days. Try our rental filters now and experience filtration made easy.

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Agitated Nutsche Filter: Design & Options

Each ZWAG filter consists of four main parts: The vessel, the agitator assembly, the bottom plate, and the side discharge port.


The largest part of the ZWAG filter is the vessel, which is cylindrical in form with an integral spherical top. The head closes the top of the vessel and supports the agitator assembly. The vessel is built in accordance with ASME’s latest standard and is designed for pressure filtration and vacuum cake drying.


The agitated Nutsche filter has a vertically oriented shaft, with horizontal blades mounted at the bottom. The agitator is motor driven and can rotate in forward and reverse. In addition, the agitator can move vertically, driven by hydraulic cylinders. The movement of the agitator allows for cake smoothing, reslurrying, and cake discharge.


The bottom plate supports the filter screen. The side discharge employs a sealed plunger port which can be manually or automatically operated.


Any accessory that your process requires can be designed in, right from the start. Steri offers custom made containment systems that can be fitted to any nozzle or to the side discharge as needed.



Anatomy of a ZWAG Filter

ZWAG: Industrial Filter Version of the Buchner Funnel

A comprehensive set of options and Steri’s applications experience assure your precise requirements are met quickly and easily.


The ZWAG Nutsche Filter is the industrial filter version of the “Buchner Funnel” except that it is designed to operate under vacuum or pressure. With numerous standard options and knowledgeable decision support from process experts, your ZWAG filter can be easily configured to meet your specifications. What’s more, you’ll benefit from the flow of design enhancements Steri has been bringing on line each year.


Various options are offered for all ZWAG Filter systems. Steri offers a complete range of off-the-shelf options. Coupled with the engineering applications know-how, we can configure your filtration system to your exact specifications. Choosing from a selection of standard components, that have been proven effective many times over, is a sure way to bring a customized filtration system on line quickly and without problems.




Your ZWAG filter is customer-configured to your specifications from standard components that have been proven effective many times over. It’s the surest way to bring a new system on-line quickly and without problems. With a complete range of off-the-shelf options plus engineering applications know-how, ZWAG filters by Steri can meet your special needs.

Zwag Standard 11 Zwag Standard 21 Zwag Standard 51 Zwag Standard 61



Size Surface Area Vessel Diameter Nominal Working Volume* Total Volume* Solid Volume Agitator Stroke
m2 m2 mm liters liters liters mm
0.25 0.27 600 150 189 75 300
0.50 0.49 800 300 352 150 300
0.75 0.76 1,000 450 572 225 300
1.0 1.13 1,200 1,000 1,190 500 500
1.6 1.77 1,500 1,600 1,930 800 500
2.0 2.26 1,700 2,000 2,510 1,000 500
3.0 3.14 2,000 3,000 3,680 1,500 500
4.0 4.15 2,300 4,000 5,030 2,000 500
5.0 5.31 2,600 5,000 6,430 2,500 500
6.0 6.15 2,800 6,000 7,800 3,000 500
8.0 8.04 3,200 8,000 10,630 4,000 500
10 10.17 3,600 10,000 14,020 5,000 500
12.0 12.56 4,000 12,000 18,010 6,000 500

*Vessel height can be extended to increase batch volume.

ZWAG Filter Driers. The Exact Solution

With ZWAG filter driers by Steri, you can depend on cost-effective performance from the most efficient manufacturer. These filter driers meet ASME or other industry standards and incorporate important functional enhancements designed by Steri engineers, each with a quarter century of hands-on ZWAG filter experience. With hundreds of systems in place worldwide, this technology has an extensive record of reliable performance across a broad range of applications. ZWAG filters are typically used as:


  • Pharmaceutical Filters
  • Vacuum Filter Driers
  • Petrochemical Filters
  • Food Industry Filters requiring FDA approval
  • Fuel and Oil Additive Filters
  • Hazardous Materials Filters
  • Precious Metal and other Catalyst Recovery Filters
  • High Solid Content Filters: up to 70%

Users appreciate the ZWAG filter’s compact design for performance excellence and simple, safe, reliable operation.


At a glance you will notice the superior design of ZWAG filters. Unlike most other filters, it’s a single, compact skid mounted unit with an uncluttered exterior designed with the operator in mind. Look beneath the clean exterior; you’ll see design excellence throughout the system that delivers a top quality filtrate efficiently, reliably and safely.


Built by Steri to the most stringent quality standards, ZWAG filters can stand up to the rigorous demands of operation with proven reliability in hundreds of applications around the world.



Safety Standards

When ordered with the optional gas-tight side discharge housing and customized seals, ZWAG filters can meet EPA standard for toxic vapor emissions. If standards are raised, modifications can be incorporated with relative ease and low cost.


Operators can safely perform all functions, including filter removal and replacement. All unnecessary handling and its associated risks have been designed out of the ZWAG filter with the integrated, fully automated vacuum drying system.


Zwag Applications Images

ZWAG Pressure Filter: Theory of Operation

The ZWAG Nutsche pressure filter is a single plate filter which is located at the bottom of the vessel. The single-plate filter allows build-up of a large amount of cake. This is beneficial for slurries that contain up to 70% solids.


During filtration, externally applied pressure forces the slurry downwards through the filter plate and the filtrate exits through a nozzle centered under the filter plate. Most filters rely, to varying extents, on the solids left behind on the filter surface to achieve maximum effectiveness, essentially using the solids, commonly called cake, to trap more solids. The thick cake that builds-up in a Nutsche filter can crack. Slurry will take the path of least resistance and flow through the cracks and not the cake, thus compromising filtration.


The ZWAG Nutsche filter uses a motor driven, rotating agitator inside the vessel to continuously smooth the cake and keep it evenly distributed. Simultaneously, hydraulically driven actuators move the agitator vertically to follow the growth of the cake.


Once the filtration process is complete, the cake can be washed and re-slurried by the agitator to achieve greater cake purity. The ZWAG pressure filter offers the flexibility of vacuum and/or hot gas drying to achieve the correct cake consistency. After the cake has been dried the side discharge valve is opened. The agitator rotation is reversed to push the cake out through the open valve.



  1. ALL-IN-ONE OPERATION: Sized for your production batch, your ZWAG is never a bottleneck.
  2. STIRRING FOR SLOWFILTERING PRODUCTS: After filling, continuous stirring just above the filter plate reduces filtration time.
  3. UNIFORMITY FOR QUICKFILTERING PRODUCTS:  The cake is layered with evenly distributed particles by progressively raising the agitator blades.
  4. PRESS FOR QUALITY: The agitator smooths down the cake to close cracks and create a uniformly permeable structure.
  5. WASH FOR QUALITY: Liquid is sprayed evenly over the cake for thorough diffusion washing, and can be easily re-slurried for greater purity.
  6. UNIFORM DRYING: Solids are kept moving over the heated bottom for speedy, complete drying.
  7. TOP DOWN DISCHARGE: The agitator blades scrape the cake through the side door from top to


Simple concepts, well-orchestrated, enhance performance:


  • Active agitation promotes homogeneous cake and speeds filtration
  • Washing and reslurrying eliminates impurities
  • The single plate filter speeds cleaning and/or change-over for successive batches of different products and eliminates cross contamination
  • Built-in vacuum drying reduces product handling

Its compact design makes one person operation easy and safe. Engineered and built to the most exacting standards, the ZWAG filter is a reliable, low maintenance workhorse.

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Frequently Asked Questions

Answer: Slurry is the generic term for the liquid product before undergoing filtration. In other words, the slurry contains the solids that are to be filtered out.

Answer: Filter cake, or just cake, refers to the solids that collect on the screen.

Answer: Steri recommends no more than 70% solids by volume.

Answer: Approximately 1⁄2 of the total interior volume of the ZWAG filter.

Answer: Yes, Steri Technologies ZWAG filter is a pressure Nutsche filter.

Answer: It filters mainly by using the cake itself as the filter medium. The single screen on the bottom dish is there only to start building the cake.

Answer: The agitator for the ZWAG filter has several uses. The agitator can be used to smooth the cake during filtration. This prevents fissures from forming in the cake. Fissures reduce the efficiency of filtration. The agitator can be used for mixing, washing, reslurrying, and drying. The agitator is also used to discharge the cake.

Answer: Yes, A suitable fluid can be pumped through the cake to aid in the removal of contaminants.

Answer: Cake discharge is very simply achieved by rotating the agitator and opening the side discharge port.

Answer: No. Various clean in place accessories are available for the ZWAG filter.

Answer: Yes. Steri Technologies has the experience to design and build a skid mounted system to your unique requirements.

Answer: Yes, the ZWAG filter can be portable. The largest size of portable units Steri Technologies’ offers is 0.6m2.