How It Works


VLM mixes.
Other systems stir.

The VLM Mixer uses vertical linear motion technology to create a distinct flow pattern that produces highly efficient mixing.

Due to the combined effects of oscillating velocity and pulsating pressure waves, true isotropic mixing keeps all grit in suspension with 100% axial flow patterns and low energy consumption.

Most conventional mixers, on the other hand, use a circular motion to “stir” liquid. This requires a large quantity of power, as well as expensive digester cleaning protocols to remove scum and sediment build-up.


The innovative cam-scotch-yoke electric motor system operates above the tank.


The shaft transfers the up-and-down motion to the hydro-disk.


The hydro-disk is the heart of the mixing process, producing 100% axial mixing through momentum exchange.


The energized currents continually flow, eliminating surface scum and floor sediment.


The oscillating velocity and pressure waves enhance mass transfer to produce a homogeneous mixture.

Specifications for the main VLM Mixer configuration

Customization through
CFD Modelling

The Computational Fluid Dynamics (CFD) process is available to meet unique mixing needs.

The frequency (or oscillating speed), the stroke length, and the size and positioning of the hydro-disk control the force and velocity of the liquid core. By varying these four elements according to each tank’s configuration, we can meet the mixing needs of a wide variety of operations.

The CFD process allows for:

  • Modelling and analysis of variety of tanks
  • Proper mixer sizing for optimal results
  • Pre-set features to ensure efficient mixing at any liquid level

CFD Input Data for VLM Mixer


Parameter Value Comment
Diameter (ft)90-
Overall tank height (ft)52Cylindrical tank plus bottom
Maximum sludge elevation (ft)38From bottom of cylinder
Conical height (ft)8.5From bottom apex
Cylindrical height (ft)40Total wall height
Maximum tank capacity (gal)2,000,000Sludge bulk volume


Parameter Value Comment
Sludge inlet diameter (in)(2) 6ӯTWAS & thickened PS lines
Sludge Inlet Pipe Elevation above bottom wall (ft)8Changed from 16.11 ft


Parameter Value Comment
Sludge outlet diameter (in)6ӯ-
Sludge outlet pipe elevation (ft)2162.512.5 below bottom of the wall


Parameter Value Comment
Bulk density (kg/m3)1,034.2Typical value
Viscosity (cP)265-
Sludge flow rate (gpm)92.6Estimated


Parameter Value Comment
Density (kg/m3)2,650Grit particles (worst case)
Solids content (% wt)3.5Average grit and organics
Solids particle size (μm)100-150Typical grit size (worst case)

Tracer Injection

Parameter Value Comment
Bulk density (kg/m3)1,034.2Same as sludge
Viscosity (cP))265Same as sludge
Concentration (mg/L)7.5Lithium Chloride solution
Flow rate (kg/s)3.48-
Injection duration (s)15-
Elevation of injection location (ft)8At sludge intake


  Parameter Value Comment
Point 1Circulated sludge out, elevation(ft)2175.5Radial distance 44.5 ft
Point 2Primary sludge out, bottom cone (ft)2163Tank axis
Point 3Sampling port 1 elevation (ft)2212.5Radial distance 40 ft
Point 4Sampling port 1 elevation (ft)2198.5Radial distance 40 ft
Point 5Sampling port 1 elevation (ft)2176.5Radial distance 40 ft
Point 6Sampling port 2 elevation (ft)2212.5Radial distance 10 ft
Point 7Sampling port 2 elevation (ft)2198.5Radial distance 10 ft
Point 8Sampling port 2 elevation (ft)2176.5Radial distance 10 ft

VLM Disk

Parameter Value Comment
Outer diameter (in)96-
Inner diameter (in)64-
Stroke length (in)20Changed from 16 inch
Oscillating frequency (cpm)32Changed from 30 cpm
Bottom of stroke location (ft)20Above bottom tank cone
*Geometry for the 90 ft diameter digester tank

Tracer Concentration at Probe Locations

Tracer concentration at sample probe locations. Results indicate that after 1 hour 50 minutes of mixing the sample probes depict asymptotic behavior of the tracer approaching mean concentration value “MEAN”. The asymptotic trend of all probe concentrations indicates complete mixing. (The MEAN concentration corresponds to 6.0E-5).

Percentage of Tracer Distribution in Tank Volume

The histogram chart indicates that about 90% of the tank volume is fully mixed. The 90% mixed volume corresponds to the tracer concentration of 5.762E-5 (which is very close to the mean value of 6.0E-5). Also, the results indicate that about 8% of the tank volume has tracer concentration of 3.601E-5.

Two-dimensional view across a vertical plane parallel to the sludge intake. Zones of highest velocity (max 0.86 m/s) correspond to the hydro-disk location. The average tank (bulk) velocity is about 0.012 m/s and is distributed nearly uniform in the whole tank. This uniform velocity creates isotropic turbulence resulting in uniform mixing when coupled with oscillating pressure waves.

Two-dimensional view across a vertical plane at 5 meter high from tank bottom. The velocity is clipped at 0.012 m/s which corresponds to the tank mean (bulk) velocity. The flow pattern indicates that the mean velocity is uniformly distributed across the tank diameter, consequently providing uniform mixing of the whole tank.


The Installation

The VLM Mixer is a top-entry mixer that can be installed in both new and existing tanks. When compared with conventional mixing systems, installation is simple and costs are low.

Installation features:

  • A single mixer can be installed in one day or less
  • Additional piping or core drilling is not required
  • Optimal for easy, quick and low-cost retrofits
  • Existing structures require few or no changes prior to installation

Frequently Asked

Q. How is the VLM Mixer able to operate with such low power requirements?

A. For a VLM Mixer, the energy required for a given mixing performance (such as in an Anaerobic Digester) is only a small fraction of the energy that would have been consumed in conventional mixers. This is because the VLM Mixer produces a purely radial/axial circulation, whereas rotary mixers (such as impellers or turbines) produce rotary fluid motion.

What circulation pattern does the VLM Mixer produce in a large tank?

A. When the reciprocating disk is located at the centre of a large tank, a circulation pattern is produced with a central up-flow above the disk and a central down-flow below the disk. The liquid circulates outwards through the tank and returns inwards towards the reciprocating disk. Two circulation loops are formed when the disk is located half-way in the fluid level. However, if the Hydro-Disk is moved closer to the bottom of the tank, a single circulation loop is formed.

Q. How does the hydro-disk produce its unique flow pattern?

A. The reciprocating hydro-disk which generates an upward-moving liquid core on each downstroke, and a downward-moving core of liquid on each upstroke. These high-energy cores (macro-eddies), which are continuously produced, dissipate into the liquid and create a steady bulk circulation in the tank. The tank volume can be several orders greater than the volume swept by the drive disk. Although the hydro-disk is oscillating, the majority of the liquid in the tank does not oscillate, but instead circulates in response to the directional movement from the hydro-disk.

Q. Can a VLM Mixer be installed on existing tanks?

A. Yes, the VLM Mixer can be installed on existing tanks, with any digester cover that can withstand the additional loads of the mixer. These can include concrete covers, radial beam steel covers (either floating or fixed) and truss covers. The mixer is designed for the center of the digester, so prior to installation, we verify the location of the gas collection piping, gas handling equipment and any other interior piping. Also, one should verify that the digester cover has sufficient structural strength to withstand the mixer’s loads.

Q. How often is digester cleaning required after the VLM Mixer is installed?

A. With conventional mixers, scum and solids gradually build up in digesters. Over time, tank volume is reduced, mixing becomes less effective, and the entire digester needs to be shut down, emptied and professionally cleaned. Because VLM Mixers™ generate axial mixing, the continuous flow keeps grit in suspension and prevents sediments from accumulating. Companies with VLM technology report that these cleaning protocols, and the costs associated with them, are rendered almost completely unnecessary.

Q. What kind of maintenance can be expected?

A. The shaft and hydro-disk are constructed out of stainless steel and have no mechanical parts below the mounting flange that would require regular maintenance. This means that the shaft and hydro-disk do not need to be removed from their mounting location for maintenance. Rather, all the components that will wear are easily accessible in the drive head, above the cover and outside the tank.

See the VLM Mixer in Action