Kobold VKG Viscosity Compensated Flowmeter / Switch

The KOBOLD flowmeters and switches model VKG have a spring-loaded float, which slides within a cylindrical measuring tube and has an integral orifice which is believed to be unique.

This and other design features means that it has for the first time become possible to create a flowmeter and switch which fully compensates for viscosity and to a large extent for density even with very low flows.

The float of these patented devices contain permanent magnets which actuate a potential free bistable reed contact mounted outside the flow thus ensuring hermetic separation between the medium and the electrical contact system. The contact is embedded within a height adjustable plastic housing to prevent damage to the contacts by mechanical action or aggressive atmospheres.

Viscosity Compensation

If the viscosity changes from 1 mm2/s to 540 mm2/s the indicated value is still accurate within ±5%, even with very low flows, for example, 0.1 l/min.

Comparable devices, for instance conventional float-type flowmeters, are, if the viscosity changes to such an extent, subject to indicating errors up to 2500%, especially with comparable low flows. Other instruments with spring-loaded floats, which are allegedly viscosity compensated, still produce indicating errors of more than 500% with the same change in viscosity and a flow of 0.1 l/min.

Thanks to the virtually perfect viscosity compensation and good density compensation the flowmeters and switches of the latest generation are suitable both for water and highly viscous oil, without having to change the scale and without readjustment.

This constitutes an extremely important advance especially in the critical area of oil lubrication circuits where measurement and switching are necessary at changing media temperatures.

  Another Article:



  • Lubrication circuits
  • Paper-making machines
  • Machine tools
  • Oil lubrication circuits
  • Hydraulics
  • Extruding plant
  • Printing press


Technical Details

  • Housing: aluminium, anodised (not media-contacted)
  • Screwed fitting:
    VKG-x1...: brass, nickel-plated
    VKG-x2...: stainless steel 1.4301
  • Float:
    VKG-x1...: brass, nickel-plated
    VKG-x2...: stainless steel 1.4301
  • Orifice: stainless steel 1.4310
  • Spring: stainless steel 1.4310
  • Magnet: oxide ceramic
  • Measuring glass: borosilicate glass
  • Seals:
    VKG-x1...: NBR
    VKG-x2...: FPM
  • Max. temperature: +100°C
  • Max. pressure: 12 bar
  • Installation position: any
  • Basic accuracy: ±4% of full scale (for a viscosity of 105 mm2/s)
  • Measuring error with change in viscosity: for changes in viscosity within 1...540 mm2/s the additional deviation is ±5% of full scale maximum
  • Viscosity range: 1...540 mm2/s

Download Datasheet: Kobold VKG Viscosity Compensated Flowmeter / Switch 

Reference : kobold.com