A leading brand of instrumentation for kinematic viscosity, PSL Rheotek instruments manufactured by Poulten Selfe & Lee Limited, hold a strong position on the world market in this field. Test results from PSL Rheotek instruments are used in product specifications, quality control and process optimisation by process industry across the world. Lubricants, fuel oils, plastics, cellulose and biopolymers are among the products measured.


Poulten Selfe & Lee Ltd, (PSL) was established in 1850. Starting as just Poulten, Selfe & Lee were later acquired, with the company “Poulten Selfe & Lee Ltd” being incorporated in 1931.

Originally located in the East End of London, the company moved to purpose made works in 1947, being the first factory to be built on the Russell Industrial estate in Wickford, Essex. The company became a significant employer, with an extensive glassblowing shop as well as graduation and calibration laboratories.

In the early 1950’s the company set up a dedicated Viscometer Calibration Laboratory. A joint project with the National Physical Laboratory (NPL) and the Shell Petroleum Company enabled the company to develop a way of routinely calibrating glass capillary viscometers. The company also manufactured the special Shell pattern viscometers, and these were supplied to petroleum laboratories all over the world. During its history, PSL has manufactured nearly every type of glass capillary viscometer, as specified in British Standards (BS), DIN, ASTM, GOST and ISO.

RHEOTEK Instruments

In the early 1990’s, PSL commenced to develop techniques for automating the measurement of viscosity, using glass capillary viscometers, NiR detection methods, as well as other pneumatic and electronic systems to control the automation of the viscosity method.

The new instruments were given the name “RHEOTEK” in order to differentiate them for the “PSL” glass instruments.

Poulten Selfe & Lee has developed the range of RHEOTEK instruments in-house, building up a dedicated team of engineers and application specialists.

Development work has normally been carried out in conjunction with customer application requirements. Some examples include:

  • RUV Viscometer sýstems for measuring the kinematic viscosity of petroleum products
  • Polymer viscometer (RPV) – for dilute solution viscosity measurement of a wide range of polymers.

RHEOTEK automated viscometers can be split into two categories – petroleum and polymer. Whilst there are common features between the ranges, each instrument is developed and optimized for their respective applications.