A leading manufacturer of instrumentation for kinematic viscosity, PSL Rheotek holds 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. The on-site calibration laboraotory is accredited to ISO 17025 by UKAS. 



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.


First accreditation

In 1989, PSL was the first company to be accredited by the United Kingdom Accreditation Service (UKAS) for viscometer calibration and testing.The next move of the company was in 2000 when it re-located to its present factory in Burnham-on-Crouch, Essex. By this time, the company was greatly in need of new and more specialist space for electronic assembly of instruments, as well as glassblowing, calibration and testing.In 2000, PSL established a master viscometer scale in its new laboratory.


The company manufactures its own master viscometers, and a primary viscosity scale was established using the step up procedure from a primary master viscometer and standard. At the same time, PSL compared its new scale with other National Laboratories in Europe and the USA, including the PTB in Germany, in order to meet the requirements for ISO 17025. Today, every calibration PSL performs is just one step away from its master scale. PSL prides itself in providing the very best uncertainties of measurement for viscometers used for both manual and automated measurement purposes.


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.


PSL Rheotek

In 2010, the management decided to merge the two in-house brand names of PSL and Rheotek. The purpose of this, was to send a clear signal to the marketplace, that Poulten Selfe and Lee Ltd is the leading manufacturer of both manual and automated viscometers for precision measurements.


Polymer Testing

PSL maintains a polymer viscosity testing laboratory. The laboratory is on hand to evaluate the total variability of a customer’s polymer samples. A report is prepared by our specially trained technicians and this is typically used as the basis for discussion on how customers can improve their measurement accuracy.

The PSL Polymer Testing Laboratory also prepares a range of polymer standards. These are designed to verify the user’s ability to determine common values such as relative, inherent, specific and intrinsic viscosity.


Technical & Service Support

PSL has established a wide base of users throughout the world. Whilst some customers are more than proficient to look after their own instruments, PSL is on hand to provide further technical and service support. Typically, on-site service is provided by dedicated RHEOTEK service engineers or by authorized agents.



PSL established RHEOTEK USA, Inc in 1999 to sell and provide support to RHEOTEK instruments throughout North America. Based in Indiana, the company is well located to support customers throughout the States. Local sales representatives support the company on the West coast, as well as Texas, Mid West and the North East.


The Company Today

Poulten Selfe & Lee Ltd  maintains its position as a privately owned company specializing in the measurement of viscosity of petroleum products and polymers.