FAQ - About capillary viscometers and how to use them

How do you use a glass capillary viscometer?
You use a stopwatch to time the meniscus of the sample as it passes the timing lines. The sample flows under gravity.
What equipment do you need to use a capillary viscometer?
The viscometer itself, a viscometer holder for the viscometer, a constant temperature viscometer bath and a stopwatch. Depending on the type of glass viscometer, other accessories such as silicone tubing, a clamp, a stopper and a disposable syringe may also be required. For beginners, we supply ready packed viscometer operating kits for the different types of tubes.
What material are the PSL Rheotek viscometers manufactured from?
All PSL Rheotek Capillary Viscometers are made from low thermal expansion borosilicate glass tubing.
Why do I need a constant temperature viscometer bath?
Kinematic viscosity and temperature are inter-linked. Viscosity decreases, when temperatue increases. In order to state the viscosity of a sample in a meaningful way, it is necessary to include the temperature at which the viscosity was determined.
What if I just measure the sample at room temperature?
Then the result will represent only an approximation. At a nominal temperature. It is unlikely that repeatable flow times will be measured. Repeatability provides the user with an indication of the precision of the result obtained.
Do I need to use a thermometer?
Yes, a liquid in glass or digital thermometer is essential to verify the bath temperature. The thermometer should conform to the specifications set out in a test method (e.g. ASTM D445, IP71, ISO3104) and be calibrated e.g. by an ISO 17025 laboratory. .
Why do I need a chiller for the bath, when running it at 25 degrees C?
In order to make an accurate kinematic viscosity determination, it is essential to use a constant temperature viscometer bath. The tolerance band for temperature variation is typically +/- 0.02 degrees C. In order to achieve this level of temperature control, the bath heaters are not sufficient when the test temperature is close to ambient. Even with modern high tech heaters, there will be temperature spikes, which go outside +/- 0.02 degrees C. With external cooling, the spikes can be countered and the temperature stability achieved.
What material are the PSL Rheotek viscometers manufactured from?
All PSL Rheotek Capillary Viscometers are made from low thermal expansion borosilicate glass tubing
Why should I buy a PSL Rheotek branded viscometer?
The flow properties of the viscometer are determined by the interior surface of the glass. This should also be as smooth as possible in order to allow the sample to flow with the minimum of turbulence. Look out for smooth transitions between the different parts of the viscometer tube, when trying to assess the quality of a viscometer tube. At Poulten Selfe & Lee Limited, we take pride in manufacturing viscometers with superior flow properties.
I want to save money, can you sell me an uncalibrated viscometer?
Yes, we can. However, you will need to perform a calibration yourself, before you can use the viscometer tube. In order to perform the calibration, you will need to buy two viscosity reference standards from us and then conduct the calibration procedure as described in ASTM D446 or ISO 3105. Our preference is to sell you a capillary viscometer complete with an ISO 17025 certificate of calibration. This certificate will state the serial number of your tube as well as the viscometer constant of that specific tube to 4 significant figures. The calibrated viscometer is ready to use out of the box.
I need some help with finding the right viscometer for my samples, who can I talk to?
Send your question to us on the website chatline or give us a ring on +44 1621 787100. You are also welcome to contact us by email on sales@psl-rheotek.com
We have an audit coming up and have lost our calibration certificates, can you send us a replacement certificate?
Please contact us on sales@psl-rheotek.com or +44 1621 787100 and give us the serial number and the type of viscometer for possible reissue of certificates. If it is possible to reissue the certificate, there will be a fee for this service.
How long is the calibration of the viscometer valid for?
There is no universal recalibration interval for glass viscometers. Our recommendation is for users to validate the calibration constant by running a viscosity reference standard in the tube as and when Quality Control of the measurement is required. See https://www.psl-rheotek.com/psl-certified-reference-materials-kinematic-viscosity-1149-html.html to find the appropriate standard. If in doubt about the correct standard to use for this purpose, please feel free to contact us on sales@psl-rheotek. com or phone us on +44 1621 787100 for guidance.