Procedures for Flow Cup Calibration

Purpose and Application

Viscosity cups remain the most important quick and simple method to measure the consistency of fluids in the laboratory and in production. Viscosity Cups are, however only suitable for lower viscosities and not for highly viscous substances such as pastes etc. The most accurate results are achieved with fluids within the range complying with Newton’s Law.

Design Details

Viscosity cups consist of a hollow cylinder, which terminate in a nozzle in the bottom. Excess fluid is collected in the gutter channel.

Measuring Principle

The viscosity is established in terms of the time in seconds in which a precisely controlled volume of fluid flows out through a nozzle of the viscosity cup.

Test Procedure

The general test process is described as follows:

1. Level stand using spirit level
2. Place cup in the stand or in temperature control vessel
3. Close nozzle
4. Fill with fluid
5. Wipe off surplus material across the edge of the cup with a glass plate, and close cup with finger or glass plate.
6. Open nozzle
7. Pull off glass plate horizontally and simultaneously set stop watch in motion
8. At the first break off in the fluid flow stop watch and note time

Further details are described in the various standards.  It is to be noted that the cups are only calibrated for the specified ranges and for the specified flow times.

In addition, it is particularly important to follow the instructions concerning temperatures carefully. Only a small difference could lead to considerable changes and hence wrong measuring results.

Of particular importance is to understand that it is not sufficient just to make sure that the fluid is at the right temperature: the Viscosity cup must also be at the correct temperature, if necessary by surrounding it with a temperature control cover so that the intended temperature is maintained. It is also essential to check the temperature of the jet of fluid coming out of the cup, since it is at this point that the actual temperature of the fluid being measured can be established. Comparable reproducible results are only possible if the temperature is kept fully under control.

Care and Maintenance

After making a measurement the flow cup particularly the nozzle must be carefully cleaned without, however, using any hard or sharp implements. If remnants of fluid (paint) remain in the nozzle the diameter of the orifice will be altered and the cup can no longer give accurate measuring results.

Calibration Oils supplied by the Quality Control Lab are traceable to the National Bureau of Standards / NIST.