# Zahn Cup

Last Updated: September 18, 2017

## Definition - What does Zahn Cup mean?

A Zahn cup is a device to measure viscosity that is frequently used in the paint and coating industries. It is a field instrument used to check a fluid's viscosity at the job site and is made from stainless steel with a small hole in its bottom center.

A Zahn cup is also known as a viscosity cup.

## Corrosionpedia explains Zahn Cup

Determining fluid viscosity is helpful in corrosion prevention. A highly viscous substance is less likely to cause corrosion because it has a lower flow rate of freely moving molecules to react with a metallic surface.

A Zahn cup is used to determine a fluid's thickness and flow resistance. This is done by introducing a sample of the fluid into a container with a hole in its bottom and recording the time it takes for the container to empty when draining the fluid through the opening. This time is called efflux time. The faster the fluid is drained, the less viscous the fluid is and vice versa.

There are five cup specifications, labeled Zahn cup #x, where x is a number from one through five. Large number cup sizes are used for high viscosity fluids, while low number cup sizes are used for low viscosity fluids. Using a Zahn cup, one can estimate the kinematic viscosity of fluid in centistokes.

• Zahn Cup #1: v = 1.1(t - 29)
• Zahn Cup #2: v = 3.5(t - 14)
• Zahn Cup #3: v = 11.7(t - 7.5)
• Zahn Cup #4: v = 14.8(t - 5)
• Zahn Cup #5: v = 23t

where v stands for kinematic viscosity and t stands for efflux time.

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