In our first Viscometer Series blog, we discussed the “what” and “why” of viscometers — what they are and why they’re useful. In this blog, we’ll be going over the “how” — that is, how six different types of viscometers work. This list is by no means exhaustive; there are other types of viscometers out there, but not all of them are useful for industrial processes.
Here are the six types we’ll cover:
- Orifice viscometers
- Capillary viscometers
- Falling piston viscometers
- Rotational viscometers
- Falling ball viscometers
- Vibrational viscometers
#1 — Orifice viscometers
An orifice viscometer usually consists of a cup with a hole, through which the fluid flows. Viscosity is determined by timing how long it takes the cup to empty, and is measured in cup seconds. Orifice viscometers are easy to use manually, thanks to the fact that they’re simply dipped into the fluid being worked with — making them popular in painting industries. They include Zahn Cups, Ford Cups, and more.
#2 — Capillary viscometers
Also known as U-tube viscometers, capillary viscometers include the Ostwald and Ubbelohde variations. They’re straight-forward and simple to use, consisting of a U-shaped glass tube with two bulbs (one higher and one lower). Fluid passes from the higher bulb to the lower bulb through a capillary, and viscosity is measured by timing how long it takes the fluid to pass through the tube.
#3 — Falling piston viscometers
According to Wikipedia, falling piston viscometers were invented by Austin Norcross, which is why they’re also called Norcross viscometers. They function by drawing the fluid being measured into the piston cylinder while the piston is raised; the time it takes the piston to fall (time-of-fall seconds) due to the resistance of the fluid is used to determine viscosity. Falling piston viscometers are easy to use and simple to maintain, and offer long product life.
#4 — Rotational viscometers
Rotational viscometers measure viscosity by immersing a rotating spindle in the fluid to be tested. The amount of power (torque) required to turn the spindle indicates the viscosity of the fluid, and because rotational viscometers do not use gravity to function, their measurements are based on the fluid's internal shear stress.
#5 — Falling ball viscometers
Falling ball viscometers work in a similar fashion to falling piston viscometers. With this type of viscometer, a ball is dropped into a sample of the fluid being measured. The dimensions of the ball are already known, so viscosity is determined by timing how long it takes the ball (again, using time-of-fall seconds) to fall through the fluid via gravity.
#6 — Vibrational viscometers
Vibrational viscometers use a powered vibrating rod to measure viscosity. Different fluids are more or less resistant to vibrations depending on how viscous they are. Therefore, by measuring the dampening of the vibration, or by measuring how quickly the vibration of the viscometer degrades, viscosity can be determined. Vibrational viscometers are very popular thanks to the fact that they offer high sensitivity with no moving parts.
If you’d like more information on the best type of viscometer for your particular application, contact Saint Clair Systems.