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Viscosity of a Fluid

Viscosity is the measurement of a fluids internal resistance to flow. It is usually represented in centipoise (cps) or poise (100 Centipose = 1 poise).

There are several categories of fluid viscosities which include:

Newtonian - at a fixed temperature their viscosity does not change through agitation or pumping. Water and oils are classed as newtonian.

Thixotropic - at a fixed temperature these reduce their viscosity with agitation or pressure increase. Ketchup and mayonnaise are good examples as they appear thick but pump quite easily.

Paste - some paste viscosity materials will seek their own level or flow slowly. The shorter the time it takes the easier they are to pump. Some do not seek their own level or flow at all and require pressure to move them. To reduce the viscosity of paste materials usually heat is applied. Special consideration needs to be given during the design to ensure they remain at the correct temperature in all stages of the process.


Common Material Viscosities at Room Temperature (Approximate)

 Material Viscosity (cps)
Water 1
Milk 3
SAE 10 Motor Oil 85 - 140
SAE 20 Motor Oil 140 - 420
SAE 30 Motor Oil 420 - 650
SAE 40 Motor Oil 650 - 900
Castrol Oil 1,000
Syrup 5,000
Honey 10,000
Chocolate 25,000
Ketchup 50,000
Mustard 70,000
Sour Cream 100,000
Peanut Butter 250,000