The Marsh funnel is a simple device for measuring viscosity by observing the time it takes a known volume of liquid to flow from a cone through a short tube.
When the fluid level reaches the mesh, the amount inside is equal to the rated volume.
[3] While the most common use is for drilling muds, which are non-Newtonian fluids, the Marsh funnel is not a rheometer, because it only provides one measurement under one flow condition.
[4] μ = ρ (t - 25) where μ = effective viscosity in centipoise ρ = density in g/cm3t = quart funnel time in seconds For example, a mud of funnel time 40 seconds and density 1.1 g/cm3 has an effective viscosity of about 16.5 cP.
Some manufacturers supply devices which they call Marsh cones, with removable tubes with size ranges from 5 to 15 mm.