If the time is less than this the tube is probably enlarged by erosion, if more it may be blocked or damaged, and the funnel should be replaced. If water is used, the time should be 26 +/- 0.5 seconds. In American practice (and most of the oil industry) the volume collected is a quart. A 10-mesh screen is fixed near the top across half the cone. It consists of a cone 6 inches (152 mm) across and 12 inches in height (305 mm) to the apex of which is fixed a tube 2 inches (50.8 mm) long and 3/16 inch (4.76 mm) internal diameter. A Marsh funnel is a Marsh cone with a particular orifice and a working volume of 1.5 litres. The Marsh Funnel īased on a method published in 1931 by H.N.Marsh, a Marsh cone is a flow cone with an aspect ratio of 2:1 and a working volume of at least a litre. Marsh Funnel top view showing the mesh through which drilling fluid is poured to retain particles which would not pass through the orifice. The time in seconds is recorded as a measure of the viscosity. To take the measurement, the finger is released as a stopclock is started, and the liquid is allowed to run into a measuring container. When the fluid level reaches the mesh, the amount inside is equal to the rated volume. The liquid to be measured is poured through the mesh to remove any particles which might block the tube. In use, the funnel is held vertically with the end of the tube closed by a finger. Other cones with different geometries and orifice arrangements are called flow cones, but have the same operating principle. It is standardized for use by mud engineers to check the quality of drilling mud. 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. Marsh Funnel: plastic with brass flow tube and mesh
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