Marsh Funnel Viscometer Model MLN-3

The Marsh Funnel Viscometer MLN-3 is a rugged, easy to operate instrument that is used for making rapid, on the spot measurements of drilling mud viscosity. The Marsh Funnel readings are only general measurements, but the frequent reporting of the Marsh Funnel Viscosity will alert the mud engineer to sudden changes in the mud viscosity that could require corrective action.

The Marsh Funnel Viscosity is the ratio of the speed of the mud as it passes through the outlet tube (the Shear Rate) to the amount of force - the weight of the mud itself - that is causing the mud to flow (the Shear Stress). Marsh Funnel Viscosity is reported as the number of seconds required for one quart of mud to flow out of a full Marsh Funnel.

In addition to the Marsh Funnel, this procedure requires a container to collect a mud sample, a graduated container to receive the mud as it flows out of the funnel, some way to measure elapsed time (preferably a stop watch), and a centigrade or fahrenheit thermometer or measuring the temperature of the mud sample.

Procedure

1. Collect a fresh mud sample.
2. Hold the funnel erect with a finger over the outlet tube, and pour the mud into the funnel through the screen until the mud level reaches the bottom of the screen (The screen will filter out the larger particles that could clog the outlet tube). NOTE C When the Marsh Funnel is filled to the proper level it holds more than one quart of mud.
3. Quickly remove the finger from the outlet tube, and at the same time, begin timing the mud outflow.
4. Allow one quart (946 cc) of mud to drain from the Marsh Funnel into a graduated container.
5. Record the number of seconds it takes for the quart of mud to flow out of the funnel, and report this value as the Marsh Funnel Viscosity. Also record the temperature of the mud sample in degrees F or C.

Care of the Funnel

1. Clean and dry the funnel thoroughly after each use.
2. Take special care not to bend or flatten the brass outlet tube at the bottom of the funnel. The Marsh Funnel Viscosity readings are computed using the exact diameter of this outlet and if the outlet is distorted the readings will be inaccurate.

Calibration check

Periodically check the calibration of the Marsh Funnel by measuring the viscosity of fresh water. The funnel is dimensioned so that the outflow of one quart (946 cc) of fresh water at a temperature of 70‘±5‘F (21‘±3‘C) is 26±0.5 seconds. If the Marsh Funnel checks out of calibration, it should be cleaned again, using a pipe cleaner, to make sure that there is nothing obstructing the outlet. If the Marsh Funnel continues to give an incorrect reading for fresh water after cleaning then the outlet tube probably has been bent out of shape and the funnel should be replaced.