Abstract: A viscometer system to measure the viscosity at high shear rates of thick liquids such as coal slurries includes a vessel to contain the liquid and a nitrogen pressure source connected to the vessel to apply nitrogen pressure to the liquid. A valve operated by a pneumatic actuator, preferably controlled by a computer, controls the orifice through which the liquid flows. The valve includes a ball member having a bore therethrough which bore, upon actuation of the valve, is aligned with the input and output orifices of the valve block to permit flow of the liquid.