Method and apparatus for controlling the flow of a liquid, and viscosity measuring method therefor

Apparatus for controlling the flow of a liqud from a supply pipe to a receiving device, to assure that only a preselected liquid is permitted to flow to the receiving device, comprising:

• a normally closed main valve controlling the flow of the liquid from the supply pipe to the receiving device;
• a sampling receptacle for receiving a sample of the liquid from the supply pipe;
• a stirring device to be immersed in the liquid when received in the sampling receptacle;
• an electrical motor for rotating said stirring device;
• and a control circuit for testing a sample of the liquid in said sampling receptacle by measuring the load current of the electrical motor while rotating said stirring device, comparing the measured load current with a reference value of load current for the preselected liquid, and automatically opening said main valve to permit the flow of the liquid from the supply pipe to the receiving device only when the measured load current matches the reference value for the preselected liquid.