New approach to maintaining liquid flow rate stability in national primary standard

Abstract

New approach to maintaining liquid flow rate stability in primary standard calibration facility is proposed. It takes advantage of primary standards with constant static head and does not require high-altitude installation of the pressure tank. To implement the proposed approach, the pressure tank is installed in the water pipeline of the Standard between the pumping station and the measurement pipeline. Pressure in the air cushion above the liquid in this tank is maintained automatically, as well as the liquid level in the pressure tank. It has been demonstrated that in order to stabilize the flow, it is sufficient to employ the controlling impacts in the form of air supply/withdrawal and adjustment of variable-frequency drives of pumps. The air is supplied and withdrawn from the air cushion by a set of critical flow nozzles, which are activated depending on the absolute pressure of air in the cushion. The liquid level in the tank is controlled by adjustment of variable-frequency drives of pumps based on the information on the hydrostatic head (liquid level) in the tank. Experimental study of the flow stabilization system of the National Primary Standard GET 63–2017 for mass and volume of liquid, mass and volumetric flow rates of liquid (Kazan, Russia) confirmed high efficiency of the proposed approach.