Metering of compressed liquid with pressures ranging from atmospheric to the critical point

In the calorimetric investigation of heavy water, a metering valve capable of controlling liquid flow in the range of 0.5 to 5.0 grams per minute, with adjustments of 0.1 grams per minute, at a pressure up to 210Kg/cm2 is essential. Two commercial needle valves were tested to determine their suitability for withdrawing liquid within the required ranges of flow rate and pressure. These valves were found unsuitable due to the fact the flow rates were reproducible to only +-1 gram per minute at 70Kg/cm2, and at line pressures of 140 and 210Kg/cm2, the scatter increased two and three fold respectively. Difficulty in obtaining reproducible flow consistently was attributed to eccentricity of the needle and the dead space at the orifice. It would appear that eccentricity in turn is influenced by the magnitude of pressure drop across the orifice. A new design based on capillary action incorporating a flow resistor, and elimination of the dead space, has yielded highly reproducible flows