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Unlike commercial turbine and Venturi-type sensors, which are flow intrusive and prone to high error rates, NASA's new flow sensor technology uses an optical technique to precisely measure the physical characteristics of a liquid flowing within a pipe. It generates a reading of the flows density, which provides a highly accurate mass flow measurement when combined with flow velocity data from a second optical sensor. NASA's sensor technology provides both a void fraction measurement, which is a measurement of the instantaneous gas/liquid percentage of a static volume and a quality measurement, which is the fraction of flow that is vapor as part of a total mass flow. It also provides a direct measurement of the gas/liquid concentration within the flow, making it suited for real-time measurement of multi-phase flows. The technology was originally developed to accurately determine the flow rates and tank levels of multi-phase cryogenic fuels used on various NASA vehicles including the Space Shuttle and in ground-based propulsion testing. It can also be used for a wide range of gas/liquid ratios, flows with complex cross sectional profiles, flows containing bubbles or quasi-solids, and essentially any liquid, gas, or multi-phase flow that can be optically characterized. Because it is insensitive to position, the new technology also has potential for use in zero-gravity tank level sensors.

The VARR valve has been designed to provide a variable-size aperture that proportionately changes in relation to gas flow demand. When the pressure delta between two chambers is low, the effective aperture cross-sectional area is small, while at high delta pressure the effective aperture cross-sectional area is large. This variable aperture prevents overly restricted gas flow. As shown in the drawing below, gas flow through the VARR valve is not one way. Gas flow can traverse through the device in a back-and-forth reversing flow manner or be used in a single flow direction manner. The contour shapes and spacing can be set to create a linear delta pressure vs. flow rate or other pressure functions not enabled by current standard orifices. Also, the device can be tuned to operate as a flow meter over an extremely large flow range as compared to fixed-orifice meters. As a meter, the device is capable of matching or exceeding the turbine meter ratio of 150:1 without possessing the many mechanical failure modes associated with turbine bearings, blades, and friction, etc.