Abstract: A metering device for delivering a fluid at a predetermined rate and a mixing device for delivering first and second fluids at a predetermined rate mixed in a predetermined ratio. The devices include a flexible fluid bladder having flexible inlet and outlet conduits, a flexible inlet conduit clamp tube overlying the inlet conduit, and a flexible outlet conduit clamp tube overlying the outlet conduit, all of which are positioned between a pair of abutting rigid plates having matching voids. As each of the clamp tubes are pressurized, the inlet or outlet conduits over which they lie are collapsed to prevent fluid flow therethrough. A valve system is provided for alternating between a fill cycle wherein the outlet conduit clamp tube is pressurized and the inlet conduit clamp tube is depressurized to allow fluid to flow into the fluid bladder, and a discharge cycle wherein the inlet conduit clamp tube is pressurized and the outlet conduit clamp tube is depressurized to allow fluid to flow from the fluid bladder.

Abstract: An apparatus for monitoring the performance of a reverse osmosis water purification system. The resistivity of the water, and hence its dissolved ionic material concentration, is measured at both the inlet and product ports of the system by resistance sensors forming two legs of a wheatstone bridge. The bridge is powered by two oppositely phased AC signals. The output of the bridge drives a phase sensitive null detector which generates a null error signal. After thresholding, the null error signal actuates a bidirectional meter to indicate the degree of bridge unbalance, as well as to actuate an alarm circuit if the outlet resistance falls below a predetermined value, thereby indicating an unacceptable degree of purification. The bridge is balanced by a potentiometer forming a pair of bridge legs on each side of the potentiometer wiper. Thus, when the bridge is balanced, the setting of the potentiometer wiper corresponds to a given ratio of inlet resistance to outlet resistance.