Abstract: A variable impedance circuit for use in an external circuit is disclosed. The impedance value is selected by an external circuit. The variable impedance is generated between two terminals which are accessible for connection to external circuitry. The impedance provided between these terminals is determined by a control circuit responsive to electrical signals coupled to the control circuit. An internal register in the control circuit stores a value which specifies the impedance between the two terminals. The stored value is copied into a programmable nonvolatile read-only memory in response to a first predetermined electrical signal. Similarly, the value stored in the read-only memory is selectively copied into the internal control circuit register in response to a second predetermined electrical signal.

Abstract: An apparatus and method of supplying feedwater to a forced flow boiler or the like as described. A positive displacement pump having a plurality of discrete pumping elements is arranged to pump feedwater from an inlet to the boiler. The pump includes bypass valves which, when open, disable the pumping action of an associated pumping element. Control means responsive to the demand for water in the boiler are arranged to disable a selected number of the pumping elements so that the rate of water supplied by the remaining elements, if operated continuously, would just exceed that required. The control means is further arranged to disable at least one of the remaining pumping elements on a periodic basis so that the ratio of time that the element is enabled to the time for one period multiplied by the water flow rate supplied by said element, if operated continuously, equals the difference between the total demand for water and the rate supplied by the pumping elements enabled on a full-time basis.

Abstract: A pressurized hot fluid washer includes a combination pumping unit driven by a closed hydraulic system which applies driving impulse forces to an interlocked liquid pump member and a fuel pump member. The liquid pump and fuel pump are hydraulically interlocked so that when liquid is not being discharged through the cleaning gun, the fuel will definitely be stopped. A static pressure line senses the pressure downstream of the liquid pump and transmits the pressure to one end of a spring biased by-pass spool valve. At a predetermined liquid pressure, the spool valve will sequentially close a hydraulic conduit first to deactivate the fuel pump and then open a by-pass conduit to deactivate the liquid pump member. Thus, both the fuel pump and the liquid pump will be automatically stopped, for example, when the cleaning gun is not being used. In addition, a differential area piston is provided in the hydraulic system between the by-pass spool valve and the fuel pump.