Patent Number: 041845145
Section: description

DETAILED DESCRIPTION OF THE BEST MODE CONTEMPLATED The invention involves a valve system composed of a valve combination or composite valve, which allows actuation or de-actuation of a device, such as a hydraulic cylinder or other mechanism, integral with or separate from the valve assembly, by means of three independent input signals combined in a function known as two-out-of-three logic. Representing the mutually exclusive actuation and de-actuation signals respectively by the logic symbols a, b, c, and a, b, c, the conditions for actuation and de-actuation can be expressed respectively by the Boolean equations ab+bc+ca+abc and ab+bc+ca+abc, or equivalent variations thereof. Using the input signals as independent and redundant actuation/de-actuation signals, a single signal failure, or failure of the corresponding valve assembly or valve set, will neither prevent the desired action nor cause the undesired action of the associated mechanism. In addition, it is possible to test the functioning of all system components during normal operational conditions without preventing desired action or causing undesired action of the associated mechanism, by inverting one and one only of the input signals at a time relative to the condition corresponding to the desired action. The simplified logic configurations, illustrated in FIG. 1, utilizing a minimum number of valves and no external logic circuits, result in greatly improved system reliability. The valve system of this invention applied to reactor protective systems, such as for example, scram actuation valves, meets the single failure criteria established for the control rod system of liquid metal breeder reactors, and, in addition, protects against spurious action in case of a single failure. This valve system also allows testing of the reactor protective system actuating valves during normal operational conditions without either causing or preventing the safety action as required by the reactor protective system. FIG. 1 illustrates three simplified logic configurations identified as Illustrations #1, 2, and 3, with the valve symbols, legends, and reference components identified therein, and described in greater detail hereinafter. An example of test sequence for tests in normal operational conditions with all tests starting from abc conditions, with reference to Illustration #1 of FIG. 1 is set forth in FIG. 3. FIG. 2 illustrates an embodiment of the physical configuration of the valve system for the logic configuration of Illustration #1 of FIG. 1, with corresponding references. With respect to the FIG. 2 embodiment, note the following: (1) a,b,c represents valve actuation/de-actuation forces, the valves being shown in the energized position; (2) a,b,c can be initiated by solenoids, pilot valves, or other mechanisms (pilot valves can use supply P if flow restriction R between P and C is provided). (3) Safety action corresponds with the de-energized condition of the valves; (4) The valve system is fail-safe in the sense that any leakages can only result in the safety action; (5) The 3-way valve section of b is designed for negligible bypass during change-over. The following specific forms of the Boolean equation referenced above constitute an equivalent definition of the utilization of a minimum number of valves (or switching functions) to perform a two-out-of-three logic function, as symbolically represented in Illustrations #1, 2 and 3 of FIG. 1: For Illustrations #1 and 2: EQU a.sub.1 (b.sub.1 +b.sub.2 c.sub.1)+b.sub.3 c.sub.1 Wherein: Prob a=Prob a.sub.1 PA1 Prob b=Prob b.sub.1 =1- Prob b.sub.2 =Prob b.sub.3 PA1 Prob c=Prob c.sub.1 PA1 Prob a=Prob a.sub.1 PA1 Prob b=Prob b.sub.1 =Prob b.sub.2 PA1 Prob c=Prob c.sub.1 =Prob c.sub.2 and a, b, c are independent actuation events. For Illustration #3: EQU a.sub.1 (b.sub.1 +c.sub.2)+b.sub.2 c.sub.1 Wherein: and a, b, c are independent actuation events. It has thus been shown that the present invention provides a valve system incorporating single failure protection logic wherein a valve combination or composite valve allows actuation or deactuation of a device, such as a hydraulic cylinder, by means of three independent input signals, a, b, c combined in a function known as two-out-of-three logic and expressed in the Boolean equation ab+bc+ca or equivalent variations of this equation. The valve system of this invention, when applied to reactor protective systems, meets the single failure criteria, and protects against spurious action in case of a single failure. This allows testing of the scram valves during operational conditions without either causing or preventing the safety action as required by the reactor protective system. While particular embodiments of the invention have been illustrated or described, modifications will become apparent to those skilled in the art, and it is intended to cover in the appended claims all such modifications as come within the spirit and scope of the invention.