Patent Number: 044908369
Section: summary

This invention relates to a shut-off valve. More particularly, this invention relates to a shut-off valve which is controlled by the medium passing through the valve. Still more particularly, this invention relates to a vapor isolating shut-off valve for a nuclear reactor plant. As is known, nuclear reactor plants have been provided with various types of shut-off valves for controlling a flowable medium. In many cases, the shut-off valves have been controlled by the medium passing through the valve. For example, as described in Swiss Pat. No. 528,693, one known valve employs three double acting valves in an insert in a housing cover of the shut-off valve. This valve provides good service but has the disadvantage of a complicated construction which places high requirements on the fabrication of the valve. In addition, the valve has been expensive to manufacture. Accordingly, it is an object of the invention to provide a shut-off valve which can be simply constructed and which is reliable in operation. It is another object of the invention to provide a low cost shut-off valve for use in a nuclear reactor plant. It is another object of the invention to provide a low cost reliable shut-off valve which is controlled by the medium flowing through the valve. Briefly, the invention provides a shut-off valve having a housing which defines a valve chamber and a cover mounted on the housing and defining a cylinder. In addition, the valve has a valve stem which has a lid at one end and a piston at the opposite end which is slidably disposed in the cylinder. The piston divides the cylinder into a first chamber on one side of the piston and a second chamber on the opposite side of the piston. In accordance with the invention, various ducts extend through the cover to the respective chambers. That is, one duct extends from the first chamber through the cover to the outside, a second duct of fixed minimum cross-section extends from the second chamber through the cover to the outside and a third duct extends from the valve chamber through the cover to communicate with the first chamber. In addition, a fixed throttle means is disposed in the first duct within the cover while at least one control valve is disposed in the third duct within the cover. Further, each of the first two ducts connect to connecting lines which extend to a low pressure chamber. Each of these connecting lines also has a closing valve to selectively connect the respective cylinder chambers to the low pressure chamber. In addition, a third connecting line extends from the control valve for controlling of the control valve. One particular advantage of the valve construction is that, the use of the fixed throttle means in the duct from the first cylinder chamber eliminates the need for any valves in the cover. Further, due to the reduction in size of the sliding surfaces and the number of moving parts, a number of potential sources of breakdown are eliminated. This greatly increases the reliability of the valve. Additional features can be added to the valve in order to provide additional redundance, so that the valve can be switched into both end positions when not under pressure, even if the control line is leaking. For example, a non-return valve is disposed in the duct between the valve chamber and the control valve and a connecting line is connected to the cover to communicate with the first chamber for delivering an external pressure medium into the chamber. In addition, a closing valve is provided in this connecting line for controlling flow therethrough and a non-return valve is provided in the cover in communication with the connecting line in order to prevent a return flow into the connecting line. In addition, the connecting line leading from the control valve may also be provided with a closing valve for controlling the flow of the control medium therethrough. When used with a nuclear reactor plant, the connecting lines may extend through a wall of the plant defining a containment vessel (safety container) and which separates the shut-off valve from the low pressure chamber. In this case, the closing valves for the connecting lines leading to the cylinder chambers and the control valve may be positioned adjacent to and within the wall of the plant and may be remotely controlled. In addition, a non-return valve can be provided in the fourth connecting line leading to the non-return valve in the cover. The closing valve for this line may also be disposed outside of the wall. In use, if a pipe breaks, no contaminating medium can escape from the containment vessel, through the lines for operating the shut-off valve. The valve may also be provided with a redundant control valve in the third duct as well as with a cylindrical insert for mounting the two control valves within the cover in coaxial relation to each other. In this way, the control valve is protected from blockage by asymmetrical deformation resulting from thermal expansion. These and other objects and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawing wherein: