| 摘要 |
An operably automatic valve assembly for being received in a cavity of a short drill string subassembly, preferably a kelly saver subassembly, for preventing mud spills when the kelly assembly is disconnected when adding additional sections of drill pipe. An eccentric butterfly disc across the valve opening is biased closed by suitable air spring action. Fluid pump pressure in excess of the bias pressure opens the disc and telescopes closed the air springs located on either side of the valve housing within suitable pockets. A stop on one air spring and not on the other causes a slight twist to the disc as the disc reaches its full open position and eliminates any operating flutter of the disc. Pressure within the stem in excess of the closing bias pressure provided by the air springs keeps the disc open even in the presence of back fluid pressure. Stopping the drilling fluid circulating pump subjects the valve to a sufficiently lower pressure to allow the air spring to close the disc against mud weight of the mud trapped in the kelly assembly. The disc is made frangible for being destroyed in the event a wire line tool has to be run through the valve opening.
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