A low-noise plug valve in which a plug is rotatably mounted in a valve body to control the flow between an inlet port and an outlet port, the improvement comprising:
means in said plug defining a through passage, wall means in said plug defining one side of said through passage,Plug Valves said wall means having an outer surface defining a clearance space with the adjacent inside wall of said valve body and movable into partial flow-blocking relation with said valve body outlet port in partially closed positions of said plug,API Cast Steel Valves and means in said plug wall means defining a plurality of openings leading from said passage into said clearance space providing for throttled flow therethrough into said clearance space in partially closed positions of said plug. This invention relates to a low-noise plug valve and more particularly to a plug valve which may be operated in a throttled or partial flow blocking condition at substantially decreased sound levels as compared to conventional plug valves.CHECK VALVES The problem of valve noise has been the subject of investigation, and valves have been designed for the purpose of reducing the generated noise. The problem of noise, in a plug-type valve, is difficult to control because of the straight through flow design defined by the plug through passage. Such designs have introduced high noise at medium to high pressure drops, due to flashing and cavitation.
Flashing occurs when the pressure downstream of a control valve, or a restriction, is less than the upstream vapor pressure, so that part of the liquid changes to the vapor state. Accordingly, bubbles of vapor are formed. Downstream, due to pressure recovery, the vapor bubbles rapidly condense back into the original liquid. As this process continues, the bubbles form, grow and collapse downstream, thereby causing conventional cavitation. Not only is this the major source of noise in a valve, it is also a source of physical injury to valve components, by reason of the shock waves which are created by the collapsing of the large cavitation voids or bubbles. The invention is directed to a low-noise plug valve, and more particularly to a plug valve in which the plug component is provided with a control grid or wall defining one side of the passage, which wall is movable into partial flow-blocking relation between the valve inlet and the valve outlet. The wall is formed with a plurality of openings therethrough. The openings provide for a controlled throttling or diversion of the flow through the valve in the partially throttled or partially closed position of the plug. The plug at the flow control wall is relieved with respect to the valve in that a clearance space is defined between the grid or wall and the tapered plug opening in the valve body. The openings through the wall are aligned generally to the direction of flow between the valve inlet and valve outlet ports, so that flow of liquid through the plug passage may be diverted for flow through the valve outlet with a minimum of change of direction. Also, in partially throttled positions, the valve outlet port is unblocked with relation to the through passage through the plug, so that particles of material which could not pass through the openings, may proceed through the plug and into the outlet port. A particular object and advantage of the plug-type control valve of this invention is that it provides decreased flashing and cavitation, and thereby substantially reduces noise. Further, the plug valve design is one which can take relatively high pressure drops across the valve without inducing cavitation and flashing at such high pressure drops.

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