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Jet pump slip joint with axial groovesJet pump slip joint with axial grooves description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080031741, Jet pump slip joint with axial grooves. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001]This application is a non-provisional application claiming priority to provisional patent application Ser. No. 60/834,929 filed Aug. 2, 2006. BACKGROUND OF THE INVENTION [0002]1. Field of the Invention [0003]This invention relates generally to tubular jet pumps used in various industries to transport and/or circulate cooling liquid in heat-generating systems, such as nuclear reactors and hydroelectric generation systems. More particularly, this invention relates to means for uniformly controlling the leakage flow rate through a slip joint to thereby eliminate detrimental vibration in the slip joints of such jet pumps. [0004]2. Description of Related Art [0005]Pipes, tubes and cylinders are used to transport a variety of fluids, such as water, oil, and liquid chemicals in various industries including the nuclear industry, the electric power industry, such as for internal components of heat exchangers, the hydroelectric power generation industry, the petroleum industry, such as piping used in refining of oil, the chemical industry, such as the piping used in processes for making chemical based products, and the space industry, for spacecraft heat exchangers and other similar devices. [0006]Oftentimes, the piping components in such industrial systems are submerged in the same fluids which the piping is transporting. As an example, the tubular components that make up a jet pump assembly are housed within a nuclear reactor pressure vessel and reside in the fluid that the jet pump is used to transport. That is, the jet pump assembly transports the cooling water to the reactor core, but the jet pump assembly itself is also submerged in that same fluid. The pipes and tubes that comprise such submerged systems are supported within the surrounding structures by support or restraining apparatus. The surrounding structures (e.g., a reactor vessel) may be of a different material, such as carbon steel (reactor pressure vessel), than the material that the piping is made of, such as stainless steel (jet pump assembly) with different thermal coefficients of expansion. In order to accommodate the different amounts of axial thermal expansion that will occur between the tubes and the surrounding support structure at higher operating temperatures, designers install slip joints along the piping to minimize thermal stress build up within the tubes. [0007]Recent engineering experience has shown that if a sufficient pressure gradient exists across these slip joint interfaces, the connecting tubular components may incur detrimental flow-induced vibration, and failure results from either excessive wear or fatigue of the piping material or support/restraining apparatus. One exemplar system where such failure occurs is the jet pump assemblies used in nuclear reactors. [0008]A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends with typically a bottom head and a removable top head. A top guide typically is spaced above a core plate within the RPV and a core shroud, typically surrounds the core and is supported by shroud support structure. The shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. A space, or annulus, is located between the cylindrical reactor pressure vessel and the cylindrically shaped shroud. A plurality of jet pumps are positioned within the annulus. An typical example of such reactor cores is disclosed in U.S. Pat. No. 4,675,149 to Perry, et al. [0009]In a BWR, the hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. Examples of such jet pump assemblies are disclosed in U.S. Pat. No. 6,587,535 to Erbes, et al. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and supported against opposing contacts within the restrainer bracket by a gravity-actuated wedge and two set screws. The restrainer brackets support the inlet mixer by attaching to the adjacent jet pump riser pipe. [0010]The lower portion of the jet pump, known as the diffuser, is coupled to the inlet mixer by a slip joint. This construction facilitates the disassembly and repair of the jet pump. The slip joint between the jet pump inlet mixer and the jet pump diffuser collar has about a 0.015 inch diametral operating clearance which accommodates the relative axial thermal expansion movement between the upper and lower parts of the jet pump and permits leakage flow from the driving pressure inside the pump. A limited amount of leakage may be beneficial to clean the joint of corrosion product build up. [0011]Excessive leakage flow, however, can cause oscillation motion in the slip joint, which is a source of detrimental vibration excitation in the jet pump assembly. The slip joint leakage flow rate can increase due to single loop operation, increased core flow, or deposition of jet pump detritus, or crud, in the slip joint. Additional detrimental conditions that may lead to damaging vibration between the inlet mixer and diffuser of the jet pump assembly are well-known, such as loss of the set screw support in a jet pump assembly as described in U.S. Pat. No. 6,394,765 to Erbes, et al. [0012]In addition to affected set screw gaps, thermal and pressure displacements of the shroud and the pressure vessel can diminish alignment interaction loads in the jet pump assembly which are beneficial in restraining vibration. The resultant increased vibration levels and corresponding vibration loads on the piping and supports can cause jet pump component degradation from wear and fatigue. [0013]High levels of flow-induced vibration (FIV) are possible in some jet pump designs at some abnormal operational conditions having increased leakage flow rates. Reducing leakage flow through the slip joint prevents or reduces oscillatory slip joint motion and suppresses FIV. Prior efforts to reduce the leakage flow rate in jet pump slip joints have been disclosed in U.S. Pat. No. 6,394,765, which discloses an external clamp apparatus for laterally stabilizing the slip joint; U.S. Pat. No. 6,438,192 to Erbes, et al., which discloses a split ring seal and latch assembly positioned at the upper end of the diffuser tube to stabilize the inlet mixer; U.S. Pat. No. 6,450,774 to Erbes, et al., which discloses a device for producing a lateral support load on the slip joint by causing an ovate deformation in the diffuser when attaching it to the inlet mixer; and U.S. Pat. No. 6,587,535 to Erbes, et al., which discloses a labyrinth seal in the slip joint for reducing slip joint leakage flow. [0014]Each of the previously disclosed inventions has demonstrated some characteristic which has rendered the device or method insufficient in producing effective reduction of slip joint-induced vibration, and none has been directed to providing a means for selectively controlling leakage flow rate through the slip joint to ameliorate the damaging effects of excessive leakage flow rate through the slip joint. In addition, those devices and methods that impose a lateral force on the slip joint also prevent axial movement in the slip joint, which does not properly allow for thermal expansion in the slip joint. [0015]It would be advantageous in the industry to provide a device for reducing or eliminating non-uniform, or unsteady, leakage flow rates though a slip joint by selectively controlling the uniform leakage of fluid through a slip joint in order to control, and thereby eliminate, the detrimental vibration and other damaging conditions that occur in unsteady slip joints, i.e., those slip joints through which non-uniform leakage flow occurs. BRIEF SUMMARY OF THE INVENTION [0016]In accordance with the present invention, a uniform leakage flow device is provided in a slip joint between intercoupled pipes to selectively control the amount of fluid allowed to leak through the slip joint, thereby selectively eliminating the amount of detrimental vibration or oscillation that otherwise occurs at the slip joint. The present invention may be adapted for use in any slip joint between intercoupled pipes, but is disclosed herein with respect to jet pump assemblies of the type used in reactor pressure vessel, by way of example. [0017]The uniform leakage flow device of the present invention comprises forming a selected number of axial grooves in the slip joint between an inlet mixer and the diffuser. The axial grooves may be formed in either the outer wall surface of the inlet mixer at the slip joint or in the inner wall surface of the diffuser at the slip joint. The axial grooves are machined into the wall surface either at initial assembly of the jet pump components, or after operation of the reactor pressure vessel has taken place. Methods for effecting formation of the axial grooves both prior to and after operation of the reactor pressure vessel are disclosed. [0018]The axial grooves are formed in a precise manner to selectively control and make uniform the flow of fluid leakage through the slip joint. The number, size and positioning of the axial grooves in the wall surface is determined by the application of equations as disclosed herein. [0019]In known slip joint structures, mechanical devices have been invented to eliminate or reduce the slip joint leakage flow and in turn eliminate the detrimental slip joint flow induced vibration mechanism. The present invention is directed to a completely different approach by providing a means to directly destroy the flow induced vibration mechanism by allowing the leakage flow to pass uniformly through the slip joint by way of machined axial grooves. In the presence of these axial grooves, the slip joint leakage flow will always be uniform and even around the circumference of the slip joint. [0020]Further, in known slip joint structures, both the total leakage flow and the leakage flow around the annulus and within the slip joint varied depending on the relative position of the mating parts. Non-uniform slip joint leakage flow, in both the total flow and peripheral flow, incurred time-varying lateral forces on the mating parts of the slip joint. These time-varying lateral forces incurred relative motion of the mating parts. This relative motion lead to increased non-uniform flow and higher fluid forces that, in turn lead to higher levels of vibration and wear of the mating jet pump components. This spiraling condition lead to higher and higher vibration levels of the mating parts. The axial grooves of the present invention impose uniform leakage flow at the slip joint location. The imposed uniform leakage flow does not change in its total amount, nor periphery within the slip joint annulus due to relative motion of the slip joint mating parts. The uniform leakage flow cannot incur net, time-varying lateral fluid forces that cause detrimental vibration and relative lateral motion of the slip joint mating parts. [0021]The placement of axial grooves in the slip joint reduces or eliminates non-uniform or unsteady leakage flow through the slip joint and thereby reduces or eliminates vibration levels associated with non-uniform or unsteady slip joint leakage flow. The present invention provides the further advantage of allowing axial movement between the jet pump components and supporting structure to accommodate thermal expansion in the jet pump assembly, and does not impose undue stress in the inlet mixer. The present invention also eliminates the use of structures, such as clamps and the like, which present a potential detriment of having loose parts moving in the jet pump assembly, recirculation system or reactor core. These and other advantages of the present invention will become more clear in light of the following detailed description. Continue reading about Jet pump slip joint with axial grooves... Full patent description for Jet pump slip joint with axial grooves Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Jet pump slip joint with axial grooves patent application. Patent Applications in related categories: 20090297367 - Ejector and manufacturing method thereof - A housing is configured into a tubular form and receives at least a portion of an ejector functional unit, which includes a nozzle and a body. A housing side opening radially penetrates through an outer peripheral wall surface and an inner peripheral wall surface of the housing and communicates with ... ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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