Abstract:
A strainer is disclosed for filtering a flow stream passing therethrough, while reducing vortex shedding and related minimizing noise and vibration. The strainer includes an elongated member which defines a generally longitudinal axis, and having an opening at one end and a closed end at the opposite end. The opening has a greater dimension than the closed end. The elongated member includes a plurality of rows of apertures located between the opening and the closed end, with the apertures of each row being of generally equal dimension and located in a plane generally perpendicular to the longitudinal axis. The pluralities of rows of apertures are of distinct dimensions and form a semi-random pattern such that a flow stream passing therethrough causes distinct frequencies associated with each row, which frequencies generally reduce or cancel any pulsation resulting therefrom.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a strainer for filtering a flow stream of liquid or gas passing therethrough. 
         [0003]    2. Description of the Related Art 
         [0004]    A filtering strainer which retains larger pieces while permitting smaller pieces and liquids to pass therethrough has many applications. In particular, a strainer can be utilized in the oil and gas industries where it is installed upstream of rotating equipment such as gas compressors or pumps to protect the internal components from being damaged due to carried over solid objects. 
         [0005]    The use of a strainer for straining a fluid flow is well known. One example of a strainer is disclosed in U.S. Pat. No. 4,839,038 to McLain, II which relates to a fluid strainer and flow corrector for use with a fluid flow measurement device such as a turbine-type flow meter. 
         [0006]    Another example of a strainer is illustrated in U.S. Pat. No. 5,500,115 to Nehm, et al. 
         [0007]    Conventional strainers are known for generating pressure pulsation in association with vortex shedding and/or eddies due to the stream flow of liquid or gas passing through them. In some cases, the pressure pulsation could coincide with a system&#39;s natural frequencies and cause serious damage to the system. In other cases, the pressure pulsation may cause piping vibrations, damage rotating equipment internals, and result in associated high level noise as well as high pressure drop. For instance, vibrations created by the vortices can cause cracks in the strainer mounting parts. 
         [0008]    One of the previous approaches was to remove the strainer, which is not acceptable because it will leave internal components such as a compressor without protection against foreign objects. Another approach was to relocate the strainer, which is not practical and did not solve the root case nor resolve the noise issue. Yet another approach was to change the angle of inclination for the strainer, which fails to prevent the pressure pulsation problem. Some other designs of strainers purporting to reduce vibration are flawed by their inherent design. Due to these necessary constraints, they could not be manufactured with a large enough size to be usable in many industries, making those solutions not viable. 
         [0009]    Thus, a strainer is needed that can filter a flow stream passing therethrough, while reducing vortex shedding and related noise and vibrations. Such strainer would solve the root cause and not be sensitive to location of the strainer in piping machinery. 
       SUMMARY OF THE INVENTION 
       [0010]    A primary feature of the preferred embodiment of the present invention, which will be described subsequently in greater detail, is to provide a strainer or the like for filtering a passing flow stream, which has many of the advantages over presently known strainers heretofore. A feature of the present invention also provides many novel features that result in a new strainer which overcomes the shortcomings of, and is not anticipated, rendered obvious, suggested, implied or even predicted by any of the known strainers, either alone or in any combination. 
         [0011]    To attain this objective, a primary feature of the preferred embodiment generally provides a strainer that includes an elongated member defining a generally longitudinal axis, and having an opening at one end and a closed end at the opposite end. Another feature of the preferred embodiment is that the opening is generally circular and of greater dimension than the closed end, and the elongated member has a generally tapered conical configuration. The closed end has a generally arcuate shape to reduce the passing flow stream at a downstream location. 
         [0012]    Another feature of the preferred embodiment is to provide an improved strainer with the plurality of rows that includes a first row of apertures of a predetermined dimension, a second row of apertures located adjacent first row, each aperture of the second row having a dimension lesser than the dimension of the apertures of the first series, at least one of the first row and the second row causing the passing flow stream to produce a pressure pulsation of a first frequency. The preferred embodiment also features a third row of apertures located adjacent the second row and defining a third series of apertures of dimension at least equal to or greater than the dimension of the apertures of the second series, and a fourth row of apertures located adjacent the third row and defining a fourth series of apertures of a dimension at least equal to or greater than the dimension of the apertures of the third series, at least one of the third row and the fourth rows causing the passing flow stream to produces a pressure pulsation of another frequency that at least substantially reduces, or even nullifies the pressure pulsation produced by the first frequency. 
         [0013]    Still another feature is to provide an improved strainer with the plurality of rows further including a fifth row of apertures located adjacent the first row on the opposite side of the second row, and defining a fifth series of apertures of a dimension at least greater than the dimension of the apertures of the first series; and a sixth row of apertures located adjacent the fourth row and defining a sixth series of apertures of a dimension at least greater than or equal to the dimension of the apertures of the fourth series. 
         [0014]    Still another feature is to provide a plurality of rows further including a seventh row of apertures located adjacent the fifth row of apertures and defining a seventh series of apertures of a dimension at least equal to or less than the dimension of the apertures of the fifth row, and an eighth row of apertures located adjacent the seventh row and defining an eighth series of apertures of a dimension at least equal to or less than the dimension of the apertures of the seventh series; and a ninth row located adjacent the eighth row and defining a ninth series of apertures of a dimension at least equal to or less than the dimension of the apertures of the eighth series. Another feature of the invention relates to the plurality of rows extending from the ninth row to the sixth row of apertures being repeated as a continuous arrangement between the opening and the closed end. 
         [0015]    Another preferred feature is to provide an improved strainer with apertures in each of the plurality of rows formed with a dimension distinct from other apertures of the plurality of rows in a non-recurrent manner to define a random arrangement of the plurality of rows of apertures. Yet another feature of the invention relates to the rows being formed in a staggered manner such that a plane passing through the longitudinal axis will intercept alternate rows of apertures. 
         [0016]    A method of using the non-shedding strainer of the invention is also disclosed. 
         [0017]    Other objects, features and advantages of the present invention will become obvious to the reader, and it is intended that these objects, features and advantages are within the scope of the present invention. 
         [0018]    To the accomplishment of the above and related objects, features and advantages, the present invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Preferred embodiments of the invention are described hereinbelow with reference to the drawings, wherein: 
           [0020]      FIG. 1  is a front perspective view from below, of a strainer for filtering a flow stream which passes therethrough, according to a preferred embodiment of the invention; 
           [0021]      FIG. 2  is a view of a portion of the strainer of  FIG. 1 , taken along lines  2 - 2  of  FIG. 1 , and illustrating the plurality of apertures of different dimensions; 
           [0022]      FIG. 3  is a cross-sectional view of the strainer of  FIG. 1 , taken along lines  3 - 3  of  FIG. 2 , and illustrating the depth of the apertures and the direction of the flow stream passing therethrough; 
           [0023]      FIG. 4  is a cross-sectional view of the strainer of  FIG. 1 , taken along lines  4 - 4  of  FIG. 1 , and illustrating the support ring with its gasket, and a backing ring located at the upper end of the strainer; 
           [0024]      FIG. 5  is a cross-sectional view of the strainer of  FIG. 1 , taken along lines  5 - 5  of  FIG. 1 , and illustrating an installation in a typical pipe machinery system with the cone facing the direction of the flow stream which passes therethrough; 
           [0025]      FIG. 6  is a cross-sectional view of another preferred embodiment of the invention, illustrating the plurality of apertures having alternative dimensions; and 
           [0026]      FIG. 7  is a cross-sectional view of yet another preferred embodiment of the invention, illustrating the plurality of apertures that are generally rectangular. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Definitions:
       Eddy, as discussed herein, is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. As the moving fluid creates a void on the downstream side of the object, fluid behind the obstacle flows into the void creating a swirl of fluid on each edge of the obstacle, followed by a short reverse flow of fluid behind the obstacle flowing upstream, toward the back of the obstacle.   Strainer, as discussed herein, is an apparatus of any size and application, that, in operation, retains larger pieces while passing through smaller pieces and liquids.   Vortex shedding, as discussed herein, is an unsteady flow that takes place in special flow velocities which is caused when air or liquid flows past a blunt object, creating alternating low-pressure vortices on the down stream side of the object.   Gas compressor, as discussed herein, is a mechanical device that increases the pressure of a gas by reducing its volume. As gases are compressible, the compressor also reduces the volume of a gas. Most liquids are relatively incompressible, so the main action of a pump is to transport liquids.   Gas piping system, as discussed herein, is a piping mechanism that transports gas.   Pressure pulsation, as discussed herein, is used interchangeably with turbulence or turbulent flow to characterize chaotic, stochastic property changes in a fluid regime. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time such as various eddies and vortices.       
 
         [0034]    Referring to the drawings, in which similar reference characters denote similar elements throughout the several views, the attached FIGS. illustrate a strainer for filtering a flow stream passing therethough, which is constructed according to a preferred embodiment of the invention. Referring initially to  FIG. 1 , the strainer  10  comprises an elongated member  14  having a generally tapered conical configuration and a flange-shaped support member  16  located at one of its ends, the overall structure defining a longitudinal axis A-A as shown in  FIG. 1 . 
         [0035]    In this preferred embodiment, the elongated member  14  tapers toward a closed end  18  which is shaped as a conical nose tip  20 . The conical nose tip  20  has a generally arcuate shape and is smooth and round to promote laminar flow at the tip end. Also, the rounded conical nose tip  20  has no structural discontinuities with the rest of the elongated member  14 . 
         [0036]    On the elongated member  14 , an annular skirt edge  24  defines an opening  22 , more clearly illustrated in  FIG. 5 , which is located at the distal end, which is located opposite the closed end  18 . In most cases, this opening  22  has a dimension that correlates with the width dimension of the pipe machinery in which the strainer  10  is typically installed. 
         [0037]    Referring now to  FIG. 4 , the flange-shaped support member  16  is illustrated in a detailed cross-sectional view.  FIG. 4  shows a support hoop  26  formed in an annular shape and being connected to the annular skirt edge  24  by weld  28 . In addition, a strengthening unit such as a backingring  30  is fixed over the annular skirt edge  24  with weld  32 , and also joined to the support hoop  26  by weld  34  as shown. This backing ring  30  provides additional strength to the support hoop  26  against possible damages, for instance, due to the pressure pulsation as discussed above. It will be readily apparent to those skilled in the art that the connection of the support hoop  26  with the elongated member  14  and other elements may be achieved by other means besides welding, including casting, fabrication, forging, grinding, machining, milling, tube bending, turning or the like. 
         [0038]      FIG. 4  also illustrates an annular gasket  36  having a generally reverse-c-shaped (concave) cross-section. This gasket  36  is secured over the outer edge  38  of the support hoop  26 . The gasket  36  can be made with any type of soft material such as a foam material, cork, or other gasket material, and provides an airtight sealing connection between the support hoop  26  and a mount  74  as shown in  FIG. 5 , on an installation site of the pipe machinery where the strainer is installed, so as to prevent the escape of gas or fluid. 
         [0039]    Referring again to  FIG. 1 , the elongated member  14  is defined by a screen plate  40  such as a mesh screen  42  of the types shown in  FIGS. 2 ,  6  and  7 . As can be seen in  FIG. 2 , the mesh screen  42  includes a plurality of apertures  44 . Although the plurality of apertures  44  is shown discretely in  FIG. 1 , to avoid overly complicating the drawing, it will be readily apparent to those skilled in the art that the apertures are located throughout the elongated member  14 , extending from near the conical nose tip  20  to the extent of the annular skirt edge  24  as shown in  FIG. 4 . 
         [0040]      FIG. 2  illustrates the plurality of apertures  44  located on the screen plate  40  in a detailed cross-sectional view. As can be seen, the plurality of apertures  44  can be segregated into different rows, with each row of apertures being adjacent another row of apertures. As featured, apertures in certain rows have different dimensions from apertures of their adjacent rows. For instance, in the preferred embodiment shown in  FIG. 2 , each aperture of the plurality of apertures in a first row  52  has an inner dimension (or diameter) of 7 mm. The apertures in the second row  54  located adjacent the first row  52  have a dimension of 6 mm. The apertures in the third row  56  located adjacent the second row  54  have a dimension of 6 mm. The apertures in the fourth row  58  located adjacent the third row  56  have the dimension of 7 mm. 
         [0041]    In this preferred embodiment, the apertures in the fifth row  60  located adjacent the first row  52  on the opposite side of the second row  54  have a dimension of 8 mm. A sixth row  62  is located adjacent the fourth row  58  and defines a sixth series of apertures having a dimension of 8 mm. As can be noted, the size differences of apertures for adjacent rows do not increase nor decrease continuously. For instance, the plurality of apertures at row  64  adjacent the fifth row  60  of apertures (with dimension of 8 mm) also have the dimension of 8 mm. Similarly, the apertures at row  66  adjacent the sixth row  62  of apertures (with dimension of 8 mm) also have the dimension of 8 mm. 
         [0042]    The rows of apertures described above are separated from each adjacent row by approximately 2 mm spacing therebetween. Thus formed, the spacing  72  located between the rows of apertures define the boundary of each of the two adjacent rows of apertures. 
         [0043]    As noted above, in this preferred embodiment, the aperture dimensions do not remain constant all throughout the screen plate  40 . Additionally, the aperture dimension of each row neither increases nor decreases continuously through out all the rows. Instead, it will be readily apparent to those skilled in the art that the aperture dimensions of the preferred embodiment are provided as examples, and the aperture dimension vary in a random or semi-random pattern according to the present invention. For instance, the aperture dimensions for other embodiments may vary from 10 mm to 4 mm in a different row arrangement to define a semi-random aperture location pattern and so forth. In addition, it will also be readily apparent to those skilled in the art that, in another embodiment, the dimension of certain apertures in a particular row can vary from the dimensions of other apertures in that same row. In another embodiment, the plurality of apertures in each row may be located closer to the next adjacent row to define a staggered location of apertures such that a plane passing through the longitudinal axis  12  will intercept alternate rows of apertures  44 . Further, in another embodiment, the location of apertures may not correlate into any definable rows and instead the apertures may be located on the screen plate  40  in a cluttered random configuration. 
         [0044]    This special configuration (where the apertures  44  are of variable size and are arranged in a random or semi-random pattern) results in improved features for the strainer  10 . For instance, in this preferred embodiment, when air or liquid flows through the apertures  44  in the first row  52  (or the second row  54 ), an unsteady flow creates alternating low pressure pulsation or vortices on the downstream side of the apertures  44 . Vortices are generally present whenever there is stream flow over an obstruction. This set of vortices could lead to a larger problem when the generated vortices add up to each other and create a dominant single tuned vortex. 
         [0045]    However, when air or liquid flows through the apertures  44  in the third row  56  (or the fourth row  58 ), the unsteady flow creates yet another low pressure pulsation or vortices with a different frequency. The variation in aperture dimension by one millimeter difference allows the generated vortices to be of different frequencies from the frequencies of the vortices created by the first and second rows ( 52 ,  54 ). As a result, the vortices generated by the stream flow with different frequencies will cancel each other. In other words, the second generated vortices will have different frequencies from the first generated vortices, and when they add up to each other, the vortices will prevent the creation of a dominant single tuned vortex. The semi-random pattern also ensures that no momentum coupling will occur between adjacent vortices with the same frequencies. 
         [0046]      FIG. 3  illustrates the thickness of the elongated member  14 , the depth of the apertures  44  located thereon, and the direction of the flow stream passing therethrough in a cross-sectional view. The apertures  44  extend through the depth of the screen plate  40  in a substantially perpendicular direction to its surface. The minimum thickness of the strainer is driven mostly by the size of the strainer. In this preferred embodiment, as used in gas industries, the thickness is preferably approximately 9 mm to ensure the structural strength and integrity of the strainer. In addition, the maximum thickness of the strainer is preferably approximately 12 mm to ensure the ease of fabrication and to avoid the production of a high pressure drop across the apertures  44  at a downstream. 
         [0047]    The apertures  44  are located on the screen plate  40  in such a way that the flow stream passes through the apertures  44  in a generally perpendicular direction to the general flow stream direction. This placement of the apertures provides more surface area to the moving flow stream which also helps in reducing the pressure pulsation. Although not shown, a preferred configuration of the apertures  44  features smooth or round edges along the circular cut which defines each aperture. The curvilinear aperture edges aid in reducing the vortices. However, fabricating round apertures can be costly. It has been observed that when such strainers which do not have this feature, are installed in a flow stream system, the strainers functioned excellently. Accordingly, it was concluded that of the edges, while sometimes preferred, the roundness is not mandatory. 
         [0048]    The preferred construction material for the strainer is stainless steel such as A304 or higher. Carbon steel is not as preferred as high alloy steel. However, other materials such as plastic, glass, or other types of material are also encompassed by the present invention. 
         [0049]      FIG. 5  illustrates the preferred embodiment of the strainer  10  installed on a mount  74  in a pipe machinery with the opening  22  facing the flow stream direction (or the flow direction facing the conical nose tip  20 ) in a cross-sectional view. For reducing the vortex and other pressure pulsation, the strainer is generally installed with the orientation of its opening  22  facing opposite the flow direction as shown. However, from the functionality of protecting the downstream equipment, the strainer can also be installed with the orientation such that the conical nose tip  20  faces the flow direction. In other words, the strainer  10  can be oriented with the opening  22  facing the oncoming flow stream and still function as desired according to the present invention. 
         [0050]      FIG. 6  illustrates yet another embodiment of the invention which can be incorporated into the elongated member  14  of  FIG. 1 . In this embodiment, the screen plate  40  includes the plurality of rows of apertures having a different series of dimensions in a cross-sectional view. In  FIG. 6 , the range of aperture dimensions range from 6 mm to 8 mm, and the defined semi-random row pattern for the rows of apertures  70 ,  68 ,  64 ,  60 ,  52 ,  54 ,  56 ,  58 , and  62  are 6 mm, 7 mm, 8 mm, 8 mm, 7 mm, 6 mm, 6 mm, 7 mm, and 8 mm respectively. Further, this semi-random row pattern for the rows of apertures repeats after space  72  shown in  FIG. 6 , and continuously repeats the aforementioned pattern throughout the extent of the elongated member  14 . 
         [0051]      FIG. 7  illustrates yet another preferred embodiment of the invention in a cross-sectional view. As can be seen, each of the plurality of apertures  44  is generally rectangular. This configurational arrangement costs less to manufacture than the previous embodiments in a preferred size and dimension of the strainer  10  as used in gas and oil industries. The various dimensions of the apertures in this preferred embodiment range from 8 mm to 6 mm. The locations of the rows of apertures correspond to the row-location of the first embodiment described above. In general, the nominal aperture is dictated by the needs of the pressure drop control and filtration requirements to protect rotating equipment or any other sensitive equipment downstream of the flow. Although not shown, it will be readily apparent to those skilled in the art that, in addition to the circular or rectangular aperture shape described above, the aperture shape may also be hexagonal, oblique or any other design and still encompass the features of the present invention. 
         [0052]    The preferred embodiment of the present invention provides several benefits. Generally, strainers are installed in pipe machinery upstream of the internal component to protect it from being damaged due to carried over solid objects. However, as described above, conventional strainers are known for generating pressure pulsation caused by vortex shedding. In addition, pressure pulsation could coincide with the machinery&#39;s natural frequencies and cause serious damage to the overall system. 
         [0053]    The newly designed strainer shown in the several views reduces vortices by its configuration, its aperture dimensions, and the aperture locations and arrangements. For instance, the aperture dimensions of the strainer  10  of  FIG. 1  varies by 1 (one) mm difference in the inside diameter of the apertures in the preferred embodiment where only three different aperture sizes are provided. Also, the semi-random row arrangement of the apertures ensures that apertures of the same size are not located in a repeating pattern. This newly designed strainer will protect the gas compressors or pump from being subject to pressure pulsation which can excite natural frequencies of the impeller, compressor rotor, piping system as well as acoustic natural frequencies of the system. 
         [0054]    In addition, the round smooth characteristics of the conical nose tip  20  will enable the flow stream to pass the tip of the strainer smoothly; i.e., occurrence of eddies or vortices will be prevented at the tip. Also, because the conical nose tip  20  has no structural discontinuities with the rest of the elongated member  14 , structural stress is minimized in that location (the location with repetitive failure in older designs). Further, the conical nose tip  20  together with thicker material enable the strainer  10  to have higher resistance to buckling which is another serious problem facing older designs with thin material. In addition, the tapered conical shape of the elongated member provides more area for stream flow passage further minimizing the pressure pulsation. 
         [0055]    Therefore, the particular shape configuration, aperture dimension, and its arrangement ensure that the generated vortices from different aperture dimensions will cancel each other and the vortex shedding will not occur, resulting in a stream flow without pressure pulsation of any distinct frequency. 
         [0056]    The new strainer can be utilized in the oil and gas industries where it is installed upstream of rotating equipments especially gas compressors or pumps. The particular fluid materials which are contemplated to be strained by the strainer include any gas service as well as liquid service. In this application, the type of apertures and flow conditions will generate frequencies in the range of 1500 Hz for gas service and around 500 Hz in liquid services. However, the present invention is not so limited to the oil and gas industries. For instance, the strainer can be utilized in power industries. 
         [0057]    Although the invention has been described in terms of specified embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art in view of the disclosure. Accordingly, modifications are contemplated which can be made without departing from the spirit of the described invention.