Patent Publication Number: US-6709227-B2

Title: Pitot tube insert

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a non-provisional application claiming priority to provisional application Ser. No. 60/318,196 filed Sep. 7, 2001. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates to centrifugal pumps of the pitot tube type, and specifically relates to a modified inlet opening of a pitot tube for contacting and removing accumulated solids from the pump rotor. 
     2. Description of Related Art 
     Centrifugal pumps of the pitot tube type are well-known in the pumping industry as being useful in low flow/high pressure applications. Centrifugal pumps of the pitot tube type are generally structured with a closed rotor which is housed within the casing of the pump. A pitot tube assembly is positioned through a central opening of the rotor and is secured to the pump casing. A pitot tube arm of the pitot tube assembly is positioned within the rotor and is radially-oriented relative to the axis of the pump. The pitot tube arm is stationary while the rotor rotates about the pitot tube arm. 
     In operation, fluid enters into the rotor along the axis of rotation through radially-oriented fluid channels formed in the rotor cover. The fluid enters the internal space of the rotor where it picks up momentum and is subjected to centrifugal forces as the rotor spins. The fluid maintains its velocity at nearly the rotational speed of the rotor. 
     The pitot tube arm is structured with an inlet to receive fluid, and the inlet opening of the pitot tube is positioned near the inner periphery, or internal diameter, of the rotor. As the fluid is directed to the periphery of the rotor the fluid moves into the inlet of the pitot tube, through an inner channel of the pitot tube and out of the pump by way of a discharge outlet. 
     Traditionally, pitot tubes have been cast and machined with the inlet opening formed or configured as it will be used in the pump. However, after continued use of the pump, particularly when abrasive fluids are being processed by the pump, the impact of the fluid on the opening of the pitot tube causes degradation of the inlet and eventually pump efficiencies are adversely affected. The pitot tube arm must then be replaced in its entirety, which is very costly and increases operation costs. 
     The development of an insert for a pitot tube and the advantages of such inserts was first described in U.S. Pat. No. 5,997,243 to Shaw, issued Dec. 7, 1999 and assigned to the same assignee as the present application. U.S. Pat. No. 5,997,243 is incorporated herein by reference. The &#39;243 patent discloses a pitot tube inlet insert which allows the inlet opening of a pitot tube to be replaced after it has been degraded or damaged with use. The inlet insert eliminates the need to replace the entire pitot tube arm thereby reducing operating costs. The pitot tube insert described in the &#39;243 patent improves the efficiency of the pump and reduces or eliminates cavitation and degradation of the pitot tube inlet. 
     An additional problem occurs in pitot tube pumps which has not been previously addressed. That is, when the fluid being pumped contains particulate matter or solids, the impact of the fluid and solids on the pitot tube can be very damaging, with a resulting loss in head. Additionally, when solids are present in the fluid, the solids are thrown against the inside peripheral surface of the rotor under centrifugal force and can build up on the rotor. The accumulated solids built up on the interior peripheral surface of the rotating rotor then impact with the stationary pitot tube as the rotor spins and can cause an increase in drag on the rotor. Consequently, pump efficiency is sacrificed. The impact of the inlet against the solids further contributes to the degradation of the inlet and pitot tube arm. 
     Thus, it would be advantageous in the art to provide a pitot tube inlet which is designed to provide improved pump efficiencies when the pitot tube pump is used to process liquids containing solids that can build up on the rotor, and it would be advantageous to provide a pitot tube inlet insert which is designed to provide improved pump efficiencies under such conditions while also providing the advantage of being easily replaced at a relatively low cost. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a pitot tube inlet is configured to contact and remove the solids that build up on the inside peripheral surface of the rotor of a centrifugal pump to thereby improve the operational efficiency of the pump. While the present invention is principally described herein with respect to providing a pitot tube inlet insert that is configured for removing solids from the inside peripheral surface of the rotor, the design and configuration characteristics of the invention are equally applicable to a pitot tube which is unitarily cast in the traditional mode. 
     The pitot tube inlet of the present invention generally comprises an opening, which is positioned and sized to receive fluid from the peripheral portion of the rotor of a pitot tube pump, and a lip portion surrounding at least a part of the circumference or perimeter of the opening such that the lip portion is positioned to contact and remove solids that tend to accumulate and adhere to the inner peripheral surface of the rotor. The lip portion of the pitot tube inlet is generally directed away from the opening to provide a scoop-like portion which is capable of excising solids from the inner peripheral surface of the rotor. 
     The lip portion of the pitot tube inlet is also configured with a curved inner surface oriented about the opening of the inlet to direct solids into the opening of the pitot tube for discharge. The curvature of the inner surface not only facilitates directing the solids into the pitot tube, but increases the longevity of the pitot tube inlet by efficiently deflecting solids and liquid in a manner which decreases the usual degradation experienced in pitot tube inlets. The size, shape, dimension, angle, extension and/or circumferential extent of the lip portion may vary as long as the lip portion is capable of contacting and removing accumulated solids from the inner peripheral surface of the rotor to reduce or eliminate drag on the rotor to improve the operational efficiency of the pump. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     In the drawings, which illustrate what is currently considered to be the best mode for carrying out the invention: 
     FIG. 1 is a view in cross section of a portion of a centrifugal pump of the pitot tube type which illustrates the pitot tube inlet of the present invention positioned within the pump; 
     FIG. 2 is a front view of a first embodiment of the pitot tube inlet of the present invention, shown as an insert and looking into the opening of the inlet; 
     FIG. 3 is an enlarged view in cross section of the pitot tube inlet shown in FIG. 2, taken at line  3 — 3 ; 
     FIG. 4 is a perspective view of the pitot tube inlet insert shown in FIG. 2; 
     FIG. 5 is a view in cross section of the pitot tube inlet insert shown in FIG. 2 taken at line  5 — 5 ; 
     FIG. 6 is a computer-generated three-dimensional model of the pitot tube inlet insert shown in FIGS. 2-5 illustrating a view of the inlet opening; 
     FIG. 7 is a computer-generated three-dimensional model of the pitot tube inlet insert shown in FIG. 6 tilted downwardly approximately forty-five degrees; and 
     FIG. 8 is another alternative embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a centrifugal pump of the pitot tube type  10  which generally comprises a pump casing  12  that houses a rotor  14  and a pitot tube assembly  16 . The rotor  14  is caused to rotate within the pump casing  12  by a drive means  18  while the pitot tube assembly  16  remains stationary by virtue of its securement to the pump casing  12 , or more specifically, as shown here, a manifold  20 . The rotor  14 , which may be said to be bowl-shaped, has an internal space  22  in which is positioned a pitot tube arm  26  of the pitot tube assembly  16 . Fluid enters the pump  10  through an inlet (not shown) that directs the fluid to an annular space  28  surrounding the pitot tube assembly  16 . Fluid moves from the annular space  28  through radially-oriented channels  30  formed in the cover  32  of the rotor, and then enters the internal space  22  of the rotor  14 . 
     As the rotor  14  spins, the velocity of the fluid in the internal space  22  increases and centrifugal forces act on the fluid to move it to the inner peripheral surface  36  of the rotor  14 . There the fluid is intercepted by an inlet  40  that is formed at the outer or radial extremity of the pitot tube arm  26 . The fluid enters into the opening  42  of the inlet  40  and flows through a channel (not shown) internally formed in the pitot tube arm  26 . The fluid then enters the pitot tube assembly  16  and flows in an axial direction through a discharge channel  44  defined by a bore formed within the pitot tube assembly  16 . 
     It can be seen from FIG. 1 that the pitot tube arm  26  is sized in length to extend to near the inner peripheral surface  36  of the rotor  14  such that a very small gap  46  exists between the inlet  40  of the pitot tube arm  26  and the inner peripheral surface  36  of the rotor  14 . The opening  42  of the pitot tube arm  26  provides a means for entry of fluid into the pitot tube arm  26 , but some of the fluid that is encountered by the inlet  40  merely strikes the inlet  40  or edge of the opening  42  at high velocity and pressure. The damage that results has been previously described in the literature. 
     When fluids containing solids or particulate matter are processed in pitot tube pumps  10 , there is a tendency for the solids or particular matter to accumulate and build up on the inner peripheral surface  36  of the rotor  14  since the solids material or particular matter is, itself, forced radially outwardly as the rotor  14  spins. It can be seen, therefore, that given the small gap  46  between the inlet  40  of the pitot tube arm  26  and the inner peripheral surface  36  of the rotor  14 , the inlet  40  will impact with the accumulated solids layer and drag on the rotor  14  will increase with a corresponding increase in horsepower required to maintain rotational speed. The impact of the inlet  40  on the solids layer will also act to degrade the inlet  40  of the pitot tube arm  26 . The pump efficiency is adversely effected as a result. 
     The present invention addresses that concern by providing a pitot tube inlet  40  which is configured to contact and remove the accumulated solids so that the rotor  14  may rotate freely and not adversely effect the operating efficiency of the pump. The pitot tube inlet  40  is especially designed to withstand the otherwise destructive action of impact with the solids layer. Accordingly, the pitot tube inlet  40  of the present invention comprises an opening  42  the surrounding perimeter edge of which is shaped, at least in part, with a lip portion  50  that is positioned and oriented to contact the solids layer at the inner peripheral surface  36  of the rotor  14 . 
     The pitot tube inlet  40  of the present invention is shown more clearly in FIGS. 2-7 which illustrate the invention as an insert  52  that is particularly designed for attachment to the formed inlet of a pitot tube arm  26  (FIG. 1) and that can be replaced when damaged with wear. However, it is understood that the pitot tube inlet  40  of the present invention may also be formed as an integral part of the pitot tube arm  26 , as shown in FIG. 1, when the pitot tube arm is cast as a single body. 
     FIG. 2 illustrates the pitot tube inlet  40  from a view looking into the opening  42  thereof. The opening  42  of the inlet  40  is surrounded by a perimeter edge  54  which defines the opening  42  of the inlet  40 . A first portion  56  of the perimeter edge  54  of the opening  42  is spaced inwardly from the circumferential wall  58  of the inlet  40  to form a sloped shoulder  60 . The sloped shoulder  60  is positioned away and at a distance from the inner peripheral surface  36  of the rotor  14 . However, the sloped shoulder  60  is positioned to contact the high velocity fluid in the rotor and is especially designed to help direct fluid into the opening  42  and deflect that fluid which does not enter the opening  42  away from the inlet  40  to reduce damage to the inlet  40 . The particular angle and/or curvature of the sloped shoulder  60  may be modified to accommodate a particular fluid application. 
     A second portion  64  of the perimeter edge  54  of the opening  42  is oriented outwardly from the center of the opening  42  such that it flares or extends away from the opening  42  and from the lower portion  56  of the perimeter edge  54  to provide a lip portion  50 . The lip portion  50  is positioned in the pump to be located in near proximity and orientation to the inner peripheral surface  36  of the rotor  14 . The second portion  64  of the perimeter edge  54  contacts the solids which accumulate on the inner peripheral surface  36  of the rotor  14  and the lip portion  50  effectively scoops out the solids that have built up. 
     The lip portion  50  further comprises an inner sloping surface  66  which is configured to direct the removed or captured solids into the opening  42  of the inlet  40  from where the solids are transported through the pitot tube assembly for discharge. The inner sloping surface  66  has a curvature which not only facilitates directing solids into the opening  42 , but facilitates deflection of solids and liquid in a manner which reduces the damaging effects that fluid and solids typically have on pitot tube inlets. Consequently, the longevity of the pitot tube inlet  40  (and insert  52 ) is enhanced. 
     There is a transition zone  70  of the perimeter edge  54  where the inwardly oriented first portion  56  of the perimeter edge  54  transitions to the outwardly oriented second portion  64  of the perimeter edge  54 . The cross section view of FIG. 5 further illustrates that in the transition zone  70  of the perimeter edge  54 , the circumferential wall  58  of the inlet  40  becomes less curved, as compared with the sloped shoulder  60  of the inlet  40 , to provide a transition shoulder  74 , and the inner surface  76  of the inlet  40  also transitions to curve outwardly toward the perimeter edge  54  to provide a transitional inner sloping surface  78 . The configurational elements which comprise the first embodiment of the invention are further viewable in the computer-generated three-dimensional models of FIGS. 6 and 7. 
     Again, as illustrated in FIGS. 2-7, the pitot tube inlet  40  of the present invention is illustrated as an insert  52  that may be attached to a pitot tube arm that has been cast and/or machined with an opening to receive the insert  52 . To allow the insert  52  to be received in the pitot tube arm, the insert  52  is further formed with a neck portion  80  the outer diameter  82  (FIGS. 3 and 5) of which is less than the outer diameter  84  of the circumferential wall  58  of the inlet  40 . A ledge  86  is thus formed which abuts against an edge surrounding the cast or machined opening formed in the pitot tube arm. 
     The lip portion  50  of the inlet  40  is configured to not only scoop out solids that have accumulated on the inner peripheral surface of the rotor, but is also configured to direct free-moving solids into the opening  42  of the inlet  40  so that those solids may be removed as well. Further, the sloped shoulder  60  of the inlet  40  is configured and dimensioned to provide an aerodynamic surface against which fluid flows, thereby improving pump efficiencies. While the lip portion  50  of the inlet  40 , by virtue of its flared configuration and inner sloping surface  66 , produces some drag on the fluid and solids moving in the inner periphery of the rotor which can tend to reduce pump efficiency, it has been demonstrated that what may be lost in some pump efficiency caused by the drag is overcome by the increased efficiencies and improved longevity of the pitot tube derived from addressing the accumulated solids problem. 
     The first embodiment of the invention shown in FIGS. 1-7 illustrates an inlet  40  having a lip portion  50  which extends approximately 180° about the circumference of the opening  42 , which is defined by the perimeter edge  54 . However, as shown in the alternative embodiment illustrated in FIG. 8, the lip portion  50  may extend 360° about the opening  42  of the inlet  40  thereby providing a scooping capability about the entire circumference of the opening  42 . FIG. 8 is a longitudinal cross section through the inlet  40  of the alternative embodiment and the view would be identical regardless of where the cross section was taken through the longitudinal axis  90  of the inlet  40 . 
     The lip portion  50  of the pitot tube inlet  40 , particularly facilitated by the inner sloping surface  66 , is effective at directing solids and fluids into the opening  42  of the inlet  40  and scooping out built-up solids at the periphery of the rotor. However, the 360° extent of the lip portion  50  presents some increase in drag on the fluid and may reduce efficiencies accordingly. In applications where fluids of high solids content are being processed, a pitot tube inlet  40  having a 360° lip portion  50  may, nonetheless, be especially advantageous and provide increased pump efficiencies as compared with prior art pitot tube inlets having no lip portion. The lip portion  50  of the inlet  40  of the present invention may encircle or extend anywhere from about 5° to 360° about the circumference of the opening  42  of the inlet  40 . 
     The inlet  40  of the present invention has been described and illustrated as having a substantially round opening  42  defined by the perimeter edge  54  and a substantially round outer circumference defined by the circumferential wall  58 . However, the shape and dimension of the inlet  40  and its opening  42  need not be round. Indeed, the inlet  40  and/or opening  42  may be any suitable shape which is appropriate to the application for which it is being used. By way of example only, the inlet  40  and opening  42  may be ovoid in shape. 
     The inlet  40  of the present invention may be made by casting in a mold by known methods, whether the inlet  40  is integrally formed as part of the pitot tube arm or is formed in the manner of an insert. Alternatively, and particularly with respect to the embodiment of the invention comprising a 360° lip portion  50 , the inlet  40  may be made by machining from stock by methods that are known in the art. The inlet may be made from any suitable material which has increased erosion-resistant character such as tungsten carbide, by way of example only. Numerous other materials are equally suitable. 
     The pitot tube inlet is configured to provide increased pump efficiencies when processing fluids that contain solids, particularly when the solids are of a type or concentration which causes the solids to accumulate along the inner peripheral surface of the rotor of the pump. The pitot tube inlet of the present invention is modifiable in shape and dimension to adapt to any application. Therefore, reference herein to specific details of the structure and function of the present invention is by reference only and not by way of limitation.