Patent Publication Number: US-2004057852-A1

Title: Suction diffuser

Description:
[0001] The present invention relates to a suction diffuser. It is intended particularly but not exclusively for use in liquid pumping systems where the pump is of the centrifugal type.  
       [0002] There is a general requirement in pumping systems for the conditioning of the liquid before entering the suction side of the pump to ensure that the liquid is clean and that its flow velocity is reasonably uniform. This is to avoid damage to the pump from solid particles in suspension and from irregular flow patterns which can cause damage to the impeller and impair pump performance. These requirements are satisfied by the fitting of a strainer valve upstream of the pump and the provision of a length of pipe and a long sweeping bend between strainer valve and pump inlet to achieve as close to fully developed flow as the space will allow.  
       [0003] The disadvantage of this arrangement is the large space required to accommodate the straight length of pipe and long sweeping bend.  
       [0004] A prior solution to this arrangement is to replace the long sweeping bend with a compact 90°fitting and simultaneously, incorporate the strainer valve element in the fitting. Providing flow straighteners in the outlet port of the fitting to the inlet of the pump compensates for the absence of the long sweeping bend.  
       [0005] In this solution the cylindrical strainer element is positioned co-axially and horizontally with the bore of the pump inlet. Liquid flow enters the fitting vertically downwards and passes through the strainer element from the outside surface to the inside and then into the pump.  
       [0006] Such arrangements are susceptible to particles in the liquid accumulating in the limited geometry around the strainer element and restricting flow. The space around the element is dependent on the body cavity dimensions and in practice, is insufficient to allow continual collection of particles, which should fall freely around the external surface of the element to the internal base of the device. Experience has indicated that this is not always consistent.  
       [0007] It is an object of the present invention to mitigate or eliminate this disadvantage.  
       [0008] According to the present invention, there is provided a suction diffuser for use in a liquid pumping system comprising a pump having an inlet and an outlet and strainer having a housing and a strainer element disposed in the housing and an inlet and an outlet connected to the pump in which the strainer element is arranged in relation to the inlet of the strainer so that in use liquid flows through the strainer element and into the housing of the strainer before entering the pump.  
       [0009] In a preferred embodiment of the invention, the strainer element is cylindrical and is coaxially arranged with the inlet of the strainer. Flow straighteners may be fitted between the strainer element and the pump. A drain is provided in the strainer to enable material collected by the element to be removed from the strainer. The drain may comprise a plug arranged coaxial with or parallel to the strainer element. Magnets may be provided to facilitate removal of magnetic material. The strainer housing advantageously comprises a removable cover to enable access to the strainer element. The strainer element may be provided with handles to facilitate insertion into and removal from the strainer housing. The strainer may be provided with a support to alleviate strain on the body of the pump.  
     
    
    
     [0010] In order that the invention may be more clearly understood, one embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which:  
     [0011]FIG. 1 diagrammatically shows a known suction diffuser arrangement,  
     [0012]FIG. 2 shows a further known suction diffuser arrangement, and  
     [0013]FIG. 3 shows a suction diffuser arrangement according to the invention. 
    
    
     [0014] FIGS.  1  illustrates the first prior art arrangement referred to in the introductory part of the specification. A strainer  1  is disposed upstream of a centrifugal pump  3  and is connected to that pump via a length of pipe incorporating a long sweeping bend  2 . Liquid enters via a flow inlet  4  to the strainer  1  and exists via outlet  5  from the centrifugal pump. This arrangement is disadvantageous because it occupies a large amount of space.  
     [0015]FIG. 2 illustrates the second prior art arrangement referred to in the introductory part of the specification. The long sweeping bend  2  of the arrangement of FIG. 1 has been replaced by a compact 90°fitting  6  in which the strainer comprising a strainer element  7  is fitted. Flow straighteners  8  compensate for the absence of the bend. The disadvantage here is that material  9  accumulates in the restricted space  10  between the strainer element of the housing surrounding it restricting flow.  
     [0016] Referring to FIG. 3, which shows an embodiment of the invention, cylindrical strainer element  11  is arranged within the housing  12  (in the form of a 90°fitting) of the strainer with its axis in line with the direction of inlet flow into the strainer (in this case vertical). The incoming (contaminated) liquid therefore flows first into the interior of the cylindrical strainer element  11  and then out through the element to the exterior of the element in the direction of arrows  13 . Particles suspended in the liquid are retained within the cylindrical element where there is more space and sink to the base of the element at  14  where they may be removed via a drain plug  15  in the strainer housing  12 . The plug  15  may be disposed coaxial with or parallel to the axis of the element  11 . Collected particles may be blown out and magnets may be provided to assist in the removal of metal particles. Flow straighteners  16  are disposed adjacent the inlet of the centrifugal pump  3 .  
     [0017] To provide access to the strainer element  11  a bolted cover  17  is attached to the strainer housing  12 . The element  11  is fitted with handles  19  for ease of inserting and removal. This enables “start up” elements to be fitted and removed after commissioning a system. A pipe support  18  is provided on the base of the device to alleviate any strain on the body of the centrifugal pump  3 . With the above described arrangement a much greater space is provided for the collection of material and its removal is facilitated. The restricted space between the strainer element and surrounding strainer body is kept free of the material thus avoiding any resultant restriction of the flow.  
     [0018] It will be appreciated that the above embodiment has been described by way of example only and that many variations are possible without departing from the scope of the invention.