Patent Publication Number: US-9404494-B2

Title: Screw pump having an integrated pressure limiting valve

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2010/005657, filed on Sep. 15, 2010, which claims the benefit of priority to Serial No. DE 10 2009 056 218.4, filed on Nov. 28, 2009 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     The present disclosure relates to a screw pump having an integrated pressure limiting valve. 
     Screw pumps are generally self-priming positive displacement pumps preferably suitable for the low pressure range and are used to pump fluids in the form of supply and discharge pumps, for pumping heavy and light heating oils and for all lubricating fluids, used and residual oils and grease. Screw pumps can furthermore be used as lubricating, sealing, control, hydraulic, cooling and refrigerating oil pumps, and as fuel pumps for engines. 
     By way of example, the prior art has disclosed a screw pump of this kind which has three screws, which are mounted parallel to one another in a pump housing. Here, the pump housing forms a screw chamber, into which the screw or shaft sections of the three screws project and which has a fluid connection to a pressure chamber. Also formed in the pump housing is an inlet duct, which opens into the screw chamber at one axial end thereof, and an outlet duct, which forms the pressure chamber at another axial end, opening into said chamber. 
     A pressure limiting valve is inserted into the pump housing or the housing wall thereof, parallel to the screw chamber, extending coaxially with the screws and opening into the pressure outlet duct. The pressure limiting valve furthermore has a connection to the inlet duct formed in the pump housing. 
     Accordingly, if the pressure in the pressure outlet duct exceeds a predetermined value, the pressure limiting valve opens and relieves the excess pressure to the suction side of the screw pump. This prevents pressure overloading of the pump. However, the integration of the pressure limiting valve into the pump housing makes it necessary to reinforce the pump housing or the housing wall thereof at the envisaged location of installation in order to be able to create an accommodation space for the pressure limiting valve. This requires an increase in the external dimensions of the pump housing, and the pump also becomes heavier overall due to the additional cast material on the pump housing. 
     Given this known prior art, it is the object of the present disclosure to provide a screw pump having an integrated pressure limiting valve, the external dimensions of which can be kept compact and which is of lighter construction than the prior art. 
     This object is achieved by a screw pump having the features set forth below. Further advantageous embodiments of the disclosure are also set forth below. 
     The basic concept of the disclosure is based on using already existing accumulations of material on the pump housing, which are required for the operation and/or installation of the pump, for the installation of an integrated pressure limiting valve. According to the disclosure, therefore, provision is made for the pressure limiting valve to be installed in the flange section of the pump housing, which already has an accumulation of material in the pump housing or on the housing wall by virtue of the function thereof. In this way, there is no need to provide an additional cast lug on the pump housing, and therefore the external dimensions of the pump housing do not increase relative to a screw pump without the pressure limiting valve. 
     Moreover, there is little or no increase in the weight of a screw pump having a pressure limiting valve integrated in this way. 
     In the screw pump according to the present disclosure, the pressure chamber is preferably likewise formed in the flange section of the pump housing, wherein the pressure limiting valve opens directly into the pressure chamber. In this way, the wall thickness of the pump housing remains great enough in the region of the pressure chamber to withstand the pressure that may be expected in the pressure chamber, without the need to make any additional wall reinforcements here. 
     It is furthermore advantageous to form the flange plate of the pump on the pump housing at a location such that the flange plate surrounds the pressure chamber like a belt. In this way, the housing wall is additionally reinforced in the region of the pressure chamber. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a cross-sectional view of the pump housing according to a preferred embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is explained in greater detail below with reference to a preferred illustrative embodiment with reference to the single accompanying figure. This figure shows a longitudinal section through the housing of a screw pump according to the disclosure with an inserted screw and an installed (integrated) pressure limiting valve. 
     The pump housing  1  of the screw pump according to the preferred illustrative embodiment of the disclosure consists of a flange section  2  for mounting the pump on a component (not shown specifically) and a screw housing section  4  which represents a separate housing part from the flange section  2  and is screwed, caulked or riveted to the flange section  2 . 
     Formed in the flange section  2  is a pressure chamber  6 , which is connected to a screw chamber  10  within the screw housing section  4  by a connecting bore  8 . Moreover, an inlet bore  12  is formed in the flange section  2  as an axial extension of the connecting bore  8 , said inlet bore likewise opening into the pressure chamber  6  and leading to a flange-type outer side of the flange section  2 , said outer side lying opposite the screw housing section  4 . A pump cover  14  is screwed onto this outer side, and a through bore  16  is likewise formed in this pump cover, said bore being aligned axially with respect to the connecting bore  8  and inlet bore  12  of the flange section  2 . 
     The shank  18  of a screw  20  is inserted into the bores  8 ,  12 ,  16  in such a way that it is rotatably supported in the through bore  16  of the pump cover  14  by means of a ball bearing or rolling contact bearing  22 . In the region of the inlet bore  12  of the flange section  2 , the screw shank  18  is formed with a sealing section  24 , which is in sealing sliding engagement with the inlet bore  12  of the flange section  2 . Finally, the screw  20  forms a helical section  26 , which is accommodated in the screw chamber  10  of the screw housing section  4 . The pressure chamber  6  in the flange section  2  is formed non-centrally with respect to the screw shank  18 , i.e. the pressure chamber  6  forms a radially projecting section  6   a  relative to the screw shank  18  and to the connecting bore  8  formed in the flange section  2 . Opening into this radially offset or projecting section  6   a  is an outlet bore  27  of the screw pump. Moreover, the flange section  2  has an integrally formed annular flange plate  29 , which surrounds the pressure chamber  6  and, in the process, reinforces the housing wall of the flange section  2 . 
     A pressure limiting valve  28  is inserted into the flange section  2 , parallel to the screw shank  18 , at the level of the connecting bore  8  and opens into the radially offset or projecting section  6   a  of the pressure chamber  6 . More specifically, the flange section  2  forms in this region an accumulation of material  2   a  in which the pressure chamber  6  is formed on the inside and which is suitable for the formation of a bore  30  for the pressure limiting valve coaxially with the connecting bore  8  of the flange section  2 . Consequently, the pressure limiting valve  28  is positioned in a region between the screw housing section  4  and the flange plate  29 , approximately at the level of the connecting bore  8  and coaxially with the screw shank  18 . 
     In this arrangement, the pressure limiting valve  28  consists of a valve element  32  in the form of a plunger, the plunger tip  34  of which is seated in a sealing manner on a valve seat  36 , which is formed in the pump housing  1 , i.e. in the flange section  2 . In this case, the valve element  32  is preloaded onto the valve seat  36  by means of a spring  38 , the preloading force of which can be adjusted by means of an adjusting screw  40 , which is likewise screwed into the flange section  2  of the pump housing  1 . A drain bore  42  bored into the flange section  2  substantially perpendicularly to the pressure limiting valve  28  is provided underneath the valve seat  32  and is connected to a fluid tank (not shown specifically). As soon as a pressure set by means of the preloading spring  38  is exceeded within the pressure chamber  6 , the pressure limiting valve  28  opens and relieves the excess pressure directly into the fluid tank. 
     Finally, it should be noted that the position and alignment of the pressure limiting valve  28  is not limited to the illustrative embodiment described above. On the contrary, the pressure limiting valve  28  could also be inserted into the flange section  2  in a radial direction relative to the connecting bore  8 , in which case the valve plunger  32  of the pressure limiting valve  28  opens or closes a pressure relief bore between the pressure chamber  6  and a tank port, said relief bore running parallel to the connecting bore  8 . It is also conceivable to insert the pressure limiting valve  28  into the flange section  2  above the flange plate  29 , i.e. between the flange plate  29  and the pump cover  14 , in which case the accumulation of material required on the flange section  2  for the flange mounting surface of the pump cover  14  can be used for the installation of the pressure limiting valve  28 . 
     LIST OF REFERENCE SIGNS 
     
         
           1  pump housing 
           2  flange section 
           4  screw housing section 
           6  pressure chamber 
           6   a  projecting chamber section 
           8  connecting bore 
           10  screw chamber 
           12  inlet bore 
           14  pump cover 
           16  through bore 
           18  screw shank 
           20  screw 
           22  rolling contact bearing 
           24  sealing section 
           26  helical section 
           27  outlet bore 
           28  pressure limiting valve 
           29  flange plate 
           30  valve bore 
           32  valve element 
           34  plunger tip 
           36  valve seat 
           38  preloading spring 
           40  adjusting screw 
           42  drain bore