Patent Publication Number: US-11649835-B2

Title: Debris trap for capturing debris flowing in a stream of liquid and priming assembly for a pump

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to European Patent Application No. 21168863.5, filed Apr. 16, 2021, the contents of which are hereby incorporated by reference in their entirety. 
     BACKGROUND 
     Field of the Invention 
     The present disclosure relates to a debris trap for capturing debris flowing in a stream of liquid and a priming assembly for a centrifugal pump. 
     Background Information 
     Pumps are mechanical equipment which can lift a fluid from low level to high level or cause fluid to flow from a low pressure area to a high pressure area. Pump priming is the process of removing air from the pump and its suction line. Priming is only not required when the pump is either capable of removing air and gases from itself or the layout conditions are so arranged that the pump will be always adequately filled with the liquid to be pumped. 
     In the priming process the pump is filled with the liquid being pumped and the liquid forces all the air, gas, or vapor contained in the passageways of pump to escape out. 
     Conventional pumps can be primed using an ejector or a jet pump. For example, the document EP2481928A1 discloses an ejector in connection with a pump. 
     Document EP 1024293 A2 discloses a debris trap for capturing debris flowing in a stream of liquid, which debris trap comprises a housing having a space inside the housing, a fluid inlet channel in connection with the space, a fluid outlet channel in connection with the space, the fluid outlet channel comprising a fluid outlet port, a float member arranged in the space, a guide means or device configured to guide the float member&#39;s movement as the liquid level in the space changes when in use for capturing debris flowing in a stream of fluid, and a stopper in connection with the fluid outlet port configured to stop the float member&#39;s movement as liquid level in the space raises. 
     SUMMARY 
     It has been determined that an ejector, or a jet pump, has substantially narrow passageways for the fluid to be pumped. Even if the drive fluid used to operate the jet pump can easily be arranged to be clean enough, using a jet pump, operated for example with pressurized air, in connection with a pump configured to pump liquid which contains debris, can be problematic. It has been found that it is quite probable that the debris can enter into the jet pump and clog the narrow passageways, resulting in disturbance of its operation and failing of the priming of the pump. Likewise, should the priming be performed making use of another kind of source of vacuum, entering of debris, at least debris of greater size, to the source of vacuum is problematic. 
     An object of the present disclosure is to provide a debris trap for capturing debris flowing in a stream of liquid and a priming assembly for a pump, by which the operation of a priming jet pump is considerably improved compared to the prior art solutions. 
     Objects of the present disclosure can be met substantially as is disclosed herein which describe in more detail different embodiments of the invention. 
     In one embodiment, a debris trap for capturing debris flowing in a stream of liquid is provided. The debris trap comprises
         a housing having a space inside the housing,   a fluid inlet channel in connection with the space,   a fluid outlet channel in connection with the space, the fluid outlet channel comprising a fluid outlet port,   a float member arranged in the space,   a guide element configured to guide the float member&#39;s movement as liquid level in the space changes when in use,   a stopper in connection with the fluid outlet port configured to stop the float member&#39;s movement as liquid level in the space raises,   the fluid outlet port which, when the float member is against the stopper, is configured to remain partially open and the float member, when brought against the stopper, form a fluid communication path with reduced area, which restricts the size of the debris which can flow through the outlet port.       

     Such a debris trap minimizes escape of debris flowing in a stream of liquid and still causes only minimal pressure loss when used in a priming assembly for a centrifugal pump. The debris trap is particularly for capturing debris floating in a stream of liquid in a priming assembly for a centrifugal pump. In the beginning of priming, the float member is practically not effecting on the transmitting vacuum from the fluid outlet channel to the space of the housing. But, when the float member is against the stopper, the fluid outlet port is configured to remain partially open, and while being fully open, the fluid outlet port cross sectional flow area corresponds to that of the fluid outlet channel. When the float member and the fluid outlet port are brought into effect with each other, size of the debris which can flow through the outlet port is restricted, even though the flow communication is open and vacuum is still transmitted from the fluid outlet channel to the space in the housing. 
     Such a debris trap minimize escape of debris flowing in a stream of liquid and causes only minimal pressure loss when used in a priming assembly. 
     According to an embodiment of the invention the float member, when brought against the stopper, form a fluid communication path between float member and the fluid outlet port having an area of 5-90% of the area of the fluid outlet channel. Such a debris trap, in addition to minimizing escape of debris flowing in a stream of liquid and causing only minimal pressure loss when used in a priming assembly for a centrifugal pump, minimizes possible agglomeration of debris in the trap. 
     According to an embodiment of the invention the float member, when brought against the stopper, form a fluid communication path which creates pressure difference between the space in the housing and the fluid outlet channel. The pressure difference can be utilized for detecting the state of the priming process since when the float member is against the stopper, the priming has been completed. 
     According to an embodiment of the invention the float member, when brought against stopper, form a fluid communication path between float member and the fluid outlet port comprising at least two distinct flow paths. Providing a number of small, separate flow paths to form the fluid communication makes it possible to restrict escape of debris through the trap, and still causing only minimal pressure loss when used in a priming assembly for a centrifugal pump. By the distinct flow path it is possible to determine the size of the debris which is caught by the trap and problems caused by the debris to a source of vacuum can be minimized. 
     According to an embodiment of the invention the least two distinct flow paths comprise axial notches arranged to an inlet edge of the fluid outlet port. Arranging the flow path by downwardly open axial notches in the edge of the fluid outlet minimize the possibility of agglomeration of debris to the fluid outlet port since, after the space of the housing of the debris trap has emptied from the liquid the float member moves away from the fluid outlet and any debris can fall down and be conveyed with the liquid away. 
     Depending on the case, decreasing the fluid communication through the fluid outlet port, when the float member and the fluid outlet port are brought into effect with each other, can be accomplished also such that the least two distinct flow paths comprise holes arranged to extend from a side wall of the float member to a top wall of the float member. 
     According to an embodiment of the invention the least two distinct flow paths comprise holes arranged to the fluid outlet channel. 
     The guide element is advantageously a linear guide, which provides a reliable operation and simple construction of the debris trap. 
     According to an embodiment of the invention the guide element comprises at least three guide bars spaced around the outlet between which the float member is slidably supported. 
     According to an embodiment of the invention the element means is an external guide to the float member. This way the outlet port flow area can be set effectively. 
     According to an embodiment of the invention the guide element comprises a retainer coupled to the at least three guide bars at a distance from the outlet and the float member is arranged between guide bars and the retainer. 
     According to an embodiment of the invention the guide element comprises radial extensions, which extend from the float member towards inner wall of the housing of the debris trap. 
     Priming assembly according to the invention for a pump, which pump comprising a suction side and discharge side, the assembly comprises a source of vacuum controllably connected to the suction side of the pump, and a debris trap according to anyone of the embodiments herein, wherein the fluid outlet channel of the debris trap is connected between the source of vacuum and the suction side of the pump. 
     Priming assembly according to an embodiment the invention for a pump, which pump comprises a suction side and discharge side, wherein the source of vacuum comprising a jet pump having
         a first inlet for the priming fluid for connecting the assembly to a suction side of the pump   a second inlet for drive fluid for connecting the assembly to source of pressurized drive fluid and   an outlet for discharging the priming fluid and the drive fluid from the jet pump, and
 
a debris trap according to anyone of the embodiments herein, wherein the fluid outlet channel of the debris trap is connected to the first inlet of the jet pump.
       

     The priming assembly is particularly advantageous for use in priming of a centrifugal pump. 
     Embodiments of the present invention can also provide the following advantageous effect when using the air as the drive fluid. When the fluid communication path with reduced area, which is formed when the float member is brought against the stopper, is dimensioned suitably, it is possible to prevent an excess amount of liquid from entering the jet pump throat. This way a throat of the jet pump will not be clogged by the liquid, not even temporarily. If the throat becomes clogged, the drive fluid, that is the air, will find its way into the suction side of the pump via the debris trap. This is particularly undesirable in terms of operation of the pump when the working fluid is compressed air. 
     In this application the word vacuum should not be understood to mean an absolute vacuum, like a space devoid of matter, but merely a partial vacuum at suitable level providing required technical effect in the sense of embodiments of the present invention. 
     The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb “to comprise” is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be explained in more detail hereinafter with reference to the drawings. 
         FIG.  1    illustrates a priming assembly for a pump according to an embodiment of the invention, 
         FIG.  2    illustrates a debris trap of the  FIG.  1    during the priming process, 
         FIGS.  3 A and  3 B  illustrate a debris trap according to another embodiment of the invention, 
         FIG.  4    illustrates a debris trap of the  FIG.  3    during the priming process, 
         FIG.  5    illustrates a debris trap according to still another embodiment of the invention, 
         FIG.  6    illustrates a debris trap according to still another embodiment of the invention, 
         FIG.  7    illustrates a debris trap according to still another embodiment of the invention, 
         FIG.  8    illustrates a priming assembly for a pump according to another embodiment of the invention, and 
         FIG.  9    illustrates a debris trap according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    depicts schematically a priming assembly  10  for a pump  12 . A centrifugal pump is a pump type which requires priming in order to start pumping process. In normal conditions, common centrifugal pumps are unable to evacuate the air from an inlet line leading to a liquid surface level  14  of liquid storage  15  which is vertically below that of the pump  12 . The pump has a suction side  16  and discharge side  18 , more particularly the pump includes a suction pipe  20  and a discharge pipe  22  which are connected to the pump  12 . The discharge pipe  22  includes a discharge valve  24 . The priming assembly further comprises a jet pump  26  which is arranged vertically above the centrifugal pump  12 . The jet pump  26 , often an ejector, is known as such for a skilled person in the art. In an ejector, a drive fluid flows through a jet nozzle  58  into a tube that first narrows and then expands in cross-sectional area, which is referred to as a throat  56 . The high velocity drive fluid mixes with the liquid that is drawn in by the vacuum created by the ejector. The strength of the vacuum produced depends on the velocity of the drive fluid and shape of the fluid jet and the shape of the throat and mixing sections downstream the throat  56 . The jet pump is a very compact device in size and has no moving parts and is therefore advantageous for the purpose of priming the pump  12 . 
     The jet pump  26  comprises a first inlet  28  for the priming liquid. The priming assembly  10  comprises a priming conduit  27  which connects the pumps  12  suction side  16  to the first inlet  28 . There is a first control valve  29  arranged to the priming conduit  27  connected to the first inlet  28 . The first inlet is thus connected to the suction side  16  of the pump  12 . The connection to the suction side means that the actual connection is provided to the suction pipe  20  or to the pump  12  itself at a location that the impeller housing will be filled with liquid when the jet pump is operated during the priming process. The jet pump  26  comprises further a second inlet  30  for drive fluid. The second inlet  30  for the drive fluid is connected to source of pressurized drive fluid  32  by a feed pipe  33 . There is a second control valve  31  connected to the second inlet  30 . In this connection the drive fluid is advantageously pressurized air, and the source of pressurized drive fluid is a source of pressurized air. The jet pump  26  comprises further an outlet  34  for discharging the priming liquid and the drive fluid from the jet pump  26 . The outlet  34  is advantageously connected to the liquid storage  15 . 
     The priming assembly comprises further a debris trap  40  arranged to the priming conduit  27  between the suction pipe  20  and the jet pump  26 . Here the priming conduit  27  is coupled to the upper-most location of the suction pipe  20 . The debris trap  40  is arranged to capture debris flowing in a stream of priming liquid towards the jet pump  26 . The debris trap  40  is positioned in a vertical level above the pump&#39;s shaft, advantageously above the impeller of the pump  12 . The first control valve  29  is between the debris tramp  40  and the jet pump  26  in  FIG.  1   , but the debris trap  40  can also be arranged between the first control valve and the debris trap  40 . By the debris trap  40  it is ensured that the jet pump will not become clogged.  FIG.  1    shows a debris trap  40  in an extremely exemplary manner for purposes of understanding the main functions of the trap  40 . The debris trap  40  comprises a housing  42  in which a space  44  is arranged inside the housing. The housing includes a liquid inlet channel  46  in connection with the space  44  The priming conduit  27  connected to the fluid inlet channel  46 . There is a fluid outlet channel  48  arranged to the upper part of the housing  42 , in connection with the space  44 . The fluid outlet channel  48  comprises a fluid outlet port  50  which provides fluid communication between the space  44  and the fluid outlet channel  48 . 
     There is a float member  52  arranged in the space  44  of the housing  42 . The debris trap  40  further includes a guide means or element  54  in the space  44 . The guide element  54  comprises linear guides, such as bars, arranged to extend vertically around the guide element  54 . The guide element  54  is external to the float member  52 . The debris trap  40  includes a stopper  53  arranged in the space  44  at an upper end of the guide element  54 . The stopper  53  is in connection with the fluid outlet port  28  and it is configured to stop the float member&#39;s movement, as liquid level in the space rises in the space  44 , before the fluid outlet port closes totally. The float member  52  in  FIGS.  1  and  2    is a spherical ball having a slanted top regardless of its position. The float member  52  is arranged to be guided by the guide element  54  into operational contact, and from operational contact, with the fluid outlet port  50  as the liquid level in the space  44  changes vertically when in use to capture debris flowing in a stream of liquid during the priming operation of the assembly  10 . The float member  52 , the guide element  54  and the fluid outlet port  50  together control fluid communication from the space  44  to the fluid outlet channel  48  of the debris trap  40 . The float member  52  and the fluid outlet port  50 , when the float member, more particularly its upper end, is brought against the stopper  53 , decrease effective cross sectional flow area of fluid communication through the fluid outlet port, which is thus configured to remain partially open, when the float member  52  is against the stopper  53 . Depending on the practical case, the fluid outlet port is decreased so as to have an area of 5-90% of the area of the fluid outlet channel, but it does not totally close the flow connection from the space  44  to the fluid outlet channel  48 . 
     When the float member  52  is against the stopper  53  the flow communication through the outlet port remains partially open with a restricted area and therefore the size of the debris which can flow through the outlet port  50  is restricted, even though the flow communication is open and vacuum is still transmitted from the fluid outlet channel  48  to the space  44 . 
     The priming assembly  10  functions in a following manner, applicable to all embodiments of the debris trap. After the pump  12  has been stopped and it has been emptied from the pumped liquid i.e. the pump is filled with the air. When the pump is desired to be started the priming steps are executed as follows. First, the discharge valve  24  is closed separating the discharge pipe  22  from the pump  12 . Next, the second control valve  31  is opened which connects the source of pressurized air to the jet pump  26 . Pressurized air is led to the jet pump  26  and out through the outlet  34 . The first control valve  29  is now opened. This starts the operation of the jet pump. Vacuum is generated to the first inlet  28  of the jet pump and liquid begins to rise up from the liquid storage  15  to the suction pipe  20 . After the jet pump has been operating for a while, the liquid surface rises up to the debris trap  40  and the liquid level is thus so high that the pump housing is also filled with the liquid. Adequate level of the liquid can be detected in the debris trap. Now the pump  12  can be started and the discharge valve  24  opened. The first valve  29  of the jet pump can now be closed and also the introduction of the pressurized air can be stopped. 
     The priming assembly is advantageous for use in practical applications where the liquid, such as water, contains small, debris in it, wherein the debris trap is configured particularly to capture debris floating in a stream of liquid. When priming a pump, the most problematic debris is floating debris which does not experience gravity force substantially greater than the buoyance caused by the liquid. Floating debris can be floating on the surface of the liquid or it can be partially or fully submerged in the liquid. 
     Such applications where the liquid contains small debris can be found for example in the forest industry, and waste treatment processes, just to mention a few. In  FIG.  2   , which shows a debris trap  40  of  FIG.  1    during the priming process, the liquid level has risen up to the debris trap  40  which is under the effect of the under-pressure created by the jet pump  26 . The float member  52  has moved upwards from its lower position (the lowest position shown in  FIG.  1   ), where the air flow into the fluid outlet channel  48  is practically unaffected by the float member  52 , under guidance of the guide element  54  to its uppermost position (the position shown in  FIG.  2   ), where float member  52  and the fluid outlet port  50  are brought into effect with each other. The float member is against the stopper  53 . In this embodiment the fluid outlet port  50  reduces to a narrow slot formed between the float member  52  and the end of the fluid outlet channel  48 . This embodiment prevents entry of substantially compact debris into the jet pump, but can allow an escape of substantially elongated debris which has its diagonal dimension smaller than the slot. The float member  52  has a predetermined buoyancy in the liquid in question, such that its uppermost point raises above the liquid level  60  when it is floating freely. The actual height of the float member  52  above the liquid level is determined by knowledge or assessment of quantity and/or quality, such as size, of the debris present in the liquid. Advantageously the float is configured to extend more than 5 mm above the liquid surface  60 . Typically, the float member  52 , having an axial length in the direction of its guided movement in the space, has a portion of less than 50% of its axial length above the surface of the liquid. 
     As a first measure, since the float member extends above the surface liquid surface level, the float member is guided by the guide element  54  to move to in front of the fluid outlet port  50  before the rising liquid. This alone decreases the possibility of larger debris escaping through the fluid outlet port  50 . As a next measure, since the float member  52  is guided by the guide element  54  to move towards the fluid outlet port  50 , without totally closing the fluid communication through the fluid outlet port  50 , the jet pump still effects on the space  44  of the debris trap  40  and the priming conduit  27 , maintaining the liquid up in the priming conduit  27 , suction pipe  20  and the pump housing  12 . This position is shown in the  FIG.  2   . Here the float member  52  and the fluid outlet port  50 , when brought facing to, or into effect with each other, form a fluid communication path having a reduced area for a fluid communication. The area is determined to be such that any possibly escaping debris has so small size that it does not clog up the jet pump  26 . 
     Even if a spherical float member, as is shown in  FIGS.  1  and  2   , can operate adequately in some practical applications, for certain type of debris,  FIGS.  3 A and  3 B  show another embodiment, which is an improved form of the debris trap  40  of  FIGS.  1  and  2   . The debris trap  40  shown in  FIGS.  3 A and  3 B  is installed in the priming assembly in similar way as the one shown in  FIG.  1   . It also operates in a corresponding manner. More particularly, the debris trap  40  comprises a tubular housing  42  having a space  44  inside the housing. The housing is formed by a tube part  42 . 1  which includes an end plate  42 . 2  at an upper end of the tube part  42 . 1 . The end plate  42 . 2  has a fluid outlet  48  arranged coaxially with the tube part  42 . 1 . 
     The housing includes a liquid inlet channel  46  which is formed by a first flange  42 . 3 . The first flange is rigidly connected to the tube part  42 . 1 . The tube part  42 . 1  and the first flange  42 . 3  have substantially equal inner diameters forming a cylindrical space  44  in the housing  42 . The fluid outlet channel  48  is a pipe which is arranged extend through the end plate  42 . 2  into the space  44 . The fluid outlet channel  48  has smaller diameter than the tube part  42 . 1  such that an annular space is formed between the fluid outlet channel  48 . The fluid outlet channel  48  comprises a fluid outlet port  50  which provides fluid communication between the space  44  and the fluid outlet channel  48 . The fluid outlet channel comprises further a flange  42 . 4  at its upper end, rotatably assembled in respect to the outlet channel  48 . The housing structure shown in  FIGS.  3 A and  3 B  can include a float member  52  shown in  FIGS.  1  and  2   . 
     Also, in the improved form of the debris trap there is a float member  52  arranged in the space  44  of the housing  42 , which is arranged to move vertically under control of guide element  54  in the space  44 . The float member is substantially cylindrical having a lightening recess  52 . 1  at its bottom, which is the opposite end to the one configured to cooperate with the stopper  53 . By the lightening recess  52 . 1  it is possible to adjust and set the height of the float member  52  above the liquid surface, while axial length of its side wall provides adequate guidance from the guide element. The guide element comprises linear bars  54  arranged to extend vertically downwards from the end plate  42 . 2 . Each guide bar  54  is fixed to lower surface of the end plate  42 . 2  evenly around the fluid outlet  48 . The lower end of formed set of guide bars, which can also be referred to as a cage, has a retainer ring  55  at its lower end. The guide bars  54  form an external guide to the float member  52 . The retainer ring  55  has an opening at its center area for increasing flow area in the space  44  at the axial location of the retainer ring  55 . The retainer ring  55  keeps the float member  52  inside the cage.  FIGS.  3 A and  3 B  show four guide bars  54  but even three spaced guide bars results in proper guidance for a cylindrical float member  52  and therefore the presented four guide bars can be replaced with a setup of three guide bars. 
     The float member  52  is arranged to be guided by the guide bars  54  into contact, and from contact, with the fluid outlet port  50  as the liquid level in the space  44  changes vertically when in use for capturing debris flowing in a stream of liquid during the priming operation of the assembly  10 . The end of the fluid outlet channel  48  is also the stopper  53  for the upwards movement of the float member  52 . The fluid outlet port  50  comprise several axially extending notches  50 . 1  arranged to the inlet edge of the fluid outlet channel  48 . This way the outlet port, when the float member  52  is against the stopper  53 , comprises several separate, or distinct flow paths. Here the distal ends of the notches form the stopper  53 . The float member  52 , the guide element  54  and the notches  50 . 1  of the fluid outlet port  50  together control fluid communication from the space  44  to the fluid outlet channel  48  of the debris trap  40 . Now the notches have an axial depth which is substantially equal to its width. This way the embodiment prevents escape of substantially compact debris, and also prevents efficiently escape of substantially elongated debris which has its diagonal dimension smaller than the slot. 
     In  FIG.  4    liquid level has risen up to the debris trap  40  under the effect of the under-pressure created by the jet pump  26 . The float member  52  has moved upwards from its lowest position (the situation in  FIG.  3   ), where the air flow into the fluid outlet channel  48  is unaffected by the float member  52 , under guidance of the guide element  54  to its uppermost position (the situation in  FIG.  4   ), where float member  52  and the fluid outlet port  50  are brought into effect with each other. The float member has a predetermined buoyancy in the liquid in question, such that is uppermost point raises above the liquid level  60 . The actual height of the float member  52  above the liquid level is determined by knowledge or assessment of quantity and/or quality, such as size, of debris present in the liquid. Advantageously the float is configured to more than 5 mm above the liquid surface  60 . 
     The float member  52 , when the float member is brought against the stopper  53 , decreases fluid communication through the fluid outlet port such that the separate notches have a common area of 5-90% of the area of the fluid outlet channel, but does not totally close the flow connection from the space  44  to the fluid outlet channel  48 . 
     Also, in the embodiment of  FIGS.  3 A,  3 B and  4    the float member extends above the surface liquid surface level, when floating freely, and the float member is guided by the guide element  54  to move to in front of the fluid outlet port  50  before the rising liquid can reach the outlet port  50 . This alone decreases the possibility of larger debris escaping through the fluid outlet port  50 . As a next measure, since the float member  52  is guided by the guide bars  54  to move against the stopper, without totally closing the fluid communication through the fluid outlet port  50 , the jet pump still effects on the space  44  of the debris trap  40  and the priming conduit  27  maintaining the liquid up in the priming conduit  27 , suction pipe  20  and the pump housing  12 . This position is shown in the  FIG.  4   , where the float member  52  and the fluid outlet port  50 , when brought to face each other, form a fluid communication path having an area for a fluid communication. In  FIGS.  3 A,  3 B and  4    the float member  52 , when brought against the stopper  53 , form a fluid communication path comprising at least two distinct flow paths. The distinct flow paths are formed by the notches in rim the fluid outlet channel  48 . The area of each distinct flow path is determined to be such that any possibly escaping debris has so small size that it does not clog up the jet pump  26 . In practice this can be achieve for example such that the area of each distinct flow path is smaller than the area of the throat of the jet pump. 
       FIG.  5    shows another embodiment which is otherwise similar to that in  FIGS.  3 A,  3 B and  4    except that instead of the notches, the outlet channel  48  includes holes  50 . 2 , preferably round holes, arranged near the edge of the channel  48 . The holes are arranged at a small distance from the edge which is smaller than the diameter of the holes. Alternatively or additionally to other embodiment which result in decreasing the area of the fluid communication port  50  when the float member  52  and the fluid outlet port  50  are brought into effect with each other,  FIG.  5    describes holes  52 . 2  arranged to extend from a side wall of the float member to a top wall of the float member, forming least two distinct flow paths in the fluid communication port. The area of each distinct flow path, i.e. the holes, is determined to be such that any possibly escaping debris has such a small size that it does not clog up the jet pump  26 . 
       FIG.  6    shows another embodiment which is otherwise similar to that in the  FIGS.  3 A and  3 B and  4    except that instead of the notches being arranged to the outlet channel  48 , the float member  52  includes radial grooves  52 . 3  at its upper end. The grooves extend from the side wall of the float member  52  towards its center. The top end can be slanted to improve removal of debris from the top of the float member  52 . Also in the other embodiments described the top of the float member can be slanted of conical. 
       FIG.  7    shows still another embodiment which is otherwise similar to that in  FIGS.  3 A,  3 B and  4   , except that the guide element  54  is integrated to the float member  52  replacing the guide bars. The guide element comprises radial extensions, which extend from the float member  52  towards an inner wall of the housing  42  of the debris trap  40 . The radial extension has a guide surface  54 . 1  parallel to the inner surface of the space  44  of the housing  42 . The guide surface  54 . 1  can be comprised of outer edges of several separate extensions. The guide element can also comprise a sleeve (not shown) arranged against the inner surface of the space  44  connected with radial supports to the float member  52 . It is also conceivable to arrange the float means or member  52  such that its diameter is so large that it takes its guidance directly from the inner surface of the space  44  and provided with axial flow through channels with adequate area radially outside the region of the fluid outlet channel  48 . 
       FIG.  8    discloses schematically a priming assembly  10  for a pump  12 . A centrifugal pump is a pump type which requires priming in order to start a pumping process. In normal conditions, common centrifugal pumps are unable to evacuate the air from an inlet line leading to a liquid surface level  14  of liquid storage  15  which is vertically below that of the pump  12 . The pump has a suction side  16  and discharge side  18 , more particularly the pump includes a suction pipe  20  and a discharge pipe  22  which are connected to the pump  12 . The discharge pipe  22  includes a discharge valve  24 . The priming assembly further comprises a source of vacuum  11 . The source of vacuum can be for example an ejector, a vacuum pump, blower or even a general vacuum system, such as a paper machine vacuum system. The source of vacuum  11  is connected to the suction side  16  of the pump  12 . The connection to the suction side means that the actual connection is provided to the suction pipe  20  or to the pump  12  itself at a location that the impeller housing will be filled with liquid when source of vacuum is in flow connection, controlled by a valve  29 , with the suction side of the pump. 
     The priming assembly further comprises a debris trap  40  arranged to the priming conduit  27  between the suction pipe  20  and the source of vacuum  11 . Here the priming conduit  27  is coupled to the upper-most location of the suction pipe  20 . The debris trap  40  is arranged for capturing debris flowing in a stream of priming liquid towards the jet pump  26 . The debris trap  40  is positioned to a vertical level above the pump&#39;s shaft, advantageously above the impeller of the pump  12 . The first control valve  29  is between the debris trap  40  and the source of vacuum  11 . By the debris trap  40  it is ensured that only debris of limited size can proceed towards the source of vacuum  11 .  FIG.  8    shows a debris trap  40  in extremely exemplary manner for purposes of understanding the main functions of the trap  40 , and it can be constructed according to anyone of the embodiments of the debris trap described here, and modified within the skills of a person in the art. 
       FIG.  9    discloses a further developed embodiment of the invention, The debris trap  40  shown in  FIG.  9    is installed in the priming assembly in a similar way as the one shown in  FIG.  1   . It is otherwise similar to the embodiment that is shown in  FIGS.  3 A and  3 B  but including a device or means for determining a position  80  of the float member  52  in the housing  42 . The device for determining a position  80  of the float member is utilized for detecting the level of the liquid in the priming assembly  10  such that the state of priming is reliably recognized. The device for determining the position  80  of the float member comprises at least a first sensor  82  which detects the state where the float member  52  is against the stopper  53 . There can be optionally a second sensor  84  which detects the state where the float member  52  off from the stopper  53 , in other words it is not against the stopper. The type of proximity sensor can be selected as required by the practical solution, and it can be e.g. type of capacitive, magnetic, radar or sonar, just to mention a few feasible types of such sensors. The device for determining position  80  of the float member can also comprise a dedicated electronic control unit  86  to process signals provided by the sensor or the sensors into more usable form, if so desired. When the level of the liquid is reliably determined function of the priming assembly  10  is more efficient because unnecessary delay between starting of jet pump and start of pump is avoided. The device for determining position  80  of the float member can be arranged to practically any embodiment, regardless of the actual design of the float member  40 . 
     While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above can be used in connection with another embodiment when such combination is technically feasible.