SELF-PRIMING CENTRIFUGAL PUMP

Technical field

[01] The present invention relates to a self-priming centrifugal pump.

Prior art

[02] The use of self-priming centrifugal pumps which provide for an ejector group connected on one side to the suction of the liquid and on the opposite side to the inlet of the impeller group, coaxially thereto, is currently known.

[03] More specifically, the known self-priming centrifugal pumps comprise a substantially cylindrical shaped body having a front-facing liquid suction opening and an outlet opening located on an upper side. The impeller group, adapted to be rotated by a suitable motor member, generally of the electric type, is housed inside a pumping chamber, which is associated with the pump body.

[04] The ejector group is arranged inside the cavity defined by the pump body. The ejector group comprises an ejection nozzle and a collecting suction conduit shaping a divergent profile. The collecting suction conduit is connected on one side to the suction opening and on the opposite side to the inlet of the impeller group, coaxially thereto. The recirculation of the liquid is carried out through the ejection nozzle; the liquid, on exiting from the pumping chamber of the impeller group, fills the internal cavity of the pump body.

[05] In use, the total flow rate passing through the impeller group is partly delivered through the outlet opening and partly recycled through the ejection nozzle thanks to the Venturi effect produced in the collecting suction conduit.

[06] Patent EP 0.401.670 illustrates, for example, a self-priming centrifugal pump of this type.

[07] The main problem in the use of centrifugal pumps of the aforementioned type is the performance decay that occurs when a certain value of the flow rate is reached. This effect is caused by the incipient cavitation that is generated in the area surrounding the ejection nozzle at the opening of the Venturi tube. It follows that the maximum flow rate achievable in centrifugal pumps of the aforementioned type finds a limit caused by the aforementioned performance decay.

[08] Figures 2 and 3 illustrate in graphical form, with the dotted lines FI and P, the variation respectively of the hydraulic head and the percentage efficiency of a known self-priming centrifugal pump as a function of the flow rate. It is clearly visible that once a predetermined flow rate value Q' is reached, both the head and the efficiency of the pump fall. Ultimately, this Q' value represents the maximum flow rate achievable in centrifugal pumps of the aforementioned type.

[09] US patent 2,634,680 illustrates a self-priming centrifugal pump, selectively operable in a first mode (so-called shallow-well system) and a second mode (so-called deep well system). The pump provides for a by-pass conduit, through which the liquid may flow from the outlet opening to the impeller group, without engaging the ejector group.

[10] GB 397,035 discloses a further embodiment of a self-priming centrifugal pump equipped with a by-pass conduit.

[1 1 ] However, these solutions are not exempt from improvements.

Disclosure

[12] The aim of the present invention is to solve the aforementioned problems by devising a self priming centrifugal pump, which allows the maximum achievable flow rate to be increased while maintaining high levels of performance.

[13] Within this aim, a further object of the present invention is to provide a self-priming centrifugal pump, which ensures the maintenance of the maximum pressure.

[14] Another object of the invention is to provide a self-priming centrifugal pump which allows the efficiency of the pumping group to be improved.

[15] Still another object of the invention is to provide a self-priming centrifugal pump of simple constructive and functional conception, provided with a certainly reliable operation, of versatile use, as well as of relatively economical cost.

[16] The aforementioned objects are achieved, according to the present invention, by the self priming centrifugal pump according to claim 1 .

[17] The self-priming centrifugal pump comprises a pump body having an inner cavity having a longitudinal axis arranged in a horizontal position in use configuration; a pumping chamber associated with said pump body and having at a frontal part thereof an axial inlet opening; an ejector group which extends inside said inner cavity of the pump body according to said longitudinal axis and which is axially associated with said pumping chamber, within said inner cavity of the pump body being defined an upper zone and a lower zone with respect to said ejector group; a suction opening made on a frontal surface of said pump body at said upper zone located above said ejector group; an auxiliary suction conduit arranged inside said inner cavity of the pump body, at said upper zone with respect to said ejector group, and configured for directly connecting said suction opening with said inlet opening of the pumping chamber.

[18] Inside said pumping chamber an impeller group provided with an axial hub adapted to be associated with a motor shaft coaxial thereto according to said longitudinal axis is arranged.

[19] Said ejector group comprises an ejection nozzle and a collecting suction conduit shaping a divergent profile, connected, at the end of the wider section thereof, to said inlet opening of the pumping chamber.

[20] Preferably, said divergent profile is made up of a first portion with constant inclination and a second section with increasing inclination which engages in said axial inlet opening of the pumping chamber. [21] Preferably, said auxiliary suction conduit opens into the upper part of said first portion at a constant inclination of the collecting suction conduit.

[22] Advantageously, the pump comprises a non-return valve arranged inside said auxiliary suction conduit.

[23] Advantageously, said auxiliary suction conduit has a substantially rectilinear arrangement.

[24] Preferably, said auxiliary suction conduit is inclined at an angle of predetermined width with respect to said longitudinal axis of the pump body.

[25] Preferably, said angle of predetermined width is approximately 45°.

[26] Preferably, said auxiliary suction conduit has a slightly curved upper portion which may be inserted into the top of said feeding conduit in front of said suction opening.

[27] Preferably, said upper portion of the auxiliary suction conduit engages at the top of said feeding conduit according to an axis substantially parallel to the horizontal axis of said suction opening.

[28] Advantageously, said collecting suction conduit is connected, at said ejection nozzle, to a feeding conduit which extends substantially in a radial direction at said upper zone of the pump body and is connected to said suction opening at the top.

[29] Preferably, said feeding conduit opens into a portion of said collecting suction conduit arranged in a toroidal shape around said ejection nozzle.

[30] Advantageously, at a high flow rate, the pressure at the region of said collecting suction conduit near the mouth of said inlet opening of the pumping chamber is lower than the pressure at the top of said auxiliary suction conduit.

[31] In this way, the non-return valve opens the said auxiliary suction conduit, allowing the pump to achieve a high flow rate and efficiency.

[32] Advantageously, at a low flow rate, the pressure at the zone of said collecting suction conduit near the mouth of said inlet opening of the pumping chamber is higher than the pressure at the top of said auxiliary suction conduit.

[33] In this way, the non-return valve closes the said auxiliary suction duct, allowing the pump to maintain a high head.

Description of drawings

[34] The details of the invention will become more apparent from the detailed description of a preferred embodiment of the self-priming centrifugal pump according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, where: Figure 1 shows an axial section view of the self-priming centrifugal pump;

Figures 2 and 3 show a graph respectively of the head and the efficiency of the pump as a function of the flow rate.

Embodiments of the invention

[35] With particular reference to these figures, the reference numeral 1 indicates the self-priming centrifugal pump according to the invention. The centrifugal pump 1 comprises a pump body 10, which shapes an inner cavity 1 1. The pump body 10 defines the casing of the operating members of the pump.

[36] The pump body 10 has for example a substantially cylindrical shape and has a longitudinal axis A arranged in a horizontal position in the use configuration. As specified in the following, the longitudinal axis A represents the motor axis of the rotating parts of the pump.

[37] The longitudinal axis A divides the inner cavity 1 1 of the pump body 10 into an upper zone S and in a lower zone I.

[38] A suction opening 12 is made on a frontal surface 13 of the pump body 10. The suction opening 12 is arranged at the upper zone S of the pump body 10 located above the longitudinal axis A.

[39] An outlet opening 14 is made on an upper surface 15 of the pump body 10. The outlet opening 14 is in communication with the upper zone S of the inner cavity 1 1 of the pump body 10. The outlet opening 14 is arranged radially with respect to the longitudinal axis A of the pump body 10.

[40] A pumping chamber 20 is associated with the pump body 10. The pumping chamber 20 has an axial inlet opening 21 at the frontal part thereof, facing the inner cavity 1 1 of the pump body 10. The pumping chamber 20 substantially closes the inner cavity 1 1 of the pump body 10 on the opposite side the frontal surface 13.

[41] Inside the pumping chamber 20 an impeller group 22 is arranged, of a known shape; the impeller group 22 is provided with an axial hub 23, which is axially associated with a motor shaft 24 coaxial thereto. The motor shaft 24 is adapted to be rotated by a motor member 25, for example of an electric type, represented only partially in the figure.

[42] An ejector group 30 is axially associated with the pumping chamber 20 and extends inside the inner cavity 1 1 of the pump body 10. The ejector group 30 comprises an ejection nozzle

31 and a collecting suction conduit 32 shaping a divergent profile. The collecting suction conduit 32 is connected at the end of the wider section thereof to the mouth of the inlet opening 21 of the pumping chamber 20; at the opposite end, the collecting suction conduit

32 is connected to a feeding conduit 33 which extends substantially in a radial direction at the upper zone S of the pump body 10 and at the top is connected to the suction opening 12.

[43] Preferably the feeding conduit 33 opens into a portion of collecting suction conduit 32 arranged in a toroidal shape around the ejection nozzle 31 .

[44] In the illustrated embodiment, the ejector group 30 is made up of a rear part 30a and a frontal part 30b. The rear part 30a substantially shapes the collecting suction conduit 32 and the feeding conduit 33; the frontal part 30b is constituted by a cover which frontally closes the rear part 30a and shapes the ejection nozzle 31 and a sleeve 36 which is inserted tightly in the suction opening 12.

[45] According to the present invention, the self-priming centrifugal pump has an auxiliary suction conduit 34 adapted to put the suction opening 12 in direct communication with the inlet opening 21 of the pumping chamber 20. The auxiliary suction conduit 34 has a substantially rectilinear arrangement and is contained at said upper zone S of the inner cavity 1 1 of the pump body 10 located above the longitudinal axis A. In particular, the auxiliary suction conduit 34 is inclined at an angle of predetermined width with respect to the longitudinal axis A; this angle is included for example in a range around 45°, depending on the size of the pump.

[46] In practice, the auxiliary suction conduit 34 has a slightly curved portion at its top, which is inserted into the top of the feeding conduit 33 in front of the suction opening 12. Preferably, the upper portion of the auxiliary suction conduit 34 engages in the top of the feeding conduit

33 with its axis substantially parallel to the horizontal axis of the suction opening 12.

[47] A non-return valve 35 is arranged inside the auxiliary suction conduit 34, in a substantially central position. The non-return valve 35 is adapted to close the auxiliary suction conduit

34 when the pressure at the area of the collecting suction conduit 32 near the mouth of the inlet opening 21 of the pumping chamber 20 is higher than the pressure at the top of the auxiliary suction conduit 34.

[48] The operation of the self-priming centrifugal pump may be easily understood from the above description.

[49] In use, the total flow rate passing through the impeller group 22 is introduced into the inner cavity 1 1 of the pump body 10. This total flow is partly delivered through the outlet opening 14 and partly drawn back into circulation through the ejection nozzle 31 , thanks to the Venturi effect, which is produced in the collecting suction conduit 32.

[50] When the required flow rate exceeds a predetermined value, the non-return valve 35 opens the auxiliary suction conduit 34 and allows the liquid to pass directly from the suction opening 12 to the inlet of the pumping chamber 20. In this way cavitation phenomena are avoided in the area surrounding the ejection nozzle, at the inlet of the collecting suction conduit 32, while allowing the overall flow entering the impeller group 22 to increase up to the desired value.

[51] In particular, when working with high flow rates, the pressure at the area of the collecting suction conduit 32 near the mouth of the inlet opening 21 of the pumping chamber 20 is lower than the pressure at the top of the auxiliary suction conduit 34 and therefore the non return valve 35 opens the auxiliary suction conduit 34. In this way, a greater flow rate and greater efficiency are obtained than with a traditional self-priming pump.

[52] Conversely, when working with low flow rates, the pressure at the area of the collecting suction conduit 32 near the mouth of the inlet opening 21 of the pumping chamber 20 is higher than the pressure at the top of the auxiliary suction conduit 34 and therefore the non return valve 35 closes the auxiliary suction conduit 34. In this way, a greater prevalence is obtained compared to a traditional centrifugal pump.

[53] In practice, it has been found that the self-priming centrifugal pump according to the present invention has a trend of the head and of the efficiency which maintain relatively high values for flows significantly higher than the traditional pumps, as shown in the graphs of Figures 2 and 3 where it is indicated with the continuous lines h and p the variation respectively of the head and the percentage efficiency of the pump in question according to the flow rate, compared to that of a traditional pump represented with the dotted lines H and P. It should be noted that the head and efficiency of the pump according to the present invention maintain a satisfactory value even when the Q' value, which represents the maximum flow rate achievable in the centrifugal pumps of the traditional type, is exceeded.

[54] The self-priming centrifugal pump according to the present invention thus reaches the purpose of increasing the maximum flow rate achievable while maintaining high levels of performance.

[55] The self-priming centrifugal pump described by way of example may change according to the different requirements.

[56] In the practical embodiment of the invention, the used materials, as well as the shape and the dimensions, may vary depending on requirements.

[57] Should the technical features mentioned in any claim be followed by reference signs, such reference signs were included strictly with the aim of enhancing the understanding of the claims and hence they shall not be deemed restrictive in any manner whatsoever on the scope of each element identified for exemplifying purposes by such reference signs.