JP2012097696A - Volute pump device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a volute pump device with simple constitution, which can be reduced in a requested NPSH (Net Positive Suction Head) to enhance its suction performance.SOLUTION: This volute pump device 1 includes an impeller 10 cantilevered to the tip side of a rotary shaft 3 within a casing 2, wherein a first and a second blades 11, 12 are provided to the front and rear sides of a main plate 13 of the impeller 10, and the casing includes a first and second suction openings 4, 5 and one discharge opening 6. The fluid sucked in from the first suction opening 4 and discharged in the rotary circumferential direction of the first blade 11 caused by the action of the first blade 11, is combined with the fluid sucked in from the second suction opening 5 and discharged in the rotary circumferential direction of the second blade 12, caused by the action of the second blade 12, to be discharged from the one discharge opening 6.

Description

  The present invention relates to a centrifugal pump apparatus suitable for transporting slurry or sand fluid containing fresh water or solid matter.

  In a centrifugal pump device, it is an important issue to reduce the required NPSH (Net Positive Suction Head) and improve the performance of the pump sucking (pushing) fluid into the impeller. The reason why a low NPSH pump is necessary will be described below. In the following description, a case will be described in which the pump suction pressure is negatively pumped regardless of the liquid level in the tank.

  In FIG. 6, if the level of the fluid in the liquid tank 400 is L 1 and the pump 300 is operated, a negative actual head (−hs 1) acts, and a negative pressure acts on the suction port of the pump 300. Further, if the fluid level is located at L2, a positive actual lift (+ hs2) acts, and normally a positive pressure acts on the suction port of the pump 300. However, depending on the temperature of the fluid, positive pressure does not necessarily act on the suction port of the pump 300, and negative pressure may also occur. This is because as the temperature of the fluid increases, the saturated vapor pressure also increases (however, explanations of various losses in the suction pipe are omitted).

Here, the required NPSH (R-NPSH) is a head required for the pump 300 to suck (push) the fluid F into the impeller 310, and is the maximum pressure drop at the inlet of the impeller 310. That is, at the inlet portion of the impeller 310, the fluid suddenly changes its direction from the axial direction to the radial direction, causing a pressure drop. This R-NPSH is expressed by the following equation (1).
R-NPSH = αxQ ^2/3 xN ^4/3 x10 ⁻⁵ m (1)
Where α is an experimental coefficient that varies depending on the structure and design (6.0 to 8.0 is used)
Q: Flow rate (m ³ / min)
N: Rotational speed (min ⁻¹ )

On the other hand, assuming that atmospheric pressure is acting on the suction liquid level of the pump, the drop between the pump and the suction liquid level from the atmospheric pressure, the head loss of the suction pipe, and the saturated vapor pressure of the fluid (liquid temperature, liquid specific gravity) A value obtained by subtracting the total suction head is referred to as effective NPSH (A-NPSH). This A-NPSH is expressed by the following equation (2).
A-NPSH = Ha + hs-hv-hfm (2)
However, Ha: atmospheric pressure (m)
hs: Actual suction head (m) Push-in is positive, suction is negative
hv: Saturated vapor pressure against liquid temperature (m)
hf: Total loss head of suction pipe (m)

  Here, when A-NPSH ≦ R-NPSH, that is, when the fluid is reduced to the vapor pressure or lower, the cavity where the gas is generated becomes hollow and the cavity is broken at the high pressure. (Cavity phenomenon) occurs. The pump operation status at this time is accompanied by sound and vibration, and if the degree of the phenomenon becomes severe, the pumping will eventually become impossible. Further, if the operation is continued with the cavitation phenomenon occurring, the blades of the pump and the body (case) will fall and corrosion will proceed.

The method for eliminating the cavitation phenomenon is to increase the A-NPSH,
Either R-NPSH is reduced. In the former case, it is difficult to change the arrangement of the pump and the suction liquid level, the suction pipe (size, length), fluid conditions, etc. at general sites. It is common practice to reduce R-NPSH.

  The simplest method for reducing the latter R-NPSH is to reduce the flow rate by restricting the control valve provided on the pump discharge side if the fluid is fresh water. However, if the fluid is a slurry or sand containing solid matter, the solid matter may be caught in the gap between the valve body and the valve box in the control valve, or the solid matter may settle in the middle of the transportation pipe due to the low flow rate. Problem arises.

  On the other hand, when a new facility is planned, a pump model suitable for A-NPSH can be selected for the above suction conditions (Ha, hs, hv, hf). When A-NPSH is small, it is preferable to select a low R-NPSH pump model having a low rotational speed with respect to the design flow rate and head specifications. After all, in any field where the suction conditions are a problem, a low R-NPSH pump is required.

  Here, the most typical low R-NPSH centrifugal pump is a double suction centrifugal pump having a structure in which the blades are back-to-back and the fluid is sucked from both sides. The reason why the R-NPSH is lowered by both suction type centrifugal pumps is that the flow rate Q can be calculated by halving in the above equation (1). This is based on the principle that two pumps are operated in parallel. A cross-sectional view of both suction pumps is shown in FIG.

  As shown in the figure, a general double suction type centrifugal pump 201 has a structure in which a case (body) 202 is vertically divided or vertically divided and a rotary shaft 203 is supported at both ends for assembly. (For example, refer patent document 1) Since it has the structure which sucks fluid from the both sides of the impeller 210 back-to-back with respect to the main board 213, there exists a fault that a structure becomes very complicated.

On the other hand, the single suction centrifugal pump has a simple structure. As a prior art, there is one having an impeller in which a main plate is provided with a single or a plurality of through-holes as disclosed in Patent Document 2, for example. The through hole provided in the main plate is called a balance hole.
In addition, as shown in FIG. 8, for example, there is an inverse pump 100 in which the suction port 104 is provided in the vicinity of the shaft seal device 140. Unlike an ordinary single suction pump, the inverse pump 100 has a structure that reduces the pressure of the shaft seal device 140 by disposing the impeller 110 in a direction opposite to the rotational axis direction. This is a pump, and its structure is very simple compared to the double suction pump. In the figure, auxiliary blades 112 are provided on the back side 113r of the main plate 113, but this purpose is to reduce axial thrust.

JP 2003-148390 A JP 2004-116454 A (FIG. 1)

However, the double suction type centrifugal pump described above has a drawback that the structure becomes extremely complicated. On the other hand, although the single suction type centrifugal pump (inverse type pump) has a simple structure, the suction NPSH is reduced by reducing the required NPSH. It is insufficient for improving the performance as compared with the double suction type.
Therefore, the present invention has been made paying attention to such problems, and an object thereof is to provide a centrifugal pump device having a simple structure that can reduce the required NPSH and improve the suction performance.

  In order to solve the above-mentioned problems, the present invention provides a centrifugal pump device having an impeller that is cantilevered on the tip end side of a rotating shaft in a casing, and a shaft seal device that is disposed on the back side of the impeller. The impeller includes a main plate, a first blade provided on a surface facing the suction port side of the main plate, and a second blade provided on a surface facing the shaft seal device side of the main plate. The casing has a first suction port provided on the front end side in the rotation axis direction from the impeller, a second suction port provided on the rotation shaft direction shaft seal device side from the impeller, and The fluid sucked in from the first suction port by the action of the first blade and discharged in the rotational circumferential direction of the first blade, and sucked from the second suction port by the action of the second blade. One discharge that combines and discharges the fluid discharged in the rotational circumferential direction of the second blade Characterized in that it has and.

  According to the centrifugal pump device of the present invention, since the impeller is cantilevered on the tip end side of the rotating shaft in the casing as in the single suction type, the structure is simpler than that of the double suction type centrifugal pump. It is. Then, a first blade and a second blade (hereinafter also referred to as “blades on the front and back of the main plate”) are formed on the surface facing the suction port side of the main plate and the surface facing the shaft seal device, respectively. One suction port and one discharge port are provided, and these two suction ports and one discharge port are sucked from the first suction port by the action of the first blade, and the rotation circumference of the first blade is The fluid discharged in the direction and the fluid sucked from the second suction port by the action of the second blade and discharged in the rotational circumferential direction of the second blade are joined together from one discharge port. Since it is configured to discharge, the flow path of each blade on the front and back of the main plate is generated, and this causes the principle that two pumps are operated in parallel by the blade on the front and back of the main plate. It is possible to distribute the flow accordingly. To reduce the maximum pressure drop of each of the vane suction unit, the request NPSH is reduced, thereby improving the suction performance.

  As described above, according to the present invention, it is possible to provide a centrifugal pump device having a simple structure that can reduce the required NPSH and improve the suction performance.

It is explanatory drawing of 1st embodiment of the centrifugal pump apparatus which concerns on this invention, The figure has shown the principal part of the pump apparatus with the cross section along an axial direction. It is a figure explaining the impeller of 1st embodiment, The figure (a) is an A arrow directional view in FIG. 1, The same figure (b) is a B arrow directional view in FIG. It is explanatory drawing (perspective view) of the blade | wing provided in the impeller of 1st embodiment. It is explanatory drawing of the flow path (Two suction inlets and one discharge outlet) of the spiral pump apparatus which concerns on this invention. It is a figure explaining the structural classification | category of an impeller, The figure (a) is a semi-open blade | wing, (b) is a closed blade | wing, (c) is an open blade | wing. It is a schematic diagram explaining the reason why a low NPSH pump is necessary. It is a figure explaining an example of the conventional double suction vortex pump apparatus. It is a figure explaining an example of the conventional inverse type pump device.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate.
A schematic diagram of an embodiment of a centrifugal pump according to the present invention is shown in FIG.
As shown in the figure, the centrifugal pump 1 is provided with a rotary shaft 3 supported in a casing 2 so as to be rotatable by driving a motor (not shown), and an impeller 10 on one end side of the rotary shaft 3. Has been supported. Note that the structure of the impeller 10 is a semi-open type (see FIG. 5A) in this example.

  A shaft seal device 40 is arranged on the back side of the impeller 10 (on the right side in the figure and opposite to the suction port 4) so as to surround the rotary shaft 3. The impeller 10 uses a wear-resistant material or a corrosion-resistant material, and has a disk-shaped main plate 13 and a surface facing the first inlet 4 side of the main plate 13 (the surface of the main plate, A first blade 11 provided on the surface close to the suction port 4) and a second blade 12 provided on the surface of the main plate 13 facing the shaft seal device 40 (the back surface of the main plate). Yes.

  As shown in FIG. 2, the first blade 11 and the second blade 12 are equally distributed at six locations with respect to the surface of the main plate 13, and each blade is directed in the circumferential direction from the center of the main plate 13. And is formed so that the distance in the facing direction between adjacent blades is increased. Here, in this embodiment, the design of the curved shape of each blade and the width (b) and thickness (t) shown in FIG. 3 are basically the same, and the performance of the front and back blades is the same. It has become.

  As shown in FIG. 1, a first suction port 4 is formed at the front end side of the impeller 10 in the rotational axis direction, and the rotational shaft direction shaft seal device 40 side is closer to the impeller 10. A second suction port 5 is formed. A discharge port 6 is provided in the rotational circumferential direction of the impeller 10. In addition, about the 1st suction port 4 and the 2nd suction port 5, as shown in FIG. 4, with respect to the two suction ports 4 and 5, the 1st suction port 4 and the 2nd suction port 5 are set. They are connected to each other by piping so that the suction port is one place (suction port 8). The fluid F is sucked from the first suction port 4 and the second suction port 5, respectively, and the fluid F is discharged from the discharge port 6 through the flow paths F1 and F2.

  That is, in the centrifugal pump 1, when the rotary shaft 3 is rotated by driving a motor (not shown), the fluid F flows along the arrows F 1 and F 2 in both the first blade 11 and the second blade 12. So that it is pumped by the action of centrifugal force. Then, the second suction port is formed by the action of the second blade 12 and the fluid sucked from the first suction port 4 by the action of the first blade 11 and discharged in the rotational circumferential direction of the first blade 11. The fluid sucked from 5 and discharged in the rotational circumferential direction of the second blade 12 is merged again and discharged from one discharge port 6.

Next, the operation and effect of the centrifugal pump device 1 will be described.
The above-described centrifugal pump 1 is configured so that the impeller 10 is cantilevered on the front end side of the rotating shaft 3 in the casing 2 as in a single suction type (inverse type), compared to a general double suction type pump. Not only is the structure simple and easy to disassemble and assemble, but also the manufacturing cost can be reduced. Further, similarly to the conventional balance hole and auxiliary blade, the pressure reduction of the shaft seal device 40 and the reduction of the axial thrust can be achieved. Further, by using an abrasion-resistant material or a corrosion-resistant material for the impeller 10, it is possible to use it over the fluid F such as slurry, sand, or a chemical fluid.

And according to this centrifugal pump 1, the 1st blade | wing 11 and the 2nd blade | wing 12 are formed in the surface which faces the 1st inlet 4 side of the main plate 13, and the surface which faces the shaft-seal device 40 side, respectively, and a casing 2 is provided with two suction ports 4 and 5 and one discharge port 6 formed at different locations, and these two suction ports 4 and 5 and one discharge port 6 are connected to the first blade 11. The fluid F1 sucked from the first suction port 4 by the action and discharged in the circumferential direction of the first blade 11 and the second blade 12 are sucked from the second suction port 5 by the action. Since the fluid F2 discharged in the rotational circumferential direction of the second blade 12 is joined and discharged from one discharge port 6, the flow paths of the blades 11 and 12 on the front and back of the main plate 13 are respectively Is generated by the blades 11 and 12 on the front and back of the main plate 13. The principle of operating two pumps in parallel works, and it is possible to distribute the flow rate according to the capacity of the blades on the front and back of the main plate, reducing the maximum pressure drop at each blade suction part, so compared to single suction pumps Therefore, the required NPSH is reduced, and the suction performance can be improved. Further, since the two suction ports 4 and 5 are connected to each other and discharged from one discharge port 6, the structure can be simplified as compared with the double suction pump.
As described above, according to the centrifugal pump device 1, the required NPSH can be reduced and the suction performance can be improved with a simple structure.

The single suction centrifugal pump device according to the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the performance (the width dimension (b) and the thickness dimension (t) shown in FIG. 3) of the front and back blades 11 and 12 of the main plate 13 has been described as being the same. However, the performance may be different from each other in the same manner as two pumps having different capacities are operated in parallel. For example, the outer diameter of the second blade 12 may be configured to be larger than the outer diameter of the first blade 11. Moreover, it is good also as a structure which joins, changing the performance of the 1st blade | wing 11 and the 2nd blade | wing 12, and balancing the flow volume.

  Further, for example, in the above-described embodiment, the first blade 11 and the second blade 12 are described as being semi-open, but the present invention is not limited thereto, and the first blade 11 and the second blade 12 are It is good also as a closed type which has the side plate 14 as shown in FIG.5 (b). Here, when the impeller is classified structurally, as shown in FIG. 5A, a semi-open blade provided with a blade on the main plate, and a side plate provided on the front surface of the semi-open blade shown in FIG. 5B. There are closed blades and open blades provided with blades using a part of the main plate shown in FIG. In the present invention, the impeller 10 can be constituted by a first blade 11 and a second blade 12 which are semi-open blades or closed blades.

DESCRIPTION OF SYMBOLS 1 Centrifugal pump 2 Casing 3 Rotating shaft 4 1st suction port 5 2nd suction port 6 Discharge port 10 Impeller 11 1st blade | wing 12 2nd blade | wing 13 Main plate 14 Side plate 20 1st flow path 30 2nd flow path 40 Shaft seal device F Fluid F1 Flow of fluid to the first flow path F2 Flow of fluid to the second flow path

Claims (1)

A centrifugal pump device having an impeller that is cantilevered on the front end side of the rotating shaft in the casing, and a shaft seal device disposed on the back side of the impeller,
The impeller has a main plate, a first blade provided on a surface facing the suction port side of the main plate, and a second blade provided on a surface facing the shaft seal device side of the main plate,
The casing includes a first suction port provided on the front end side in the rotation axis direction from the impeller, a second suction port provided on the rotation shaft direction shaft seal device side from the impeller, and the first suction port. The fluid sucked from the first suction port by the action of the blade and discharged in the circumferential direction of the rotation of the first blade, and the second suction blade sucked from the second suction port by the action of the second blade. A centrifugal pump device comprising: a single discharge port that combines and discharges fluid discharged in the rotational circumferential direction of the two blades.

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