JPH0426720Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a double suction volute pump, and particularly to an improved structure for preventing damage caused by cavitation of the double suction volute pump.

[Prior art]

FIG. 4 shows a schematic configuration of a conventional double suction centrifugal pump of this type. In FIG. 4, reference numeral 1 is a casing forming a suction part 1a and a discharge part 1b, 2 is a pump shaft, 3 is an impeller fixed to this pump shaft 2, and 4 is a suction water flow to this impeller 3. The suction port 5 is a liner ring attached to the suction port 4. In addition, in a dual-suction centrifugal pump with such a conventional configuration, the suction port 4, which is the part where the suction water flow flows into the inlet of the impeller 3, is shown enlarged in FIG. 5 or 6. It is configured as shown below.

In the case of the conventional configuration, the structure of the inlet part of the impeller 3 into which the suction water flow flows, that is, the suction port part 4, is mainly due to problems in casting, processing, cost, etc. It is usually designed solely from the casing and has an integral structure with the casing.

By the way, in the case of the double-suction centrifugal pump as described above, it is common knowledge that cavitation near the impeller inlet, unlike in the case of a single-suction centrifugal pump, does not occur. In other words, it is well known that in single-suction centrifugal pumps, cavitation occurs near the lowest pressure, especially near the impeller inlet, due to changes in the inflow velocity in areas where the radius of curvature of the impeller differs. On the other hand, in a dual-suction pump, the required net effective suction head is small, so cavitation near the impeller inlet generally does not occur when operated at the design water flow rate.

[Problems to be Solved by the Invention] However, the inventor of the present invention has found that damage to the pump casing due to cavitation erosion actually occurs even in such double-suction centrifugal pumps. According to this, double-suction volute pumps are often operated with a water flow rate lower than the designed water flow rate, but cavitation erosion in a double-suction volute pump with a conventional configuration as shown in Fig. Damage is caused by the symbol 6 in Figures 5 and 6 during operation with such a small amount of water.
Almost all of the occurrences occur in the casing portion of the suction port 4 shown in . FIG. 7 is a graph showing the relationship between the operating water amount and the amount of damage in the suction port 4, and the relationship between the operating water amount and the damage range, obtained through experiments. As is clear from this graph, during normal operation ( At around ±20% of the design water flow), almost no erosion occurs in the suction port 4.
It is confirmed that both the amount of damage and the extent of damage increase in a quadratic curve as the water flow becomes smaller.
The damage range is expressed as D'/D, where D is the inner diameter of the suction port of the impeller and D' is the diameter of the outermost damaged part. Next, Figure 8 shows the extent of damage to the suction port when ten types of double suction centrifugal pumps No. 1 to 10 are operated with a small amount of water. It can also be seen that damage due to erosion occurs within a region surrounded by an outer diameter 1.5 times the inner diameter D of the suction port.

According to the inventor's observation, damage caused by erosion to the suction port during low water volume operation in a double suction centrifugal pump is caused by the damage that occurs once the water enters the impeller 3, as shown by the arrow in FIG. This is caused by ivy water flowing backwards due to the small amount of water. That is,
This is because the swirling flow velocity during this reverse flow is approximately equal to the circumferential velocity at the impeller 3 inlet, so this strong swirling flow jumps out of the impeller 3 and spreads from the impeller inlet along the casing wall, that is, the suction port 4. be. This swirling flow velocity decreases as it moves away from the impeller inlet, so the degree of erosion is large at the innermost part of the suction port 4 immediately before the impeller inlet, and becomes smaller as it goes outward. As mentioned above, it almost no longer occurs at 1.5D.

If the casing is damaged in this way, the treatment is generally to spray material on the area,
Possible methods include filling and processing the casing, or replacing the casing itself, but both of these methods are extremely difficult to repair at the site where the pump is installed, and with the former method, there is a risk of peeling later. However, the latter method is expensive and will eventually require repair, which has the disadvantage of increasing the cost of countermeasures.

In addition, as a recent trend, there are many requests from users for pumps with high suction performance specifications, and in order to satisfy this request, manufacturers are making designs such as increasing the eye diameter of the impeller. In an impeller with such high suction performance, compared to an impeller with normal performance, even if the water volume deviates even slightly from the maximum efficiency point to the low water volume region, backflow is likely to occur, and this backflow is caused by Cavitation damaged the impeller inlet portion of the casing.

This invention was made in view of the above-mentioned circumstances, and provides a double suction centrifugal pump that can protect the casing surface from cavitation erosion that occurs when operating at a small water volume lower than the designed water volume. The purpose is to

[Means for solving the problem] In order to solve the above problem, in this invention,
A region of the casing surface forming the suction port to the impeller, which is surrounded by an outer diameter 1.5 times the inner diameter from the inner diameter of the suction port, is made of a material with good cavitation and erosion resistance. A ring-shaped inlet member is detachably installed.

[Function] In this invention, in a region where cavitation erosion is significant, that is, on the casing surface forming the suction port of the impeller, from the inside diameter of the suction port to the outside diameter 1.5 times the inside diameter. By equipping the enclosed area with a ring-shaped inlet member made of a material with good anti-cavitation erosion properties, cavitation erosion in said area can be significantly controlled. Moreover, since the ring-shaped inlet member is detachably attached, it is easy to replace the ring-shaped inlet member if it becomes damaged over time, especially at the site where the pump is installed. It can be carried out.

〔Example〕

Hereinafter, embodiments of the double suction centrifugal pump according to this invention will be described in detail with reference to FIGS. 1 to 3.

The first embodiment shown in FIG. 1 is an explanatory cross-sectional view of the suction port shown in FIG. 5 in the conventional example, and the same reference numerals in these figures represent the same or equivalent parts. ing.

First, in this example, in order to solve the drawbacks of the conventional example described above, we visualized the pump configuration and repeated continuous tests with small water volumes to examine the range of influence of cavitation. It has been confirmed that the affected area, that is, the casing area that is damaged, is a portion that is 1 to 1.5 times the inlet diameter of the suction port 4 to the impeller 3, in this case the inner diameter D of the liner ring 5.

Therefore, in the first embodiment shown in FIG. 1, the casing surface portion of the suction port 4 corresponding to 1 to 1.5 times the inner diameter D of the liner ring 5 is defined as a flat portion 1c, and with respect to this flat portion 1c. , a ring-shaped inlet member 7 made of a material with good cavitation and erosion resistance, such as stainless steel,
It is removably attached using an appropriate mounting screw 8 or the like.

Therefore, in the case of this first embodiment, the casing surface portion of the suction port 4 in the area easily damaged by cavitation, that is, 1.5 from the inner diameter of the liner ring 5 corresponding to the inner diameter of the suction port 4. A ring-shaped entrance member made of a material with excellent cavitation erosion resistance is installed in the area surrounded by an outer diameter of 1.5D, which is twice as large. Even if damage occurs, it is easy to replace at the installation site, and compared to the conventional integral structure made of cast material, that is, FC material, the inlet member made of stainless steel has a much longer erosion life. It was possible to extend it to about 6 times.

Regarding the shape of the inlet member 7, the side to be attached to the casing flat part 1c needs to be formed into a flat shape similar to the same surface 1c, but the side that comes into contact with the water flow is the same as in the first embodiment. It can be formed into a planar shape as shown in FIG.
The liner ring 5 may have a curved shape suitable for water flow, as in the embodiment, or may be formed integrally with the liner ring 5 as necessary, as in the third embodiment shown in FIG. .

[Effect of idea]

As described in detail above, according to this invention, in a double suction centrifugal pump, the inner diameter of the suction port of the casing surface forming the suction port to the impeller is surrounded by an outer diameter 1.5 times the inner diameter. A ring-shaped inlet member made of a material with good cavitation erosion resistance is removably attached to the area where the casing is easily damaged by cavitation erosion. In addition, the structure is extremely simple and can be easily applied to existing ones, and the inlet member can be made of any material with good cavitation and erosion resistance. In addition to being inexpensive because the entrance member can be installed partially, it is also easy to replace when damage occurs, and it also has various practical effects such as being able to be treated at the installation site. It is something that you have.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram of a suction port showing a first embodiment of a double-suction centrifugal pump according to the invention, and FIGS. 2 and 3 show a suction port according to the second and third embodiments of the same. FIG. 4 is a front sectional view showing the general configuration of a conventional double suction centrifugal pump, and FIGS. 5 and 6 are suction ports of the conventional double suction centrifugal pump. FIG. 7 is a graph showing the amount of damage and damage range with respect to the amount of operating water, and FIG. 8 is an explanatory diagram showing the damage range of each of a plurality of double-suction centrifugal pumps. DESCRIPTION OF SYMBOLS 1... Casing, 1a, 1b... Suction part of casing, discharge part, 2... Pump shaft, 3... Impeller, 4... Suction port part, 5... Liner ring, 7...
...Inlet member, D... Inner diameter of suction port, 1.5D...
...The outer diameter is 1.5 times the inner diameter of the suction port.

Claims (1)

[Claims for Utility Model Registration] (1) A pump having an impeller, a pump shaft to which the impeller is fixed, and a casing that covers these, and the water flow sucked in by the rotation of the impeller within the casing. In a double-suction centrifugal pump in which the air flows into the impeller through the suction port, an outer diameter of the casing surface forming the suction port to the impeller is 1.5 times the inner diameter from the inner diameter of the suction port. A double suction centrifugal pump characterized in that a ring-shaped inlet member made of a material with good cavitation and erosion resistance is removably attached to the area surrounded by. (2) The area of the casing surface that forms the suction port to the impeller, which is surrounded by an outer diameter 1.5 times the inner diameter from the inner diameter of the suction port, is defined as a flat surface, and the inlet member is attached to and removed from this flat surface. The double suction centrifugal pump according to claim 1, which is characterized in that it can be freely mounted. (3) The double-suction centrifugal pump according to claim 1, wherein the inlet member is integrated with the liner ring.