DE3414105A1 - CENTRIFUGAL PUMP - Google Patents

Description

description

The invention relates to centrifugal pumps and more particularly relates to entrifugal pumps with spiral diffusers.

In a centrifugal pump with a diffuser, the diffuser takes flow from the impeller at a relatively high speed or impeller and provides a connection to the outlet. The spiral-shaped diffuser widens in cross section by to reduce the flow velocity and a corresponding increase in the static pressure or the pressure head at To generate the outlet of the spiral diffuser.

Pumps of this type are usually subject to significant problems, when the outlet of the pump is throttled in order to reduce the flow or the flow rate to a relatively low level Reduce. At a certain low level of flow or flow rate, the pressure or head ceases to increase as the flow or flow rate decreases. This condition is undesirable because it causes one unstable pump operation and reduced efficiency result and because it creates flow problems if several Pumps are operated in parallel to each other.

The invention provides a pump which, at low flow rates or low flows, the pressure-flow-performance characteristics stabilized to reduce or eliminate the usually unstable characteristic. details and advantages of the invention emerge from the following description of an exemplary embodiment.

_ II _

Pig. 1 is a simplified cross-sectional end view of the impeller and vane-free space of a centrifugal pump according to the invention;

Figure 2 is a side cross-sectional view of the device disclosed in Pig. I. pump part shown;

Fig. 3 is a graph showing the pressure-flow characteristic of the pump under certain operating conditions.

As FIGS. 1 and 2 show, a pump housing 10 forms one not further shown pump an outlet part in which a pump outlet chamber 12 between a housing wall 11 and a Diffuser body 13 is formed. The pump also has a vane-free space 15, which is shown in dash-dotted lines illustrated impeller or impeller 14 surrounds.

The outlet portion of the pump also has a spiral diffuser 16 which communicates between the vane-free Space 15 at a diffuser inlet 17 with a water breaker 21 and the outlet chamber 12 with an outlet 18 As is known, the diffuser is arranged to allow pumped liquid to escape when the impeller according to FIG graphic representation rotates clockwise in order to pump liquid which is taken up in the vane-free space 15 and comes from a pump inlet 20 through which the liquid enters.

Means for connecting the spiral diffuser 16 to the vane-free space 15 has a slot 30 therein Diffuser body 13 on. The slot 30 communicates at one end at a selected point with the helical Diffuser 16 and at the other end at a selected point in communication with the vane-free space 15. The slot is below a certain selected distance from the inlet 17

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and the water breaker 21 on the diffuser side and at a certain selected distance from the inlet 17 or the Water breaker 21 arranged on the side of the vane-free space.

During operation of the pump, liquid is received through inlet 20 and through impeller 14 into diffuser inlet 17 and driven out through outlet 18 into outlet chamber 12. If the slot 30 were not present, one would operate with low flow the pressure or head instead of increasing in many situations will tend to decrease. In FIG. 3, a dashed curve N shows a typical example of how the pressure head decreases with low flow can when the flow decreases, creating an unstable condition.

If the slot 30 is present and establishes a connection between the diffuser and the vane-free space, the in Fig. 3 in the Kuive S shown relationship between pressure height and flow for any pump of this type can be achieved by changing the size and / or the shape and / or the orientation of the slot can be selected accordingly.

Although some empirical determination of the nature and arrangement of the slot is necessary for any particular pump design and installation, this determination of the slot can be can be easily carried out. The primary factor to consider when determining the slot and when correcting it is that there is improved stability at low flow rates because the pressure in the spiral diffuser would normally be higher at point A in the diffuser duct than at point B in that shovel-free space. The slot 30 allows flow of the point A to the point B, and the slot must be chosen so that it lies at those points at which a maximum Pressure head occurs, reducing the pressure head at a counter

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Zero flow is stabilized as shown in curve S.

Even if the pump works at higher delivery rates, the pressure difference between points A and B is reduced either side of the slot as the flow increases and the pressure differential is about equalized when about the best Efficiency of the pump is achieved. This pressure equalization between points A and B switches a flow between them points A and B through the slot substantially, so that the pressure-flow characteristics under normal operating flow conditions is relatively unaffected.

If the flow rises above the point of maximum efficiency, the pressure at point B will tend to be the Pressure at point A to exceed, and flow occurs from point B to point A. To lessen this phenomenon, the orientation of the slot and its size is chosen so that the amount of this flow is limited, so that the rise the flow at the higher flow rates as shown in Figure 3 is not significant. This restriction, although they is not essential, is helpful in limiting the maximum size of the drive motor required for the pump.

Claims (5)

34U105 HELMUT SCHROETER KLAUS LEHMANN DIPL.-PHYS. DIPL.-ING. PATENTANWÄLTE - EUROPEAN P ATE NT ATTO R N E YS Ingersoll-Rand Company ir-98 L / Be April 12, 1984 Centrifugal Pump Claims 1. Centrifugal pump with an outlet chamber (12), a vane-free one Space (15), a spiral-shaped diffuser (l6), which has an inlet (17), which is in connection with the vane-free Space (15) is, and has an outlet (18) which is in communication with the outlet chamber (12), and with a device (30) for connecting the spiral diffuser (l6) at a selected point with the vane-free space (15) at a selected point. 2. Centrifugal pump with a vane-free space (15), one Outlet chamber (12) outside of the vane-free space (15) and a spiral-shaped diffuser (l6), which is a connection between the vane-free space (15) and the outlet chamber (12), characterized by a device (30) for connecting the vane-free space (15) with the spiral diffuser (16) between a selected point in the spiral diffuser (16) and a selected point in the vane-free space (15). -7O7O SCHWABISCH GMClND ACCOUNTS: D-8000 MÖNCHEN 70 SCHROETER Telephone: (07171) 56 90 Deutsdie Bank AG Munich 70/37 369 (BLZ 700 700 10) K. LEHMANN Telephone: (089) 7252071 iisga »e49 Telex: 7248 868 paedd Pojtsdiedckonto Munich 1679 41-804 (BLZ 700 100 80) Lii» wskv «raß <. in TI «-. k-uva » · 3. Centrifugal pump according to claim 1 or 2, characterized in that the means for connecting has a slot (30). 4. Centrifugal pump according to claim 1 or 2, characterized in that the means for connecting has a slot (30) of selected size and / or shape and / or orientation. 5. Centrifugal pump according to claim 3 or 4, characterized in that the slot (30) on one Point at a certain selected distance from the inlet (17) into the spiral diffuser (16) and at one Point at a certain selected distance from the inlet (17) opens into the vane-free space (15).