GB2138504A

GB2138504A - Diffusers for centrifugal pumps

Info

Publication number: GB2138504A
Application number: GB8404857A
Authority: GB
Inventors: Jules L Dussourd; Donald P Sloteman; George Pfannebecker
Original assignee: Ingersoll Rand Co
Current assignee: Ingersoll Rand Co
Priority date: 1983-04-15
Filing date: 1984-02-24
Publication date: 1984-10-24
Also published as: JPS59200100A; GB8404857D0; DE3414105A1; FR2544402A1; CA1222903A

Abstract

The diffuser body 13 is formed with a slot or passage 30 for connecting the vaneless space 15 surrounding an impeller 14 with the diffuser 16. The slot allows fluid flow between points A and B to stabilize the operation of the pump at low flow rates. <IMAGE>

Description

SPECIFICATION Pumpvolute communicating slot for stability This invention relates to centrifugal pumps, particu larly centrifugal pumps having volute type diffusers.

In a centrifugal pump having a diffuserthe diffuser receives relatively high velocityflowfrom the impeller and connects with the discharge. The volute increases in cross-sectional area to reduce the flow velocity and cause a corresponding increase in the static pressure head at the volute discharge.

Pumps of íhis type normally encounter significant problemswhenthe pump discharge is throttled to reducetheflowto relatively low levels. At a certain low flow level the head ceases to rise as flow drops. This condition is undesirable because it results in unstable pump operation and decreased efficiency and creates flow problems when several pumps are operated in parallel.

With this invention a pump is provided that stabilizes the head/flow performance characteristic at low flows to decrease or eliminate the usual unstable characteristic. According to the present invention there is provided a centrifugal pump having a discharge chamber, a vaneless space amd a volute diffuser having an inlet communicating with the vaneless space and an outlet communicating with the discharge chamber, and a means for connecting the volute diffuser at a selected point to the vaneless space at a selected point.The invention also provides a centrifugal pump comprising a diffuser body mounted within a housing to provide a discharger chamber between the body and the housing, a vaned impeller rotatably mounted within the diffuser body with clearance to leave a vaneless space not swept by the impellervanes, a volute diffuser extending between the vaneless space and the discharge chamber to discharge fluid underpressurefromthevaneless spacethrough the volute diffuser to the discharge chamber and a passage opening at one end to the volute diffuser intermediate the length thereof and at the other end to the vaneless space at a location downstream ofthefluid discharge from the vaneless space to the volute diffuser considered in the direction of rotation of the impeller to permitthe return offluid discharged to the volute diffuser to the vaneless space when the fluid pressure atthe one end of the passage exceeds that at the other end of the passageway. One embodiment of the invention will now be described by way of example reference being madetotheaccom- panying drawings in which:- Figure lisa simplified cross-sectional end view of the impeller and vaneless space of a centrifugal pump according to this invention; Figure 2 is a cross-sectional side view of the pump portion shown in Figure 1; and Figure 3 is a curve showing pump head/flow characteristics under certain operating conditions.

Referring to Figures 1 and 2, a pump housing section 1 sofa pump (shown in part) creates a discharging portion by forming a pump discharge chamber 12 between a housing wall 11 and a diffuser body 13 and creates a vaneless space 15 surrounding a vaned impeller 14 (shown in phantom).

The discharging section also comprises a volute diffuser 1 6that connects between vaneless space 15 at a diffuser inlet 17 having a cut water 21 and discharge chamber 12 atan outlet 18. As known intheart,the diffuser is arranged to discharge pump fluid as the impeller rotates in a clockwise direction (as shown) to pump fluid that is received into the vaneless space from a pump inlet 20that receives fluid.

Ameansforconnecting volute diffuser 16to varieless space 15 comprises a slot or passage 30 in diffuser body 13 that communicates at one end at a selected point in a volute diffuser 16 and at the other end to a selected point in vaneless space 15. The slot is positioned at a selected distance from inlet 17 and cutwater 21 on the diffuser side and at a selected distance from the inlet or cutwater on the vaneless space side.

In the operation of the pump, fluid is received through inlet 20 and driven by impeller 14 into diffuser inlet 17 and out through outlet 18 into discharge chamber 12. During low flow operation if slot 30 is not present the head instead of increasing tends in many situations to decrease. In Figure 3 a dotted curve N shows atypical exampleofhowatlowflowsthe head may drop as flow decreases creating an unstable condition.

With slot 30 present communicating between the diffuser and the vaneless space. The head/flow relationship as shown in curve S in Figure 3 can be obtained for any pump of this type by selecting the size, shape and orientation ofthe slot.

While some empirical evaluation of the type and arrangement of the slot is necessary for each particular pump configuration and installation,these can be readily established. The primary factor to beconsi- dered in evaluation and correction is that increased stability results at low deliveryflows because the pressure in the volute diffuserwould normally be higher at a point A in the diffuser channel than at a point B in the vaneless space. Slot 30 allows flow from pointAto point B, selected to be the point at which maximum head occurs,which stabilizes the head toward zero flow as shown in curve S.

Also as the pump operates at higher deliveryflows the pressure differential between points A and B on each side of the slot diminishes as the flow increases and equalizes at about the best efficiency level of the pump. This equalization of pressure between points A and B substantially eliminates the flow between points A and B through the slots so thatthe head/flow characteristic is relatively unaffected at the operating flow rates.

When the flow is increased beyond the point of maximum efficiency, the pressure at point Btendsto exceed that at pointAand flow occurs from point B to A. To diminish this the orientation of the slot and the size is selected to limitthe amount ofthis flow so that the increase in flow at the higher flow rates, as shown in Figure 3, is not significant. This limitation while not essential is helpful in limiting the maximum driving motor size requiredforthe pump.

1. Acentrifugal pump having, a discharge chamber, a vaneless space,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Pumpvolute communicating slot for stability This invention relates to centrifugal pumps, particu larly centrifugal pumps having volute type diffusers. In a centrifugal pump having a diffuserthe diffuser receives relatively high velocityflowfrom the impeller and connects with the discharge. The volute increases in cross-sectional area to reduce the flow velocity and cause a corresponding increase in the static pressure head at the volute discharge. Pumps of íhis type normally encounter significant problemswhenthe pump discharge is throttled to reducetheflowto relatively low levels. At a certain low flow level the head ceases to rise as flow drops. This condition is undesirable because it results in unstable pump operation and decreased efficiency and creates flow problems when several pumps are operated in parallel. With this invention a pump is provided that stabilizes the head/flow performance characteristic at low flows to decrease or eliminate the usual unstable characteristic. According to the present invention there is provided a centrifugal pump having a discharge chamber, a vaneless space amd a volute diffuser having an inlet communicating with the vaneless space and an outlet communicating with the discharge chamber, and a means for connecting the volute diffuser at a selected point to the vaneless space at a selected point.The invention also provides a centrifugal pump comprising a diffuser body mounted within a housing to provide a discharger chamber between the body and the housing, a vaned impeller rotatably mounted within the diffuser body with clearance to leave a vaneless space not swept by the impellervanes, a volute diffuser extending between the vaneless space and the discharge chamber to discharge fluid underpressurefromthevaneless spacethrough the volute diffuser to the discharge chamber and a passage opening at one end to the volute diffuser intermediate the length thereof and at the other end to the vaneless space at a location downstream ofthefluid discharge from the vaneless space to the volute diffuser considered in the direction of rotation of the impeller to permitthe return offluid discharged to the volute diffuser to the vaneless space when the fluid pressure atthe one end of the passage exceeds that at the other end of the passageway. One embodiment of the invention will now be described by way of example reference being madetotheaccom- panying drawings in which:- Figure lisa simplified cross-sectional end view of the impeller and vaneless space of a centrifugal pump according to this invention; Figure 2 is a cross-sectional side view of the pump portion shown in Figure 1; and Figure 3 is a curve showing pump head/flow characteristics under certain operating conditions. Referring to Figures 1 and 2, a pump housing section 1 sofa pump (shown in part) creates a discharging portion by forming a pump discharge chamber 12 between a housing wall 11 and a diffuser body 13 and creates a vaneless space 15 surrounding a vaned impeller 14 (shown in phantom). The discharging section also comprises a volute diffuser 1 6that connects between vaneless space 15 at a diffuser inlet 17 having a cut water 21 and discharge chamber 12 atan outlet 18. As known intheart,the diffuser is arranged to discharge pump fluid as the impeller rotates in a clockwise direction (as shown) to pump fluid that is received into the vaneless space from a pump inlet 20that receives fluid. Ameansforconnecting volute diffuser 16to varieless space 15 comprises a slot or passage 30 in diffuser body 13 that communicates at one end at a selected point in a volute diffuser 16 and at the other end to a selected point in vaneless space 15. The slot is positioned at a selected distance from inlet 17 and cutwater 21 on the diffuser side and at a selected distance from the inlet or cutwater on the vaneless space side. In the operation of the pump, fluid is received through inlet 20 and driven by impeller 14 into diffuser inlet 17 and out through outlet 18 into discharge chamber 12. During low flow operation if slot 30 is not present the head instead of increasing tends in many situations to decrease. In Figure 3 a dotted curve N shows atypical exampleofhowatlowflowsthe head may drop as flow decreases creating an unstable condition. With slot 30 present communicating between the diffuser and the vaneless space. The head/flow relationship as shown in curve S in Figure 3 can be obtained for any pump of this type by selecting the size, shape and orientation ofthe slot. While some empirical evaluation of the type and arrangement of the slot is necessary for each particular pump configuration and installation,these can be readily established. The primary factor to beconsi- dered in evaluation and correction is that increased stability results at low deliveryflows because the pressure in the volute diffuserwould normally be higher at a point A in the diffuser channel than at a point B in the vaneless space. Slot 30 allows flow from pointAto point B, selected to be the point at which maximum head occurs,which stabilizes the head toward zero flow as shown in curve S. Also as the pump operates at higher deliveryflows the pressure differential between points A and B on each side of the slot diminishes as the flow increases and equalizes at about the best efficiency level of the pump. This equalization of pressure between points A and B substantially eliminates the flow between points A and B through the slots so thatthe head/flow characteristic is relatively unaffected at the operating flow rates. When the flow is increased beyond the point of maximum efficiency, the pressure at point Btendsto exceed that at pointAand flow occurs from point B to A. To diminish this the orientation of the slot and the size is selected to limitthe amount ofthis flow so that the increase in flow at the higher flow rates, as shown in Figure 3, is not significant. This limitation while not essential is helpful in limiting the maximum driving motor size requiredforthe pump. CLAIMS

1. Acentrifugal pump having, a discharge chamber, a vaneless space, a volute diffuser having an inlet communicating with the vaneless space and an outlet communicating with the discharge chamber, and a means for connect ingthevolutediffuserata selected pointtothe vaneless space at a selected point.

2. Acentrifugal pump according to claim 1 wherein the means for connecting comprises a slot.

3. Acentrifugal pump according to claim 1 wherein the meansforconnecting comprises a slot having selected size, shape and orientation.

4. Acentrifugal pump according to claim 2 or3 whereinsaid slot connects into the volute diffuser art a point ata selected distance from the inlet and into the vaneless space at a point at a selected distance from the inlet.

5. In a centrifugal pump having a vaneless space, a discharge chamber outward of the vaneless space, and a volute diffuser communicating between the vaneless space and the discharge chamber; a meansfor connecting the vaneless space to the volute diffuser between a selected point in the volute diffuser and a selected point on the vaneless space.

6. Acentrifugal pumpaccording toclaim Swhere- in the meansfor connecting comprises a slot.

7. Acentrifugal pump according to claim 5 wherein the means for connecting comprises a slot having a selected size.

8. Acentrifugal pump according to claim Swhere- in the means for connecting comprises a slot having a selected size, shape and orientation.

9. Acentrifugal pump according to claim 6,7 or8 wherein said slot connects into the volute diffuser at a point at a selected distance from the inlet and into the vaneless space at a point at a selected distance from the inlet.

10. Acentrifugal pumpcomprising adiffuserbody mounted within a housing to provide a discharge chamber between the body and the housing, a vaned impeller rotatably mounted within the diffuser body with clearance to leave a vaneless space not swept by the impeller vanes, a volute diffuser extending be tween the vaneless space and the discharge chamber to discharge fluid under pressure from the vaneless spacethroughthevolutediffusertothedischarge chamber and a passage opening at one end to the volute diffuser intermediate the length thereof and at the other end to the vaneless space at a location downstream ofthefluid discharge from the vaneless space to the volute diffuser considered in the direction of rotation ofthe impellierto permitthe return of fluid discharge to the volute diffuserto the vaneless space when the fluid pressure atthe one end of the passage exceeds that atthe other end of the passage.

11. Acentrifugal pump constructed, arranged and adapted to operate substantially as herein described with reference to the accompanying drawings.