GB2030225A

GB2030225A - Centrifugal pumps

Info

Publication number: GB2030225A
Application number: GB7929597A
Authority: GB
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1978-09-13
Filing date: 1979-08-24
Publication date: 1980-04-02

Abstract

The pump housing 10 defines a pumping chamber of circular cross-section. A rotor 14 within the chamber has its periphery closely adjacent the periphery of the chamber. The rotor 14 has a plurality of radial blades 17 adjacent its periphery, and a low-angle spiral vane 18 extending from adjacent an inlet 11 for the chamber to a part of the rotor adjacent the blades 17. An outlet 12 opens into the chamber periphery and extends tangentially therefrom. The pump is particularly adapted for pumping volatile fuels at inlet pressures which may result in separation of the fuel into liquid and vapour. <IMAGE>

Description

SPECIFICATION Pumps for fluids This invention relates to pumps for fluids, and in particular to pumps intended for use with aircraft fuels.

It is known, in aircraft fuel systems, to provide a low pressure backing pump which delivers fuel from a tank to a main high pressure pump. In such pumps a core of separated air and fuel vapour may form adjacent the axis of the pump rotor. An increase in the amount of such separated air and vapour is accompanied by a reduction in pump delivery pressure. Furthermore, the size of the vapour core tends to increase with altitude, thereby limiting the maximum altitude attainable by an aircraft in which such a pump is fitted.

It has been proposed to overcome this problem by providing a pump rotor having blades whose blade angle is small, the blade angle being defined as the angle, at the rotor periphery, between a tangent to the rotor and the plane of the adjacent portion of the blade. Such rotors, while being relatively insensitive to the amount of separated air and vapour, are nevertheless sensitive to the volume flow through the pump, delivery pressure decreasing sharply with increased flow.

It is an object of the invention to provide a pump in which delivery pressure can be maintained at an acceptable levei over a range of fuel flows in conditions in which separated vapour would otherwise prevent effective pump operation.

According to the invention a pump has a housing, defining a chamber of substantially circular section, a rotor mounted in said housing, an outlet adjacent the chamber periphery, an inlet opening into said chamber at a location radially inwardly of the periphery thereof, the rotor having a plurality of substantially radically extending walls adjacent its periphery and a spiral impeller extending from a radially inner portion of the rotor to a location thereon adjacent said walls, said rotor including means for permitting fluid flow between said impeller and said walls to be accompanied by relative angular movement between said fluid and said rotor, about the axis of said rotor.

An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1, is a longitudinal section through a pump and, Figure 2 is a section on line 2-2 in Figure 1.

The pump has a housing 10 which defines a pumping chamber of circular cross-section. An inlet 11 opens into the housing 10 at the axis of the chamber, and an outlet 12 opens into the periphery of the chamber and extends tangentially therefrom. The outlet 12 has a portion 13 which is divergent in the direction of flow of liquid leaving the pump. A rotor 14 is mounted within the housing 10, upon a shaft 15 which is coaxial with the inlet 11, the periphery of the rotor 14 lying, as shown, closely adjacent the periphery of the chamber defined by the housing 10.

The rotor 14 comprises a circular base plate 16 hav ing adjacent its periphery a plurality of integral radial blades 17. Also integral with the base plate 16 is a spiral impeller 18 which has a relatively small blade angle and which extends from a radially inner zone of the rotor 14 to a location adjacent the periphery thereof. Blade angle is to be understood as the angle between the plane of the impeller surface at any point, and a tangent to a cylinder which passes through that point and which is coaxial with the rotor. In the particular embodiment described the radially outer end of the impeller 18 is contiguous with an inner end of one of the blades 17. The rotor 14 may be provided with a shroud 19 which engages, or is integral with, the axial ends of the blades 17 and impeller 18, remote from the base plate 16.

As shown in Figure 1 the chamber defined by the housing 10 has a reducing axial dimension with increasing radius. Pumped fluid is thus accelerated by the rotor 14 as this fluid moves radially outwards towards the outlet 12. This movement of the fluid causes fluid to be drawn into the inlet 11 and to move radially into contact with the inner end of the impeller 18. The radial pitch of the impeller 18 is such that the product of this pitch and the rotor speed corresponding to the radial velocity of the pumped fluid adjacent the inlet 11.

Very little rotational movement will be imparted to the pumped fluid before it contacts the impeller 18.

As indicated above, rotational movement of the fluid tends to result in separation of air and vapour, and in the pump of the present invention there is therefore little separation upstream of the impeller 18. The helical channel defined by the impeller 18 imparts a steady acceleration to the pumped fluid, and hence a progressive increase in the static pressure of the fluid. The impeller 18 by virtue of its small blade angle, does not impart a significant angular velocity to the fluid. The relatively small angular velocity together with the aforesaid pressure increase and the long residence time of the fluid within the impeller 18, allows the separated air and vapour to recombined with the liquid fuel. The recombined fuel passes radially outwardly across a zone 20 of the impeller and is subsequently given a high tangential velocity by the blades 17.

In one application a low pressure centrifugal pump according to the invention is intended for use in delivering fuel to the main pump of a helicopter engine, the centrifugal pump being located well above the tank and acting as a suction pump. In such a comfiguration any damage to the fuel line between the tank and the centrifugal pump will not result in substantial leakage of fuel. A centrifugal pump is, when used in this way as a suction pump, particularly sensitive to increase in the size of a vapour core, and a pump according to the present invention is thus particularly adapted for use in the manner described.

1. A pump having a housing defining a chamber of substantially circular section, a rotor mounted in said housing an outlet adjacent the chamber periphery, an inlet opening into said chamber at a location radially inwardly of the periphery thereof, the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Pumps for fluids This invention relates to pumps for fluids, and in particular to pumps intended for use with aircraft fuels. It is known, in aircraft fuel systems, to provide a low pressure backing pump which delivers fuel from a tank to a main high pressure pump. In such pumps a core of separated air and fuel vapour may form adjacent the axis of the pump rotor. An increase in the amount of such separated air and vapour is accompanied by a reduction in pump delivery pressure. Furthermore, the size of the vapour core tends to increase with altitude, thereby limiting the maximum altitude attainable by an aircraft in which such a pump is fitted. It has been proposed to overcome this problem by providing a pump rotor having blades whose blade angle is small, the blade angle being defined as the angle, at the rotor periphery, between a tangent to the rotor and the plane of the adjacent portion of the blade. Such rotors, while being relatively insensitive to the amount of separated air and vapour, are nevertheless sensitive to the volume flow through the pump, delivery pressure decreasing sharply with increased flow. It is an object of the invention to provide a pump in which delivery pressure can be maintained at an acceptable levei over a range of fuel flows in conditions in which separated vapour would otherwise prevent effective pump operation. According to the invention a pump has a housing, defining a chamber of substantially circular section, a rotor mounted in said housing, an outlet adjacent the chamber periphery, an inlet opening into said chamber at a location radially inwardly of the periphery thereof, the rotor having a plurality of substantially radically extending walls adjacent its periphery and a spiral impeller extending from a radially inner portion of the rotor to a location thereon adjacent said walls, said rotor including means for permitting fluid flow between said impeller and said walls to be accompanied by relative angular movement between said fluid and said rotor, about the axis of said rotor. An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1, is a longitudinal section through a pump and, Figure 2 is a section on line 2-2 in Figure 1. The pump has a housing 10 which defines a pumping chamber of circular cross-section. An inlet 11 opens into the housing 10 at the axis of the chamber, and an outlet 12 opens into the periphery of the chamber and extends tangentially therefrom. The outlet 12 has a portion 13 which is divergent in the direction of flow of liquid leaving the pump. A rotor 14 is mounted within the housing 10, upon a shaft 15 which is coaxial with the inlet 11, the periphery of the rotor 14 lying, as shown, closely adjacent the periphery of the chamber defined by the housing 10. The rotor 14 comprises a circular base plate 16 hav ing adjacent its periphery a plurality of integral radial blades 17. Also integral with the base plate 16 is a spiral impeller 18 which has a relatively small blade angle and which extends from a radially inner zone of the rotor 14 to a location adjacent the periphery thereof. Blade angle is to be understood as the angle between the plane of the impeller surface at any point, and a tangent to a cylinder which passes through that point and which is coaxial with the rotor. In the particular embodiment described the radially outer end of the impeller 18 is contiguous with an inner end of one of the blades 17. The rotor 14 may be provided with a shroud 19 which engages, or is integral with, the axial ends of the blades 17 and impeller 18, remote from the base plate 16. As shown in Figure 1 the chamber defined by the housing 10 has a reducing axial dimension with increasing radius. Pumped fluid is thus accelerated by the rotor 14 as this fluid moves radially outwards towards the outlet 12. This movement of the fluid causes fluid to be drawn into the inlet 11 and to move radially into contact with the inner end of the impeller 18. The radial pitch of the impeller 18 is such that the product of this pitch and the rotor speed corresponding to the radial velocity of the pumped fluid adjacent the inlet 11. Very little rotational movement will be imparted to the pumped fluid before it contacts the impeller 18. As indicated above, rotational movement of the fluid tends to result in separation of air and vapour, and in the pump of the present invention there is therefore little separation upstream of the impeller 18. The helical channel defined by the impeller 18 imparts a steady acceleration to the pumped fluid, and hence a progressive increase in the static pressure of the fluid. The impeller 18 by virtue of its small blade angle, does not impart a significant angular velocity to the fluid. The relatively small angular velocity together with the aforesaid pressure increase and the long residence time of the fluid within the impeller 18, allows the separated air and vapour to recombined with the liquid fuel. The recombined fuel passes radially outwardly across a zone 20 of the impeller and is subsequently given a high tangential velocity by the blades 17. In one application a low pressure centrifugal pump according to the invention is intended for use in delivering fuel to the main pump of a helicopter engine, the centrifugal pump being located well above the tank and acting as a suction pump. In such a comfiguration any damage to the fuel line between the tank and the centrifugal pump will not result in substantial leakage of fuel. A centrifugal pump is, when used in this way as a suction pump, particularly sensitive to increase in the size of a vapour core, and a pump according to the present invention is thus particularly adapted for use in the manner described. CLAIMS

1. A pump having a housing defining a chamber of substantially circular section, a rotor mounted in said housing an outlet adjacent the chamber periphery, an inlet opening into said chamber at a location radially inwardly of the periphery thereof, the rotor having a plurality of substantially radially extending walls adjacent its periphery and a spiral impeller extending from a radially inner portion of the rotor to a location thereon adjacent said walls, said rotor including means for permitting fluid flow between said impeller and said walls to be accompanied by relative angular movement between said fluid and said rotor, about the axis of said rotor.

2. A pump as claimed in claim 1 in which said inlet is substantially coaxial with said rotor.

3. A pump as claimed in claim 1 or claim 2 in which said walls comprise a plurality of radial blades.

4. A pump as claimed in claim 3 in which a radially outer end of said impeller is contiguous with one of said blades.

5. A pump as claimed in any preceding claim in which said rotor has a periphery lying closely adja centthe periphery of said chamber,

6. A pump as claimed in any preceding claim in which said outlet opens into the periphery of said chamber and extends tangentially therefrom.

7. A pump substantially as hereinbefore described with reference to and as shown in the accompanying drawings.