GB2385381A

GB2385381A - Synchronised rotary lobed pump

Info

Publication number: GB2385381A
Application number: GB0203648A
Authority: GB
Inventors: Philip Robert Stokes
Original assignee: Alfa Laval LKM AS
Current assignee: Alfa Laval Kolding AS
Priority date: 2002-02-15
Filing date: 2002-02-15
Publication date: 2003-08-20
Also published as: WO2003069160A1; AU2003244989A1; GB0203648D0

Abstract

A rotary lobed pump comprises a sealed pump section 1, containing a first lobed rotor and a second lobed rotor, a first motor 9 and a second motor 9a, for independently driving and engaging the first and second rotors respectively, and a controller and encoder system 10, for controlling and preventing contact between the rotors. The controller and encoder system may be a SIN-COS single turn absolute encoder. The first and/or second motor may be servo or stepper motors.

Description

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SYNCHRONISED ROTARY LOBED PUMP

Technical Field

The invention relates to rotary lobed pumps and a method of operating such pumps.

Background to the Invention

Conventional rotary lobed pumps comprise a pump section, a gearbox and a drive system. The pump section of a typical rotary lobed pump system includes two impellers or rotors which can engage with one another to provide the pumping 10 action. The impellers/rotors are typically contained within a housing having inlet and outlet ports and a front cover. The housing is typically sealed.

The remainder of a conventional rotary lobed pump comprises a gearbox, which usually contains a drive shaft and lay shaft drivingly connected to two gears to time 15 the rotors and prevent rotor contact, and a drive unit. The drive unit usually contains fixed speed motors, variable speed motors, inverter driven motors or geared motors which are coupled to the drive shaft. The whole assembly is then mounted on a base plate ready for installation.

20 One of the problems with conventional rotary lobed pumps lies in the timing of the two rotors. This timing is critical to ensure that the rotors do not come into contact with each other or open beyond a predetermined limit. During assembly of a conventional pump, setting the rotor timing is very time consuming and often requires several attempts to achieve the correct setting if the mechanical locking 25 methods slip.

Conventional rotary lobed pumps are manufactured so as to be specific to a particular application. This means that they cannot easily be adjusted to use different pumping speeds or to alter the displacement of the pump. If the application of the pump 30 changes after its initial set-up, a new drive train operating at a different speed is often

- À -2 required. Conventional pumps are also very heavy, bulky pieces of equipment and are therefore expensive to transport and install. They are made up of a large number of 5 parts and their assembly is complicated and time consuming.

It is therefore an aim of the present invention to provide a rotary lobed pump which is simple to control, particularly with regard to timing the rotors, which is suitable for use with a wide range of different applications without complex adjustment and 10 which addresses the further problems of conventional pumps described above.

Summary of the Invention

The present invention provides a rotary lobed pump comprising: - a sealed pump section having inlet and outlet ports, which sealed 15 pump section comprises a first lobed rotor and a second lobed rotor, - a first motor and a second motor for independently driving and engaging said first and second lobed rotors respectively, and - a controller and encoder system for controlling, and preventing contact between, said first and second lobed rotors.

The use of the two independently operating motors (which are preferably servomotors or stepper motors) and the controller/encoder system simplifies the process of timing the two rotors. The pump of the invention can be timed electronically by synchronizing the two motors. Each time the unit is switched on, 25 the controller can retime the pump automatically, for example using electronic positioning methods. The invention also takes advantage of all the benefits offered by modern electronic control systems.

Furthermore, the pump of the invention is a flexible system. It can be operated at 30 different speeds and can thus be tailored to suit any application including

- - - applications with varying duty parameters.

The present invention also removes the need for an integral gearbox, inline drives, couplings, spacers (required in conventional systems to achieve alignment between 5 the pump and drive) or bespoke base plates. This leads to a significantly reduced building time, not only due to the reduced time required for assembly, but also for painting. Further, only a small number of motor specifications are needed in order to

cover the complete range of rotary lobed pump applications currently in use. This is in contrast to the large number or parts and differing gearbox specifications which

10 are required for conventional systems.

The pump of the invention is also significantly reduced in weight compared with conventional systems due to the removal of many components. This reduces distribution, packaging and installation costs. The noise levels produced by the 1 S pumps are also reduced since noise from the gearbox, geared motor and coupling is eliminated. The present invention also provides a method of operating a rotary lobed pump, which method comprises driving a first lobed rotor of said rotary lobed pump with a 20 first motor and driving a second lobed rotor of said rotary lobed pump with a second motor. Brief Description of the Drawings

The present invention will be described further below with reference to an exemplary 25 embodiment and the accompanying drawings, in which Figure 1 schematically depicts a rotary lobed pump according to the present invention, 30 Figure 2 sectionally depicts a rotary lobed pump according to the present invention;

- -4 and Figure 3 depicts the pump section and gearbox of a conventional rotary lobed pump.

5 Detailed Description of the Invention

A rotary lobed pump of the present invention is depicted in Figure 1. The pump comprises a pump section 1 which contains the two rotors. The rotors are adapted to engage with one another such that a pumping action occurs when the rotors are turned. more detailed depiction of a pump of the invention is shown in Figure 2. In this embodiment, the rotors 2 are positioned within a rotor housing 4 having a removable front cover 7 and a rear cover 11. The housing is supported by mounting feet 12.

The housing also contains rotor retention means 13, seals 14 to contain the fluid to be 15 pumped and oil seals 15 to isolate oil from the rotor area.

In the embodiment of the present invention shown in Figure 2, the pump section comprises a bearing arrangement 16. The bearing arrangement of a conventional rotary lobed pump is typically housed in the gearbox. Since the pump of the present 20 invention does not require a gearbox, the bearing arrangement may be contained in the pump section instead. The pump of the invention may also be provided without bearings. The two rotors within the puking section are each connected to a motor, 9, 9a (which 25 is for example a servomotor or stepper motor) either directly or via a gearbox 17, 1 7a. The two motors drive the two rotors independently. The motors are typically connected to the rotors by conventional means, for example using keys or male/female splines with the motor being filled to the pump section via, for example, a flange.

i -5 The motors employed may be any motors which are suited to the application of the pump. In particular, the motors should be suited to the power requirements of the pump and, physically, they should be as small as possible to facilitate handling and transportation. The pump section, or wet end, of the pump of the invention is typically substantially the same as a conventional pump section. A conventional pump section is depicted in Figure 3. The pump section 8 of Figure 3 comprises rotors 2 and 3, a housing 4 having inlet and outlet ports 5 and 6. The housing has a removable front 7 and is 10 sealed from the remainder of the pump.

The pump of the present invention is controlled by a controller/encoder system 10.

The controller/encoder may be of any known type, but SIN-CDS single turn absolute encoders are preferred. The controller/encoder system automates the timing of the 15 two rotors and electronically locks the radial position of both rotors with respect to each other. In this way, the encoder/controller system is able to ensure that the two rotors do not contact one another. Re-timing of the rotors is typically carried out automatically on re-starting the machine. The use of a SIN COS single turn absolute encoder provides particularly high positional accuracy and is thus reliably able to 20 avoid contact between the rotors. Lower cost encoders may be used for less radially positionally sensitive design of rotor profile.

Whilst we have described above specific embodiments of the invention, it will be appreciated that the invention may be practiced otherwise than described. The 25 description is not intended to limit the invention.

Claims

-6- CLAIMS

1. A rotary lobed pump comprising: - a sealed pump section having inlet and outlet ports, which sealed 5 pump section comprises a first lobed rotor and a second lobed rotor, - a first motor and a second motor for independently driving and engaging said first and second lobed rotors respectively, and - a controller and encoder system for controlling, and preventing contact between, said first and second lobed rotors.

2. A rotary lobed pump according to claim 1, wherein the controller and encoder system is a SIN-CDS single turn absolute encoder.

3. A rotary lobed pump according to claim 1 or 2, wherein said first and/or said 15 second motors are servo or stepper motors.

4. A rotary lobed puking according to any one of the preceding claims substantially as hereinbefore defined.

20

5. A method of operating a rotary lobed pump, which method comprises driving a first lobed rotor of said rotary lobed pump with a first motor and driving a second lobed rotor of said rotary lobed pump with a second motor.