NZ203561A - Centrifugal fan with co-axial damper to regulate output at constant impellor speed - Google Patents

Description

Priority Date(s): '.&<?.

Complete Specification Filed: .

Class: ttXf&tfjQQ Publication Date: ... .P. J, . P.O. Journal, No: NEW ZEALAND 2 03do1 ^'jsTbWr^- [■ft 14 MAR 1983 ^ A , C £ | V""' PATENTS ACT 1953 COMPLETE SPECIFICATION J. P. & • % Improvements In or, rolating to Centrifugal Fans.

P. & S. " *y ;We, KEITH BLACKMAN LIMITED, of -S4H-Bough ton Road, Rugby, ;s y f ;Warwickshire CV21 +BU-England, a Company incorporated under the Laws of England, hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described and ascertained in and by the following statement ;-1- ;2 035 " ;-2- ;The invention relates to centrifugal fans of the kind in which the impeller comprises a back plate carrying an array of blades disposed around a peripheral region of the back plate with their inner 5 edges equally spaced from the axis of rotation to provide en inlet region, commonly known as the i.T.pellor eye, into which a gas, such as air, is drawn to replace that which is expelled outwards between the blades as the impeller rotates. In such fans the 10 impeller is normally housed within a casing in the form of a volute provided with an inlet opening which communicates with the eye of the impeller, and an outlet opening communicating with the space around the impeller through which the gas is discharged in 15 use of the fan. ;The flowrate of a centrifugal fan can be varied by varying the speed of rotation of the impeller but this is not always desirable or practicable. ;20 An alternative is to provide dampers, which may be positioned either on the inlet or outlet side of the fan, depending on the nature of the fan and the characteristics required, and although such dampers tend to lower the fan efficiency to some exrfcent 25 depending on the form employed they have the advantage of simplicity and low initial cost compared with most methods uned for varying the impeller speed. ;One form of damper in common use consists of a plurality of parallel pivot able blades, usually 30 disposed across the fan outlet, and providing a greater or lesser resistance to the gas flow depending upon their angular setting. ;Another form of damper makes use of radially extending pivotable vanes at the fan inlet. In use of 35 a centrifugal fan full pressure is developed by the fan only when gas enters the impeller eye axially and without swirl. The radial vane damper is arranged to develop ;203561 ;3- ;a degree of pre-rotation of the gas in the direction of impeller rotation, and as a result the pressure developed by the fan is reduced, with a consequential reduction in flowrate and power absorption. Such 5 damper permits the fan to operate at a greater efficiency than the parallel blade daapers referred to above, but the mechanism required to enable the blades to rotate in synchronism is considerably more complicated. ;10 and speed of impeller rotation the flowrate is a function of the blade width, and this is made use of in providing an alternative form of damper which has advantages over the forms of dampers above described, as will be apparent from the following description. 15 According to the invention a centrifugal fan of the kind referred to has the inner edges of impeller blades extending parallel to the impeller axis and incorporates a damper plate in the form of a circular disc supported coaxially non-rotatably within the array of blades, 20 with its edge closely adjacent the inner edges of the blades, the disc being movable in an axial direction within the array of blades. ;varies the useful width of the impeller blades, and 25 enables the fan to operate at an efficiency which is comparable with one having a radial vane camper, but is considerably simpler mechanically, requiring only a single primary moving part, and moreover, is able to give stable control to almost zero flow, added resistance 50 being virtually negligible. ;is conveniently supported in a non-rotatable manner, may be achieved by means of a pneumatic, hydraulic or electrically operated actuator, which may be controlled 35 automatically in response to a control signal derived ;It is known that for a given blade arrangement ;It has been found that such a damper effectively ;The axial movement of the damper plate, which ;-4- ;in any suitable way, for example in dependence, either directly or indirectly, upon the fan output; however manual control means may alternatively or additionally be provided if required. ;5 The fan impeller can be driven by an electric n;otor or by any other suitable drive means- A variable speed electric aotor may be used in association with the movable damper plate to give an additional degree of control. ;10 The invention is particularly applicable to blowing systems utilising relatively wide impellers of high specific speeds, a substantial range of control being possible. With the damper plate acting on width operation is unaffected by blade shape, and the impeller 15 blades can therefore take any of the forms commonly employed in centrifugal fans; for example the blades may be backvardly inclinaed, backwardly or forwardly curved or of aerofoil section, provided their inner edges are parallel to the impeller axis as above des-20 cribed. ;One centrifugal fan in accordance with the present invention -will now be described by way of example with reference to Figures 1 and 2 of the accompanying schematic drawing, in which 25 Figure 1 represents in diagrammatic form an axial section through the fan, and Figure 2 represents a transverse section in the plane indicated by the line II-II of Figure 1. ;The fan comprises, in the usual way, an outer 50 casing 1 in the form of a volute having inlet and outlet openings 10, 20 and rotatably supporting within it an impeller 2, the impeller comprising a backplate 3 carried by a shaft 4 which extends through a bearing 5 mounted in the rear wall 6 of the casing for connection 35 to a suitable drive member (not shown) such as an ;*7 A electric motor.

The backplate 3 supports an array of blades 7 disposed uniformly around the front face of the backplate, and having radially inner edges extending 5 parallel to, and spaced ecuidistantly from, the impeller axis. An annular shroud 8 is attached to the front edges of the blades 7> its inner edge curving forwardly and surrounding the adjacent end of a stationary inlet venturi 9 which communicates with the 10 inlet opening 10 in the front wall of the casing in known manner.

In accordance with the invention the fan incorporates a damper comprising a circular plate 11 supported coaxially within the array of impeller blades 7> and 13 of a diameter such that its edge lies close to the inner edges of the blades with only a small clearance. The plate 11 is carried by an axially extending rod 12 which projects outwards through the inlet venturi 9» and is movable axially by means of an actuator 13 of 20 any convenient kind, supported from the casing 1 by radially extending tie rods 14-.

Movement of the actuating rod 12 alters the position of the damper plate 11 with respect to the impeller blades 7j ana it has been found that this 25 effectively controls the flowrate, by varying the useful width of the blades, without any substantial loss of fan efficiency, and with the minimum of moving parts. The flowrate can be varied from practically zero with the damper plate 11 in a withdrawn position 30 closely adjacent the inlet venturi 9j "to a maximum value when it lies close to the backplate 3« The actuator 13 can be operated pneumatically, hydraulically or electrically or in any other convenient manner, either by manual or servo control as 35 be convenient, depending on the nature of the 2 033 61 installation of which the fan forms part.

In one arrangement the fan may be associated with a temperature responsive sensor, as at 15 arranged to generate an output signal dependent upon 5 temperature and located in a position at which the temperature is responsive to changes in the output of the fan, the output signal controlling the actuator, and hence the position of the damper plate, in the sense which tends to maintain the temperature 10 substantially constant. In an alternative arrangement the temperature sensor may be replaced by another form of sensor responsive to a different condition, for example humidity, which is variable in response to changes in the fan output. Means may be provided for 15 adjusting the output signal, in order to vary the tenperature or other condition obtainable by adjustment of the fan output.

Although the impeller blades 7 are shown as planar and backwardly inclined in Figure 2, it will 20 be understood that they can take any of the forms commonly employed in centrifugal fans of the kind with which the invention is concerned.

Claims (9)

203561 What we claim is:-

1. A centrifugal fan of the kind referred to having the inner edges of the inpeller blades extending parallel to the inpeller axis, in v;hich there is incorporated a dr.sper plate in the form of a circular 5 disc supported coaxially non-rotatably within the array of blades, with its edge closely adjacent the inner edges of the blades, the disc being movable in an axial direction within the array of blades. 10

2. A centrifugal fan according to Claim 1 incorporating, for producing the axial movement of the damper plate, an actuator which is controllable 15 automatically in response to a control signal.

3. A centrifugal fan according to Claim 2 including a sensor arranged to generate a signal which is dependent upon a condition variable in response to changes in the output of the fan, and means for 20 applying said signal as a control signal for controlling the actuator, and hence the position of the damper plate, in a manner which tends to maintain said • * condition substantially constant.

4. . A centrifugal fan according to Claim 3 wherein 25 the sensor is responsive to temperature changes.

5. A centrifugal fan according to Claim 1,2,3 or 4 wherein the actuator is operable electrically.

6. A centrifugal fan according to Claim 1,2,3 or 4 wherein the actuator is operable pneumatically 50 or hydraulically.

7. A centrifugal fan according to Claim 1 wherein the actuator is controllable in response to a manually produced control signal.

8. A centrifugal fan according to any precedii 35 Claim wherein the impeller is driven by a variabl^V 0 KB 203561 -8- speed electric motor.

9. A centrifugal fan of the kind referred to constructed and adapted to operate substantially as shown in and as hereinbefore described with reference to the accompanying drawing. By His/Their Authorised Agents, fcj. PARK & SON Per