GB2041513A - Fluid damper - Google Patents

Abstract

A fluid damper comprising a line of blades (20) which are supported in a surrounding frame (10 and 12) for rotary motion about substantially parallel axes between positions in which they fully open and fully close a fluid opening in the frame (10 and 12). A blade drive mechanism for effecting rotary movement of the blades (20) comprises smooth-rimmed rotary caps or discs (22), one for each blade (20), which are connected to one or more drive elements (23). <IMAGE>

Description

SPECIFICATION Fluid damper This invention relates to a fluid damper comprising a line of blades which are supported in a surrounding frame for rotary motion about substantially parallel axes between positions in which they fully open and fully close a fluid opening in the frame.

In a number of prior British and foreign Patent Applications, we have described different dampers which are constructed as described above. Thus, for example, in British Patent Application No. 26387/77 filed on 23rd June, 1977, corresponding U.S. Patent Application Serial No. 916,357 filed on 16th June, 1978, in the name of R. J. Magill et al, and corresponding Canadian Patent Application Serial No. 305,812 filed on 20th June, 1978, we have described a combination smoke and fire shield damper which is effective as a barrier against both smoke and fire and which incorporates the "movable biade" construction outlined above. In that particular form of damper the blades are provided with "opened-out" trailing edge so that the ieading edge of each blade interlocks with the trailing edge of an adjacent blade when the blades are in their full-closed positions.

In another British Patent Application and its corresponding U.S. and Canadian Applications (British Application No. 53581/76 filed on 22nd December, 1976; U.S. Application Serial No. 862,920 filed on 21st December, 1977, in the name of Sydney J. Field; and Canadian Application Serial No. 293,354 filed on 19th December, 1977), we have described a control damper for controlling the flow of air or other gaseous fluid through a duct which likewise makes use of the movable blades described above, the blades being movable at will to intermediate positions between their fully-open and fully-closed positions and being of aerofoil shape.

Further, in the single Compiete Specification filed on our cognate British Patent Applications Nos. 6184/77 of 15th February, 1977, and 10895/77 (Serial No. 1521955) of 19th April, 1977, we have described a shut-off damper which again has movable blades as described above with the trailing edges of such blades comprising fluid sealing means extending along those edges so that a seal is formed between adjacent blades when the latter are in their full-closed positions. This shut-off damper is also described in the corresponding U.S. Patent Application Serial No.

877,185 filed on 13th February, 1978, in the name of R. J. Magill et al, and in Canadian Patent Application Serial No. 297,107 filed on 14th September, 1978.

Reference has been made to all these earlier Applications because the present invention is applicable to the different forms of fluid damper shown in them. In short, therefore, the present invention is applicable to control dampers. shut-off dampers, smoke dampers, fire shield dampers and to combination smoke and fire shield dampers.

All the prior Patent Applications specifically mentioned above show blade drive means for rotating the blades about their parallel axes in the form of intermeshing gear wheels, one for each blade, which are rotatable in unison to cause corresponding swinging movement of the blades between their fully-open and fullyclosed positions. Such gear wheels have been found to be entirely satisfactory in operation but they give rise to backlash between the intermeshing teeth of the gear wheels. The greater the number of gear wheels, the greater the backlash, and this mitigates against precise blade control. In addition, such gear wheels have to be made carefully if undesirable torque "stiffness" in the blade drive means is to be avoided.

With this consideration in mind, the present invention is directed to an improved form of blade drive mechanism in which undesired torque stiffness or backlash is greatly reduced or substantially avoided.

To this end, a fluid damper in accordance with the invention and constructed as outlined in the opening paragraph of the Specification is provided with a blade drive mechanism for effecting rotary movement of the blades about their parallel axes comprising smooth-rimmed rotary caps or discs, one for each blade, which are connected to one or more drive rods or bars, or some other form of drive element.

Such a construction ensures that the accumulative backlash factor as backlash, if any, is confined to a selected driving cap or disc, or at most two driving caps or discs, and, is not exaggerated by the other caps or discs.

Where, as is frequentiy the case in such fluid dampers, alternate blades need to be swung in opposite senses, alternate caps or discs can have a pin-and-hole connection with a longitudinally-movable drive rod or bar which is common to alternate caps or discs. In other words, there will be two drive bars or rods, one for rotating some of the caps or discs in one direction while the other rod or bar rotates the remaining discs in the opposite direction.

The caps or discs can be made very simply by being pressed out from sheet metal with extruded rectangular holes for accurate blade bearing shaft alignment and with circular peripheral indents to reduce friction and ensure stability throughout the total operating arc. Their production does not therefore give rise to the same manufacturing tolerance difficulties as precision-made gear wheels.

The drive bars or rods are equally simpie to make from sheet metal and preferably have pre-punched square holes for minimum con tact area with the round pin connections to the caps or discs, thus reducing friction and the possibility of mechanical seizure.

Circular metal bushes will generally be fitted over selected blade bearing shafts to act as stops in controlling the movement of the drive bars or rods so that the overall angle of blade rotation, which would otherwise be from 0" to about 115 , is precisely from 0" (which is the completely open blade position wherein the blades offer minimum resistance to flow) to 90 which is the fully closed position wherein the blades provide the absolute lowest flow ieakage, there being also the choice of any intermediate blade position to suit operating requirements.

Some examples of fluid dampers in accordance with the invention are shown in the accompanying drawings, in which: Figure 1 is a perspective view of one form of damper with a smail portion shown in section; Figure 2 is an exploded view in perspective of part of the damper shown in Fig. 1; Figure 3 is an exploded view in perspective of another part of the damper shown in Fig.

1; Figure 4 is an exploded view in perspective of part of a second form of damper; Figures 5 and 6 are both front views of caps and drive bars forming parts of the dampers shown in Figs. 1 to 4; Figure 7 is a perspective view of the caps and drive bars shown in Figs. 5 and 6; Figure 8 is a slightly-enlarged section through one of the caps shown in Figs. 5 to 7; and Figure 9 is a reduced-size perspective view of a third form of damper which is designed to be installed within a duct.

The damper shown in Figs. 1 to 3 is a combination smoke and fire shield damper, but it could equally well be another form of fluid damper as mentioned above. It comprises a roll-formed galvanised sheet steel outer frame 10 of flanged channel section and a sheet steel channel-section inner frame 1 2.

The outer frame 10 has continuously-welded corners and has outwardly-extending flanges 14 adapted to enter the ends of two air ducts arranged end-to-end but with a gap between them to receive the damper, which is normal practice in the United Kingdom. The attachment by welding. bolting, rivetting, or other means of the inner and outer frames together produces a double-skin air-tight casing of high rigidity and substantial strength.

As will be seen from Fig. 2, the inner frame 1 2 has a series of circular holes 1 6 punched in its two vertical sides. The holes 1 6 support the shafts 1 8 of blade-bearing components 1 9 which fit into and onto the open ends of blades 20 which are thus mounted for rotary movement in the frame about parallel axes.

The blades 20 are low-profile aspect ratio aerofoil stainless steel blades to provide low resistance to air or other gaseous fluid fiowing through the damper, especially when the blades are in their fully-open positions (i.e., the positions of the blades shown in Fig. 1 of the drawings). The aerofoil section of the blades also reduces turbulence and noise and provides excellent protection against corrosion resulting from the presence of corrosive particies in the air stream. Another advantage is that the narrow blade width readily permits the withdrawal of the complete damper from a duct, regardless of the positions of the blades within the damper casing, without materially disturbing the flow of air through the duct frame as a whole.

Rotation of the blades about their respective axes is effected through smooth-rimmed, punched-out metal caps or discs 22, there being a respective cap or disc 22 for each blade 20. As will be seen from Fig. 2, the shft 1 8 of each blade bearing component 1 9 has a keyed end 24. The shafts 1 8 on one side of the damper have their keyed ends 24 arranged to enter rectangular-section central holes 26 in the caps or discs 22 (see Fig. 7) which are arranged in rim-to-rim engagement and disposed in a line vertically of the damper. The caps or discs 22 rotate in unison due to the fact that each one is pivotally attached by a respective pivot pin 22a to one of two parallel connecting bars or rods 23.Longitudinal displacement of the bars or rods 23 in the same direction will thus cause all the blades 20 to move together about their respective axes. However, as shown by the arrows in Fig. 2, alternate caps or discs 22 will rotate in opposite senses so that adjacent pairs of blades 20 will likewise rotate in opposite senses or directions to open or close the central passage through the damper.

The caps or discs 22, or, alternatively, the bars or rods 23, are acted on, directly or indirectly, by one or more springs or other resilient means so as to urge the blades 20 towards their closed positions. This can be done in various ways, using various forms of spring. In this particular instance, two of the caps or dics 22 are rotatably fast with two spring-loaded drive wheels 28 (see Fig. 3), each of the wheels 28 being acted on by a coiled spring 30 which is connected at one end to the periphery of its respective wheel 28 by a pin 32 and is supported on a pin 34 in a control box 36 having a removable cover 38. The two drive wheels 28 have stub-shafts 40 projecting from each side, and these enter circular holes 46 in the control box cover 38.

The positions of the wheels 28 and the coiled springs 30 in the control box 36 are shown in broken lines in Fig. 3.

The effect of the springs 30 on the wheels 28 is to urge the latter to rotate in opposite senses or directions as shown by the arrows in Fig. 3. Because the two wheels 28 are rotationally fast with two adjacent caps or discs 22 (by, for example, coupling the stub shafts 40 passing through the holes 42 to the shafts 1 8 which enter those caps or discs, or by connecting the ends of those stub shafts 40 direct to the respective caps or discs 22), all the caps or discs 22 will be urged to rotate in such directions that the blades 20 are urged into their fully-ciosed positions so as to completely close the central passage formed by the frames 10 and 1 2 of the damper.

It is to be understood that many other forms of spring-loading could be used to obtain the desired effect-namely, to urge the blades resiliently into their fully-closed positions. For example, one or more of the caps or discs 22 could be provided with a torsion spring, or a tension spring could be attached to a peripheral portion of one or more of the caps or discs, or to the two connecting bars or rods 23.

Because the particular damper shown in Figs. 1-3 has to serve both as a smoke damper and as a fire shield damper, the caps or discs 22, the connecting bars or rods 23, the drive wheels 28 and the blade bearing components 1 9 are preferably all made of metal, but it may be acceptable in certain instances for these particular parts to be made partially or entirely of a synthetic plastics material instead. Whatever the material used, such caps or discs, connecting bars or rods, drive wheels and bearing are totally enclosed and completely shut off from the air stream through the damper by the outer and inner frames 10, 1 2 and by the control box 36.

This ensures that the said components do not become dirty or contaminated with impurities in the air stream.

The extent to which the blades can be rotated about their respective axes can be varied to suit the requirements of different customers. Normally they-will be rotatable through at least 90 and, in many cases, through 180 .

To seal the leading edge of the uppermost blade, the trailing edge of the lowermost blade and the ends of all the blades, springymetal sealing strips 64 are arranged along the inner surfaces of the inner frame 1 2 as shown in Fig. 2. Each sealing strip 64 is here made of springy steel and is of arched section. The two horizontal strips 64 at the top and bottom of the damper lie in the channels of the inner frame, while the two vertical strips 64 at the sides of the damper lie between the blade bearing components 1 9 and the opposing surfaces of the inner frame.For this purpose, the vertical strips 64 have holes 66 formed in them to allow for the passage therethrough of the shafts 1 8. The arched form of the strips 64 not only helps to reduce the leakage of fumes and smoke through the damper when the blades are in their fully-closed positions but allows the strips to yield as the blades expand due to the heat of a fire.

As will be appreciated, the blades 20 must be held in their fully-open positions to allow for the passage of air through the damper during normal use of the air duct or ducts in which the damper is installed. This means that a device needs to be provided which will hold the blades open against the action of the springs 30 but which will allow those springs to shut the blades, i.e., bring them into their fully-closed positions, should fire break out.

The best form of device is therefore one which is sensitive to a rise in temperature, and the damper shown in the drawings, is accordingly provided with a temperature-sensitive all-stainless steel spring-operated removable cartridge 68 carrying a replaceable fusible element 70 rated, say, at 72"C (162" F), the element 70 having a very low thermal capacity so as to be extremely sensitive to temperature rise. The cartridge 68 is easily removable from the inner casing 12, without the use of tools, by simply unscrewing it from the latter. The fusible element 70, which lies prominently in the airstream (see Fig. 1), can likewise be readily replaced in the event of fire or damage by unscrewing the captive end of the cartridge.Fusing of the element 70 or removal of the fusible element or the cartridge as a whole provides the fail-safe feature of instant blade closure.

The control box 36 shown in Fig. 3, besides housing the drive wheels 28 and the springs 30, also supports and partially contains a siiding operating member 72 which acts on the spring-loaded drive wheels 28 so as to rotate them into a position where the blades 20 are held in their fully-open positions. It should be mentioned, incidentally, that the torque available from either spring 30 is more than sufficient to close all the damper blades, thus providing a fail-safe feature in the unlikely event of failure of one of the two springs. Thus, linear movement of the operating member 72 to its completely extended position shown in Fig. 2, either by hand or by a motor (not shown), causes two shoulders 74 on the member 72 to engage two pins 76 on the drive wheels 28, the pins being located in holes 78 and arcuate peripheral grooves 80 in the drive wheels.

Fig. 4 shows, in perspective view, part of a shut-off damper which, like the damper shown in Figs. 1-3, makes use of the caps and drive bars illustrated in Figs. 5-8 to open and close rotatable blades 20. The shut-off damper of Fig. 4 is basically of the same construction as the damper shown in Figs.

1-3 except that it has additional sealing means to provide an even more tight seal when the blades are in their fully-closed positions. These additional sealing means comprise rubber linings 64a on the two vertical springy sealing strips 64 and hollow D-section rubber seals 20a along the trailing edges of the blades 20. In addition, the damper of Fig.

4 has somewhat different mechanism to drive the caps 22 and the bars 23, the said mechanism involving the provision of two, but only two, meshing gear wheels 81 which serve to drive a selected one, or at most two, of the caps 22 from a shaft 81 a driven by a motor (not shown) or turned by hand.

Figs. 5-8 show the caps 22 and the bars 23 in a little more detail. The angular positions of the caps 22 and the longitudinal positions of the bars 23 shown in Fig. 5 correspond to the fully-open positions of the blades 20, while their positions illustrated in Fig. 6 correspond to the fully-closed positions of the blades.Fig. 7 shows how the caps and bars are pivotally connected together. it being noted that circular metal bushes 1 8a are fitted over selected blade bearing shafts 1 8 to act as stops in controlling the movement of the bars 23 so that the overall angle of blade rotation, which would otherwise be from 0" to about 115 or more, is precisely from 0" (which is the completely open blade position wherein the blades offer minimum resistance to flow) to 90 which is the fully closed position wherein the blades provide the absolute lowest flow leakage, there being also the choice of any intermediate blade position to suit operating requirements.

The caps or discs 22 are made very simply by being pressed out from sheet metal with their extruded rectangular holes 26 providing accurate blade bearing shaft alignment. As will be seen from Fig. 8, the caps 22 each have a circular peripheral indent or flange 22bto reduce friction and ensure stability throughout the total operating arc. It will also be noted that a raised radial rib 22c is formed in each cap so as to reduce friction between the caps and the bars 23. The production of such caps does not give rise to the same manufacturing tolerance difficulties as precision-made gear wheels.

The drive bars or rods 23 are equally simple to make from sheet metal and have prepunched square holes 23a for minimum contact area with the round pins 22a, thus reducing friction and the possibility of mechanical seizure.

As already indicated, the damper illustrated in Figs. 1-3 is designed to be inserted in a duct by arranging for the flanges 14 of the outer casing 10 to be inserted in the opposing ends of two duct portions. In other words, the damper is inserted in a "break" in a duct so that the inner frame 1 2 is substantially flush with the internal surfaces of the duct. However, in certain countries-particularly the United States of America-it is customary to position dampers entirely within a duct. Fig. 9 illustrates a damper having a frame 82 which permits this to be done. The frame 82 is, in effect, the same as the inner frame 1 2 in Fig.

2 except that the frame 82 has flanges 84 which lie against the inner surface of a duct 86. The duct 86 itself therefore forms an outer frame for the damper so that the outer frame 10 of Fig. 1 and 2 is no longer needed.

The remaining parts of the damper shown in Fig. 4 are essentially the same as those shown in Figs. 1-3.

It will be seen, therefore, that the blade drive mechanism described above does not call for the precision-made gear wheels, one for each blade, used in the blade drive mechanisms of the dampers shown in the earlier Patent Applications referred to above. Further, by means of the present invention, the problem of backlash and undesirable torque stiffness in operation of the mechanism is overcome.

Claims (11)

1. A fluid damper comprising a line of blades which are supported in a surrounding frame for rotary movement about substantially parallel axes between positions in which they fully open and fully close a fluid opening in the frame, and a blade drive mechanism for effecting rotary movement of the blades about their parallel axes, in which the blade drive mechanism comprises smooth-rimmed rotary caps or discs, one for each blade, and one or more drive rods, bars, or other elements, the drive element or each drive element being connected to more than one cap or disc.

2. A damper according to claim 1, in which one drive element is connected to the caps or discs of alternate blades to rotate them in one sense for closing the fluid opening in the frame, and another drive element is connected to the caps or disc of the other blades to rotate them in the opposite sense for closing the fluid opening.

3. A damper according to claim 1 or claim 2, in which the caps or discs of all the blades are in alignment with one another.

4. A damper according to claim 3.ap- pended to claim 2, in which the caps or discs are arranged in rim-to-rim engagement.

5. A damper according to any preceding claim, wherein the or each drive element is a longitudinally-movable drive rod or bar.

6. A damper according to claim 5 appended to claims 2 and 3, in which circular bushes are provided at the centres of the caps or discs between the drive rods or bars to act as stops in limiting movement of the rods or bars so that the overall angle of blade rotation allowed is 90 , from the full open position to the fully closed position.

7. A damper according to any preceding claim, in which the drive element or elements are connected to the caps or discs by means of pin-and-hole connections.

8. A damper according to any preceding claim, in which the caps or discs are punchedout pressings from sheet metal.

9. A damper according to any preceding claim, in which the caps or discs have rectangular holes at their centres into which fit blade-bearing shaft portions of rectangular cross-section.

1 0. A damper according to any preceding claim, in which one side of each cap or disc rests against a fixed part of the.damper.

11. A damper according to claim 10, in which that side of each cap or disc has a circular indent extending to the periphery of the cap or disc.

1 2. A damper according to any preceding claim, in which each cap or disc has a raised radial rib or crank portion extending from its centre to the connection with the drive element or one of the drive elements.

1 3. A damper according to any preceding claim, wherein the driving element or the driving elements have pre-punched square holes by means of which it or they are connected to the caps or discs.

1 4. A damper according to any preceding claim, in which the drive mechanism is springloaded to bias the blades into their closing positions.

1 5. A damper according to any one of claims 1 to 13, in which the drive mechanism is spring-loaded to bias the blades into their opening positions.

1 6. A damper according to claim 14 or claim 15, in which the spring-loading comprises two drive wheels which are rotationally fast with respective adjacent caps or discs, and respective coiled springs each connected at one end thereof to the periphery of its respective drive wheel.

1 7. A damper according to any preceding claim, in which the blade drive mechanism is totally enclosed.

1 8. A fluid damper substantially as described herein with reference to Figs. 1, 2, 3 and 5 to 8, or to Figs. 4 to 8, or to Figs. 5 to 9 of the accompanying drawings.