AU4922597A - Fume cupboard having more than one sash - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicant: RONALD EDMOND LUCAS Actual Inventor: RONALD EDMOND LUCAS Address for Service: Chrysiliou Moore Martin CMC Centre 143 Sydney Road Fairlight Sydney NSW 2094 Invention Title: Fume Cupboard Having More Than One Sash The following statement is a full description of this invention, including the best method of performing it known to me/us: e:\karen\work\2713.dockr \\search\e\patents\comp\6560_1.doc This invention relates to fume cupboard systems for chemical laboratories and similar use. In particular, this invention relates to fume cupboard systems with more than one sash opening.

A fume cupboard is intended to prevent, as far as possible, the escape of fumes and chemical gases into the laboratory and surrounding areas. Thus, a fume cupboard normally operates to extract air, fumes and gases from the cupboard and exhaust them into the atmosphere at a safe distance from personnel.

Working access to a fume cupboard is provided by a sash opening, the sash being movable vertically or horizontally from a substantially closed to a fully opened position. The size of the sash opening is a factor in determining the air velocity through the sash opening. When the sash is fully opened, there is a potential problem, in that the air velocity must be sufficiently high to ensure extraction from the fume cupboard.

Many countries have set safety standards in this regard. For example, in Australia, standard AS 2243.8-1992 stipulates that the average face velocity across a fully opened sash in a fume cupboard must not be less than 0.5 m/s.

While it is possible to comply with such safety standards in the case of fume cupboards with a single sash opening, previously it has not been possible to comply in the case of fume cupboards with two or more sash openings.

Fume cupboards which are fitted with moving sashes, usually located opposite one another, are commonly called double-sided fume cupboards. This type of fume cupboard is frequently used in schools, commonly being installed between a classroom and a preparation room. Chemicals and solvents are stored in the locked preparation room and loaded into the fume cupboard from the sash in the preparation room. The other sash is accessible from the classroom. This system limits access to chemicals and solvents by students, since only a teacher, lab assistant or other responsible person would have access to the key to the locked preparation room.

Double-sided fume cupboards may also be located between two classrooms, thereby allowing each class access to the fume cupboard and saving space and capital cost.

There is presently a problem in manufacturing double-sided fume cupboards to comply with safety standards such as AS 2243.8-1992. Because double-sided \\search\e\patents\comp\6560_1 .doc fume cupboards have two operational sashes, to comply with standard AS 2243.8 the extraction rate from the fume cupboard needs to be such that the face velocity across both sashes when fully raised would not be less than 0.5 m/s. While this minimum extraction rate is practical in the case of single-sash fume cupboards, to date it has not been practical with double-sided fume cupboards. If the extraction rate was of the order required by the standard, the extraction system would inevitably be extremely noisy. More significantly, perhaps, if one sash were closed, the face velocity across the other sash when open would be far too high for practical use. In addition, in cases where the environment is air-conditioned, a large quantity of conditioned air would be wasted.

It is an object of the present invention, at least in some embodiments, to overcome or at least substantially alleviate the problems described above in relation to double-sided fume cupboards. It is a further object of the present invention to provide double-sided fume cupboards which at least in some embodiments meet the minimum requirements of Australian standard AS 2243.8- 1992.

Accordingly, this invention provides a fume cupboard comprising a housing, a working chamber within the housing, a plurality of displaceable sashes providing access to the chamber, exhaust ducting for the chamber, an extraction fan for extracting fumes from the chamber via the exhaust ducting and control means for controlling the rate of extraction of fumes from the chamber, whereby there is associated with each sash a sensory means adapted to generate a signal to the control means in response to position of the sash and the control means is adapted to respond to the signals.

The fume cupboard of this invention may be made of any suitable material or combination of materials.

If desired, a sink, for example, may be included in the fume cupboard.

Each sash is preferably a counter-balanced sash window of the vertically sliding sash type supported on stainless steel cables and running on ball-bearing pulleys. Ideally, the glass in the sash window is 6 mm toughened glass.

Optionally, the sash glass can be covered with a special safety film. The invention is not limited to vertically sliding sash windows; horizontally sliding windows, for example, are also within the scope of the invention.

\\search\e\patents\comp\6560 1.doc It is contemplated that by far the most common application of this invention will be to fume cupboards which have two displaceable sashes, one located opposite the other. However, other configurations are within the scope of this invention. For example, the fume cupboard may have two displaceable sashes located at right angles to each other. As another example, the fume cupboard of the invention may have three or more sashes. For convenience, in the remainder of this description, reference will be made to fume cupboards having two displaceable sashes. However, it is to be understood that the invention is not so limited.

The exhaust ducting and extraction fan may be of any suitable design and composition.

The sensory means associated with each sash is preferably a potentiometer, especially a multi-turn ratio potentiometer providing an analogue output to the control means. However, the sensory means may comprise any means capable of detecting the position of the sash, including micro switches, a series of proximity switches or infrared sensing means.

The control means for controlling the rate of extraction of fumes from the chamber may be a speed controller connected to the fan motor. Alternately, the control means may control a motorised damper in the exhaust ducting or in a by-pass system.

Where the control means controls speed of the extraction fan, the signal from each sensory means may be fed into a speed controller connected to the fan motor, the fan being preferably a centrifugal type fan. When the combined sash openings are large, the signal from the sensory means to the speed controller increases the speed of the fan. Conversely, when the combined sash openings are small or when one sash is closed, the signal from the sensory means to the speed controller decreases the speed of the fan. Desirably, the minimum speed of the fan is limited to ensure that sufficient air continues to be extracted when the sash opening is small, to ensure adequate extraction of fumes or heat from the fume cupboard. Alternatively, a damper in the exhaust ducting may close.

Where the control means controls a motorised damper in a by-pass system, the signal from each sensory means may be fed to a controller for the motorised damper, so that, as the face velocity increases as a result of relatively small sash openings, the motorised damper is adjusted by opening the by-pass to the extent necessary to obtain the proper flow through the chamber. Conversely, as the \\search\e\patents\comp\6560_1 .doc combined sash openings become larger, the motorised damper will close up the by-pass duct in order to maintain adequate air-flow through the chamber.

Preferably, there is inserted between each sensory means and the control means a device to consolidate the signals received from the sensory means, so that the control means responds to the aggregate of those signals.

In the special case where both sash openings are at their maximum, it may not be possible to achieve satisfactory extraction from the chamber. In that special case, therefore, it is preferred that the fume cupboard of the invention incorporates a shut-off facility, which cause power and gas supplies to become isolated and which may include an audible alarm, together with a visual message, such as "Excessive extraction" or "Close one sash", or both.

The fume cupboard of the invention may include a reset button to be activated for the fume cupboard could continue operation.

The invention will now be described in relation to certain embodiments thereof set out in the attached drawings, in which: Fig. 1 is a diagrammatic representation of a fume cupboard of the invention showing only one of the sashes; Fig. 2 is a diagrammatic view of one of the sashes, showing a counterbalance weight system; Fig. 3 is a plan view of a control means in respect of the sash counterbalance weight system; Fig. 4 is a diagrammatic front elevation of a further embodiment of the fume cupboard according to the invention; Fig. 5 is a side elevation of the fume cupboard of Fig. 4; and Fig. 6 is a diagrammatic front elevation of yet a further embodiment of the fume cupboard according to the invention.

Referring first to Fig.I, fume cupboard 20 has a housing 21 having a front face 22. Aperture 23 is varied by vertically sliding sash 3, to provide access to working chamber 24.

\\search\e\patents\comp\6560_1 .doc Exhaust ducting 25 has at end 26 an electric extraction fan 27 driven by a driving motor 28. Power line 29 provides power to motor 28.

Sensory means 13, which will be described in more detail in connection with Fig.

2, provides an output or signal which is fed into variable motor speed controller The output of speed controller 30 is connected by power line 29 to motor 28.

On the opposite side of fume cupboard 20, although not shown in Fig. 1, there is an identical set-up with regard to the sash and the sensory means. Also, although not shown in Fig. 1, a coordination device, such as an integrator available through Leading Edge Technology, of Sydney, NSW, Australia, is interpolated between both sensory means and speed controller One suitable form of speed controller 30 is marketed by Parametrics of Connecticut, USA, under the name "FHP Parajust". Another suitable form of speed controller is that marketed by Siemens Limited. A still further suitable controller is that marketed by Varidrive Pty Limited as its "Zener Model".

Fan motor 28 is preferably three phase and four pole, wired in delta.

As an option, emergency override button switch 31 is provided to change the cycles from 50Hz to up to 60Hz or more, thereby increasing speed of the fan motor 28, while button switch 31 is depressed to allow for rapid clearance of fumes, caused by spillage, etc.

Turning now to Fig. 2, it can be seen that one sash 3 is connected, via a stainless steel wire cable 4, and pulley 5 to a counterbalance weight 7. As sash 3 is raised to increase access to chamber 24 (Fig.1 weight 7 will fall to a corresponding degree. Conversely, as sash 3 is lowered, weight 7 will rise.

Chain 8, which has at one end a small weight 9, is connected at its other end to weight 7. Chain 8 engages a sprocket 11 fixed upon shaft 12 of sensory means 13. As an alternative, a belt could be double reeved over a pulley, in substitution for chain 8 and sprocket 11. Reference is made to Fig. 3 which illustrates these features.

Sensory means 13 in this embodiment is a five-turn ratio potentiometer. The application of 240V AC across potentiometer 13 will provide an analogue output on power line 29 of between 0 and 240V, depending upon rotation of shaft 12. As already explained, speed controller 30 receives the output from the potentiometer (ideally via a consolidation device), which consolidates the output received from a \\search\e\patents\comp\6560_1 .doc similar potentiometer connected to a second sash in mirror-reverse fashion to that shown in Fig. 2.

As will be readily appreciated, raising of each sash in the fume cupboard of the invention will cause the weight 7 to fall and increase the speed of fan 27.

Fig. 4 shows a slightly different embodiment of the fume cupboard of the invention, once again showing only one side of the fume cupboard, the other side being substantially the same. In this embodiment, fume cupboard 40 has, like the fume cupboard in Fig. 1, housing 21, front face 22 and working aperture 23.

Ducting and the exhaust fan are now shown in this figure but are substantially the same as that in Fig. 1.

Sash 3 provides access to working chamber 24.

In line with front face 22 is fascia 41 which includes LCD panel 42 for displaying a message as previously indicated if airflow is shut off as a result of this sash and the identical sash on the opposite side of the fume cupboard both being fully open. Reset button 43 is provided to restart the system after one or both sashes has been lowered.

In this embodiment, sink 44 and tap 45 are located in working chamber 24.

Fig. 5 shows how ducting 25 is concealed behind fascia 41.

Although not shown in this embodiment, a series of micro-switches detect the position of each of sashes 3 and feed this information to a consolidation device (not shown) which in turn operates speed controller 30 (as in Fig. 1).

Turning now to Fig. 6, fume cupboard 20 is essentially the same as that described in Fig. 1, except that communicating with exhaust ducting 25 is an auxiliary duct 34 in which is mounted an axially rotatable damper 36. Damper 36 is rotatable between a configuration where it is fully open and air can be sucked into auxiliary duct 34 and a configuration where damper 36 is almost closed, as shown, where the intake of air into auxiliary duct 34 is restricted.

Sensory means 13 provides an integrated signal from the position of sash 3 and the second sash (not shown) to electronic actuator 33. Electronic actuator 33 is of a type commonly used for control of dampers, such as the actuator sold under the name "Geamatic" available from C.E.R. Systems Pty Limited. As the combined \\search\e\patents\comp\6560_1 .doc sash openings in fume cupboard 20 are reduced, damper 36 is rotated into a more open position, to increase the intake of air through auxiliary duct 34.

It will be appreciated by one skilled in the art that the embodiments described are not intended to be limiting on the scope of the invention, the breadth of which is defined by the accompanying claims.

Claims (11)

1. A fume cupboard comprising a housing, a working chamber within the housing, a plurality of displaceable sashes providing access to the chamber, exhaust ducting for the chamber, an extraction fan for extracting fumes from the chamber via the exhaust ducting and control means for controlling the rate of extraction of fumes from the chamber, whereby there is associated with each sash a sensory means adapted to generate a signal to the control means in response to position of the sash and the control means is adapted to respond to the signals.

2. The fume cupboard claimed in claim 1, wherein there are two displaceable sashes.

3. The fume cupboard claimed in claim 1 or claim 2, wherein the sensory means is chosen from the group consisting of a multi-turn ratio potentiometer, a series of microswitches, a series of proximity switches and infra-red sensing means.

4. The fume cupboard claimed in any one of claims 1 to 3, wherein the control means controls speed of the extraction fan.

The fume cupboard claimed in any one of claims 1 to 3, wherein the control means controls operation of a motorised damper in a bypass duct communicating with the exhaust ducting.

6. The fume cupboard claimed in any one of claims 1 to 5, wherein the control means responds to a consolidation of the signals from the sensory means.

7. The fume cupboard claimed in any one of claims 1 to 6, wherein cut-off means cut off one or more services when all sashes are in a predetermined position.

8. The fume cupboard claimed in any one of claims 1 to 7 wherein an alarm is activated when all sashes are in a predetermined position.

9. A fume cupboard substantially as herein described with reference to Figs 1,2 and 3 of the accompanying drawings.

A fume cupboard substantially as herein described with reference to Figs 4 and 5 of the accompanying drawings. 'I \\search\e\patents\comp\6560_1.doc

11. A fume cupboard substantially as herein described with reference to Fig. 6 of the accompanying drawings. Dated this 23rd day of December, 1997 Ronald Edmond Lucas By his Patent Attorneys Chrysiliou Moore Martin