GB2061488A - Fume Cupboard - Google Patents

Abstract

A fume cupboard comprises two or more working spaces, each being defined at the front side by a vertically slidable sash 2a, 2b movable between a fully opened position and a closed position in which a residual slot remains open 3a, which spaces each connect at their upper side by means of a plurality of suction slots with a suction chamber adapted to be connected with an exhaust duct. The suction chambers are provided with an auxiliary opening 10a, 10b situated above the corresponding sash, forming a connection with the adjacent exterior space, and which is gradually covered when moving upwards the sash 2b in question, such that, in any position of the sash, the total amount of air withdrawn from the adjacent exterior space will be substantially the same. The auxiliary opening 10a, 10b of each space is provided with an additional closing means 15a, 15b which is movable between a position in which the passage through this auxiliary opening is fully open and another in which this passage is fully closed. The closing means 15a, 15b are adapted to be actuated in such a manner that, in the auxiliary openings 10a, 10b are opened, and, when opening a sash 2b of one working space, the auxiliary opening 10a of at least one other working space is closed, in such a manner that the total amount of air exhausted from the adjacent exterior space will remain substantially the same. <IMAGE>

Description

SPECIFICATION Fume Cupboard In laboratories it is usual to conduct experiments which may produce troublesome and/or noxious vapours or gases and/or dust clouds, or giving rise to fire or explosion risks, in a fume cupboard, i.e. a space which is closed at one side by means of a mainly transparent wall which is adapted to be opened, and in particular a sash or sliding window, the interior of said cupboard connecting by means of a connection situated at its upper side with an exhaust duct through which vapours, gases etc. will be drawn off, an exhaust blower being included in said duct.It is, then, not only necessary to make up for the exhausted air continuously, but, moreover, an uninterrupted air flow through the cupboard is to be maintained which is directed from the lower side towards the exhaust opening, in which flow the vapours etc., even if they are heavier than air, will be taken along. The concentration of these vapours and gases should, preferably, be maintained as far as possible below a given trouble or danger threshold, in particular in the case of inflammable or noxious gases etc. On the other hand the air flow should not be so strong that gas flames present in the cupboard would start flickering, or powdery substances would be blown away.

For maintaining this flow a sash is generally used which cannot be completely closed so that, in its most closed position, a slit remains open through which the exhausted air is supplemented from the adjacent space. If an interference in an experiment under progress should be made, the air flow in the then fully opened position of the sash should be sufficient for preventing that vapours or gases present in the cupboard, in particular if they are heavier than air, would be driven outwards by air turbulences, and would, then, arrive in the laboratory space, and moreover the person working in the sash opening may unfavourable influence the flow pattern.

These conditions are, generally, incompatible, since, at a sufficient flow velocity in the open position of the window, the air velocity in the closed position thereof will be much too high.

Morever, in the case of a plurality of cupboards, an interaction between several cupboards can arise if they are connected to a common exhaust duct.

These objections might be removed by coupling a regulator for the exhaust blower with the sash so as to adapt the exhaust capacity to the actual need. A draw-back thereof is, however, that the amount of air removed from the adjacent space will vary in function of the opening of the sash, which leads to undesirable variations in the air flows in this space, a consequence thereof being an unstable air distribution in said space leading to turbulences near the sash, so that, then, gases, vapours etc. can escape outwards.

Moreover each fume cupboard should, then, be provided with an individual exhaust blower, and such a control system is liable to disturbations. An important objection is that;then, also the air supply to the laboratory space should be variable which may have an unfavourable influence on the heating and/or cooling of this space, which will lead to additional cost.

In order to remove these objections, it has been known already for a long time in fume cupboards to connect the working space proper at its upper side with a suction chamber by means of a plurality of air slots, which chamber connects with the exhaust duct, and is, furthermore, provided with an auxiliary opening above the sash connecting with the adjacent laboratory space and being gradually covered when sliding the sash upwards, all this in such a manner that in any position of the sash the sum of the amounts of air sucked inwards through the opening below the sash and through this auxiliary opening respectively will always be substantially the same, and, moreover, the air velocity in the former opening in the opening position of the sash will be, in any point thereof, above a given minimum value, and in the closed position below a given maximum value, this minimum value being determined by the desired security against outwardly directed turbulences and the maximum value being determined by the requirement that the air flow through the residual slot below the closed sash must not cause gas flames present inside the cupboard to flicker or blow away powdery substances present therein.

Such fume cupboards have excellently satisfied, and ensure that in the presence of several fume cupboards the air flow distribution in the laboratory space will remain substantially unchanged irrespective of the number of opened or closed cupboards, which cupboards will, moreover, not influence one another. A safe velocity of the air in the fully opened window opening will, then, be about 0.25 m/s, and in the slot below the closed window an at least equal and generally higher velocity, e.g. of about 0.5 m/s, will be maintained.

Recently, however, in some laboratories more stringent requirements have been imposed in view of the security against troublesome or noxious substances leaking outwards, the safe velocity of 0.25 m/s there being considered as being insufficient, and a velocity of at least 0.4 m/s being required.

As such this can be realised in cupboards of the above-mentioned kind, taking care, of course, that the air velocity in the residual slot below the sash will not exceed the maximum value. A disadvantage, however, is that the amount of air exhausted from the laboratory space will become more than 1.5 times larger, which makes a considerable difference in the case of a plurality of cupboards, and will very unfavourably influence the air distribution in this space if the latter is still adapted to cupboards complying with the older standards.An important disadvantage, also in the case of a new building in which these more stringent requirements can be taken into account, is that the laboratory spaces are heated in the colder season and, sometimes, are cooled in the warmer season, which requires relatively much energy, and a considerable part of the heated or cooled air, as the case may be, will be exhausted by the fume cupboards, so that the energy used for heating or cooling thereof will be removed unutilised. It is, as such, feasible to arrange heat exchangers in the exhaust duct for recovering the lost heat, but the installation costs thereof are considerable, and in many cases there is insufficient space for accomodating them in the exhaust ducts, and furthermore the efficiency is often insufficient for compensating for these costs.Moreover such a solution comprising partially compensating for energy losses by means of expensive auxiliary apparatus without remedying the cause of the losses is, in principle, rejectable.

It is an object of the invention to remove these objections in a compound fume cupboard comprising at least two partial cupboards, each being provided with a sash, which compound cupboard is provided with an additional closing means movable between a position in which the passage through the additional opening is fully opened and another position in which said passage is fully closed, which additional closing means is adapted to be actuated in such a manner, that, in the closed condition of the sashes, all the auxiliary openings are opened, whereas when opening of one sash at least one closing means associated with an other sash is closed, and this in such a manner that the total amount of air exhausted from the adjacent space remains substantially unchanged.

This construction comes, in principle, up to the fact that the amount of air exhausted in the closed condition of the sashes is not larger than in the case of a corresponding number of cupboards of the above-mentioned known construction, and is sufficient for maintaining, in the residual slots below the closed sashes an air velocity which is higher than the imposed minimum velocity and mainly corresponds to that in the abovementioned current cupboards, whereas, when opening a sash, the larger amount of air required for maintaining the substantially higher air velocity according to the more stringent requirements is, now, compensated for by reducing the as such useless air flow through the auxiliary opening of an other partial cupboard of the assembly, so that the total air flow withdrawn from the adjacent space with a fully opened sash is not larger than in a cupboard of current design with a lower air velocity in the opened sash opening.

In cases that the lower velocity in the sash opening accepted until now is still acceptable, such a construction can be used as well, so that, then, the amount of air exhausted from the adjacent space can be reduced in comparison with a comparable assembly of current cupboards.

The invention is not only suitable for new laboratories, but can also be used when adapting already present cupboards to the more stringent requirements, or when enlarging the number thereof and maintaining the current standards.

In particular the closing means will be constituted by sliding panels which are vertically slidable past the auxiliary openings in question, and which are each coupled with the sash of at least one other partial cupboard in such a manner that when sliding upwards this sash said sliding panel is lowered. This provides a dependable and easily maintainable coupling between the various panels and sashes. In particular a compound cupboard according to the invention consists of two partial cupboards, in which case the latter coupling will be the simplest.

Since fume cupboards, when in use, are, in principle, closed, and will only be opened briefly for intervening in an experiment, the probability that two sashes of such an assembly will be simultaneously opened will be relatively small.

Although it is possible to interlock the sashes so as to prevent the simultaneous opening of two or more sashes, this solution is not satisfactory as it is possible that a simultaneous intervention in two or more cupboards is necessary, and releasing the locking may lead to unacceptable delays. The compound cupboard according to the invention will, in particular, be constructed in such a manner that two sashes can be simultaneously opened, and the dimensions of the various passages will be chosen so that, when simultaneously opening both windows, the air velocity in both passages will not decrease below a value which is, as such, still acceptable. e.g. the current standard of 0.25 m/s, and, at the same time, alarm can be given so as to warn the operators that a deviation from the more stringent standard has taken place, which condition should be terminated as quickly as possible.

The invention will be elucidated below by reference to a drawing, showing in: Fig. 1 is a simplified cross-section of a known fume cupboard; Fig. 2 a corresponding cross-section of a fume cupboard forming part of a compound fume cupboard according to the invention; and Fig. 3 a simplified diagram for elucidating the coupling between movable parts of a compound fume cupboard according to the invention.

The known fume cupboard schematically shown in Fig. 1 comprises a working space 1 which is defined, at its front side, by means of a sash or sliding window 2, and below this sash a passage 3 is present, even if the sash 2 is fully closed as shown. This sash is connected to a counter-weight or balancing springs by means of cables not shown so as to be kept in balance in any position.

The upper part of the space 1 is bounded by an upper wall 4 with slots 5, above which a suction chamber 6 is situated connecting, on the one hand, by means of an exhaust connection 7 with an exhaust duct not shown provided with a blower On the other hand the chamber 6 connects through a passage 9, defined by a partition 8, with an auxiliary opening 10 opening into the adjacent laboratory space. The partition 8, moreover, defines a space in which the sash 2 is movable. Furthermore a rear partition 11 is present defining an additional passage 12 connecting, on the one hand, at 13 with the lower part of the space 1, and, on the other hand, opening at 14 into the suction chamber 6.

The various passages 5 and 13 are chosen so that, under all circumstances, considerable turbulent and vortex movements of the air in the space 1 are substantially suppressed.

In the position shown of the sash 2, the greater part of the air withdrawn through the connection 7 will flow through the opening 10, and through the openings 5 and 13 so much air will be taken in that, in the residual opening 3, an air flow will be maintained with a velocity which is sufficiently higher than a given minimum velocity so as to prevent possible leaking out of heavy vapours or gases, this velocity being not so high that burners present in the space 1 will flicker, or possibly present powder will be blown away.

If the sash 2 is pushed upwards, the opening 3 is enlarged, but the opening 10 will be reduced accordingly, and this in such a manner that the total amount of air withdrawn from the adjacent space will remain substantially unchanged. The ratio between the dimensions of the respective passages is chosen so that, even if the sash is fully opened, the air velocity in the passage 3 will remain, anywhere, above a given minimum value, which, in the current cupboards, amounts to 0.25 m/s. The opening 10 has, then, such a shape that, in any position of the sash, the condition of a constant total amount of withdrawn air and the condition of maintaining a given minimum air velocity in the passage 3 are satisfied.

In Fig. 2 a corresponding cross-section of one half of a compound fume cupboard according to the invention consisting of two juxtaposed partial cupboards is shown. Parts corresponding to parts of the cupboard of Fig. 1 have been indicated by the same reference numerals. Now in the vicinity of the opening 10 an additional sliding panel 1 5 is provided which is vertically slidable, and is adapted, when moved downwards, to close the opening 10 progressively, independently of the closure of this opening caused by an upward movement of the sash 2.

This additional sliding panel is coupled with the sash of the adjacent partial cupboard of the assembly, and the sash 2 shown is coupled with the additional sliding panel 1 5 of the other partial cupboard. An example of this coupling is schematically shown in Fig. 3, in which an a is added to the reference numerals of parts of the one partial cupboard, an a b to those of the other partial cupboard. The boundaries of the sash opening 3 and of the auxiliary opening 10 have been indicated therein with interrupted lines.

As shown in Fig. 3, the sash 2a of one partial cupboard is connected by means of a cable 1 6a to the closing panel 1 sub of the other partial cupboard, and, conversely, the sash 2b of the latter is connected by means of a cable 1 6b to the closing panel 1 5a of the former. If, for example, the sash 2a is opened, the sliding panel 1 sub will be lowered, so that, then, the opening 1 0b will be closed accordingly, and also the opening 1 0a will be closed by the sash 2a accordingly.

The various passages are chosen so that, when the sash 2a or 2b is fully opened, an air flow is maintained in the opening which satisfies the more stringent requirements, i.e. is at least 0.4 m/s, and also in the closed position of both sashes a velocity is maintained in the residual opening 3a or 3b resp. which has at least this value, and is, generally, chosen somewhat higher. As soon as one of the sashes, e.g. 2a, is moved upwards, not only the corresponding auxiliary opening 1 0a is closed, but also the auxiliary opening 1 Ob of the other partial cupboard.This means that the, as such useless, air flow through this second auxiliary opening is, now, suppressed accordingly, so that, although for maintaining the aforesaid higher velocity in the fully opened passage 3a a considerably larger amount of air is required than for the usual velocity, nevertheless the amount of air withdrawn from the adjacent space will not be larger than in the case of the known cupboards.

If, however, both sashes 2a and 2b are pushed upwards, at a given instant, when both sashes are about opened half-way, a situation will be reached by lowering the corresponding sliding panels 1 5 and 1 sub in which both openings 8a and 8b will be substantially closed, and thereafter, when moving both sashes 8a and 8b further upwards, nothing will be changed anymore. A consequence thereof is, however, that, when moving these sashes further upwards, the air velocity in the openings 3a and 3b will decrease below the desired value. Precautions should now be taken that in that case the velocity in both sash openings 3 will not decrease below the previously accepted safe value od 0.25 m/s.Moreover, by means of contacts not shown co-operating with the sashes, sliding panels or counter-weights, an alarm apparatus can be switched on as soon as both sashes are moved simultaneously past the half-opened position. The operators will then be warned that a less safe condition is arising which should then be terminated as soon as possible.

It will be clear that the described construction can be modified in many ways. Instead of the sliding panels 1 5 other closing means may be arranged in corresponding air passages, and it is also possible to obtain a coupling between more than two partial cupboards, which can also be realised by other means than cables. The described embodiment is, however, the simplest one, and provides an effective and easily maintainable solution.

In view of the available space it can sometimes be useful to make the stroke length of the sliding panels 1 5 shorter than that of the sashes 2, e.g.

hy using pulleys or the like, and, of course, the dimensions of the passages should be adapted accordingly.

It can be useful to make the additional partition 8, defining the space in which the sash 2 and the corresponding sliding panel 15 are movable, removable, in particular by suspending it on a counter-weight or the like, so that it can be moved upwards so as to make the upper space of the cupboard 1 more easily accessible in the case of taller apparatus to be arranged.

The operation of such a compound cupboard can be better understood by means of a numerical example, which, for the rest, is only intended for elucidating the essential idea. It will be assumed for this purpose that the dimension of the passages 3 in the closed condition has the value 1, and in the fully opened condition the value 4, the dimensions of the openings 10 than being 1.5 and 0 respectively, taking into account the magnitude of the passages in the adjacent flow paths, such as the passages 5 and 9. If both sashes are closed, the total passage opening amounts to (1+1.5) 2=5. If one sash is opened, the passage 3 is enlarged to the value 4, and both passages 10 are reduced to 0, the total passage then being 1+4=5), thus, being kept unchanged.At a given exhausted amount of air the velocities in the passages 3 will, therefore, remain substantially the same, and also the amount of air withdrawn from the adjacent space will not change. If, on the contrary, both sashes 2 are opened, both passages 3 will obtain the magnitude 4, the total passage then becoming 8, which means that the air velocity in both passages will become 5/8 of the abovementioned velocity if the total amount of withdrawn air remains the same. If the normal velocity desired in these passages is at least 0.4 m/s, the velocity will decrease, in the latter case, to 0,25 m/s, which, however, still complies with the standard accepted until now. In this numerical example it has been left out of consideration of course that the changes in the flow conditions in the various passages will not evolve linearly.

However these numerical values provide a picture of the manner in which the air distribution over both partial cupboards will take place. In practice it is always possible to comply with the imposed requirements by a suitable choice of the shape of the various openings and passages.

Claims (6)

Claims

1. A compound fume cupboard, comprising two or more working spaces, each being defined at the front side by a vertically slidable sash movable between a fully opened position and a closed position in which a residual slot remains open, which spaces each connect at their upper side by means of a plurality of suction slots with a suction chamber adapted to be connected with an exhaust duct, which suction chambers are, moreover, provided with an auxiliary opening situated above the corresponding sash, forming a connection with the adjacent exterior space, and which is gradually covered when moving upwards the sash in question, all this in such a manner that, in any position of the sash, the total amount of air withdrawn from the adjacent space will be substantially the same, the velocity in the sash opening, in the opened position, remaining anywhere above a given minimum value, and, in the closed position, the velocity being at least equal to this minimum value but not higher than a given maximum value, characterised in that the auxiliary opening (10) of each partial cupboard is provided with an additional closing means (15) which is movable between a position in which the passage through this auxiliary opening is fully liberated and another in which this passage is fully closed, which closing means are adapted to be actuated in such a manner that, in the closed position of the sashes (2), all the auxiliary openings are opened, and, when opening a sash (2) of a partial cupboard, the additional closing means (1 5) of at least one other partial cupboard is closed, this in such a manner that the total amount of air exhausted from the adjacent space will remain substantially the same.

2. The fume cupboard of claim 1, characterised in that the additional closing means (15) are sliding panels which are slidable past the auxiliary openings (10) in question, and are each coupled with the sash of at least one other partial cupboard in such a manner that, when pushing upwards a sash (2), the panel or panels (15) coupled therewith will be lowered and vice versa.

3. The fume cupboard of claim 2, characterised in that the sliding panels (1 5) and sashes (2) are mutually coupled by means of cables (16) guided by rollers, if necessary with the intermediary of pulleys.

4. The fume cupboard of any one of claims 13, characterised in that the various passages are chosen in such a manner that, when simultaneously opening two sashes, the air velocity in both sash apertures will not decrease below a given boundary value which is lower than the afore-mentioned minimum value.

5. The fume cupboard of any one of claims 1 - 4, characterised in that, when opening two or more sashes so that the air velocity in the sash opening will decrease below the minimum value, an alarm apparatus is switched on.

6. A compound fume cupboard substantially as, hereinbefore described with reference to the accompanying drawings.