EP0106382A1

EP0106382A1 - Working table with laminar air flow protection

Info

Publication number: EP0106382A1
Application number: EP83201301A
Authority: EP
Inventors: Rudi Bianchetti
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-09-10
Filing date: 1983-09-09
Publication date: 1984-04-25
Also published as: EP0106382B1; NL8203523A; DE3364965D1; ATE21165T1

Abstract

Down flow working table having an air circulation system with two filters (8,23), one (23) upstream and the other (8) downstream a working surface, air entrance at the front side of the working surface (1) and an exhaust (17) being branched off from the connection between the filters, a single fan (10) for circulating the air and a control flap (18) adjustably mounted at the exhaust branch off (15) for controlling the proportion of the air vented through the exhaust (17).

Description

The invention relates to a working table, among others suitable for biological activities, provided with an air circulation system with a first filter for filtering air which from a space upstream of said filter is from above fed to a space downstream of said filter and above the working surface of the working table and with a second filter mounted between the space immediately above said working surface and the suction side of a fan, the pressure side of the fan being connected via a duct with an exhaust and with the said space upstream of said first filter.
Such working tables are known in practice. The publication "Nouvelle Gamme, (Sofiltra), no. R.C. Seine 67B3072, 4-70 shows working tables having an air flow system with an adjustable fan, which tables, however, create an almost dust free atmosphere above the working surface but do not prevent that air from the table ,enters the room in which the table is located. In the first mentioned working table a so-called lainar air current fulfils the double task at the one hand to prevent that the micro particles, such as aerosol particles, bacteria or other particles may come from the space above the working surface into the space in which the working table is put and at the other hand to see to it that any particles in the space above the working surface are regularly carried off. Consequently they have to comply with very stringent reliability requirements, specially if biological activities are involved. With bacteriological experiments or processes a slight escape may lead to serious consequences, which naturally may be even more so with certain so-called biological manipulations for instance with hereditary material.
For this reason filters are used with a very high filtering capacity for small particles, it being not unusual to let pass no more than3.10-5 of all particles above 0, µ m. By this high degree of filtering out of these particles not only an almost complete protection against bacteria passing said filter is obtained, but the same holds also for virus, which in practice cannot exist independently but only on a matrix or such like, which may be a bacterium for instance.
With such working tables it is of great importance that the air current complies always to the concerned requirements, namely that a good air curtain is present, such that particles present above the working surface will be carried off regularly and no such particles may move to the outside. The air circuit of such a working table contains a suction from the space above the working surface and an exit through the exhaust and further two filters. For complying with all requirements under varying conditions it is possible to equip the fan with an adjustable rotational speed, but even then adaption to changed conditions, for instance other experiments or such like is not always possible in such a way that optimum security can be guaranteed. The same is true also when the flow resistance of the filters changes during use, which mostly means that they increase.
Moreover the flow conditions with a single fan, a suction and an exhaust an two principally not completely constant flow resistances are not always sufficiently controllable.
It is remarked that from the Vutch Patent Application 7215945 a working table of the discussed down-flow type is known, having two fans. Apart from the complication this may incur the risk that one of the fans drops out in which case very abnormal flow conditions may arise, even with the effect of blowing particles into the space outside the working table.
The invention aims to improve the security of working tables with.a constructively simple means which also can be applied directly to working table that already exist.
Accordingly the invention provides that a duct at the location of its division in a connection to the exhaust and a connection to the space upstream of the first filter is provided with an adjustable flap.
By giving the flap an adjustment, which complies with conditions corresponding to a determined application of the working table and remains to do so within the reach in which these conditions can change, for instance by change of the filter resistances, avery important improvement is obtained with very simple means.
It is remarked that from Dutch Patent Specification 76.698 an air conditioning system is known having a flap that controls the recirculation air flow immediately toward a space which is the fan room of a main fan or indirectly via a space to which also the fresh air is admitted and which via a cooling means and an auxiliary fan discharges into said fan room.
According to a further elaboration of the invention it is preferably provided that the_flap has a pivot which is located at the downstream side of the flap. Such a location of an air control flap per se is known from the cited Dutch Patent Specification 76.698. With the invention this feature enables an effective possibility to modify the division of the air current without influencing the total flow resistance of the system in a considerable degree.
According to still a further elaboration of the invention it is preferably provided that the connection to the space upstream of said first filter has a passage obliquely oriented with respect to the portion of the duct which leads toward the division, the pivot of the flap being located near the side of said passage which is directed away from the portion of the duct leading to the division. Herewith is pointed to the fact that this feature per se has been shown in the cited Dutch Patent Specification 76.698. Also is this position of the passage per se known in working tables without flap.
A further important aspect of the invention is, that in order to increase the safeguarding of the room in which the working table is present, it is desired that the duct and the space upstream of the first filter are hermetically sealed from the space that contains the working table. Because in the duct and the said space upstream of the first filter one has air directly coming from the space above the working surface but having been filtered only once, it is possible that this air contains some infectious germs. Because a slight over pressure has to reign in this space with respect to the space containing the working table a high guarantee is important that this hermetical seal is maintained.
For this reason it is according a further elaboration of the invention provided that the flap has no mechanically movable control members extending outside said hermetically sealable space.
In practice it is herewith sufficient that the flap is adjusted one time for a determined application of the working table, but of course it is also possible to make the flap controllable, for instance by control means which work through a hermetical wall, such as electrical or magnetical control means.
The invention in the following is further elucidated on hand of the drawing, in which:-

Figure 1 shows a cross-section through a working table according the invention,
Figure 2 shows a cross-section over the line II-II of figure 1.

In the drawing reference 1 indicates a work sheet that serves the purpose of working surface and at its edges is provided with vent openings, for instance in the shape of a grid or sieve structure 2, by which the space 3 above the working surface is connected to the space 4 below this working surface. At the lower side of this space 4, which at its right side forms a leakage pan 5 a pre-filter 6 has been mounted the lower side of which is connected to a space 7, which at its lower side is closed.by a so-called absolute filter 8. Such a filter has the capacity to retain particles of 0,3µ m or larger with a perviousness of 3.10^-5.
The space 9 below the absolute filter 8 is connected to the suction side 9' of a fan 10 with an exit 11 which debouches in a duct 12. This duct has at 13 an enlargement toward the right, which debouches in an obliquely oriented passage opening 14 and at the other side a deviation 15 toward the left, which debouches in a vertical exhaust duct 16 with at the upper side an exhaust 17, which preferably is connected to a non shown exhaust channel which debouches outside the building containing the working table.
A flap 18 is pivotable about a pivot 19. With non shown means the flap can be fixed in a certain position. If the flap in figures 1 is swayed toward the left an important part of the air passes through the passage opening 14 and when the flap 18 is swayed toward the right a more important part passes through the exhaust 17.
The passage opening 14 debouches into a space 20 (vide fig. 1) which by means of a baffle 21 is separated from the space 3 above the working surface. At its upper end the baffle 21 is somewhat bent wherewith it debouches with little flow resistance into the space 22 above filter 23. Consequently the air enters the space 3 from above through filter 23 and through the front side 24 of the space 3 from the right above the work sheet 1 and forms therein a constant air down flow, which goes toward the vents 2, wherewith also a continuous air flow through the front side 24 of the space 3 occurs in the direction toward the working table. Both these aire currents prevent that suspended particles in space 3 remain there permanently or go outside.
The air sucked in by fan 10 passes through ducts 12 and 16, which latter duct is located in a space 20, which toward the outer side is closed by a shutter 25. This shutter can be mounted air tightly and normally is controlled with respect to its seal by means of soaping.
The proportionality between the air current which passes through the filter 23 and the one that is sucked in through the front side 24 can be controlled by adjusting flap 18. Moreover the rotational speed of the fan 10 can be adjusted for maintaining certain desired flow velocities. With both these adjustment facilities the possibility exists to adjust the working table to an optimum air flow velocity and air current distribution for a certain use. Then, when small variations occur during use, for instance because filters get a higher flow resistance, by a just choice of the starting condition it can be seen to it that is worked amply inside safe application limits. >
The filter which firstly may show a tendency to clog is the pre-filter, in which most of the coarse particles suspended in the air are caught. Naturally this filter will be replaced if this is necessary or desired.
Summarizing it can be put that the application of the flap 18 forms an extremely simple means for enlarging the adjustment possibilities of the table and consequently adjust it better to the current velocities allowable with different applications. This adjustability is obtained without the complications and dangers tied up with two fans connected in series or parallel, which flow circuits often are very sensible for relatively small changes, as is well known.

Claims

1. Working table, among other suitable for biological activities, provided with an air circulation system (3,9, 10,11,20,22) with a first filter (23) for filtering air which from a space (22) upstream of said filter is from above fed to a space (3) downstream of said filter and above the working surface (1) of the working table and with a second filter (8) mounted between the space (3) immediately above said working surface and the suction side of a fan (10), the pressure side of the fan being connected via a duct (11,16,14) with an exhaust (17) and with the said space (22) upstream of said first filter (23) characterized in that said duct (11) at the location (19) of its division in a connection (16) to the exhaust (17) and a connection (14) to the said space (22) upstream of said first filter is provided with an adjustable flap (18).

2. working table according to claim 1, characterized in that the flap (18) has a pivot (19) which is located at the downstream side of the flap.

3. Working table according to claim 2, characterized in that the connection (14) tot the space (22) upstream of said first filter (23) has a passage (13) obliquely oriented with respect to the portion (11) of the duct which leads toward the division, the pivot (19) of the flap (18) being located near the side of said passage which is directed away from the portion (11) of the duct leading to the division.

4. Working table according to one or more of the preceding claims characterized in that the duct at the location of the flap has an enlargment (13,15), wherewith one side (15) of the duct turns aside in a first side direction for further on turning back in the direction of the exhaust (17) and the opposite side (13) turns aside in the opposite direction for terminating in the passage (14) which forms the connection with the space (22) stream up of the first filter.

5. Working table according to one or more of the preceding claims, in which the duct (11) from the fan toward the exhaust (17) or the space (22) stream up of said first filter has been contained in a hermetically sealable space, characterized in that the flap (18) has no mechanically movable control members extending outside said hermetically sealable space.