GB2312633A

GB2312633A - Device for generating purified air

Info

Publication number: GB2312633A
Application number: GB9705738A
Authority: GB
Inventors: Peter Bialek; Juergen Nothdurft
Original assignee: Piller GmbH
Current assignee: Piller Group GmbH
Priority date: 1996-03-21
Filing date: 1997-03-20
Publication date: 1997-11-05
Anticipated expiration: 2017-03-20
Also published as: FR2746487B1; FR2746487A1; DE19611136A1; DE19611136C2; GB9705738D0; GB2312633B

Description

1 2312633 Device for Generating Purified Air The invention relates to a

device for generating purified air, in particular for a protection area with contaminated air present at a reference pressure level, comprising a housing, a fan and an air filter.

Such contaminated air can include any type of contamination, e.g. even types of contamination occurring in industrial or agricultural processes.

The present invention seeks to provide a device for generating purified air, which provides as high a degree of safety as possible upon installation in protected areas.

According to a first aspect of the present invention, there is provided a device for generating purified air for a protection area comprising contaminated air present at a reference pressure level, comprising a housing, a fan and an air filter, wherein the.fan and air filter are enclosed by the housing; a first partial area is provided in the housing, which lies at an underpressure level relative (P1) to the reference pressure level (PR); a second partial area separate from the first partial area is provided in the housing, which lies at an internal overpressure level (P2) relative to the reference pressure level (PR); the housing has an air outlet opening into the protection area, from which the purified air discharges with a protection area pressure level (P3) lying between the reference pressure level (PR) and the internal overpressure level (P2); the fan transports contaminated air from the first partial area into the second partial area and thus maintains the internal overpressure level (P1); between the air outlet and the second partial area, the air filter is arranged, which is responsible for the pressure drop between the internal overpressure level (P2) and the protection area pressure level (P3); and between the second partial area and the protection area in the housing, a safety area (S) is provided, in which a safety pressure level (PS) is present, 2 which lies below the protection area pressure level (P3).

According to a second aspect of the present invention, there is provided a device for generating purified air for a protection area comprising contaminated air present at a reference pressure level, comprising a housing, a fan and an air filter, wherein the air filter is constructed as a filter cartridge, and that the housing has a filter cartridge channel extending in the direction of a longitudinal axis and passing through the housing in this direction and said filter cartridge channel, on the one hand, can be closed off with an outer housing cover opening towards the contaminated air and, on the other hand, is accessible from the protection area.

According to the third aspect of the present invention, there is provided a device for generating purified air for a protection area comprising contaminated air present at a reference pressure level, comprising a housing, a fan and an air filter, wherein the air filter has a housing case; that the air filter may be inserted with the housing case into a receiving case of a filter cartridge seat; that two guide elements spaced from one another in the direction of passage through the filter are provided between the housing case and the receiving case; and that an intermediate area between the two guide elements, the housing case and the receiving case lie at a safety pressure level (PS), which lies below the pressure level (P2) at the inlet of the air filter and below the pressure level (P3) at the outlet of the air filter.

An advantage of arrangements according to the present invention is that the safety area enclosing the second partial area ensures that all leaks occurring in a housing shell of the second partial area cause the contaminated air to pass through this to enter the safety a--ea, and does not allow it to enter the protection area from, the housing, since this lies at a safety area pressure -evel, so that even leaks in the housing shell enclosing:he protection area cause the purified air to flow into the safety area from the protection area, but the case is never permitted to occur where contaminated air flows into the protection area from the safety area.

Hence, devices according to the present invention may be installed directly into a protection area itself without there being any risk of contaminated air flowing into the protection area in the case of a leak in the housing shell surrounding the second partial area.

Arrangements according to the present invention even allow the possibility of constructing the housing shell surrounding the second partial area with leaks restricted in their leakage rate, since because of the pressure drop the contaminated air always flows out of the second partial area into the safety area, and because of the pressure drop between the external overpressure level and the safety pressure level, cannot discharge from there into the protection area.

Moreover, a leak in the housing shell surrounding the first partial area is also insignificant, since the underpressure level in the first partial area also lies below the protection area pressure level, and therefore also in this case only purified air can flow from the protection area into the first partial area, but contaminated air can never pass from the first partial area into the protection area.

Within the scope of the present invention, it would be possible, in principle, that the safety area surrounds the second partial area on all sides. However, if the housing of the device according to the invention on one side adjoins the surrounding area with contaminated air, it is not necessary that the safety area extends between the surrounding area with contaminated air and the second partial area, since in this case a leak in the second partial area leads to direct discharge of the contaminated air lying at the internal overpressure level into the 4 surrounding area with contaminated air. It is therefore sufficient if the safety area surrounds the second partial area in the region of its side adjoining the protection area.

In the case of preferred arrangements according to the invention, it is necessary that the safety area is held at the safety pressure level, and therefore the contaminated air flowing in, for example, from the second partial area is always discharged from the safety area.

This can be achieved particularly simply if the safety area communicates with the contaminated air outside the protection area via an opening and the safety pressure level lies essentially closed to the reference pressure level. This means that in this embodiment, the safety area must merely have an opening, via which the contaminated air entering the safety area can flow off to the contaminated air in the surrounding area of the protection area. This is possible without difficulty because of the pressure drop, since all that is necessary is that the safety pressure level lies below the protection area pressure level. Because of the opening between the safety area and the surrounding area of the safety area it is possible in a simple manner to reduce the safety pressure level to a value close to the reference pressure level, so that the contaminated air flowing into the safety area always flows out into the surrounding area outside the protection area lying at the reference pressure level.

Alternatively, it is advantageous if the safety area is connected to the first partial area and the safety pressure level lies essentially close to the underpressure level. This possibility is particularly advantageous where there would be problems in creating a connection between the surrounding area of the protection area and the safety area.

Moreover, it is advantageous to reduce the safety pressure level to close to the underpressure level, and thus create a large pressure gradient, which at all events ensures that none of the contaminated air flowing into the safety area can pass into the protection area, but always flows into the first partial area because of the pressure drop, and is thus transported from this again into the second partial area by means of the fan.

In order to assure in the manner according to the invention that leakages occurring in the region of the air filters do not cause the contaminated air to flow into the protection area, it is preferably provided that the air filters are surrounded by the safety area.

A wide variety of possibilities are conceivable with respect to the construction of the safety area. The safety area can be of large-volume construction and constitute an intermediate area between the housing and the second partial area.

An advantageous embodiment of particularly compact construction provides that the safety area is constructed as a cavity of a double wall, whereby it is at least necessary that such double walls are provided on all the sides of the second partial area facing the protection area and possibly also of the air filter.

In this case, it would be conceivable, for example, to provide individual double-walled wall sections and bring the respective cavities individually to the safety pressure level, whereby the safety pressure level could also be different, depending on whether the cavity is connected to the surrounding area of the protection area or to the first partial area.

However, a particularly advantageous embodiment provides that the cavities of all double walls are connected to one another and form a uniform safety area, in which an essentially uniform safety pressure level is present, in which case this can lie, for example, either close to the 6 underpressure level or close to the reference pressure level.

Purely in principle, it would be possible in arrangements according to the present invention to merely provide the air filter between the second partial area and the air outlet. However, it is particularly advantageous if the device according to the present invention has additional filters.

In this case, it is expediently provided that a flow filter is arranged in the second partial area. The arrangement of a flow filter in the second partial area is possible, for example, because this is sub-divided into two regions and the flow filter lies between the two regions of the second partial area, and this causes the inner overpressure level to be different in the two regions of the two partial areas. However, this has no effect on the principle of arrangements according to the present invention so long as the inner overpressure level is higher than the reference pressure level and the protection area pressure level and the safety pressure level.

In this case, this flow filter is preferably constructed as a cyclone, which divides the air flow coming from the fan into a dust-free air flow and a dust air flow, whereby the dust air flow discharges from the housing into the surrounding area of the protection area, in which the contaminated air lies.

Hence, an advantageous embodiment provides that the air filter comprises a particulate filter and a gas filter.

No further details have so far been given in conjunction with the previous explanation of individual features of arrangements according to the present invention with respect to the arrangement of the air filter in a device according to the present invention for generating purified air. Therefore, a further embodiment, which represents either a further development of the above-mentioned arrangement or an 7 alternative arrangement provides that the air filter is constructed as a filter cartridge, that the housing has a filter cartridge channel extending in the direction of a longitudinal axis and passing through the housing in this direction, and said filter cartridge channel, on the one hand, can be closed off with an external housing cover opening towards the contaminated air and, on the other hand, is accessible from the protection area.

The provision of such a filter cartridge channel enables used filter cartridges to be replaced either from outside the protection area, i. e. from the surrounding area with the contaminated air, or by inserting a new filter cartridge into the filter cartridge channel from the protection area and enabling the used filter cartridge to be passed through this and out of the housing into the surrounding area with the contaminated air.

Such a device is particularly advantageous when the filter cartridge has a filter. cartridge seat, and when contaminated air flows in between the outer housing cover and the filter cartridge seat in the filter cartridge channel, and after passing through the filter cartridge, flows into the protection area as purified air. The substantial advantage of this arrangement is that the contaminated air still flows in on the side of the filter cartridge, towards which the used filter cartridge may be moved, thus allowing a new filter cartridge to be inserted in a simple manner from the direction of the contaminated air or from the protection area.

The complete replacement of the filter cartridge is particularly favourable when, in the direction of the longitudinal axis of the filter cartridge channel, the filter seat has a guide length, which during replacement assures a closure preventing the passage of contaminated air between a first filter cartridge still partially disposed in the filter cartridge seat and a second filter cartridge inserted partially into the filter cartridge seat, whereby 8 in this case preferably both filter cartridges sit one directly behind the other in the direction of the longitudinal axis.

With this arrangement it is possible to replace a used filter cartridge with a new filter cartridge despite operation of the fan of the device according to the present invention, without resulting in contaminated air entering the protection area.

It is even more advantageous if, in the device according to the present invention, the filter cartridge channel has a second guide section for the filter cartridge located between the entry of the contaminated air and the housing cover, and if a filter cartridge partially sitting both in the filter cartridge seat and in the second guide section prevents the entry of contaminated air into the filter cartridge channel. In this arrangement, the entry of contaminated air into the protection area is prevented in an even better manner, since the contaminated air cannot enter the filter cartridge channel at all and therefore cannot flow through this into the protection area.

Moreover, this solution has the substantial advantage that when opening the outer housing cover, the internal overpressure level maintained by the fan in the second partial area does not collapse as a result of opening the housing cover during replacement of a filter cartridge by moving the used filter cartridge from the filter cartridge seat in the direction of the outer housing cover. Instead, in the guide section, the used filter cartridge also separates the second partial area from the surrounding area of the protection area containing contaminated air, so that, between the complete removal of the filter cartridge from the filter cartridge channel and closure c_ the outer housing cover, only brief contact is possible between that of the contaminated air standing under internal overpressure in the filter cartridge channel and the c=taminated air in the surrounding area of the protection area, and as a result 9 of this, a brief collapse of the internal overpressure level in the second partial area occurs.

A further advantageous device according to the present invention, which may be used to supplement the abovementioned embodiments, but also constitutes an alternative arrangement, provides that the air filter has a housing case; that the air filter may be inserted with the housing case into a receiving case of a filter cartridge seat; that two guide elements spaced from one another in the direction of passage through the filter are provided between the housing case and the receiving case; and that an intermediate area between the two guide elements, the housing case and the receiving case lie at a safety pressure level, which lies below the pressure level at the inlet of the air filter and below the pressure level at the outlet of the air filter.

This arrangement has the substantial advantage that it is not necessary to seal.the housing case in relation to the receiving case with the guide elements so that no contaminated air located close to the inlet of the air filter can flow through between the receiving case and the housing case to the outlet of the air filter, since the safety pressure level always causes contaminated air flowing between the housing case and the receiving case to remain in the intermediate area, and not exit from the intermediate area in the direction of the protection area, and thus in the direction of the outlet of the filter, since the safety pressure level lies below the pressure level at the outlet of the air filter. It is even the case that purified air also flows into the intermediate area from the outlet of the air filter because of the pressure drop between the pressure level at the outlet of the air filter and the safety pressure level in the intermediate area. However, this may be tolerated without problem, and must merely be compensated by a higher air throughput in the case of the device according to the invention. In particular, the guide elements in this device according to the present invention do not need any lip seals known from the prior art, for example, for this purpose. It is sufficient if the guide elements have a low leakage rate in comparison to the air flow passing through the air filters.

It is also particularly expedient in this embodiment, if the receiving case is surrounded by a safety area which lies at the safety pressure level. In this case, it is possible in a particularly simple manner to prevent air from flowing out of the intermediate area into the protection area, and thus render further leakages in the receiving case harmless, and prevent contaminated air from flowing into the protection area through the receiving case. Moreover, the intermediate area can be held at the safety pressure level in a simple manner.

In this case, the safety pressure level in the aforementioned embodiments can either be such that this lies close to the reference pressure level of contaminated air outside the protection.area or that the safety pressure level lies close to an underpressure level generated by the fan.

A particularly advantageous arrangement in this case provides that the receiving case is part of a double wall surrounding the housing case of the air filter, and the cavity of said double wall lies at the safety pressure level and is part of the safety area.

In order to produce the safety pressure level in the intermediate area, a particularly simple embodiment provides that the receiving case has perforations, which open into the intermediate area between the housing case and the receiving case and the spaced sealing elements, preferably centrally between the sealing elements when the air filter is installed.

It is particularly advantageous if the de:-ce according to the present invention is arranged in a mcbile or fixed 11 protection area, whereby in the case of a mobile protection area, this may also be the driver's cabin of a vehicle distributing plant protection agents.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 shows a schematic representation of a first embodiment; and Figure 2 shows a schematic representation of a second embodiment.

A first embodiment of a device according to the invention for generating purified air, given the overall reference 10 in Figure 1, is installed in a protection area 12 close to the wall thereof, whereby the wall 14 of the protection area 12 protects this from a surrounding area 16, in which contaminated air is present at a reference pressure level PR.

The device 10 according to the invention comprises a housing, given the overall reference 20, which has an air intake 22 connected via a bellows arrangement 24 to an air inlet 26 provided in the wall 14 of the protection area 12.

In the housing 20, adjoining the air intake 22, a first partial area, given the overall reference 30, is provided, into which the contaminated air from the surrounding area 16 can enter through the air inlet 26 and the air intake 22.

For aspiration of the contaminated air into the first partial area 30, a fan, given the overall reference 32, is provided in this area, which has a fan housing 34 in which a radial impeller 36 is arranged. In this case, the radial impeller 36 aspirates air via an inlet 38 with a rotational axis member 40 of the impeller 36 passing through it, accelerates this air in radial direction to the rotational 12 axis member 40, so that the air flows to an outlet channel 42 of the fan housing 34.

An insulation cone 44, which engages over the fan housing 34 and over a motor housing 46 of the fan 32, is preferably provided in the first partial area 30 for noise insulation, said insulation cone 44 being arranged so that it prevents air flowing through the air intake 22 into the first partial area 30 from entering the inlet 38 of the fan housing 34, and initially forces the air to flow around the insulation cone 44 on the outside, then flow into an interior thereof, from which entry of air into the inlet 38 is then possible.

The inlet 38 is preferably arranged to face the air intake 22, but located between these two is a cone base 48 of the insulation cone 44, from which a cone shell 50 extends, i.e. in the opposite direction to the air intake 22, said cone shell enclosing the fan housing 34 as well as the motor housing 46 so that an opening 52 of the insulation cone 44 located opposite the cone base 48 lies at such a distance from the cone base 48 that both the motor housing 46 and the fan housing 34 lie between this.

Moreover, at a distance from the opening 52 in the first partial area 30, an additional insulation wall 54 is arranged, so that a passage 56 remains between this and the opening 52 through which the air can flow into the interior of the insulation cone 44.

The outlet channel 42 of the fan housing 34 passes through the insulation cone 44, and leads through an inside wall 58 defining the first partial area 30 to a second partial area 60.

In this case, the fan 32 in the second partial area 60 generates an overpressure level P2, while the fan 32 in the first partial area 30 maintains an underpressure P1, which is responsible for the effect that contaminated air always flows through the air inlet 26 and the air intake 22 into the first partial area 30 and is transported by the fan 32 into the second partial area 60, in which case the contaminated air therein is present at the internal overpressure level P2.

In the present embodiment, the second partial area 60 is additionally subdivided into a region 60a and a region 60b, in which case the contaminated air flows initially into region 60a and no uniform overpressure level is present in regions 60a and 60b.

Starting from region 60a with the overpressure level P2a, the contaminated air then flows into a flow filter, given the overall reference 62, a cyclone precipitator in the present embodiment, which serves to divide the contaminated air into a substantially dust-free air flow 64 and a dust air flow 66, the dust air flow 66 discharging from region 60a via a dust air outlet 68 out of the protection area 12. The dust air outlet 68 in this case is likewise directed to a wall 14 of the protection area 12, and conducts the dust air flow through this.

The dust air outlet 68 is preferably constructed as a tube 70, which is sealed relative to the wall 14 by means of a seal 72 in the region of the passage through it.

The dust-free air flow 64 then enters region 60b with the overpressure level P2b, in which two filter cartridge channels 74a,b are arranged.

The two filter cartridge channels 74a,b extend parallel to one another in the direction of their longitudinal axes 76a,b and are closed off on a side facing the surrounding area 16 by means of an external housing cover 78a,b. In this case, the external housing cover 78a,b preferably lies at the height of the wall 14 of the protection area 12, so that an outer face 80a,b thereof lies flush with an outer face 82 of the wall 14 in this region.

14 Each of the external housing covers 78a,b is sealed relative to an inside wall 86a,b of the respective filter cartridge channel 74a,b by means of a seal 84a,b.

Moreover, each filter cartridge channel 74a,b comprises a filter cartridge seat 88a,b to receive a respective filter cartridge 90a,b. Each filter cartridge seat 88a,b is preferably formed by a receiving case 92a, b, in which the respective filter cartridge 90a,b may be inserted with its housing case 94a,b, whereby the housing case 94a,b has two spaced annular guide means 96a and 98a and 96b and 98b respectively, which ensure closure with a determined leakage rate relative to housing case 94a,b and the receiving case 92a,b, and holds the housing case 94a,b in relation to the receiving case 92a,b so that intermediate areas 100a and 100b respectively are formed between the two annular guide means 96a, 98a and 96b, 98b respectively as well as the sections located between these of the respective housing case 94a and the corresponding receiving case 92a and 94b, 92b respectively.

Moreover, it is preferably provided that each of the filter cartridge channels 74a,b has a guide section 102a,b directly adjoining the external housing cover 78a,b, and that the air flow 64, with the dust previously removed, enters the filter cartridge channels 74a,b between this guide section 102a,b and the respective filter cartridge seat 88a,b.

Each of the filter cartridges 90a,b is preferably constructed so that the air flow, with the dust previously removed but still contaminated, initially passes through a particulate air filter 106 in the direction of throughflow 104a,b, and thereafter passes through a gas filter.

Each of the filter cartridges 90a,b is in this case passed through in the direction of throughflow 104a,b so that, after passing through the gas filter 108, the air respectively flowing through the filter cartridge 90a, b enters the end region 110a,b of the respective filter cartridge channel 74a,b located opposite the respective outer housing cover 78a,b, and flows over a transverse channel 112 to an air outlet 114, via which the purified air then enters the protection area 12. In the transverse channel 112, the air outlet 114 and the protection area, in this case, a protection area pressure level P3 prevails, which lies below the internal overpressure level P2, i.e. also P2a and P2b, but above the reference pressure level PR.

The end regions 110a, 110b of the filter cartridge channels 74a,b are preferably closed off by inner housing covers 116a, 116b accessible from the protection area 12, whereby these inner housing covers 116a, 116b are located in an internal housing wall 120, on the side of which facing a housing interior the transverse channel 112 extends.

All the walls 130 enclosing the second partial area 60, in particular the separating wall 58 between the first partial area 30 and the second partial area 60, external walls 130A of the housing 20 defining the second partial area and also walls 132a, 132b of the filter cartridge channels 74a,b are constructed with double walls, and respectively have cavities 134, 138a,b which are all connected to one another, and form a cohesive safety area S completely surrounding the second partial area 60, lying at a safety pressure level PS, which lies below the protection area pressure level P3, but above the reference pressure level PR.

In the first embodiment, the entire safety area S communicates with the surrounding area 16, so that any air entering the safety area S via leakage points in turn flows into the surrounding area 16 and back to the contaminated air. For example, an external wall 140a,b surrounding the internal wall 98a,b of the filter cartridge channels 74a,b is firmlyconnected to the wall 14 of the protection area 12 so that annular areas 142a,b are formed around the sections of the internal wall 86a,b of the filter cartridge channels directly adjoining the seals 84a,b, said annular areas 16 communicating with the surrounding area 16 with respect to fluid flow via a gap 144a,b between the wall 14 and the outer housing cover 78a,b, and communicating with the safety area S via a throttle location 146a,b. As a result, all the air flowing into the safety area S flows via the throttle location 146a,b into the annular area 142a,b and from this through the gap 144a,b and into the surrounding area 16.

Moreover, the seal 80a,b of the outer housing cover 78a,b relative to the internal wall 86a,b is also non-critical, since air discharging through this from the second partial area with the internal overpressure level P2 flows into the annular areas 142a,b, and flows from these through the gap 144a,b and into the surrounding area 16.

In addition, a connection opening 150a,b is also provided between the safety area S and the intermediate areas 100a,b so that all the air entering the intermediate areas 100a,b via the ring seals 96a, 98a and 96b, 98b respectively also flows via the openings 150a,b into the safety area, and finally from this into the surrounding area 16 with the contaminated air.

The advantage of the safety area S according to the invention, which surrounds the second partial area with the internal overpressure level P2, is that neither leakages in the walls surrounding the second partial area 60 nor leakages in the region of the annular guide means 96 and 98 pose any problems whatsoever, nor, in particular, do they lead to at least partially contaminated air additionally entering the protection area 12, since the safety pressure level PS in the safety area S, which lies below the pressure level P3, ensures that the air always flows into the safety area S, and from this into the surrounding area 16 with the reference pressure level PR.

Moreover, it is also possible with the solution according to the invention to replace the filter cartridge 90a,b in a simple manner, namely by inserting a replacement filter 17 cartridge 90a,b into the respective filter cartridge channel 74a,b after removing the inner housing cover 116a,b, whereby the filter cartridge 90a, b already sitting in this channel is moved out of the filter cartridge seat 88a,b in the direction of the external housing cover 78a,b. Once the fouled filter cartridge moved out of the filter cartridge seat 88a,b reaches the guide region 102a,b of the respective filter cartridge channel 74a,b, then this prevents the air flow 64, with dust previously removed, from flowing into the respective filter cartridge channel 74a,b, while the filter cartridge for subsequent insertion is already partially inserted into the filter cartridge seat 88a,b with its housing case 94a,b. Once the used filter cartridge 78a,b is pushed further in the direction of the external housing cover 78a,b, then the unused filter cartridge slides further into the filter cartridge seat 88a,b, and when the external housing case 78a,b is opened, then the used filter cartridge 90a, b may be completely removed from the filter cartridge channel 74a,b, while the new unused filter cartridge reaches the filter cartridge seat 88a,b.

After full ejection of the used filter cartridge 90a,b, the new filter cartridge 90a,b stands in the respective filter cartridge seat 88a,b and the device according to the invention functions in the manner described originally.

During the entire operation of replacing the used filter cartridge 90a,b, no contaminated air can enter the safety area 12 between the receiving base 92a,b of the respective filter cartridge seat 88a,b and the housing cases 94a,b of the used and unused filter cartridges, since all the air flowing through these enters the safety area S via the openings 150a because of the pressure drop, and from there is discharged to the outside into the surrounding area 16 with the contaminated air.

In a second embodiment 10' of the solution according to the invention, shown in Figure 2, the parts identical to those in the first embodiment are given the same reference 18 numbers.

The second embodiment 101 differs from the first embodiment only in the fact that the safety area S no longer communicates with the surrounding area 16, but with the first partial area 30 via throttle locations 160, so that the pressure level PS' in the safety area S can still lie below the pressure level PR of the contaminated air, but at all events below pressure level P2 in the second partial area 60 and pressure level P3 in the protection area 12, and it is thus ensured that each leak in the walls 130, 132 enclosing the second partial area 60 likewise causes the contaminated air to flow into the safety area S, and from there into the first partial area 30, and is thus aspirated via the fan 32 and fed to the second partial area 60 again for filtering.

19

Claims

A device for generating purified air for a protection area comprising contaminated air present at a reference pressure level, comprising a housing, a fan and an air filter, wherein the fan and air filter are enclosed by the housing; a first partial area is provided in the housing, which lies at an underpressure level relative (P1) to the reference pressure level (PR); a second partial area separate from the first partial area is provided in the housing, which lies at an internal overpressure level (P2) relative to the reference pressure level (PR); the housing has an air outlet opening into the protection area, from which the purified air discharges with a protection area pressure level (P3) lying.between the reference pressure level (PR) and the internal overpressure level (P2); the fan transports contaminated air from the first partial area into the second partial area and thus maintains the internal overpressure level (P1); between the air outlet and the second partial area, the air filter is arranged, which is responsible for the pressure drop between the internal overpressure level (P2) and the protection area pressure level (P3); and between the second partial area and the protection area in the housing, a safety area (S) is provided, in which a safety pressure level (PS) is present, which lies below the protection area pressure level (P3).
2. A device according to Claim 1, wherein safety area (S) surrounds the second partial area in the region of its side adjoining the protection area.
3. A device according to Claim 1 or 2, wherein the safety area (S) communicates with the conta-;iinated air outside the protection area, and the safety pressure level (PS) essentially lies close to the reference pressure level (PR).
4. A device according to Claim 1 or 2, wherein the safety area (S) is connected to the first partial area, and the safety pressure level (PS') lies essentially close to the underpressure level (P1).
5. A device according to any preceding claim, wherein the air filter is surrounded by the safety area (S).
6. A device according to any preceding claim, wherein the safety area is constructed as a cavity with a double wall.
7. A device according to any preceding claim, wherein a flow filter is arranged in the second partial area.
8. A device according to any preceding claim, wherein the air filter comprises a particulate filter and a gas filter.
9. A device according to any preceding claim, wherein the air filter is constructed as a filter cartridge, and that the housing has a filter cartridge channel extending in the direction of a longitudinal axis and passing through the housing in this direction, and said filter cartridge channel, on the one hand, can be closed off with an outer housing cover opening towards the contaminated air and, on the other hand, is accessible from the protection area.
10. A device for generating purified air for a protection area comprising contaminated air present at a reference pressure level, comprising a housing, a fan and an air filter, wherein the air filter is cc-structed as a filter cartridge, and that the housing has a filter cartridge channel extending in the dIrection of a 21 longitudinal axis and passing through the housing in this direction, and said filter cartridge channel, on the one hand, can be closed off with an outer housing cover opening towards the contaminated air and, on the other hand, is accessible from the protection area.
11. A device according to Claim 9 or 10, wherein the filter cartridge channel has a filter cartridge seat, and that contaminated air flows in between the outer housing cover and the filter cartridge seat in the filter cartridge channel, and after passing through the filter cartridge, flows into the protection area as purified air.
12. A device according to Claim 11, wherein in the direction of the longitudinal axis of the filter cartridge channel, the filter cartridge seat has a guide length, which during replacement assures a closure preventing the passage of contaminated air between a first filter cartridge still partially disposed in the filter cartridge seat and a second filter cartridge inserted partially into the filter cartridge seat.
13. A device according to Claim 11 or 12, wherein the filter cartridge channel has a second guide section for the filter cartridge located between the entry of the contaminated air and the housing cover, and that a filter cartridge partially sitting both in the filter cartridge seat and in the second guide section prevents the entry of contaminated air into the filter cartridge channel.
14. A device for generating purified air according to any preceding claim, wherein the air filter has a housing case; that the air filter may be inserted with the housing case into a receiving case o..OL a filter cartridge seat; that two guide elements spaced from one 22 another in the direction of passage through the filter are provided between the housing case and the receiving case; and that an intermediate area between the two guide elements, the housing case and the receiving case lie at a safety pressure level (PS), which lies below the pressure level (P2) at the inlet of the air filter and below the pressure level (P3) at the outlet of the air filter.
15. A device for generating purified air for a protection area comprising contaminated air present at a reference pressure level, comprising a housing, a fan and an air filter, wherein the air filter has a housing case; that the air filter may be inserted with the housing case into a receiving case of a filter cartridge seat; that two guide elements spaced from one another in the direction of passage through the filter are provided between the housing case and the receiving case; and that an intermediate area between the two guide elements, the housing case and the receiving case lie at a safety pressure level (PS), which lies below the pressure level (P2) at the inlet of the air filter and below the pressure level (P3) at the outlet of the air filter.
16. A device according to Claim 14 or 15, wherein the receiving case is surrounded by a safety area (S) which lies at the safety pressure level (PS).
17. A device according to any of claims 14 to 16, wherein the safety pressure level (PS) lies close to the reference pressure level (PR) of contaminated air outside the protection area.
18. A device according to any of claims 14 to 16, wherein the safety pressure level (PS) lies close to the underpressure level (P1) generated by the fan.

2 -3)
19. A device according to any of claims 14 to 18, wherein the receiving case is part of a double wall surrounding the housing case of the air filter, and the cavity of said double wall lies at the safety pressure level (PS).
20. A device according to Claim 19, wherein the receiving case has perforations, which open into the intermediate area between the housing case and the receiving case and the spaced seling elements.
21. A device for generating purified air substantially as herein described with reference to Fig.1 or Fig.2 of the accompanying drawings.

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