An air-regeneration filter is provided having air regeneration agent means toward one end opening thereof and drying agent means toward an opening at the other end thereof. The direction of air flow through the filter can be chosen according to the requirement for conditioning the air to be treated as to oxygen and moisture content.

The present invention relates to an air-regeneration filter in a container 
containing an oxygen-liberating carbon-dioxide-binding chemical and a 
drying agent, with two openings on opposite sides adapted to be closed by 
friction-closing closure caps, predominately for connection to an air-feed 
device. 
Such a filter which can be traversed by air is required in closed rooms or 
in a closed respiratory system when the supplying of outside air is not 
feasible. The renewal of the respiratory air is therefore effected within 
the closed space independently of the outer atmosphere. 
Alkali peroxides and particularly potassium peroxide are advantageously 
used for the regeneration of the air. These chemicals absorb the carbon 
dioxide exhaled and the moisture present in the air within the space and 
give off oxygen accordingly. 
This principle is employed in various proposals for the development of 
air-regeneration filters. One particular problem in this connection is to 
adapt the production of oxygen to the requirement. For instance, the water 
vapor fed to the filter will under certain conditions always lead to an 
over production of oxygen while, on the other hand, a given content of 
water vapor in the air to be regenerated is necessary since the conversion 
of the exhaled carbon dioxide alone does not cover the oxygen requirement. 
In one prior apparatus of this type, screens and/or sheet metal cups on 
which layers of granulated alkali peroxide, extending from one wall of the 
housing to the other, lie, are arranged in the container transverse to the 
direction of flow. In each of the layers there is an opening at a 
predetermined distance from the wall of the housing. These openings are 
staggered with respect to each other from layer to layer. While the 
resistance to flow is reduced by this arrangement, the utilization of the 
chemical is not particularly good. In addition to this, the cost of 
producing a filter of this type is very high. Further, adaptation of the 
production of oxygen to the requirement is not possible or contemplated in 
this development of the apparatus. 
In another known apparatus, alkali peroxides pressed into the shape of 
discs are used. As a result of the greater density of chemical obtained 
thereby, a larger quantity of oxygen can be stored per unit of volume but 
the discs must be compressed which, because of their fragility, must not 
be too thin. When the discs are thicker, such results in an unfavorable 
utilization of the chemical. An over production of oxygen at the start of 
the use is tolerated. A subsequent decrease in the development of oxygen 
results from the fact that the chemical, as a compressed disc, is not 
pervious to air and accordingly the reaction can take place only on the 
surface of the discs which, during the course of the reaction, gradually 
become encrusted by spent chemical so as to be partially inactive. It is 
not possible in this way to control the production of oxygen as a function 
of the amount of water vapor offered. An oxygen deficiency can also occur 
with the passage of time as a result of the uncontrolled decrease in the 
production of oxygen. 
In another proposal, a drying agent and an absorption agent for carbon 
dioxide are arranged in the container in front of the chemical in order to 
dampen or check the production of oxygen. Since the direction of flow is 
fixed, certain disadvantages result from the fact that under certain 
conditions, this filter may not supply sufficient oxygen and furthermore 
the use of the oxygen produced may be greatly delayed. This is true when 
the moisture present in the space is slight, for instance, at low room 
temperatures, since on the one hand the exhaled carbon dioxide is 
substantially absorbed and existing moisture and moisture produced are 
taken up substantially completely by the drying agent. The desired 
dampening of the production of oxygen is not well defined and can 
therefore also lead to an oxygen deficiency. The filter can not be adapted 
to the different climatic conditions in the rooms produced by seasonal 
variations. 
An apparatus is also known in which regulation of the oxygen production is 
provided. The apparatus consists of two filters connected in parallel, one 
filter containing the oxygen-liberating chemical, while the second filter 
has the function of only absorbing carbon dioxide. The two filters are 
each provided with a separate feed device for the air in the room. By 
means of a switch or valving, the room air is conducted as desired, as a 
function of the oxygen content in the room, through the filter which gives 
off the oxygen or through the filter which binds the carbon dioxide. 
This apparatus is in principle capable of maintaining the oxygen content 
within given limits under different climatic conditions but the technical 
expenditure is great. 
One of the objects of the present invention is to disclose the construction 
of an air-regeneration filter which avoids the above-mentioned 
disadvantages and is simple to manufacture and which can be adapted for 
use under different conditions. 
This goal is achieved in accordance with the invention by the fact that the 
construction of the filter permits two directions of flow. There are 
markings on the outer wall of the container which indicate the proper 
direction of flow in each case on basis of the climate to be treated. The 
drying agent can be arranged on one side facing an opening, the agent 
being in front of the layer of chemical. The drying agent can amount to 10 
to 50%, and preferably 25 to 30%, of the volume of the total filling. 
The advantage obtained with the air-regeneration filter of the invention is 
that it is possible, corresponding to the existing climatic conditions, to 
control the development of oxygen uniformly in accordance with the oxygen 
requirement and in this way avoid unfavorable, i.e. excessively low or 
excessively high oxygen contents, and to obtain optimum utilization of the 
filter. This result is achieved by the construction of the filter which 
takes into account the content of water vapor present in the room which 
may be different, regardless of the number of persons present in the room. 
In the case of low content of water vapor, for instance, less than 13 
g/m.sup.3 in the room air, or low room temperatures, for instance, below 
15.degree. C, at which only correspondingly low water-vapor contents 
result due to the saturation values of water vapor in air, the required 
amount of oxygen is produced when the chemical which gives off the oxygen 
is acted on directly by the room air. In this case the filter is so 
connected into the air feed device that the direction of flow A is 
established or chosen by valving or insertion in the piping. 
With higher contents of water vapor or higher room temperatures, direct 
impact on the chemical would result in an overproduction of oxygen. By the 
establishment of the direction of flow in the direction indicated by arrow 
B, the air flowing into the filter is predried to such an extent that the 
amount of oxygen developed corresponds to the requirement. The drying 
agent which is arranged in front of the chemical exerts a certain 
regulating function also from the standpoint of time in the embodiment 
indicated since its water-absorbing action is large particularly at the 
start of use when the chemical still has its full effect. On the other 
hand, the action of the drying agent decreases just towards the end of the 
use of the filter when the chemical, as a result of its state of 
exhaustion, requires a higher supply of water. 
The effective surface of attack of the chemical is increased by pleated 
sieves between which the chemical is embedded and which are arranged 
90.degree. away from each other, and the danger of the upper layer forming 
a firm crust is reduced. In this way there is little resistance to flow, 
and this resistance does not increase substantially during operation. 
Finally, it is possible in this way to operate with a relatively fine 
approximately uniform particle size of chemical so that a greater density 
of chemical and simplification of the manufacture of the filter is made 
possible. 
In accordance with the invention it is furthermore proposed that 
temperature or moisture indicating devices be arranged at a visible place 
in the vicinity of the openings, i.e. the connections, in order to judge 
the climatic conditions. These indicating devices make it possible to 
note, even during operation, whether it is advisable to change the 
direction of flow when the temperature or moisture of the air entering the 
filter changes accordingly. 
The provision of such a temperature indicating device in the vicinity of 
each of the two openings affords the possibility of noting the degree of 
exhaustion of the filter from the temperature of the emerging air. The 
temperature in the filter increases during operation as a result of the 
reaction and decreases when the chemical is consumed. The temperature 
indicating means can be any conventional type of thermal indicating device 
located on the outside of the container and in thermal contact therewith 
or can be inside the container with a suitable viewing area in the wall of 
the container. Conventional moisture indicating devices also can be 
located adjacent said opening.

The container 1 contains the chemical 4, which is an oxygen-liberating 
carbon-dioxide-binding chemical, such as alkali peroxide, and the drying 
agent 5, such as alumina gel, held by the perforated plates 8 which are 
connected together by clamping bolts 9. Chemical 4 is arranged in several 
layers, C, D, E, separated from each other by inserts of wire gauze 6, 
between pleated sieves 7. Potassium peroxide is particularly efficacious 
for regeneration of air. The pleated sieves 7 are arranged with their 
folds 90.degree. apart from each other (not shown in the drawing). 
The container 1 has two openings 2 located on opposite sides, which are 
sealed by frictional closure by the caps 3 with a tin seal 12. As 
mentioned, temperature or moisture measuring devices 11 are arranged in 
visible position on or in the container near the openings 2. 
The air-regeneration filter is placed in operation by removing the caps 3 
from the container 1 and connecting an air feed device (not shown) with 
due consideration of the desired direction of flow 10, which direction is 
indicated on the container 1 by markings, for instance A and B. Also, it 
would be possible to insert the filter in piping or valving (not shown) so 
as to selectively choose flow direction. 
The drying agent may, for example, be a suitable drying agent gel, such as 
alumina gel. The drying agent is developed spherically with a diameter of 
2 to 10 mm. and preferably 4 to 8 mm. The drying agent amounts to 10 to 
50% and preferably 25 to 30% of the volume of the total filling.