FIELD OF THE INVENTION

The present invention relates to an NBC filtration system with a manually operated air exchange backup pump.

BACKGROUND OF THE INVENTION

The regulations in Israel indicate that private living units must preserve an NBC protected space also called “safe room” for use at a state of emergency caused by warfare or natural disaster. The protected space must include an NBC filtration system correctly sized to fit the volume of the protected space and the expected number of people occupying the protected space during emergency. A simple capacity calculation rule for the NBC filtration system air exchange rate is 6 cubic meters of fresh air per person per hour. Typically the smaller safe rooms designed for six occupants, are provided with filtration system capable of supplying 36 cubic meters of filtered air per hour. And the larger safe rooms designed for eight occupants are provided with filtration system capable of supplying 48 cubic meters of filtered air per hour. At ventilation mode the systems may supply about 1.5 times of the filtration mode capacity.

The regulations specifically require that such NBC filtration system for living units, should include an NBC filter unit composed of a particulate filter and a gas adsorption filter, and an electric blower appropriate for the required rate of air exchange. Furthermore, the NBC filtration system should feature a manual air exchange backup capability to be operated by human power in case of electric power failure. The air exchange backup element is usually constructed as a manually operated bellows pump.

Israeli patent application 252594 to the present applicant, discloses an NBC filtration system provided with a manually operated backup bellows pump and an actuation lever for operation thereof. Manual propulsion of the actuation lever expands and contracts the backup bellows pump. A grip-able portion of the actuation lever is accessible at a height lower than the installation height of the NBC filtration system. Israeli patent application 252921 to the present applicant, discloses an NBC filtration system where manual back and forth actuation of the backup bellows pump is carried out with at least a portion of a protective cover being actuated as well, thus eliminating the need to first detach the protective cover. The protective cover may be movably linked to the NBC filter unit with a scissors mechanism.

However, a drawback of the above applications relates to the fact that human manual operation of the backup bellows pump is limited between 30 to 50 cycles per minute. Due to the limited operating speed and the essential rate of airflow, which is 36 or 48 cubic meters per hour for living unit safe rooms, a bellows of relatively large volume is required. Translation of the above cubic meters per hour flow rates into liters per minute, yields 600 liters per minute or 800 liters per minute depending on the protected space volume as indicated by the regulations. Simple division of the required airflow (600 liters/ min or 800 liters/min) to an average of 40 cycles per minute yields a bellows pump of 15 or 20 liters capacity when expanded. As a result space requirement and manufacturing cost are high.

SUMMARY OF THE INVENTION

Accordingly it is a principal object of the present invention to overcome the problem of large volume bellows pump dictated by the limited rate of human operation. In order to provide an efficient, low volume and low cost air exchange backup pump and to support integration into the NBC filtration system.

According to an embodiment of the invention, there is provided an NBC filtration system for protected space such as a shelter or safe room, comprising: an NBC filter unit; an electric blower airflow coupled to the NBC filter unit; and a manually operated air exchange pump configured to backup the electric blower in an event of power failure. The air exchange pump further comprises: at least one variable volume chamber operative in repeated cycles of expansion and contraction; at least two non return valves per each variable volume chamber; and a frequency increasing mechanism configured for linking the manual operation to the at least one variable volume chamber. The frequency increasing mechanism converts a single stroke of the manual operation into a series of the mentioned cycles. An increase of a ratio of the conversion decreases the required physical size of the air exchange pump, thereby saving space and setup procedures.

According to an aspect of the embodiment, the air exchange pump is a positive displacement reciprocating pump.

According to another aspect, the air exchange pump may be selected from the group consisting of: a bellows pump; a diaphragm pump; a cylinder and piston pump; a barrel and plunger pump; and an angular displacement bellows pump.

According to yet another aspect, the variable volume chamber comprises a bellows and the electric blower is located within the bellows.

According to an embodiment, the frequency increasing mechanism comprises a drive system selected from the group consisting of: gear train; drive belts; drive chains; worm or bevel gears; rack and pinion; and any combination of the group elements.

According to an aspect of the embodiment, the frequency increasing mechanism comprises a two stage gear train.

According to another aspect, the gear train comprises: a sector gear; a compound intermediate gear; and a final drive pinion. The NBC filtration system may further comprise a bracket for rotateably mounting the above sector gear, compound intermediate gear, and final drive pinion, to the NBC filter unit. According to an aspect of the embodiment, the sector gear is engaged with the compound intermediate gear, and the compound intermediate gear is engaged with the final drive pinion, such that back and forth rotation of the sector gear using an operator handle, rotates the final drive pinion through the compound intermediate gear.

According to another aspect, the frequency increasing mechanism further comprises a crankshaft. The crankshaft converts rotational movement of the gear train into reciprocating linear movement configured to actuate the volume changing chamber.

According to an embodiment, the frequency increasing mechanism comprises a pair of pulling cords, The pulling cords are winded in opposite directions on a pair of pulleys. The pulleys having a perimeter which is at least two times smaller than an effective manual stroke of the pulling cords.

According to an aspect of the embodiment, each of the pulling cords is provided with a pulling handle at the free end thereof.

According to another aspect, the frequency increasing mechanism further comprises a crankshaft fitted between the pulleys, the crankshaft converts rotational movement of the pulleys into reciprocating linear movement configured to actuate the volume changing chamber.

According to an embodiment, the NBC filtration system comprises a protective cover. The protective cover is permanently fitted in place during storage and during operation of the system.

According to an aspect, the conversion ratio of cycles per stroke is selected between 3 and 8.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the way it may be carried out in practice, will be understood with reference to the following illustrative figures, by way of non-limiting example only, in which like reference numerals identify like elements, and in which:

Fig. l is a perspective front view of a filtration system made according to an embodiment of the invention;

Fig. 2 is a perspective rear view of the filtration system of Fig. 1;

Fig. 3 is a perspective view as in Fig. 1, shown with a cover removed for clarity; Fig. 4 is an exploded perspective view of the filtration system of fig. 3, depicting the various parts;

Fig. 5 is an exploded perspective view as in fig. 4, depicting another embodiment;

Fig. 6 is a perspective front view of a filtration system made according to an embodiment of the invention;

Fig. 7 is a perspective view as in Fig. 6, shown with a cover removed for clarity;

Fig. 8 is a perspective view as in Fig. 7, shown in a different viewpoint; and

Fig. 9 is an exploded perspective view of the filtration system of fig. 7, depicting the various parts.

PI TA 11 FI) DESCRIPTION OF EMBODIMENTS

Several terms relating to the present invention will be defined prior to describing the invention in detail. It should be noted that the following definitions are used throughout this application.

For the purposes of the present invention, directional terms such as “top”, “bottom”, “below”, “left”, “right ¹ , “horizontal”, “vertical”, “upper”, “lower” “down”, etc. are merely used for convenience in describing the various implementations of the present invention. The assemblies demonstrating the present invention may be oriented in various ways. For example, the assemblies shown in the figures may be flipped over, inclined or rotated by 90° in any direction.

For the purpose of the present invention the term “protected space” refers to a bomb-shelter or safe room or any sealed space where the internal volume is isolated from the external environment.

For the purpose of the present invention the term “stroke” refers to the movement, in either direction of a reciprocating motion. The entire distance passed through, in such a movement.

For the purpose of the present invention the term “revolution” refers to the act of revolving or turning of a body round an axis, until it returns to the same point again. For the purpose of the present invention the term “frequency” refers to the number of occurrences of a repeating event per unit of time.

For the purpose of the present invention the term “cycle” refers to a course or series of events or operations that recur regularly and lead back to the starting point. One complete performance of a periodic process.

For the purpose of the present invention the term “approximately” refers to a value in the range between 80% to 120% of the stated value.

For the purpose of the present invention the term “bellows” refers to any flexible container or enclosure, as one used to cover a moving joint.

The term NBC, standing for “Nuclear Biological Chemical”, is used throughout this patent application at the broad interpretation, meaning at least one of: Radiological, Nuclear, Biological and Chemical. Accordingly NBC does not mean that all of the capabilities are necessary for the application, for example a filter unit providing Biological and Chemical attack protection, but none or only partial Nuclear attack protection, is yet considered an NBC filter unit for the purpose of this application.

With reference to the figures, according to an embodiment of the present invention, there is shown in Fig. 1, an NBC filtration system for protected space such as shelters or residential safe rooms, generally referenced 10. According to the depicted embodiment, the NBC filtration system is provided with a cover 20 serving for aesthetic and protection purposes. Further shown in Fig. 1 are pulling handles 22, 24 tied to pulling cords 26, 28 respectively as will be further explained below. And an optional state selector handle 30 as will be further explained below.

With reference to Fig. 2, there is shown a rear view of the NBC filtration system of Fig. 1. In addition to the above mentioned elements, there is shown an NBC filter unit 32, an air inlet port 34 and a mounting flange 36 surrounding the air inlet port 34. During installation of the NBC filtration system in a protected space, the mounting flange 36 is airflow coupled to a complementary flange (not shown) of a wall sleeve. The wall sleeve penetrates through a wall of the protected space in order to ventilate the protected space. The wall sleeve may further include a blast valve configured to block a blast wave and a potential subsequent suction wave. With reference to Fig. 3, the NBC filtration system 10 is shown with the cover 20 removed for clarity, exposing the internal elements. It should be noted that according to the embodiment, the cover 20 may be left in position during operation of the NBC filtration system including during manual operation caused by power failure or electric blower failure.

As depicted in fig. 3, the NBC filtration system 10 comprises an NBC filter unit 32, an electric blower 40 (Fig. 5) airflow coupled to the NBC filter unit 32 and a manually operated air exchange pump generally referenced 50, configured to backup the electric blower in an event of electric power failure. The air exchange pump 50 comprises at least one variable volume chamber 54 operative in repeated cycles of expansion and contraction.

The NBC filter unit 32 may comprise an integral ventilation bypass and air flow direction means selectively operated for instance by selector handle 30 to direct air flow internally, either through the ventilation bypass, constituting a ventilation mode, or through the particulate filter and gas adsorption filter constituting an NBC filtration mode. However such arrangement is not essential to the present invention as the mentioned bypass may be external to the filter unit 32. And the mentioned direction means may be a changeover valve or connectable flexible pipes as known in the art.

Further shown in Fig. 3, is a frequency increasing mechanism generally referenced 69 configured for linking the manual operation of the pulling handles 22, 24 by a way of example, to the at least one variable volume chamber 54. The frequency increasing mechanism 69 converts a single stroke of the manual operation of handles 22 and 24, into a series of cycles of the variable volume chamber 54. An increase in the ratio of conversion (cycles per stroke) decreases the required physical size of the air exchange pump 50, thereby saving space and setup procedures involved with prior art systems.

With reference to Fig. 4, depicting an exploded view of a possible embodiment. The air exchange pump 50 further comprises at least two non return valves 56, 58 per each variable volume chamber 54. The air exchange pump 50 may be a reciprocating pump. For example as shown in the figures, the variable volume chamber 54 may include a bellows 52, having one end fixed to a stationary closure 38 being part of the NBC filter unit 32 and the other end linked by a movable closure 70 to a rotateable crankshaft 60. It should be noted that the air exchange pump may be selected between several options including: a bellows pump, a diaphragm pump, a double diaphragm pump, a cylinder and piston pump, a barrel and plunger pump, an angular displacement bellows pump, or in general any reciprocating positive displacement pump. All may be used to the same extent and fall under the scope of the present invention.

In more detail, the frequency increasing mechanism 69 may comprise a pair of pulling handles 22 and 24, tied to a pair of pulling cords 26 and 28 respectively. The other ends of pulling cords 26, 28 are winded in opposite directions on a pair of pulleys 66, 68 respectively. The pulleys 66, 68 are fitted to each end of crankshaft 60. The crankshaft 60 is rotateably mounted to the filter unit 32 by means of an elevated arms 33 spaced apart to accept the air exchange pump 50 there between. The elevated arms 33 are provided with bearings at their extremity configured to carry both ends of the crankshaft 60.

The pulleys 66, 68 are fitted to the crankshaft 60 externally to the arms 33. The pulleys 66, 68 are sized to have a perimeter which is at least two times smaller than an effective manual stroke of the pulling cords 26, 28 which are provided with the pulling handles 22, 24 respectively at the free ends of the cords 26, 28. Such that each manual stroke of the handles 22, 24 provides at least two revolutions of the pulleys 66, 68 and the crankshaft 60 fitted between the pulleys. The crankshaft 60 converts rotational movement of the pulleys 66, 68 into reciprocating linear movement configured to actuate the volume changing chamber 54 or bellows 52 as specifically shown in the figures by a way of example. A movable closure 70 of the bellows 52 is attached by bearings 72 to the cranking portion 74 of the crankshaft 60.

It will be understood that the ratio of the manual stroke length of the cords 26, 28 or handles 22, 24 to the perimeter of the pulleys 66, 68 may be much larger than 2 with a ratio of up to 1 stroke length to 10 pulley perimeters being possible. Accordingly the conversion ratio of cycles per stroke may be conveniently selected between 3 and 8. While a conversion ratio of 5 being an acceptable selection as explained herein below.

Considering the regulations related to residential safe rooms, it is required to deliver an airflow rate of between 36 and 48 cubic meters per hour or 600 to 800 liters per minute during manual operation of the NBC filtration system. Typically an average person is able to actuate the pulling handles 22, 24, back and forth 30 to 50 times per minute (60- 100 strokes). Given a 1 to 5 conversion ratio for example, each sequence (back and forth strokes) of the manual operation will provide 10 full cycles of the air exchange pump 50. Taking for example an average operator, that actuates the pulling handles 22, 24, back and forth about 40 times (80 strokes) per minute. Multiply the strokes by 5 results that the air exchange pump is cycled approximately 400 times per minute. Now division of the airflow rate of 600 or 800 liters per minute into 400 cycles per minute yields a displacement volume of between 1.5 to 2 liters of the air exchange pump 50. Accordingly, it will be possible to use for instance, a bellows 52 with a displaceable volume of approximately 1.5 to 2 liters. Which is 10 times smaller than the volume of a currently available direct driven bellows.

Such reduction in volume permits encapsulation of the NBC filtration system under a permanently fitted cover 20 even at the expanded state of the bellows 52. The upper parts of the frequency increasing mechanism 69 including the pulleys 66, 68, crankshaft 74 and portion of the pulling cords 26, 28, are also encapsulated under the protective cover 20. As shown in the figures, the cords 26, 28 are protruding downwards from the cover trough openings made to the cover. The relatively small reciprocating stroke of the bellows may be performed under the cover. As a result, the protective cover 20 is permanently fitted in place during storage and during operation of the system. There is no need to remove, slack, open or alter the position of the protective cover during operation either electric or manual.

It will be also appreciated that the direction of rotation of the crankshaft 60 is of no relevance since each cycle introduces the same amount of pumped air in either direction of rotation. Accordingly both back and forth manual strokes of the pulling handles 22, 24 will produce effective pumping of air into the protected space.

Further shown in Fig. 4, are an inlet non return valve 56 and an exit non return valve 58 of the air exchange pump 50. The inlet non return valve 56 is positioned on top of an opening or plurality of openings 42 of the stationary closure 38 of bellows 52, being part of the NBC filter unit 32. The exit non return valve 58 is positioned on top of an opening or plurality of openings 76 of the movable closure 70 of the bellows 52, serving as an outlet of the volume changing chamber 54. The non return valves 56, 58 may accept several constructions such as a spring loaded plate, a weight loaded plate, a lightweight ball seated on a round opening as well as other known implementations. The non return valves 56, 58 are optionally made of a resilient material. As shown in Fig. 4, the inlet non return valve 56 is made as a rectangular sheet of resilient material such as rubber, elastomer or thin metal spring. The inlet non return valve 56 is fitted along an edge to the stationary closure 38 which is part of the NBC filter unit 32, by plurality of headed anchors 82, by a way of example. The exit non return valve 58 can be carried out by a way of example in the shape of a disk made of resilient material such as rubber or elastomer, anchored at the center to the movable closure 70. The resilient disk is laying against openings 76 of the movable closure 70.

Upon contraction of the volume changing chamber 54, air leaves the bellows through the exit non return valve 58, while the inlet non return valve 56 is closed, and upon expansion air enters the bellows through the inlet non return valve 56 while the exit non return valve 58 is closed.

An electric blower (not shown in Fig. 4) may be located inside the NBC filter unit 32. During normal usage of the NBC filtration system the electric blower draws air through the NBC filter unit. The airflow forces open the two non return valves 56, 58 thus blowing air through the bellows 52 into the protected space.

With reference to Fig. 5, there is shown an exploded view of another embodiment. As shown in Fig. 5 an electric blower 40 may be located within the bellows 52. The blower 40 is airflow coupled to the NBC filter unit through an opening (not visible) located under the blower 40. A first inlet non return valve 44 is positioned at the outlet of the blower 40, such that air flow is possible through the electric blower 40 even when not powered. The air exchange pump 50 and the electric blower 40 can be operated alternately, independently of each other. In case of electric power failure, the air exchange pump 50 is ready for immediate manual operation without any settings or preparations. The first inlet non return valve 44 can be carried out by way of example, as a leaf like resilient surface made of rubber, plastic or thin metal spring, held in position by a retaining strip 48.

Where only the first inlet non return valve 44 is implemented, airflow is always passing through the electric blower even when not energized. Such arrangement may induce an additional airflow restriction caused by the non-operating blower permanently located in the airflow path. The increased pressure drop require increased level of manual energy that is needed to run the system during power failure. Accordingly an optional second inlet non return valve 46 located adjacent the blower 40, may be provided. In a similar manner to the inlet non return valve 56 described above with reference to Fig. 4.

When the electric blower is energized, airflow is directed through the first inlet non return valve 44 and to the outlet non return valve 58. In case of power failure, when the air exchange pump 50 is manually actuated, air flow is naturally redirected through the second inlet non return valve 46, having lower resistance to flow, and therefrom to the outlet non return valve 58. The additional non return valve 46, provides an airflow path free of restrictions which reduces the manual energy needed to preserve the desired air exchange rate in the protected space.

Due to the wavy wall structure of the bellows 52, the movable closure 70 will not come in contact with the stationary closure 38 even when the bellows 52 is fully contracted, leaving a residual amount of air in the bellows internal volume. According to the present embodiment, the electric blower is fitted in the residual space of the bellows when fully contracted. Internal placement of the electric blower is saving space that would otherwise be needed to position the blower externally to the bellows. Internal placement of the blower also increases the efficiency of the backup bellows by minimizing the volume of air left in the bellows after a contraction stroke.

At normal times, the pulling handles 22, 24 may be folded upwards around the cover 20 of the NBC filtration system and secured to the cover 20 by dedicated clamps (not shown) to a storage position, being visible in case of need. In operation, during an event of emergency or when entrance to the safe room is declared, the electric blower is turned on by switch 31 (Fig. 1) to provide ventilation of the protected space. In an event of NBC contamination hazard, the state selector handle 30 is rotated to filtration state. In an event of power failure either in ventilation mode or in filtration mode, the pulling handles 22, 24 are withdrawn from the storage position to the operative position and actuated with both hands of the operator as long as the power failure persists. It will be noted that the cover 20 remains in place during all the above described operation steps.

With reference to Figs. 6 to 9, there is shown another embodiment of an NBC filtration system generally referenced 110. The embodiment uses a frequency increasing mechanism generally referenced 169 (Fig. 8) of a drive system based on a gear train instead of the pulling handles, cords and pulleys described above with reference to Fig. 3. As depicted in Fig. 6, the NBC filtration system is provided with a cover 120 serving for aesthetic and protection purposes. Further shown in Fig. 6 is a detachable operator handle 122, attached to a shaft 124 (Fig. 7) extending through an aperture made to the cover 120 as will be further explained below. Optionally the operator handle 122 is made as a collapsible telescopic rod (such as known in fishing equipment) in order to save space during normal times. Further shown in Fig. 6 is an optional state selector handle 30 as described above with reference to Fig. 3. And electric switch 131 for turning on the electric blower.

With reference to Figs. 7 and 8, the NBC filtration system 110 comprises an NBC filter unit 132, an electric blower 40 (Fig. 9) airflow coupled to the NBC filter unit 132 and a manually operated air exchange pump generally referenced 150 configured to backup the electric blower in an event of power failure. The air exchange pump 150 comprises at least one variable volume chamber 154 operative in repeated cycles of expansion and contraction.

Further shown in Figs. 7 and 8, is the frequency increasing mechanism generally referenced 169. The frequency increasing mechanism 169 implemented by way of example as a two stage gear train. The mechanism 169 is assembled to a T shaped bracket 126 attached to the NBC filter unit 132 with bolts and nuts 128, by a way of example. A sector gear 160 is provided, including a hollow shaft 124, protruding from the face of the sector gear 160 at the center of rotation. The sector gear 160 is rotateably mounted to the bracket 126. The hollow shaft 124 is provided with a square drive 125 at the extremity thereof protruding out of the cover 120 when the cover is fitted. The square drive by a way of example is of the type known in socket wrench tools. It will be understood that any shape suitable for torque transfer can be used to the same extent such as round shaft and key, spline shaft, hex drive and so on. The bracket 126 is provided with two stoppers 162 limiting the angle of rotation of the sector gear 160. The sector gear 160 is engaged with a pinion 164 causing it to rotate as the sector gear is actuated. The pinion 164 is fixedly attached to a gear 166 forming a compound intermediate gear 188 (Fig. 9). Gear 166 is engaged with a final drive pinion 168 which rotates a crankshaft 180. The crankshaft 180 converts rotational movement of the gear train into reciprocating linear movement configured to actuate the volume changing chamber 154. In more detail and with reference to Fig. 9 there is shown an exploded view of the embodiment. The bracket 126 is provided with a fixed first pivot-stud 182 located approximately at the middle of the wide portion of the T shaped bracket 126. The hollow shaft 124 of the sector gear 160 is rotatably mounted on the first pivot-stud 182 and secured by a spring clip 184 by a way of example. A second pivot-stud 186 is fixedly fitted to the narrow portion of the T shaped bracket 126. The compound intermediate gear 188 is rotateably mounted on the second pivot-stud 186 and secured by a spring clip 192 by a way of example. The distance between the center lines of the first pivot-stud 182 and the second pivot-stud 186 is calculated to provide smooth meshing engagement of the sector gear 160 and pinion 164.

The end of the narrow portion of the T shaped bracket 126 is bent backwards leaving a gap 194 between the folded portion and the main bracket body. Bearing holes 196, 198 are formed through both of the walls defining the gap 194. Bearings 202, 204 are inserted into the bearing holes 196, 198 respectively to allow free rotation of the crankshaft 180 when the centric portion 208 of the crankshaft 180 is mounted to the bracket 126 through the bearings 202, 204. A final driven pinion 168 is fitted to the centric portion 208 of crankshaft 180 between the bearings 202, 204 in a fixed manner using a key for example. The assembly is locked by a spring clip 216. Bearings 202, 204 may be shoulder bearings or externally grooved bearings provided with spring clips to assist correct positioning in bearing holes 196, 198. The final driven pinion 168 is engaged with the gear 166 such that back and forth rotation of the sector gear 160 by means of the operator handle 122 rotates the final drive pinion 168 and crankshaft 180 through the compound intermediate gear 188. The crankshaft 180 may be provided with a balancing counter weight 214 to prevent vibration at high rotation speed. The cranking portion 212 of the crankshaft 180 is fitted through bearings 172 extending from the movable closure 70 of the bellows 52.

It will be understood that the frequency increasing mechanism 169 described above by a way of example only. The mechanism may accept other construction details. The drive system may use: drive belts, drive chains, worm or bevel gears, rack and pinion, a metal cast bracket 126 or plastic injected bracket. The crankshaft may be supported at both ends and the entire assembly positioned differently. All such alternative construction details falls under the scope of the present invention. It will be appreciated that the total transmission ratio between the sector gear 160 and final drive pinion 168 becomes significant with the introduction of the compound intermediate gear 188. Transmission ratio in the range of 20:1 to 40:1 is viable, while a ratio of approximately 30:1 provides a convenient option. Taking for example a transmission ratio of 30:1, a single stroke of the hand lever 122 which corresponds to about 1/6 of a revolution (angle of 60°) of the sector gear 160, will produce 5 full cycles of the crankshaft 180 according to the simple equation: (l/6)x30=5. It will be also appreciated that the direction of rotation of the crankshaft 180 is of no relevance since each cycle introduces the same amount of pumped air in either direction of rotation. Accordingly both back and forth manual strokes of the hand lever 122 will produce effective pumping of air into the protected space.

Considering the regulations related to residential safe rooms, it is required to deliver an airflow rate of between 36 and 48 cubic meters per hour or 600 to 800 liters per minute during manual operation of the NBC filtration system. Typically an average person is able to actuate the manual operation lever 122, back and forth 30 to 50 times per minute (60-100 strokes). As explained above each manual stroke produces 5 full cycles of the air exchange pump 50. Taking for example an average operator, that actuates the operation lever 122 back and forth about 40 times (80 strokes) per minute. Multiply by 5 results that the air exchange pump is cycled approximately 400 times per minute. Now division of the airflow rate of 600 or 800 liters per minute into 400 cycles per minute yields a displacement volume of between 1.5 to 2 liters of the air exchange pump 50. The same result as calculated above with reference to the embodiment of Fig. 3. It will be understood that such moderate displacement requires a relatively small bellows 52 which may be encapsulated under the protective cover 120 even in the expanded state. The frequency increasing mechanism 169 including the sector gear 160 and its rotation path are also encapsulated under the protective cover 120. As a result the protective cover 120 is permanently fitted in place during storage and during operation of the system. There is no need to remove, slack, open or alter the position of the protective cover during operation either electric or manual.

In operation, at normal times the manual operation handle 122 is removed from the square drive 125, collapsed and secured to the NBC filtration system by dedicated clamp (not shown). Optionally the collapsed manual operation handle 122, may be horizontally fitted to the square drive 125 being visible in case of need. In an event of emergency or when entrance to the safe room is declared, the electric blower is turned on by a switch 131 (Fig.6) to provide ventilation of the protected space. In an event of NBC contamination hazard, the state selector handle 30 is rotated to filtration state. In an event of power failure either in ventilation mode or in filtration mode, the manual operation handle 122 is taken from storage position, expanded, fitted to the square drive 125 and actuated as long as the power failure persists.

It will be evident to the person skilled in the art that above described NBC filtration system is by far more convenient in operation and handling than common prior art systems.

It will be appreciated that the specific embodiments of the present invention described above and illustrated in the accompanying drawings are set forth merely for purposes of example. Other variations, modifications, and applications of the present invention will readily occur to those skilled in the art. It is therefore clarified that all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.