- 1 A FILTER ASSEMBLY HAVING A COAXIAL BREATHING VALVE INTEGRATED WITH AN EXHALATION PASSAGE TECHNICAL FIELD [0001] The present invention relates to the manufacture of breathing valves for respirator masks and in particular to a filter assembly having a coaxial breathing valve integrated with an exhalation passage. BACKGROUND [0002] It is widely known to use protection devices like respirator masks for protecting a user from hazardous airborne particulates such as dust and poisons. The breathing valves used in current known respirator masks include an input passage for receiving air during inhalation and a separate one or two output passages for expelling air during exhalation. Typically, an exhalation valve is placed on either a lower region of the mask or on two opposing sides of the mask. In each case, the exhaled air is not able to egress directly to the exhalation valve. Such breathing valve structures have a number of disadvantages. Firstly, the passage of breathing circulation is quite long because the breathing valve is manufactured separately. This results in breathing restrictions to the user. Secondly, a greater number of exhalation passages are needed to be manufactured, typically through injection moulding, to manufacture each mask. The greater number of components increases the difficulty in the manufacturing process. Thirdly, the current structures are not strongly hermetic and the lack of airtight sealing reduces the effectiveness of the mask in the filtration of particulates such as dust and poisons. Fourthly, known breathing valve structures significantly increase the volume and weight of the associated respirator mask, thereby reducing the user comfort when worn and also increasing the risk of the mask falling off during use. SUMMARY OF THE INVENTION [0003] To solve the above problems, the present invention provides a filter assembly including an inhaling valve and an exhaling valve installed coaxially to shorten the distance of the overall breathing circulation passage. The assembly also includes an exhalation passage that reduces the volume and weight of the dust and poison protection mask, thus providing smoother breathing, enhanced user comfort, improved tightness of fit and fewer injection moulding manufacturing difficulties. The present invention is achieved through the technical solution described below. [0004] The filter assembly, having a coaxial breathing valve integrated with an exhalation passage, includes a breathing filter body, an annular one-way clack valve, a one-way wafer -2 clack valve, a valve sheet baffle ring and an exhalation passage, wherein the breathing filter body is formed from two coaxial cylinders, a first cylinder being larger in diameter and a second cylinder being smaller in diameter, an upper end of the cylinders defines a first opening and the respective cylinders are connected together by reinforcing bars located within a second opening defined by a lower end of the cylinders. A core shaft is fixedly attached to the reinforcing bars and is disposed along the axial centre of the smaller diameter cylinder. The one-way wafer clack valve is sleeved onto the core shaft within the smaller diameter cylinder and is disposed against the reinforcing bars at the lower end. The valve sheet baffle ring is located at the upper end of the smaller diameter cylinder. The exhalation passage is located at the lower end of the smaller diameter cylinder. The one-way annular clack valve is sleeved within the larger diameter cylinder. The one-way annular clack valve is disposed against the reinforcing bars at the lower end of the larger diameter cylinder. The relative positioning of the one-way wafer clack valve and the annular one-way clack valve provides a coaxial design. [0005] The lower end of the larger diameter cylinder includes at least one locking formation and a curved convex flange. A locating opening is formed on an outside of a top region of the cylinder wall. [0006] Advantages of the present invention compared to the prior art are listed below. [0007] An inhalation valve and exhalation valve are installed coaxially in the filter assembly, and the exhalation passage is disposed on the lower end of the smaller diameter cylinder. This design reduces the length of the breathing circulation passage so as to provide smoother breathing through a respirator mask. The structure design also provides for a mask having a smaller volume, lighter weight, greater user comfort and more secure fastening. In addition, the structure itself is less complex as there is no need for multiple exhalation passages. This lower complexity reduces the difficulties in an injection molding manufacturing process. BRIEF DESCRIPTION OF THE DRAWINGS [0008] Figure 1 illustrates a front view of a filter assembly having a coaxial breathing valve integrated with an exhalation passage. [0009] Figure 2 illustrates a side view of the filter assembly, having a coaxial breathing valve integrated with an exhalation passage, showing the valve sheet baffle ring removed. [0010] Figure 3 illustrates the complete filter assembly, having a coaxial breathing valve integrated with an exhalation passage, the filter assembly being installed in a mask. [0011] In the above drawings, item 1 is a body of a breathing filter assembly, item 2 is an annular one-way clack valve, item 3 is a one-way wafer clack valve, item 4 is a valve sheet -3 baffle ring, items 5 are locking formations, items 6 are reinforcing bars, item 7 is a locating opening, item 8 is a flange, item 9 is a core shaft, item 10 is an exhalation passage, item 11 is an 0-ring and item 12 is a cotton filter material. DESCRIPTION OF THE PREFERRED EMBODIMENT [0012] The filter assembly according to the present invention comprises a breathing filter body 1, a one-way annular clack valve 2, a one-way wafer clack valve 3 and a valve sheet baffle ring 4. The body 1 is formed from two cylinders extending coaxially with respect to each other. A first outer cylinder is larger in diameter and a second inner cylinder is smaller in diameter. An upper end of the cylinders defines a first opening. Reinforcing bars 6 are fixed within a second opening at a lower end of the cylinders and the bars connect the respective cylinders together. A core shaft 9 is fixedly attached to the reinforcing bars 6 and is disposed along the axial centre of the smaller diameter cylinder. The one-way wafer clack valve 3 is sleeved onto core shaft 9 within the smaller diameter cylinder. [0013] The one-way wafer clack valve 3 is disposed against the reinforcing bars 6 on the lower end of the smaller diameter cylinder. The valve sheet baffle ring 4 is fixed to the upper end of the smaller diameter cylinder. The lower end of the smaller diameter cylinder includes an exhalation passage 10. The one-way annular clack valve 2 is sleeved within the larger diameter cylinder, and is disposed against the reinforcing bars 6 at the lower end. The coaxial design is formed by the relative positioning of the one-way wafer clack valve 3 and the one-way annular clack valve 2. [0014] Both the one-way wafer clack valve 3 and the one-way annular clack valve 2 are one way filtering valves. The one-way wafer clack valve 3 is configured to only allow the passage of air in a first direction during exhalation and the one-way annular clack valve 2 is configured to only allow the passage of air in a second direction during inhalation. Eight locking formations 5 and a flange 8 are disposed on the lower end of the larger diameter cylinder of the filter body 1. A locating opening 7 is formed on an outside of a top region of the cylinder wall (see Figures 1 and 2). [0015] The filter assembly, having a coaxial breathing valve integrated with an exhalation passage, is able to be incorporated into various types of respirator mask so as to reduce the overall volume and weight of the mask. The filter assembly is also able to shorten the required length of the breathing circulation passage through the mask. The front of the assembly is adapted for the installation of multiple types of filtering devices. Figure 3 illustrates a complete filter assembly installed in a respirator mask.
-4 [0016] Use of the assembly is described as follows (with reference to Figure 3). Firstly, a belt or strap having a securing buckle is used to secure the mask over the nose and mouth of a user. External air can then be inhaled by the user by ingress through the one-way annular clack valve 2. During the ingress, the air is filtered through the cotton filter material. During exhalation by the user, the waste air including carbon dioxide passes through the one-way wafer clack valve 3 and egresses through the exhalation passage 10. [0017] To avoid the mixing of the inhaled air and exhaled air, an O-ring 11 is positioned between the inhalation passage and the exhalation passage. The one-way wafer clack valve 3 is disposed just opposite the user's mouth due to the coaxial design formed by the relative positioning of the one-way wafer clack valve 3 and the one-way annular clack valve 2. Therefore, the overall breathing circulation passage is shortened to provide smoother breathing and greater comfort to the user. [0018] In the present invention, an inhalation valve is installed coaxially with an exhalation valve, which removes the need for a separately disposed exhalation passage. This design greatly enhances the airtightness of the mask. Moreover, due to the coaxial positioning of the exhalation passage, fewer components are required and the weight of the entire respirator mask is lighter and can be more strongly secured to the user. The mask can be used efficiently with overall less discomfort to the user and can be manufactured at a lower cost.