Compressed air drier
TECHNICAL FIELD 
     This invention relates to a device at a drying tower for a compressed air drier including a base with an inlet and an outlet for compressed air and with a reservoir containing a cartridge, which is filled with filter material and desiccant and which is provided with inner partition walls for accomplishing a winding path for the compressed air through the cartridge. 
     BACKGROUND OF THE INVENTION 
     Compressed air driers of the kind set out above are well known in the art and may be used for drying (and cleaning) compressed air in vehicles or in stationary systems, the former application being of most interest in the present case. 
     The basic design and function of the air drier forming the basis for the present invention are shown in the British Pat. No. 2 050 195 and in the European Patent Application No. 81201271.4. 
     The use of a cartridge, filled with filter material and dessicant, in the reservoir forming part of the drying tower of the air drier is also known. 
     Furthermore, it is known (see for example U.S. Pat. No. 2,790,512) that it is advantageous for utilizing the drying function of the dessicant to have a long and comparatively narrow path for the air through the desiccant rather than a short and wide path. In FIG. 5 of said U.S. Pat. No. 2,790,512 the possibility of obtaining the desired long path within a comparatively low tower by accomplishing a winding path for the air is suggested. 
     THE INVENTION 
     The primary purpose of the invention is to accomplish an air drier of the kind set out above making optimal use of the advantages with the cartridge and the winding path for the air within a reservoir with minimal outer dimensions. 
     This is according to the invention attained in that the cartridge has the same outer shape and dimensions as the inner shape and dimensions of the reservoir and in that--by the provision in the cartridge of two longitudinal partition walls perpendicular to each other with two openings at the end remote from the base and by the provision in the base of two corresponding walls--the compressed air will be transported consecutively through all four desiccant-filled cartridge compartments formed by the walls. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in further detail below reference being made to the accompanying drawings, in which 
     FIGS. 1 and 2 are schematic sections through prior art air driers, 
     FIG. 3 is a section through a drying tower including its base according to the invention, and 
     FIGS. 4-6 are simplified illustrations to a smaller scale aiming at elucidating the function of the drying tower, wherein FIG. 4 corresponds to FIG. 3, 
     FIG. 5 is a section along the line V--V in FIG. 4, and 
     FIG. 6 is a section (along the line VI--VI in FIG. 5) perpendicular to that in FIG. 4. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT 
     As already stated above it is known to insert a cartridge containing desiccant for absorbing moisture from compressed air and possibly filter material for removing contaminants in a drying tower. An example thereof is shown in FIG. 1. 
     In a reservoir 1 a desiccant-filled cartridge 2 is centrally located, and a spring 3 holds the cartridge against its base (not shown). The air to be dried is passed upwards past the cartridge 2 and then down through the desiccant therein. The air only passes once through the desiccant, the path being short and wide. The poor utilization of the space within the reservoir 1 is to be noted. 
     In FIG. 2 (which corresponds to FIG. 5 from U.S. Pat. No. 2,790,512) the provision of a winding path for the air through the desiccant is depicted, but also in this case the space within the reservoir is poorly utilized. 
     A drying tower according to the invention is shown in FIG. 3. This tower is preferably to be used for a so called two tower drier, where the air to be dried is passed through one tower, while a fraction of the dried air is passed through the second tower for drying the desiccant therein earlier moistened at its foregoing air drying cycle, and vice versa. For this function a control and valve system is needed; this system is not shown herein, as it is regarded as state of the art (see for example European Patent Application No. 81201271.4). 
     A metal reservoir 4 is attached to a base 5 having an inlet 6 and an outlet 7 for compressed air. A cartridge 8 (preferably of a plastic material) with the same outer shape and dimensions as the inner shape and dimensions of the reservoir 4 is inserted therein and is clamped between the reservoir 4 and the base 5, a sealing ring 9 being provided against the reservoir 4. A sealing 10 below the cartridge 8 is clamped between the latter and the base 5. 
     The cartridge 8 is completely filled with desiccant 11 and filter 12 (comprising two perforated plates, polyester filter material, and spacers). A certain compressing effect on the contents of the cartridge 8 is obtained by a resilient annular bead 10&#39; on the sealing 10. The cartridge 8 with its contents and the sealing 10 (held in position by undercuts) is delivered as a replacement unit to a customer, and the cartridge 8 can also be seen as a packing for storage and transport. 
     Integrally formed in the cartridge 8 are two longitudinal partition walls 13 and 14, which are perpendicular to each other and thus form a cross as viewed from the lower, free end of the cartridge. The first wall 13 is completely unbroken, whereas the second wall 14 at its upper end has an opening 15 at either side of the wall 13 for allowing air to pass, as will be described below. 
     Also the base 5 has two partition walls, one wall 16 forming a continuation of the cartridge wall 14 and dividing the space within the base in two halves (as can be seen in FIG. 5) and one shorter wall 17 forming a continuation of half the cartridge wall 13 and lying between the inlet 6 and the outlet 7. 
     The shown and described design of the cartridge and the base has the effect that the air flow will be as follows, reference now primarily being made to FIGS. 4-6. 
     From inlet base compartment a the air will flow upwards through cartridge compartment A and down through cartridge compartment B to base compartment b, further up through cartridge compartment C and down through cartridge compartment D to outlet base compartment c. It is obvious that the air flow path through the desiccant 11 has a four times greater length than the height of the reservoir 4 but also that the air will pass filter material 12 four times for accomplishing cleaner and drier air than in any known competing design.