Sound absorber for compressed-air operated apparatuses, in particular compressed air vibrators
The invention relates to a sound absorber in accordance with the preamble of claim 1. 
     It is already known for sound absorbers utilized for the reduction of the operating noise levels of pneumatic sledge hammers to arrange a plurality of relief chambers sequentially in the flow direction (German Laid-open Patent Application No. 2 360 430). Since such sledge hammers evidence relatively large dimensions, the arrangement of the chambers on the apparatus causes no difficulty. 
     In contrast therewith, compressed-air vibrators evidence mostly small dimensions. Accordingly, it is usual to generally equip such apparatuses with small sound absorbers in which the compressed air exits through porous inserts which, for example, are formed of felt, or through porous chamber walls, for example, of sintered metal or plastic material. These porous sound absorbers have the disadvantage that for oily or dirty compressed air the pores of the porous elements will clog so as to restrict the through-passage of air, which leads to uncontrolable changes in the frequency of the apparatuses. As a result, such sound absorbers must be frequently cleaned or exchanged already after short operating periods. 
     In particular for piston vibrators, which are mounted on transport troughs for pourable goods, the maintenance of a predetermined frequency is extremely important. The suitable frequency is hereby controlled through an additional throttle valve arranged on the air outlet side. Frequency changes through clogged sound absorbers can bring the flow of the conveyed goods in the trough to a standstill. Porous sound absorbers are thereby unsuitable for this purpose. 
     Accordingly, it is an object of the present invention to provide a sound absorber which can be economically produced with small dimensions, which is subjected to practically no contamination and which also facilitates an adjustable throttling of the exiting air, so that for predetermined purposes of application the addition of a further throttle valve becomes superfluous. 
     The foregoing object is achieved through the construction pursuant to the characterizing portion of claim 1. 
     During the passage of the pulsating compressed air through the three relief chambers, between which there are arranged through-bores acting as throttles, the noise level of exiting air will be extensively attenuated. Since no porous elements are present, there also cannot occur any clogging of the sound absorber through oil-containing compressed air. 
     The construction of the sound absorber pursuant to claim 2 provides the advantage that the cap which is threaded thereon renders an additional throttle valve to be superfluous. 
    
    
     The invention is now elucidated in detail on the basis of an exemplary embodiment as illustrated in the drawing. Shown herein: 
     FIG. 1 is an axial section through a sound absorber with a throttle valve; and 
     FIGS. 2-4 illustrate cross-sections taken along, respectively, lines 2--2, 3--3 and 4--4 in FIG. 1. 
    
    
     The sound absorber pursuant to FIG. 1 includes three main components, a central main body 1, a housing 2 mounted thereon, and a cap 3 which is threaded onto the upper portion of the main body 1. The main body 1 includes in the lower portion an inlet connector 1a with a threading 1b, by means of which it can be threaded directly into an outlet opening of a compressed-air vibrator. The connector 1a contains a first chamber 4, from which the compressed air flows through radial through-bores 4a into a second chamber 5, which is bounded by the walls of the main body 1 and thereon mounted housing 2. The chamber 5 is annularly-shaped and elongate and contains labyrinth type baffles 7 which are formed by outwardly or, respectively, inwardly projecting projections on the components 1 or 2. On the upper end of the chamber 5 there are arranged approximately tangential through-bores 5a in the main body 1, through which the compressed air is conducted into a central vortex chamber 6 which is substantially larger than the chambers 4 and 5. Within this vortex chamber 6 there will further relieve the compressed air. The air then flows after more intense swirling through the through-bores 6a, which are arranged oppositely tangential relative to the bores 5a, into an annular chamber 8 and then escapes to the outside through an annular-shaped outlet slit 8a. The widening end 9 of the outlet slit 8a considerably reduces the hissing noise of the exiting air. 
     The cap 3 is provided with an internal thread 3a and is screwed onto a corresponding external thread on the main body 1. Through rotation of cap 3 there can be varied the cross-section of the outlet slit 8a. The cap 3 thus serves also as a throttle valve for the exiting compressed air. The throttling of the exiting air within the adjustable slit 8a facilitates an additional strong reduction in the sound level; however, it results in a power reduction of the compressed-air vibrator which, nevertheless, can be accepted in general when the sound level of the apparatus must be reduced to an acceptable minimum. A rubber ring 10 acting as a friction ring prevents an unintentional rotation of the cap 3. 
     The three components 1, 2, and 3 of the sound absorber can be produced from metal or plastic material. The sound absorber is easily disassembled and thus can be readily cleaned.