GB2056563A - Pneumatic exhaust - Google Patents

Abstract

The silencer comprises a damping chamber (12) filled with a wool-like, sound absorbing material (11), preferably steel or plastics wool, and at least one perforated plate (8) is provided upstream of the damping chamber (12). A free space (13) is provided between the perforated plate (8) and the sound absorbing material (11). Outflow passages (15) and (16) are formed in a housing (2) and a plate (9) respectively. The discharge sounds are damped to a considerable extent by the combination of the perforated plate (8) the free space (13) and the sound absorbing material (11). <IMAGE>

Description

SPECIFICATION Silencer The present invention relates to a silencer for use in pneumatic systems where working air is discharged only intermittently to the atmosphere.

A silencer of this kind is known from German Utility Model No. 6607 145. In this known construction, steel wool is disposed in a square container, the walls of the container are provided with openings, and the container is mounted on a valve housing such that the container externally covers outlet openings in the valve housing which are intended as outlets for compressed air. In this manner, the compressed air has to flow through the steel wool before it enters the atmospheric air, thereby achieving a certain degree of silencing.

However, it has been found that silencing of this kind is frequently inadequate, particularly since the increasingly stringent regulations with respect to the protection of the environment are placing greater demands on silencers. Furthermore, owing to the square container, the known construction is bulky and difficult to accommodate. Finally, with the possibly straight passage for the exhaust air, satisfactory silencing cannot be obtained.

An aim of the present invention is to provide an improved silencer for pneumatic systems.

According to the present invention there is provided a silencer for pneumatic systems in which working air is discharged only intermittently to the atmosphere, the silencer comprising a housing adapted to be connected to an air discharge point, the housing containing a perforated plate downstream of which a damping chamber partially filled with a wool-like absorbing material, is located, a free space being provided between the perforated plate and the wool-like absorbing material.

An advantage of a silencer constructed according to the present invention is that it can have small dimensions but still be very effective. The perforated plate which is used, and which preferably comprises a plurality of wire lattices, constitutes a flowstabilizing element which distributes the air very uniformly to a large number of very small apertures, which, with regard to silencing, is better than a passage formed by only one aperture. Despite the perforated plate and the wool-like absorbing material, the air passing through the silencer is, at all events, throttled to a lesser extent than the maximum admissible extent for the system.

In addition to this, the further guidance ofthe air to the atmosphere from the chamber containing the wool-like absorbing material is effected predominantly in a radial direction.

The silencing values obtained by virtue of the small flow resistance of the proposed silencer are so satisfactory that no complaints are received from the customer or from the Tuv when the silencer is used in compressed air brake systems. The exhaust sounds are reduced to a considerable extent without decreasing the exhaust time essential for reliable operation of the brake system.

Moreover, the efficacy of the silencing action is increased by deflecting the flow of air in the silencer.

Furthermore, in accordance with further features of the invention, freezing of the silencer in the winter is avoided by using large outlet openings in the walls of the chamber accommodating the wool-like damping material, and a safety opening is provided through which the air can still flow off to the atmosphere even if the silencer becomes clogged or frozen up.

Finally, the silencer has the advantage that it can be subsequently fitted to compressed air valves or the like in a very simple manner.

The present invention will now be further described, by way of example with reference to the accompanying drawings, in which: Fig. 1 is a longitudinal sectional view of one embodiment of a silencer constructed according to the present invention, Fig. 2 is a longitudinal sectional view of a further embodiment of a silencer constructed according to the present invention; and Fig. 3 shows a detail of the silencer of Fig. 2.

A silencer 1 is shown in Fig. 1 which has a tubular housing 2 having a multiple stepped diameter. A minimum diameter portion of the housing 2 has a screw-threaded connection piece 3 by which the housing is screwed into an outlet connection piece 4 of a valve housing 5 (not further illustrated) of a compressed air brake system. The screw-threaded connection piece 3 is of hollow construction and has an internal diameter which corresponds approximately to the outlet of the valve housing 5.

The interior ofthe tubular housing 2 has two shoulders 6 and 7. A perforated plate 8 abuts against the shoulder 6, and a perforated plate 9 abuts against the shoulder 7. By virtue of the arrangement and size of narrow holes 10, the perforated plate 8 forms a silencing element which, although it silences the air flowing through, does not throttle it to more than the maximum venting time admissible in the system.

A free space 13 is provided between the perforated plate 8 and a chamber 12 filled with a wool-like absorbing material 11. A similar free space 14 is also located at the other side of the perforated plate 8 directly downstream of the screw-threaded connection piece 3.

The absorbing material 11 located in the chamber 12 can be either steel wool, or plastics wool, although any other suitable wool-like material can be used. In the region of the chamber 12, the housing 2 has radial outflow passages 15 in the form of holes. Similar, axially extending holes of the same size are also provided as outflow passages 16 in the perforated plate 9. The outflow passages 15 and 16 are larger than the holes 10 in the perforated plate 8 and are also spaced at a greater distance apart.

The perforated plate 8, the silencing material 11 and the perforated plate 9 are commonly retained by a clamping ring which acts upon the perforated plate 9 and which is supported in the housing 2.

The embodiment of Fig. 1 functions as follows:- During the intermittent outflow of compressed air from the outlet connection piece 4 of the valve housing 5, the airfirstflows into the expansion chamber 14 and then through the relatively narrow holes 10 in the perforated plate 8. The flow of compressed air is compressed and smoothed i.e. stabilized, when flowing through the holes 10. The compressed air can expand again in the free space 13 downstream of the perforated plate 8. In this manner, some frequency ranges of the exhaust sound are filtered out The exhaust air then enters the chamber 12 where its sound is again silenced to a considerable extent in the steel wool absorbing material. The exhaust air finally flows to the atmospherethrough the outflow passages 15 and 16.The sound which still occurs at this location is so slight that it is no longer troublesome.

The relatively large diameters of the outflow passages 15 and 16 prevent the silencer from freezing in the winter. Furthermore, it will be seen that it is a simple matter subsequently to fit the silencer 1 to any optional valve.

Another construction of a silencer constructed according to the present invention is illustrated in Figure 2, the same reference numerals being used for the parts corresponding to the construction of Figure 1. The silencer 21 shown in Figure 2 has a perforated plate 22 which chiefly comprises three wire lattices 23, 24 and 25 made from wire mesh, each lattice having a circular configuration. Wire lattice discs of this kind are very simple to manufacture.

Spacer rings 27 and 28 are located between the individual wire lattices 23, 24 and 25, thus determining the mutual spacing of the lattices. Alternatively, it is possible to manufacture the parts 23, 24,25 and 27, 28 as a built-in unit. Furthermore, the number ofthe individual parts can also be varied.

Thus, in this construction, the outlet connection piece 4 of the valve housing 5 is jointly used to accommodate a part of the silencer, that is to say, the perforated plate 22. However, it is also possible to dispose the perforated plate 22 in a screwthreaded connection piece 30. A silencer housing 29 has this screw-threaded connection piece 30 which is of the same construction as the connection piece 3 illustrated in Figure 1. However, the screw-threaded connection piece 30 is located on a cover 31 which covers the top of a housing cup 32 and which is secured thereto by means ofthree axially parallel bolts 33. Alternatively, the screw-threaded connection piece 30 can be arranged on the cup 32 instead of being arranged on the cover 31.

The underside of the cover 31 has radial ribs 37 by which the cover holds down the absorbing material (steel wool) arranged in the cup 32. The bottom 34 of the housing incorporates radial slots acting as outflow passages 34 which are disposed only in the outer region of the bottom 38 and which terminate and intersect with the outer wall. The outflow passages 34 are spaced at a relatively great distance apart. Their arrangement in the cup 32 is also shown in Figure 3. The ribs 37 on the cover 31 form on the silencer housing 29 an annular gap 36 whose significance will be explained later. The absorbing material 11 is disposed in a chamber 35 surrounded by the housing 32 and the cover 31.

In this construction, free spaces 13 and 14 are also provided in the silencer housing 29. Finally, here also, the spacer rings 27 and 28 between the wire lattices 23, 24 and 25 form chambers which act as expansion and stabilizing chambers.

The embodiment of Fig. 2 functions as follows:- During the intermittent outflow of air from the out let connection piece4 of the valve housing 5, vortices are produced whose flow is stabilized by the wire lattices 23, 24, and 25. Thus, the lattices 23, 24 and 25 infiuence the sound source, formed by the valve, with respect to sflencing. Furthermore, they improve the distribution of flow overthe throughflow cross section.

The passage is not constricted either by the perforated plate 22 formed by the lattices 23,24 and 25, or by the free spaces 14 and 13 located: upstream and downstream of the perforated plate.

The air passes via plate 22 to the cliamber35 filled with the wool-like absorbing material A radially deflected portion of the air flows freely across the absorbing material via the annular gap 36, and vents to the atmosphere. Since the gap 36 lies at an outer surface which is rounded rearwardlywith respect to the mouth ofthe gap, the gap allows the airto flow off in a particularly quiet manner. Moreover, the gap 36 constitutes a fail-safe means in the event of clogging or freezing of the silencer chamber 35 when the entire quantity of air can flow away via the gap 36. In normal operation the undeflected portion of the air flow flows through the absorbing material to the outlet passages 34 formed by the radial slots.In order to reach the outlet passages 34, the axial flow in the absorbing material 11 is deflected radially and flows out of the outflow passages 34 to the atmospheric air. Compared with bores, the slots acting as outflow passages 34 have the advantage of improved silencing, since they have a larger area and they can be spaced at a relatively large distance.

The sound still occuring during the egress of air is so slight that it is no longer troublesome.

It may again be mentioned that four silencing principles are combined with one another in the silencer in accordance with the present invention.

These four principles are: 1. The perforated disc 8 (Fig. 1) or the wire lat- tices 23, 24 and 25 (Fig. 2) prevent the occurrence of vortices and thus the occurrnnce:of sounds. The wire lattices form an interference- location for the vortices which stabilized,the flow characteristic. The sound level is thus reduced.

2. The free space 13:downstream of the perforated disc 8 or wire lattices 23, 24, 25, forms an absorption chamber which further reduces the sound.

3. Finally, the wool-like material in the chambers 12 and 35 distributes the outflowing air to a large surface having large-ama passages. The sound of the outflowing airis then further silenced. The flow through the absorbing material 11 is likewise deflected radially in the cup, thus again damping the sounds caused by the flow of air. For the purpose of further reducing the level of sound, the slots forming the outflow passages 34 are spaced as far apart as possible.

4. The radially extending outflow passages 34 are disposed around the circumference of the bot tom 38 such that a non-slotted portion of the bottom 38 is in alignment with the free space 13. The area of this non-slotted portiori of the bottom is largerthan the cross section of the free space 13 and it thus obstructs the sound components emerging from the free space 13 by reflecting them and, at this location, thereby increases to an adequate extent the silencing effect which might be too slight when effected solely by the wool-like absorbing material.

In this manner, the vortex sound occuring directly downstream of the valve can be damped and the flow sound occuring in the silencer can be reduced to a lower level, and the ratio of one to the other can be optimized.

Claims (12)

1. A silencer for pneumatic systems in which working air is discharged only intermittently to the atmosphere, the silencer comprising a housing adapted to be connected to an air discharge point, the housing containing a perforated plate down- stream of which a damping chamber partially filled with a wool-like absorbing material, is located, a free space being provided between the perforated plate and the wool-like absorbing material.

2. A silencer as claimed in claim 1, in which the perforated plate has axially parallel outflow passages extending therethrough, and defines a boundary of the damping chamber.

3. A silencer as claimed in claim 1 or 2, in which the damping chamber of the silencers partially filled with the wool-like absorbing material, has a circular outer wall and has at this location radially extending outflow passages.

4. A silencer as claimed in claim 3 in which outflow passages are also provided which extend axially of the housing.

5. A silencer as claimed in claim 1,3 or 4, in which the perforated plate comprises a plurality of wire lattices.

6. A silencer as claimed in claim 5, in which the wire lattices are spaced apart from one another.

7. A silencer as claimed in claim 3,5 or 6 in which the part of the housing defining the damping chamber partially filled with the wool-like absorbing material, is formed by a cup shaped member closed by a cover and safety venting is provided in the form of a gap between the cover and the cup shaped member.

8. A silencer as claimed in claim 7, in which ribs are formed on the underside of the cover, the ribs holding down the absorbing material in the cup shaped members and thereby ensuring an unobstructed flow of air across the wool-like absorbing material to the said gap.

9. A silencer as claimed in claim 8, in which a screw-threaded connection piece ofthe cover or of the cup shaped member retains the perforated plate and its individual parts in position in the silencer.

10. A silencer as claimed in any of the claims 7 to 9, in which the cup shaped member andlorthe cover are provided with radially extending slots for the passage of air, which slots are disposed only in the outer region of the bottom of the cup shaped member.

11. A silencer as claimed in any one of the claims 1 to 10, which is provided on a valve housing arranged in a pneumatic system, the silencer housing being directly connected to an outlet connection piece of the valve housing.

12. A silencer for pneumatic systems in which working air is discharged only intermittently to the atmosphere, the silencer being constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Fig. 1 or Figs 2 and 3, of the accompanying drawings.