EP0127550B1 - Silencer for a compressed-air system - Google Patents

Abstract

1. A silencer for a compressed air installation of the type including baffles (7, 8, 28) prolongating the path of travel of the flux of air with at least one portion of the chamber of the chamber defined by a perforated wall (5) maintaining a filling (6) of absorbing material, the baffles (7, 28) being formed with orifices (13; 27, 27', 33) separating the global flux of air into elementary streams of reduced section, the orifices (13; 27, 27', 33) and the baffles (7, 8, 28) being placed such that the streams collide against the wall of at least some of the adjacent baffles (7, 28) and/or against each other and are brought in contact with said perforated wall (5) maintaining the filling of absorbing material, characterized in that it includes means (12; 27, 27') providing for a return of said streams of air along path of travel portions which are substantially parallel but in an opposite direction with respect to the general circulation direction, the circulation in contact with the perforated wall (5) being effected according to a total path of travel which is close to the length of the silencer.

Description

The present invention relates to a silencer intended to reduce the noise resulting from an exhaust of compressed air at the outlet of a tap, a distributor, a solenoid valve, a valve, the relief valve or analogous device of a compressed air installation.

The noise resulting from an exhaust of compressed air is formed by sounds included in a wide range going from low to high and the absorption or attenuation of these sound vibrations poses problems because the known silencers effective for low are not very effective for treble and vice versa.

In FR-A-2 250 379 of October 31, 1973, the applicant proposed, to solve this problem, a silencer for compressed air installation comprising a chamber having at one end at least one connector for its connection to the outlet of compressed air and communicating at its other end with the atmosphere, chamber in which baffles are arranged, the wall of this chamber being double and formed by a solid outer wall and an inner wall perforated with between them a stuffing in an absorbent material.

In this silencer, the baffle elements consist of plates whose surface occupies the entire section, the plates being perforated alternately in the center and at the periphery. The air flow is established along a sinuous trajectory, which lengthens the flight path and dampens the long wavelength frequencies but the air streams are not forced along a trajectory bringing them into contact with the jam made of absorbent material, this contact having the effect of damping the frequencies of short wavelength.

This type of muffler therefore gives good results and a significant reduction in noise level. However, it has proved necessary to further reduce this noise level, in particular in the treble domain, therefore to increase the reflection on the stuffing with absorbent material.

In addition, if the installations and machines that the silencer is intended to equip are lubricated, the compressed air which comes from it generally entails oil which it is useful to stop as much as possible to avoid pollution of the atmosphere.

The increased attenuation of the sound level, in particular in the treble domain, is obtained, in accordance with the invention, in a silencer for compressed air installation of the type comprising baffles lengthening the path of the air flow with at least part of the chamber delimited by a perforated wall maintaining a stuffing in an absorbent material, the baffles being provided with orifices separating the overall air flow into elementary nets of reduced section, the orifices (13, 33) and the baffles being positioned so that the threads collide against the wall of at least some adjacent baffles and / or with each other and are brought into contact with the perforated wall maintaining the padding in absorbent material, characterized in that it comprises means ensuring a return of said air streams along substantially parallel path portions but in the opposite direction relative to the general direction of circulation, the circulation in contact with the perforated wall taking place along a total path close to the length of the silencer.

In accordance with the invention, the baffles can be constituted by plates perpendicular to the axis of the silencer, these plates having a solid surface with a passage for the air flow located alternately in the center and at the periphery, the peripheral passage being delimited. between the edge of the tray and the perforated wall maintaining the insulating stuffing. According to a preferred embodiment and to increase the turbulence and the path in contact with the perforated wall, this edge has a peripheral skirt parallel to said perforated wall.

It was further discovered that it was possible to obtain significant additional damping of the sound waves by creating pressure losses in the flow of the gas flow, in particular by giving rise to local turbulence by collision between partial flows.

Consequently and according to another characteristic, the overall flow is subdivided into elementary flows by passing through perforations of perforated walls parallel to the general direction of flow of the flow, the total surface of the perforations ensuring a passage through a wall being very greater than the passage section at the inlet of the silencer and the perforations ensuring the same passage being staggered so that the partial flows of the downstream perforations collide with the flows having passed through the upstream perforations.

According to an embodiment which provides part of the damping by localized turbulence, the silencer in which the baffles are constituted by concentric cylindrical walls having passages between the concentric chambers which they delimit in their alternating ends, the concentric chambers being traversed by the flow from the center to the periphery, is characterized in that the external peripheral chamber has its external wall constituted by the perforated wall maintaining the absorbent padding and in that the passages between the concentric chambers are produced by perforations distributed in staggered over a significant length. The partial flow passing through each perforation enters into turbulence by impact on the wall located opposite and by collision with the air streams having passed through the wall closer to its end.

According to another characteristic, downstream of the silencer proper is provided a chamber traversed by the air flow leaving the silencer, this chamber being provided with a filtering mass. This filtering mass which can consist of steel wool or other material The purpose of the analog is to retain oil that has not been stopped in the muffler.

According to another characteristic, the silencer is mounted with its vertical axis and comprises at its base a collecting cavity for the separated oil. In this case the baffles preferably have holes at their lowest point to allow the flow of the oil deposited on their surface. This embodiment is intended in particular for compressed air installations in which the air is loaded with oil or similar liquids.

• - la figure 1 est une vue en coupe axiale d'un silencieux à plateaux conforme à l'invention et
• - la figure 2 une vue correspondante du même silencieux avec récupération d'huile,
• - la figure 3 est une vue en coupe axiale d'un silencieux à chicanes cylindriques concentriques et
• - la figure 4 une vue correspondante du même silencieux avec récupération d'huile.
  Dans tous les dessins les mêmes références désigneront les mêmes éléments ou des éléments équivalents.

The above characteristics and other characteristics will appear more clearly on reading the detailed description of various embodiments of the silencer given below with reference to the attached drawings in which:

• FIG. 1 is an axial section view of a plate silencer according to the invention and
• - Figure 2 a corresponding view of the same silencer with oil recovery,
• FIG. 3 is a view in axial section of a silencer with concentric cylindrical baffles and
• - Figure 4 a corresponding view of the same silencer with oil recovery.
  In all the drawings, the same references will designate the same elements or equivalent elements.

1 designates the outer cylindrical casing of the silencer, 2 the bottom and 3 the upper end wall, these three elements being joined together by crimping to form a chamber. The reference 4 designates the orifices or inlet fittings integral with the wall 3 or made therein for the connection of the silencer to the compressed air exhaust such as a valve, distributor, solenoid valve, safety valve, valve pressure relief valve, compressor start valve, etc.

As described in FR-A-2 250 379, 5 designates the cylindrical wall perforated over its entire surface which maintains the mass of absorbent material 6, for example glass wool, intended to absorb acute noise.

In the embodiments of FIGS. 1 and 2, the baffles are constituted by plates alternately 7 and 8 mounted around a central axis 9 while being stacked on this axis with the interposition of spacers 10. The stack being tightened by nuts 11 screwed on the axis between an inverted upper plate 7 'and a lower plate 8'. The assembly is held by the plates 8 which extend to the wall 5 with which they are secured. The plates 7 which are of smaller diameter than the cylinder constituted by the wall 5 have at their periphery a skirt 12 directed upwards, but which could also extend downwards to channel the air flow in contact with the wall 5. The plates 8 have, in their central part, orifices 13 constituted by a U-shaped cut, the tongue 14 of which is folded obliquely downwards. Because of these characteristic arrangements of the invention, the circulation of the air flow is no longer zig-zag passing from a central orifice of a plate forming a baffle to the peripheral orifice of the following plate and vice versa but according to the path represented schematically by the arrow F. The path of the air flow has an increased length due to the sections in return in a direction opposite to the general axial direction of circulation from top to bottom and the air flow comes crashing repeatedly against the upper and lower surfaces of the plates forming the baffles against which it abandons the oil or other liquids with which it can be loaded. In addition, according to the essential characteristic of the invention, the circulation of the entire air flow in contact with the wall 5 takes place along a total path close to the length of the silencer and the sound waves of short length. wave and high frequency are damped, when they fall on the surfaces of the perforations, by absorption in the mass of absorbent material 6.

In the embodiment of FIG. 1, the air exits through perforations 15 in the zone of the peripheral wall 1 situated below the layer of absorbent material 6 which is delimited by a washer 16.

In the embodiment of FIG. 2, the silencer described above is enclosed in an external peripheral envelope 17 closed by an upper ring 18 and a lower crimped bottom 19 with a support tab 22 between the bottoms 2 and 19. The wall peripheral 17 is perforated at its upper part at 20, to produce the air outlet and, between the perforated zone 15 ′ of the peripheral wall 1 and the zone of the perforations 20 is arranged a filtration lining 21, for example made of straw of iron, which is traversed by the air flow before it leaves and which can retain traces of oil which have not been eliminated on the baffles of the silencer. This type of silencer being intended for compressed air installations whose air can be sufficiently loaded with oil, the bottom 2 is perforated to allow the oil deposited in the silencer to flow and small holes (not shown) can also be provided in the low points of the plates 7 to ensure the flow of the oil. In the case where the silencer is provided with a foot 23, a connection 24 for a flexible pipe or the like can be provided under the foot, this connection opening into the bottom of the outer peripheral envelope. The foot 23 can be replaced by a glass jar or the like, screwed or secured in any other way and removably under the bottom 19, jar in which the oil accumulates.

In the embodiments according to FIGS. 3 and 4.1. Baffle system consists of a central cylindrical wall 25 joined at its upper part to the connection 4 for the arrival of the exhaust air by a tubular sleeve 26. The wall 25 has in its lower part an area perforated 27 which, according to the invention, extends over a fairly long length so that the surface of the holes is at least equal to the section of the chambers delimited by the walls. Around the wall 25 are arranged three other concentric cylindrical walls 28 - 28 ', these walls comprising perforated areas 27' - 27 which have the same characteristics as the perforated area 27 and which are arranged alternately in their upper part or in their part lower. These baffles are kept centered and are mounted by clamping between a part in frustoconical wall 29 and stamped bottoms 31, the clamping being ensured by the wall 25 which fits at the top in the piece 29 and is clamped at the bottom towards the stamped bottoms 31 by a bolt tightening system 32.

With this embodiment of the silencer, the air flow follows the arrows F by successively circulating from bottom to top and from top to bottom in the successive tubular chambers. However, in accordance with the invention, the passage from a chamber to the peripheral chamber takes place in the form of a multiplicity of small air jets which come to crash into the solid wall located opposite each perforation and which are subjected to turbulence under the effect of the impact in the air flow which has passed through the orifices closer to the end. There is therefore effective energy dissipation and damping of the sound waves, especially of the bass. In addition, due to the large total surface area of the orifices on each tube, the expansion takes place over the entire length and not when the baffle perforations pass, which avoids detents with increasing air speed which are noise generating. Finally, on the last part of the path, the air circulates in turbulent flow in contact with the perforated wall 5 and the high frequency sound waves are absorbed, after having been transmitted through the perforations in the wall 5, in the mass glass wool. In changes of direction, the oil is "centrifuged" out of the air flow which entrains it and it accumulates at the bottom of said chambers from which it flows through the orifices 33.

When the silencer according to FIG. 3 is used in an installation whose air is loaded with oil, it can be supplemented by an oil recovery device similar to that of FIG. 2, this modification being illustrated in FIG. 4 and the same elements being designated by the same references.

Claims (7)

1. A silencer for a compressed air installation of the type including baffles (7, 8, 28) prolongating the path of travel of the flux of air with at least one portion of the chamber of the chamber defined by a perforated wall (5) maintaining a filling (6) of absorbing material, the baffles (7, 28) being formed with orifices (13; 27, 27', 33) separating the global flux of air into elementary streams of reduced section, the orifices (13; 27, 2T, 33) and the baffles (7, 8, 28) being placed such that the streams collide against the wall of at least some of the adjacent baffles (7, 28) and/or against each other and are brought in contact with said perforated wall (5) maintaining the filling of absorbing material, characterized in that it includes means (12; 27, 27') providing for a return of said streams of air along path of travel portions which are substantially parallel but in an opposite direction with respect to the general circulation direction, the circulation in contact with the perforated wall (5) being effected according to a total path of travel which is close to the length of the silencer.

2. A silencer for a compressed air installation according to claim 1, characterized in that the baffles are made of plates (7, 8) perpendicular to the silencer axis, said plates having a plain surface with a passage for the flux of air situated alternately in the centre (13) and at the periphery, the peripheral passage being defined between the edge of plate (7) and the perforated wall (5) maintaining the insulating filling.

3. A silencer for a compressed air installation according to claim 2, characterized in that the edge of plates (7) defining the peripheral passage with the perforated wall (5) includes a peripheral skirt (12) parallel to said perforated wall (5).

4. A silencer for a compressed air installation according to claim 1, characterized in that the global flux is subdivided into elementary fluxes by passing through perforations of perforated walls (28) parallel to the general flow direction of the flux, the total surface of the perforations providing for a passage through a wall being far superior to the passage section at the inlet of the silencer and the perforations ensuring a same passage being stepped so that the partial fluxes of the downstream perforations collide with the fluxes having flown through the upstream perforations.

5. A silencer for a compressed air installation according to claim 4, in which the baffles are made of concentrical cylindrical walls (28) formed with passages (27) between the concentrical chambers which they define at their alternate ends, the flux flowing in the concentric chambers from the centre to the periphery, characterized in that the outer peripheral chamber has its outer wall formed of the perforated wall (5) maintaining the insulating filling (6) and in that the passages between the concentric chambers are formed by the perforations (27) distributed in a staggered way over an appreciable length.

6. A silencer for a compressed air installation according to any one of claims 1 to 5, characterized in that downstream of the silencer as such is formed a chamber through which flows the flux of air exiting from the silencer, said chamber being filled with a filtration mass (21).

7. A silencer for a compressed air installation according to any one of claims 1 to 6, characterized in that the silencer is mounted with its axis extending vertically and includes at its base a collecting cavity (22) for the separated oil.

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