US2640557A

US2640557A - Retroverted passage type muffler with outer conduit formed of sound absorbing material

Info

Publication number: US2640557A
Application number: US200654A
Authority: US
Inventors: Joseph B Gaffney
Original assignee: Fuller Co
Current assignee: Fuller Co
Priority date: 1950-12-13
Filing date: 1950-12-13
Publication date: 1953-06-02
Anticipated expiration: 1970-06-02

Description

. J. B. GAFFNEY RETROVERTED PASSAGE TYPE MUFFLER 2,640,557 WITH OUTER June 2,1953

2 Sheets-Sheet 1 Filed Dec.

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Jossm B. Gnnuzv 2 Sheets-Sheet 2 J. B. GAFFNEY RETROVERTED PASSAGE TYPE MUFFLER WITH OUTER CONDUIT FORMED OF SOUND ABSORBING MATERIAL Filed Dec. 13, 1950 June 2, 1953 A I "g INVENTOR. JOSEPH B. Gnrrnev Patented June 2, 1953 UNITED STATES.

PATENT OFFICE WITH OUTER CONDUIT FORMED OF SOUND ABSORBING MATERIAL.

Joseph B. Gaflney, Hokendauqua, Pa., assignor to Fuller Company, Oatasauqua, Pan, 2:. corporation of Delaware Application December 13, 1950, Serial N 0. 200,654

8 Claims. 1,

This invention relates to the silencing and attenuating of pulsations in a flowing gas streamsuch as that produced in the intake and exhaust of air pumps, internal combustion engines, and

the like; and is particularly adaptable to exhaust silencers for positive pressure blowers.

It is especially concerned with the simple and effective means for silencing the exhaust noises of a pneumatic conveying system without substantially increasing the back pressure of the exhaust system. It is among the further purposes to provide a silencer that is equally effective in any position and that may be located at any point in the exhaust system with respect to the blower.

It is well known that the flOWiIlg gas stream in an exhaust system of a positive pressure blower comprises a series of separate gas slugs, or volumes of gas, at a relatively high pressure separated by volumes of gas at a relatively low pressure, and it is believed that the noise from such an exhaust system is produced by these high pressure slugs of gas hitting the surrounding air as the slugs are exhausted to atmosphere. To overcome a noise of this type the high pressure volumes and the low pressure volumes in the exhaust system must be smoothed out, or attenuated, to mean pressure to provide a constant. pressure stream of gas flowing from the exhaust system to the atmosphere.

I It has been the practice to attenuate the variable pressures in an exhaust stream of gas by providing silencers having various obstructions and expansion chambers through which the gas must fiow. The theory is that the obstructions to the flow will cause a damming up of the stream of gas and a resulting co-mingling of the separate volumes of gas to even out to a uniform pressure, while the expansion chambers will allow the high pressure volumes of gas to lose momentum and expand into the volumes of lower pressure gas. The objection to silencers of this type is the usual increase in back pressure of the gas stream incurred as the stream is forced to flow around th obstructions and into and out of the various expansion chambers through restricted openings. A further objection to silencers of this type isthe lack of any provision for the absorption of sound waves produced by the vibrations set up from the flowing gas stream striking the various elements of the silencer.

The present invention is, accordingly, directed to an apparatus for silencing the noises in an exhaust system that are produced by the variations in pressure, or pulsations, in the gas stream. The

apparatus includes novel means to-receive and attenuate the pulsations to provide for a constant pressure in the gas stream flowing to the atmosphere, and to obtain a maximum efficiency in the attentuating of the pulsations without substantially-increasing the back pressure in the exhaust system.

In general, the new silencer comprises a substantially cylindrical housing having an intake end and a discharge end. Anopen ended gas inlet conduit is positioned in the housing intake end, and is extended concentrically a substantial distance into the housing. In the same manner a gas outlet conduit of equal diameter is positioned in the housing discharge end and extended concentri'cally a substantial distance into the housing. An intermediate conduit, having one end closed and one end open, is positioned concentrically around the gas inlet conduit inside the cylindrical housing-with the closed end opposite the inner open end of the gas inlet conduit and the open end positioned adjacent the intake end of the cylindrical housing. The diameter of the intermediate conduit is such that the annular, or effective area, of this conduit for the flow of gas is substantially equal to the area of the gas inlet conduit. In a lik manner a second intermediate conduit of the same design is positioned concentrically around the gas outlet conduit and the efiective area of thls conduit is substantially equal to the area of the gas outlet conduit. An outer conduit, formed of a sound absorbing material, is positioned concentrically and externally of the two intermediate'conduits and is extended substantially the length of the housing to serve as a means of communication between the open ends of the two intermediate conduits. The effective area of the outer conduit for the flow of gas is substantially equal to the effective area of either of the intermediate conduits,- and it is seen that at al1 times the cross sectional areas of the gas stream through any part of the silencer is substantially equal.

The exhaust gas enters the silencer through the gas inlet conduit where it is discharged into the first intermediate conduit. Due to the closed end of the intermediate conduit being positioned opposite the inner opened end of the inlet conduit the flow of gas is forced to change direction as it is discharged from the inlet conduit and flow through the space defined by the inside of the intermediate conduit and the outside of the inlet conduit, which has the same area as the, inlet, conduit and therefore offers no obstruction 'to the flow of the gas. There is a co-mingling of the volumes of gas of different pressures due to turbulence as the flow of gas is reversed in direction and a further co-mingling as the gas takes the form of an annular ring of the same area, but of thinner cross section, as it flows through the intermediate conduit. There is a further attenuating of the gas pressures as the direction of flow is changed from the intermediate conduit into the outer conduit. The gas now moves the length of the silencer and in doing so, the stream is in intimate contact with a relatively large surface of sound absorbing material. The gas stream is now quite thin in radial direction and is therefore less able to maintain any vibration in a radial direction, and any such vibration would be eliminated by the absorbing material. Ihis outer conduit also prevents any sound waves set up inside the silencer from reaching the casing, thus avoiding any vibration and resulting noise from this source. The gas stream is discharged from the outer conduit into the second intermediate conduit, and from this conduit it passes into the outlet conduit through which it is discharged from the silencer in a smooth even pressure stream.

For a better understanding of the nature of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings in which:

Fig. l is a plan view of the apparatus with sec tions broken away for the purpose of illustration;

Fig. 2 is a plan view in section along with center line of the apparatus;

Fig. 3 is a sectional view taken on line 3-3 of Fi 1;

Fig. 4 is a sectional view taken on line 4-4 of Fig. 1.

Referring to the drawings the silencer is disclosed in a vertical position and will be described in such a. position for the purpose of orientation, l

but it is to be understood that although the apparatus is disclosed and usually installed in this position it will function equally eflicient in any position. The silencer will be seen to comprise the casing 5 which is of generally cylindrical form, and which is formed by two chambers G and I. Chambers 6 and I are fabricated as separate units to facilitate manufacture, but are formed into a single unit by means of flanges 8 and secured together by bolts I0. Chamber 6 will be described as the intake section of the apparatus and chamber 1 will be described as the discharge section. The casing 5 is closed at the discharge end by an end plate II secured to the casing by means of a flange and bolts 26. Positioned above the end plate II is a flange plate i2, of smaller diameter, and plates II and 12 are spaced apart and held in position by a series of spacer plates I3 positioned 90 degrees apart. In a like manner the intake end of casing 5 is closed by an end plate I 4 secured to the casing by m ans of a flange 25 and bolts 28. Positioned below the plate I 4 is a flange plate I5 of a smaller diameter than plate I4, and plates I4 and I5 are spaced apart and held in position by a series of spacer plates I5 positioned 90 degrees apart. Plates I2 and I5 are used as a means of attaching the silencer into an exhaust system.

Each end plate and flange plate is provided with aligned openings through which is mounted an open ended conduit, the conduit terminating at one end flush with the flange plate and passing through the opening in the end plate to extend concentrically a substantial distance into the casing 5. The gas inlet conduit I7, secured to the end plate I4, is used as a means for conducting the gas stream into the casing 5; while the gas outlet conduit I8, secured to end plate II, is used as a means for conducting the gas stream from the inside of casing 5. The conduit I1 is provided at its discharge end with a series of inlet ports 30 spaced around the circumference of conduit I1 and divided into equal distance center lines along a portion of the length of the conduit. The total combined area of the inlet ports is equal, or substantially equal, to the area of the conduit II. In a like manner conduit I8 is provided with a series of inlet ports 3| at its discharge end positioned with the same spacing as is provided for conduit IT.

A first intermediate conduit I9 extends concentrically into the casing 5 externally of the gas inlet conduit I1, and is attached to the end plate M by means of bars 2|. The intermediate conduit I 9 is open at one end and closed at the other end by a conical plate 22 positioned opposite the inner open end of the gas inlet conduit [1. The annular, or effective cross-sectional area, of the first intermediate conduit is defined by the space between the outside of the gas inlet conduit I! and the inside of the intermediate conduit I9, and this effective cross-sectional area is equal, or substantially equal, to the inside cross-sectional area of the gas inlet conduit IT. In a like manner a second intermediate conduit 20 extends concentrically into the casing 5 externally of the gas outlet conduit I8 and has an effective cross-sectional area equal, or substantially equal, to the inside cross-sectional area of the gas outlet conduit. The second intermediate conduit 26, attached to the end plate I I by means of bars 23, is open at one end and closed at the other end by a partially conical plate 24, the closed end being positioned opposite the inner open end of the gas outlet conduit I8. The conduit I9 is provided at its discharge end with a, series of ports 32 spaced regularly around the circumference of the conduit and divided into equal distant center lines along a portion of the length of the conduit, the total combined cross sectional area of the inlet ports are equal, or substantially equal, to the cross-sectional area of the conduit I9. In a like manner conduit 20 is provided at its discharge end with a series of inlet ports 33 positioned with the same spacing as is provided for conduit I 9.

An acoustic outer conduit is formed by two porous walls 2'! and 28 spaced apart by a blanket of sound absorbing material 29, such as fiber glass. This outer conduit extends the entire length of easing 5 and has an outer diameter slightly less than the inside diameter of the casing 5. The acoustic outer conduit is comprised of two units, outer conduit 35 positioned inside chamber 6 and outer conduit 36 positioned inside chamber I. The inside diameter of conduit 35 is of such dimension that the effective area, that is the area defined by the space between the outside of conduit I9 and the inside Walls 28 of the conduit 35, is equal, or substantially equal, to the eifective area of the conduit l9. This dimension relationship also applies to the conduit 36 with respect to the conduit 20. As stated before, this apparatus is usually installed in a vertical position and may be outside of any weather shelter. In the event that there is an installation without any shelter, there is a probability that rain or other forms of moisture will enter the apparatus. To overcome this, a drain 34 has been provided atthe bottom of conduit 20 to permit any accumulated moisture entering the conduit [8 to be removed;

In the. operation of the silencer, compressed gas, delivered: by a blower into the exhaust system, enters the silencer through the inlet conduit il in: the form of a. gasstream comprised of a series of separate gas slugs, or volumes of gas, at arelatively high pressure separated by volumes of gas at a. relatively low pressure. separate slugs of gas'move through the inlet conduit with: an inertia sufficiently high. to carry:

them rapidlypast the ports 30 spaced around the circumference of the inner end of the conduit I? and to' discharge them into the'closed end section of the firs ntermediateconduit l9. stream, entering the closed end section of the first intermediate conduit, strikes a cushion of air pocketedv in the conical plate 22. This cushion of air is maintained in the closed end section of the first intermediateconduit at all times because of the conical shape of plate 22,. and acts as a sound absorber by preventing the separate slugs of gas from. striking the'plate 22 with full force.

The gas stream, after striking the air cushion, is reversed in direction and starts: toward the open end of the first intermediate conduit [9, which by design has the same, or substantially the same, effective cross sectional area as that of the inlet conduit, and therefore offers no increased resistance to theiflow of the gas stream. There is a turbulence in the gas stream as the direction of flow is reversed, and this turbulence will cause a partial equalization of pressures. This equalization. is brought about by the comingling of the high pressure volumes with the low pressure volumes wherein the high pressures will be reducediby expanding into the lower pressures, and: the low pressures will be increased. This means that equalization of pressures is prevalent' throughout. the silencer wherever the direction of now of a gas stream is reversed. The turbulence of. the gas stream is still present as the gas moves toward the open end of the first intermediate conduit and past the ports 30 of the inlet conduit. This turbulence will cause some of the high pressure volumes, as well as the low pressure volumes now at a higher pressure, to flow through the ports 30 and expand into the low pressure volumes flowing past in the inlet conduit.

The gas stream, now in the form of a series of annular slugs, continues through the first intermediate conduit to the open end of the conduit where its inertia carries it past the ports 32 into a chamber formed by the closed end of the outer conduit 35. The gas stream strikes a cushion of air containedin the closed end of the outer conduit and is againprevented from striking an element of the silencer with full momentum as its direction of how is reversed. A second turbulence is created by the reverse flow of the gas stream into the outer conduit resulting in a further co-mingling of the separate volumes and an equalizing of pressures in addition to a further equalized pressures In flowing through. the outer conduit the gas stream is in intimate contact. with a. relatively These- The gaslarge surface of sound absorbing material; The

stream isnow quitethin radially'andthereforeless able to maintain any vibration in a radial. direction, and any such vibration is eliminated by the absorbing material; This sound absorbingmaterial is by design thick enough to absorb any additional. sound waves that may exist due to the intermittent. pulsating'action of the blower impellers andby'the vibrations set up by the-turgas making up the gas stream, and a bypassing or" a portion of the gas stream from. the second intermediate conduit through the ports 33 into theouterconduit, as describedfor other sections of the silencer. The gas stream flows through the conduit 29 where it strikes the partial conical plate 24-, which'by design ofiers a minimum resistance'to the flow of. the gas as it changes direc tion to flow into the outlet conduit H3. The convex shape of the conical plate 24 serves to facilitate the reversal of the annular how at this point and the conversion of the annular ring of gas back into a single uniform cross sectional conduit. This is a desirable feature as the separate volumes of gas are now at a uniform pressure and. have the characteristics of a constant pressurestrcam of gas and should be exhausted from the silencer through the outlet conduit IS with. a minimum amount of turbulence.

In the design of this silencer all crosssectional. areas of flow are kept equal, or substantially equal,.which results inthe velocity of the gas stream remaining constant and the only change taking place being that of. pressure equalization of the separate volumes of gas within the gas stream. This design of the silencer also furnishes a. means for creating a concentric flow of gasthrough the apparatus which progressively becomes thinner in radial cross section, and therefore more responsive. to. pressure equalization, until it reaches its thinnest cross sectional area. where. it has its greatest areaexposecl to and. in intimate contact with, a sound absorbing material.

I claim:

1. A. silencer comprising a substantially cylindrical housing having an intake end and a. discharge end, an open ended gas inlet conduit positioned in the housing intake end. and extending concentrically a substantial distance therein, the inlet conduit having a'series of gas ports positioned around. its circumference and spaced along a portion of the lengthof its inner end, an open ended gas outlet conduit positioned in the housing discharge end and extending concentrically a substantial distance therein, the outlet conduit having a series of gas ports pcsitioned around its circumference and spaced along a portion of the length from its inner end, a first intermediate conduit having one end opened and one end closed positioned concentrically and externally along a substantial. por-- tion of the" inlet conduit, the closed end of the first" intermediate conduit being positioned inwardly' from the inner end of the inlet conduit; theaopenzend of the firstiintermediate conduit being positioned inwardly from the intake end of the housing, the first intermediate conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length from its open end, a second intermediate conduit having one end open and one end closed positioned concentrically and externally along a substantial portion of the outlet conduit, the closed end of the second intermediate conduit being positioned inwardly from the inner end of the outlet conduit, the opened end of the second intermediate conduit being positioned inwardly from the discharge end of the housing, the second intermediate conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length from its open end, and an outer conduit formed of sound absorbing material positioned concentrically about and spaced from the two intermediate conduits and extending substantially the length of the housing, the outer conduit forming an annular space about the two intermediate conduits which provides a means of communication between the open ends of the two intermediate conduits.

2. A silencer comprising a substantially cylindrical housing having an intake end and a discharge end, an open ended gas inlet conduit positioned in the housing intake end and extending concentrically a substantial distance therein, an open ended gas outlet conduit positioned in the housing discharge end and extending concentrically a substantial distance therein, the cross-sectional area of the gas inlet conduit being substantially equal to the cross-sectional area of the gas outlet conduit, a first intermediate conduit having one end open and one end closed positioned concentrically and externally along a substantial portion of the inlet conduit, the effective cross-sectional area of the first intermediate conduit where it extends along the inlet conduit being substantially the same as the cross-sectional area of the inlet conduit, the closed end of the first intermediate conduit being positioned inwardly from the inner end of the inlet conduit, a second intermediate conduit having one end open and one end closed positioned concentrically and externally along a substantial portion of the outlet conduit, the effective cross-sectional area of the second intermediate conduit where it extends along the outlet conduit being substantially the same as the cross-sectional area of the outlet conduit, the closed end of the second intermediate conduit being positioned inwardly from the inner end of the outlet conduit, and an outer conduit positioned concentrically about and spaced from the two intermediate conduits and extending substantially the length of the housing, the efiective cross-sectional area of the outer conduit where it extends along the intermediate conduits being substantially the same as the effective cross-sectional area of either of the two intermediate conduits, the outer conduit forming an annular space about the two intermediate conduits which provides a means of communication between the open ends of the two intermediate conduits.

3. A silencer comprising a substantially cylindrical housing having an intake end and a discharge end, an open ended gas inlet conduit positioned in the housing intake end and extending concentrically a substantial distance therein, the inlet conduit having a series of gas ports positioned around its circumference and spaced along a portion ofv the length thereof from its inner end, the combined cross-sectional areas of the series of ports being substantially equal to the cross-sectional area of the gas inlet conduit, an open ended gas outlet conduit positioned in the housing discharge end and extending concentrically a substantial distance therein, the outlet conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length thereof from its inner end, the combined cross-sectional areas of the series of ports of the outlet conduit being substantially equal to the cross-sectional area of the gas outlet conduit, a first intermediate conduit having one end open and one end closed positioned concentrically and externally along a substantial portion of the inlet conduit, the closed end of the first intermediate conduit being positioned inwardly from the inner end of the inlet conduit, the open end of the first intermediate conduit being positioned inwardly from the intake end of the housing, the first intermediate conduit having a. series or" gas port positioned around its circumference and spaced along a portion of the length from its open end, the combined crosssectional areas of the series of ports of the first intermediate conduit being substantially equal to the enective cross-sectional area of the first intermediate conduit where it extend along the inlet conduit, a second intermediate conduit having one end open and one end closed positioned concentrically and externally along a substantial portion of the outlet conduit, the closed end of the second intermediate conduit being positioned inwardly from the inner end of the outlet conduit, the open end of the second intermediate conduit being positioned inwardly from the discharge end of the housing, the second intermediate conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length from its open end, the combined cross-sectional areas of the series of ports of the second intermediate conduit being substantially equal to the effective cross-sectional area of the second intermediate conduit where it extends along the outlet conduit, and an outer conduit formed of sound absorbing material positioned concentrically about and spaced from the two intermediate conduits and extending substantially the length of the housing, the outer conduit forming an annular space about the two intermediate conduits which provides a means of communication between the open ends of the two intermediate conduits.

4. A silencer comprising a substantially cylindrical housing having an inlet end and a discharge end, an open ended gas inlet conduit positioned in the housing intake end and extending concentricall a substantial distance therein, the inlet conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length of its inner end, the combined cross-sectional areas of the series of ports being substantially equal to the cross-sectional area of the gas inlet conduit, an open ended gas outlet conduit positioned in the housing discharge end and extending concentrically a substantial distance therein, the outlet conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length from its inner end, the combined crosssectional areas of the series of ports of the gas outlet conduit being substantially equal to the cross-sectional area of the gas outlet conduit, the cross-sectional area of the gas inlet conduit being substantially equal to the cross-sectional area of the gas outlet conduit, 2. first intermediate conduit having one and open and one end closed positioned concentrically and externally about a substantial portion of the inlet conduit, the closed end of the first intermediate conduit being positioned inwardly from the inner end of the inlet conduit, the open end of the first intermediate conduit being positioned inwardly from the intake end of the housing, the first intermediate conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length from its open end, the combined cross-sectional areas of the series of ports of the first intermediate conduit being substan tially equal to the eiiective cross-sectional area of the first intermediate conduit, the effective cross-sectional area of the first intermediate conduit Where it extends along the inlet conduit being substantially the same as the cross-sectional area of the inlet conduit, a second intermediate conduit having one end open and one end closed positioned concentrically and externally about a substantial portion of the outlet conduit, the closed end of the second intermediate conduit being positioned inwardly from the inner end of the outlet conduit, the open end of the second intermediate conduit being positioned inwardly from the discharge end. of the housing, the second intermediate conduit having a series of gas ports positioned around its circumference and spaced along a portion of the length from its open end, the combined cross-sectional areas of the series of ports of the second intermediate conduit being substantially equal to the eifective cross-sectional area of the second intermediate conduit, the effective cross-sectional area of the second intermediate conduit where it extends along the outlet conduit being substantially the same as the cross-sectional area of the outlet conduit, and an outer conduit formed of sound absorbing material positioned concentrically about and spaced from the two intermediate conduits and extending substantially the length of the housing, the efiective area of the outer conduit where it extends along the intermediate conduits being substantially the same as the effective area of either of the two intermediate conduits where they extend along the inlet and outlet conduits, the outer conduit forming an annular space about the two intermediate conduits which provides a means of communication between the open ends of the two intermediate conduits.

5. The silencer defined in claim 4 wherein the closed end of the first intermediate conduit is a plate having a concave shape with respect to the inner end of the inlet conduit, and the closed end of the second intermediate conduit is a plate of convex shape with respect to the inner end of the outlet conduit.

6. The silencer defined in claim 4 wherein the closed end of the first intermediate conduit is a plate having a concave conical shape with respect to the inner end of the inlet conduit, and the closed end of the second intermediate conduit is a plate having a convex partially conical shape with respect to the inner end of the outlet conduit.

7. The silencer defined in claim 6 wherein the second intermediate conduit is provided with means for removing accumulated condensate.

8. The silencer defined in claim 1 in which the gas ports in the intermediate conduits are positioned axially outwardly substantially from the inner end of the series of gas ports in the inlet and outlet conduits, respectively.

JOSEPH B. GAF'FNEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,051,130 Lattime Jan. 21, 1913 1,057,485 Knollmann Apr. 1, 1913 1,115,873 Spencer Nov. 3, 1914 1,553,264 Reasonover Sept. 8, 1925 1,772,589 Beamer Aug. 12, 1930 1,966,620 Flour July 17, 1934 2,455,965 Wohlberg Dec. 14, 1948 FOREIGN PATENTS Number Country Date 461,065 Great Britain Feb. 9, 1937 593,282 Great Britain Oct. 13, 1947