Classifying Muffler

Abstract

Muffler for classifying and separating entrained oil and water from exhaust air of pneumatic devices. Exhaust air is led into a relatively unrestricted expansion chamber and passes into a silencing chamber through a collector against which droplets of entrained liquid and condensed vapors impinge. The relatively liquid-free air is diffused through the porous side of the silencing chamber. Impinged droplets collect to allow liquid to fall to base of silencing chamber in drops sufficiently large to prevent re-entrainment. Base of silencing chamber provided with means to permit draining, which may be automatic.

Description

This invention relates to improvement in mufflers for silencing the exhausts of pneumatically operated tools and equipment and, more particularly, to means which, on the one hand, diminish the hazards to health inherent in the frequently unpleasant working conditions where such tools are employed and, on the other hand, prolong the life of such mufflers and increase the efficiency of pneumatically operated devices. These results are obtained by classifying and separating, prior to final silenced dissemination of the exhaust air to the ambient atmosphere, various vapors and droplets of liquid characteristically entrained in the air entering the muffler.

Pneumatic tools, such as drills, grinders, hammers, wrenches, screw-drivers, etc.; pneumatic equipment such as cylinders, brakes, clutches, etc.; and other pneumatic devices, such as valves, operated by compressed air nearly always require some sort of muffler or silencer for quieting the shrill exhaust noise which would otherwise be intolerable. Such exhaust noise may otherwise vary from a relatively continuous scream, in the case of relatively constantly operated tools and motors to sharp, startling reports, in the case of intermittently operated clutches, brakes, cylinders, valves, etc. In theory such exhaust air should be relatively free of contaminants such as dust and liquid particles; the air is usually filtered as it enters the compressors and, after the air is compressed, efficient in-line filters, equipped with collecting bowls and automatic emptying valves, are normally installed in the high-pressure air line between the compressors and the pneumatically operated means. In actual practice, however, the exhausted compressed air contains moisture resulting from vapor which remains in the air throughout its travel from the entrance of the compressor to its exhaust and both the compressors and the pneumatically operated devices must be well lubricated. Thus, very fine droplets and vapors of lubricants become entrained with droplets of moisture in the exhaust air.

Unless removed by the exhaust silencing means, the presence of entrained lubricants and like contaminants in the exhausts of pneumatic devices may create working conditions that are unpleasant to many and a definite health hazard to some operators. The mixture of moisture and lubricant in the exhausts to ambient atmosphere in a plant leave a noticeable rancid or fetid odor which is objectionable to many operators; even in plants which are well-ventilated and air-conditioned, pneumatic tools can create a noticeable haze in the area of use. Some workers have or develop allergic responses to such contaminated air.

Aside from the threat to the health and comfort of operators, another problem created by the contaminants in the exhausts of pneumatic devices arises from the fact that efficient sound mufflers depend at least in part upon diffusion of the exhaust through porous accoustical elements (which may vary from perforated metal and screens to loosely felted or packed fibrous or granular material or porous sintered metal or ceramic materials or various combinations). The tortuous passages and interstices of these porous elements become clogged, and often relatively rapidly, with the entrained contaminants which may form gums and gels in the passages. Such clogging of the accoustical elements can create back-pressures which interfere with the efficiency of the pneumatic devices, particularly valves, brakes, and clutches whose effective operation may depend on instantaneous exhaust of the operating air. In any given muffler the rate of clogging and the consequent build-up of back-pressures beyond tolerable limits is relatively unpredictable; heretofore the only cure for the problem was a maintenance program requiring frequent changes of the mufflers or at least their accoustical elements regardless of whether a change was actually needed or not.

It is an object of this invention to provide an accoustical muffler which is provided with means to classify and separate from the exhausts of pneumatic devices the entrained moisture and lubricants in liquid form and to cause or allow the separate discharge of such liquid. The effective life of the accoustical element is thereby greatly prolonged and the hazard to health and pleasant working conditions is greatly increased. Other and further objects and advantages of this invention will be apparent from the following specification, claims and drawings, in which:

FIG. 1 is a top plan view of an embodiment of this invention.

FIG. 2 is a vertical cross-section through the line 2--2 of FIG. 1.

FIG. 3 is an enlarged fragmentary view, partly in section, of the collector shown in FIG. 2.

Referring to the drawings, the muffler is comprised of a top cap member 10 having a central internally threaded boss 11 provided with nut faces permitting the muffler to be connected to the exhaust pipe or fitting of a pneumatic device. The cap 10 has a peripheral internal flange 12 providing a seat for the body 20. The seat of the flange 12 is axially spaced from the boss 11 by the wall 14 to provide a dome-shaped expansion chamber 15, having a pair of small internal bosses 16 tapped to receive the tie-bolts 17.

The body 20 comprises a cylindrical wall 21 constituting the porous accoustical element of the muffler; in this instance, the wall 21 is comprised of loosely felted cellulosic fibers bonded together to the extent necessary for mechanical strength by suitable resinous binders. To protect the relatively soft and highly porous wall 21 and provide strength for the axial compression load imposed by the tie-bolts 17, an outer covering of perforated metal or screen 22 is provided. The thickness of the wall 21 should be sufficient so that, as the exhaust air escapes through the tortuous passages provided by the wall 21, its energy is dissipated and thus its noise is reduced to the noise level or less of the ambient noise at the site of the muffler. The length and diameter of the silencing chamber 23 thus provided by the body 20 depends upon the porosity of the wall material 21 and should provide an area for escape of the exhaust air whereby the pressure differential between the chamber 23 and the ambient atmosphere will create a minimal back-pressure well below that tolerated by the equipment to which the muffler is connected.

Extended into the chamber 23 is a collector 24 comprised of a downwardly extending frustro-conical metal collector shell having an upper peripheral outwardly extending flange 25 engaged between the flange 12 and the upper edge of the body 20 to support the collector 24 within the silencing chamber 23, allowing the domed expansion chamber 15 to open into the collector. The lower open end 26 of the collector 23 has a diameter at least equal to the bore of the boss 11 so that there will be no significant restriction on the air leaving the collector sufficient to create a consequent pressure differential between the exhaust air as it enters the domed expansion chamber 15 and as it enters the chamber 23 from the end 26; in the preferred construction shown, the cross-sectional area of the opening 26 is substantially greater than the area of the bore of the pipe to which the muffler is connected so that there will necessarily be a drop in the static pressure and velocity of the air leaving through the opening 26 from the pressure and velocity of the air as it enters the domed expansion chamber 15. In the preferred construction of the shell 24, the opening 26 is defined by an inwardly extending flange 27 provided on its inner edge with drop-forming dimples 28. To allow the tie-bolts 17 to pass through the collector 24, it and its flange 25 are drilled or provided with slots 29 on opposite sides of the collector.

The silencing chamber 23 may be closed by a base 30 which is preferably an inverted substantial duplicate of the cap 10. That is, it is provided with a central internally threaded boss 31 and a circumferential internal flange 32 providing a seat for the body 20, the flange 32 and boss 31 being axially spaced and connected by a wall 34 to provide a sump 35. The base is preferably completed by a baffle plate 37 held between seats of the flange 32 and the lower end of the body 20 to partly close off the lower end of the silencing chamber 23. In this particular embodiment, the baffle plate 37 is a disk of perforated metal, but may be of screening or other porous material, such as sintered metal, which will allow liquid dropping from the collector 24 to pass into the sump 35 but impede the turbulence of the air escaping through the opening 26 of the collector to minimize any re-entrainment of the liquid by such air so as to carry it to the porous wall 21. The base 30 is provided with a pair of small internal bosses 36 similar to the bosses 16 but drilled to receive the tie-bolts 17 by which the muffler cap 10, body 20, and base 30 may be assembled and disassembled to allow eventual replacement of the wall 21 of accoustical material.

Various means for the necessary draining of the sump 35 may be employed, depending upon the maintenance requirements and program of the user. If the general working conditions are such that optimum noise reduction is not required and slow but a relatively continuous drip from the muffler can be tolerated, the simplest expedient is to simply leave the boss 31 open so that the separated liquid can drop to a receptacle as it flows from the sump; as discovered in connection with the Fail-safe Muffler disclosed in my copending application, Ser. No. 175,175, filed Aug. 26, 1971, (now U.S. Pat. No. 3,688,868) it is not necessary for substantial, though less than optimum, noise reduction to completely close off the silencing chamber 25; rather, so long as the porous material of the wall 21 is relatively unclogged, a baffle plate, such as the plate 37, and an open base, such as the base 30, will produce such substantial noise reduction. If continuous dripping from the sump 35 can be tolerated but optimum noise reduction is desired, the boss 31 may be closed by a conventional "breather" plug having a center section of porous sintered metal through which the accumulated liquid can drain. The pores of the sintered metal in such a breather plug will eventually clog and need to be replaced or cleaned, but only at relatively infrequent intervals.

If optimum noise reduction is desired but continuous drainage of the odorous liquid from the muffler is undesirable, the automatic discharge means shown in FIG. 2 may be employed. That is, a length of accumulator tube or pipe 40 is threaded into the boss 31, the lower end of the tube 40 being closed by a cap 41. The longer leg of an inverted U-shaped siphon tube 42 extends through the cap 41, its shorter leg ending above the inside of the cap. Separated liquid from the sump 35 accumulates in the tube 40 until its level rises to the upper end of the siphon. Aided slightly by the small static pressure differential between the silencing chamber 23 and the ambient atmosphere, gravity then starts the flow through siphon 42 to quickly empty the liquid in the accumulator tube 40 into a suitable receptacle or the like placed below it. The siphon tube 42 and cap 41 shown in FIG. 2 may, of course, be omitted and replaced by a conventional pipe cap; in such case the accumulator tube will require emptying at scheduled periods unless a small drain hole is drilled through the upper end of the accumulator so that dripping from it signals the need for emptying the accumulator. If either alternative of the above described accumulator tube is employed, the baffle 37 becomes relatively superfluous and may be omitted; the velocity of the portion of the air from the collector opening 27 which can enter the tube 38 is baffled by the opening in the boss 31 and by the tube; any drops which may then fall directly to the floor of the sump 35 will tend to drain into the tube 38 rather than be re-entrained by air which is directed by the sump to its escape through the wall 21.

Irrespective of the various available means which may be employed for the necessary drainage of the sump 35, the key to the operation of a muffler made according to the invention lies in the collector means exemplified by the collector 24. Air enters the expansion dome 15 with substantial kinetic energy. As such air rapidly expands in the dome and its extension provided by the collector 24, the majority of it loses its velocity and capacity for entraining liquid droplets while striking the converging internal surface of the collector, which surface is configured so as to have a substantial component perpendicular to the flow of the incident expanding air and to reflect such impinged air downwardly toward the collector opening 26. Droplets of moisture and lubricant are either entrained in the exhaust as it enters the dome 15 or are formed by the rapid cooling of the vapors in the exhaust as it expands upon discharge from the line to which the boss 11 is connected; such droplets tend to adhere to the wall of the collector as the exhaust impinges upon it. As shown in FIG. 3, these adhered droplets then drain down the steep internal surface of the collector 24, merging into larger droplets as they approach and collect on the lower flange 27 of the collector 24. The ring of liquid which then collects on the flange 27 is drained in large drops by gravity and the flow of air through the opening 26; these drops being of sufficient mass to minimize re-entrainment by the exhaust air as it re-expands into the silencing chamber 25. The dimples or ruffles 28 in the inner edge of the flange 27 aid in the formation of such relatively massive drops which fall to the baffle 37 or directly onto the floor of the sump 35.

The stripping of entrained moisture and lubricant from the exhaust entering the dome 15 is by no means totally complete, but the substantial amount separated greatly reduces the rate of clogging of the porous wall 21 and allows that wall to function longer as an effective further filter of the exhaust dissipated through it.

This invention is not to be limited to the specific embodiment disclosed in the drawings and its modifications as described but may be further modified by those skilled in the art without departing from the scope defined in the appended claims.

Claims

What is claimed is:

1. A muffler for classifying and separating entrained liquid from a pneumatic exhaust before dissipation of the exhaust to ambient atomosphere comprising a top member adapted to be connected to the exhaust outlet of a pneumatic device and provided with an inlet for introducing exhaust air into said muffler, a bottom member having a drain opening through which separated liquid may be drained, a vertically-extending porous wall between said top member and bottom member to define an internal silencing chamber, said wall comprising sound-deadening acoustical material providing tortuous passages through which said exhaust air may dissipate at a velocity substantially less than that at which the exhaust enters said muffler and the entrance of said drain opening through said bottom member being located inwardly of said wall, and a collector mounted within said muffler to define an expansion chamber which extends from said top member into said silencing chamber, said collector having an internal frusto-conical surface converging toward a lower opening larger than the inlet in said top member and spaced from said bottom member to permit a pressure drop from said inlet to said lower collector opening and the expansion of air within said expansion chamber, said collector surface being positioned with respect to the direction of flow of a majority of said expanding air so as to be impinged upon thereby at an angle having a substantial component perpendicular to said surface to reflect such impinging air downwardly through the lower opening of said collector so that substantially all air leaving said expansion chamber is directed toward said bottom member, whereby droplets of liquid entrained in said air as it impinges upon said collector surface will collect thereon to then drain through said lower collector opening and drop through said silencing chamber to said bottom member in substantially reentrainment-inhibiting drops.

2. A muffler as defined in claim 1 wherein said lower opening in said collector is defined by an inwardly extending flange upon which said droplets may collect prior to dropping through said silencing chamber to said bottom member.

3. A muffler as defined in claim 2 in which said collector has an internal frusto-conical surface converging toward said lower opening, said surface being positioned with respect to the direction of flow of a majority of said expanding air so as to be impinged upon thereby at an angle having a substantial component perpendicular to said surface and to reflect such impinging air downwardly toward said lower opening.

4. A muffler as defined in claim 2 in which the inner edge of said flange on said lower opening is provided with irregularities to aid in the formation of drops of liquid flowing from the flange which are of sufficient mass to allow such drops to fall through the air in said silencing chamber to said bottom member without substantial re-entrainment as said air re-expands from said lower opening into said silencing chamber.

5. A muffler as defined in claim 2 in which said bottom member is depressed below said porous wall to provide a sump for receiving drops from the lower opening of said collector for flow to the drain opening therein.

6. A muffler as defined in claim 5 including baffle means over said sump to permit liquid from said lower opening of said collector to drain through to said sump but to impede the flow of air into and out of said sump.

7. A muffler as defined in claim 6 including porous means in the drain opening of said sump to allow liquid to drain therethrough but closing the interior of said silencing chamber from direct access to the ambient atmosphere.

8. A muffler as defined in claim 5 in which the drain opening of said sump is connected to a removable receptacle for accumulating the drainage of said sump and means therein for signalling the accumulation of sufficient drainage to require removal and emptying of said accumulator receptacle.

9. A muffler as defined in claim 5 in which the drain opening of said sump is connected to a receptacle for accumulating drainage from said sump and automatic means for emptying the accumulator receptacle of drainage therein.

10. A muffler as defined in claim 9 in which said automatic means comprises an inverted U-shaped siphon tube having a longer downward leg extending through the bottom of said accumulator receptacle and a shorter upward leg having an opening terminating within the receptacle above the bottom thereof and the connection of the downward leg to the upward leg is at a height sufficient to provide a head above the opening in the shorter leg which is greater than the static pressure differential between the interior of the accumulator receptacle and the ambient atmosphere whereby, when said drainage accumulates in said receptacle to a level commencing to submerge said siphon tube, the accumulator receptacle is drained by gravity to the level of the opening of said shorter leg.