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jug? 3%; 1946“ PULSATION ‘F.ELIMINATION M. IN GAS LINES Filed Jan. 11, 1944 //4 .x- I30 gig. I I fiezw'lycr JZsrrae/(J?rzvrms INVENTOR. Patented July 30, 1946 2,405,100 k. . .. . UNITED STATES vPATENT OFFICE ‘ _ ’ 2,405,100 ‘ PULSATION ELIMINATION'IN GAS LINES Foster M. Stephens, Los Angeles, Calif., assignor to‘ The Fluor Corporation, Ltd., Los Angeles, Calif., a corporation of California Application January 11, 1944, Serial No. 517,857 12 Claims‘. (01. 230—236) I 1 This invention relates generally to the dampen ing or elimination of pressure pulsations in the compressible ?uid, and is concerned particularly with the problem of effectively eliminating the pressure pulsations created in gas lines connect ing with piston-type mechanisms, "especially gas compressors, because of the e?ects of the inter mittent gas displacements by the pistons. 2 to in order to eliminate as much line vibration as possible. The existence of pulsations in the gas line lead ing to or from the compressor frequently reduces to a considerable degree the operating efiiciency of the compressor. Where it is attempted to me ter the gas flow through the lines, pulsations in the gas stream may render the metering inaccu It is a matter of common experience in the rate, or impractical in instances Where the mag The present ral gas compressor plants and the connecting gas system obviates these difliculties by assuming operation and maintenance of , for example, natu- ‘ 10 nitude of the pulsations is great. smooth ?ow promotive of high volumetric com pressor efficiency and of a steady gas flow sus the compressor operations frequently assume such ceptible of accurate metering. magnitude as to set up vibratory movements 01' Most efficient operation of the apparatus re the pipe excessive to the extent of endangering 15 quires maintenance of certain size relationships the necessary strength of the pipes and joints, between the pair of chambers and the intercon and, rendering it most difficult to anchor and necting passage. The method of determining properly maintain the lines in place. Insofar as such relationships may be explained to best ad I am aware, no satisfactory solution heretofore has been available, of the problem of obviating 20 vantage during the course of the following and further detailed description of the invention, and such conditions whatever may be such factors as by reference to the accompanying drawing, in the gas pressure, compressor displacement, and which: the frequencies of the vibrations or pressure pul Fig. 1 is a diagrammatic View of the pulsa sations. It has been proposed, and attempted with vary 25 tion eliminating system and connected compres sor; and ing degrees of success, to dampen out pulsations Fig. 2 is a graph illustrative of the transmission in the gas stream, by installing a. single relatively and frequency absorption characteristics of the large chamber in the offending line. with the idea pipe lines, that pulsations created in the lines by of providing a zone of sufhcient volume for dissi pation of the pressure impulses. Under ideal 30 conditions, this proposal has served the purpose, but most generally it has been found to be unsuit system. The gas compressor, diagrammatically indi cated at I, may in practice be one or more of any of the usual piston-type compressors em ployed in gas compressor plants. Such compres able for various reasons,among which is the sors may be single or multi-cylinder and may necessity of using a chamber of such large size be single-acting or double-acting. A given com as to be impracticable. pressor will operate to produce pulsations in a The invention affords a simple, effective and connecting gas line at What may be referred to as thoroughly practical solution, and is character the fundamental frequency of the compressor. ized by the fact that it is capable of being pre In the case of a single-acting compressor, this designed to meet any of various conditions that may exist in different situations giving rise to 4.0 fundamental frequency will correspond to the compressor R. P. M., and in the case of a double the necessity for pulsation elimination. Gener acting compressor, the fundamental frequency ally speaking, the present system involves the use will of course be twice the compressor R. P. M. of a pair of chambers in the nature of acoustical The gas is discharged by the compressor through capacitances adapted to be connected into the line H containing the chambers and intercon pipe line, and of su?iciently small size as to ob- . necting passage, as will appear. It Will be under viate the above mentioned limitations of single stood that where pulsations are to be eliminated chamber installations. This pair of chambers is at the intake side of the compressor, line H may interconnected by one- or more relatively re be regarded as the inlet pipe carrying gas ?ow stricted passages serving in the nature of an ing through the chambers to the compressor. acoustical inductance, all in a manner such that Under the assumed conditions, gas having pul the gas stream flows from the line into one cham sating flow is discharged through line H into an ber, then through said passage and into the other enlarged zone or chamber [2 from which the gas flows through pipe it into a second chamber it, Since the line pulsations may occur at either or both the gas intake or discharge sides of the com 55 which preferably has substantially the same vol ume as chamber i2. Leaving chamber Hi, the pressor, it will be understood that the present gas passes into the continuance of the main line apparatus may be installed in the gas lines at H in a condition of substantially uniform or either or both of such locations. Also the instal chamber. lation may be at any desired proximity to the non-pulsating ?ow. Preferably the pipe connec compressor, though usually somewhat close there 60 tions “with chambers 12 and M are arranged to 2,405,100 3 A prevent straight-line flow of the gas through the chambers. Typically, lines H and I3 may have S6" connections with chamber l2, as illustrated, wherein pulsation transmission is plotted against frequency Of the pulsations, the fundamental frequency may be assumed to have the magnitude indicated at “F.” For purposes of calculation and design, it is only necessary to locate the cut off frequency of the apparatus to the left of this fundamental compressor frequency, and then the fundamental, as well as its harmonics, will not and the outlet end H'la of pipe [3 may be extended down into the chamber ill so that the gas reverses. its flow in passing to the line H. At this point it may be. observed‘ that the lengths of all L’s used in the chamber inter connecting pipe 13 are added in making- tih? _ hereinafter explained calculations, as equivalent be, transmitted down-stream in the line i l. ' lengths of straight pipe. The overall length of the pipe [3 is measured between the actual ends Generally speaking, the Value for may be taken within the range of about 85% to 100%, or more strictly speaking, just less than the com pressor fundamental frequency. Where the com pressor is operable at variable frequencies, or speeds, the value for "F” preferably is selected to be just less than the lowest frequency. Satis~ factory results have been obtained at a value for below) is determined by subtracting the volume “F” corresponding to about 90% of the com of the pipe when extended within the chamber, pressor fundamental frequency, at which the from the volume otherwise of the chamber. substantially as As observed above, best results are obtained by 20 transmission-frequency curve shown in Fig. 2. It is to be noted that at the evaluating or pred'etermining the volumes of‘ the cut-off‘ point, i. e. 90% of “F,” the curve Il may chambers 12 and 1.4, and the dimensions’ of the have an abrupt or steep drop indicative of the interconnecting passage in pipe i3, with relation of the pipe even though one or both ends of the pipe may extend within one or both of the cham bers l2 or M, as the case may be. The net volume of the chamber (the value of “V” in the equation to particular conditions for which the installa tion is to be made. The basis for these deter- ~ minations is the following equation: L 02 Fix V_ 78.674172 whereinv L=the length in inches of the passage in pipe I3. Rv=radius in inches of that passage. V=thevolume in cubic inches of one of the equal volume chambers E2 or I4. 30 effectiveness of the higher frequency elimination. Having determined the value for “F,” it then remains necessary to evaluate the physical dimen sions of the chambers 12 and i4, and the inter connecting pipe I 3. The left-hand side of the equation, i. e. L EEXV de?nes the volume of each chamber and the length and inside radius of the connecting pipe l3. Accordingly it is Only necessary to determine C=net velocity, as de?ned below, in feet per 35 the value for ‘ C” in order to have an arithmetic minute of sound in the gas and of the gas value for the entire right-hand side of the equa stream in pipe I 3. tion. The value of- the velocity of sound in the F=fundamental frequency per second of‘ pulsa gas being compressed is first approximated from tions created in the gas line H by the com pressor and at the compressor outlet. 40 existing tables under standard conditions, and is then corrected for pressure and temperature con Relative to determination of the value of “C,” siderations to meet those conditions actually ex if the apparatus is installed at. the discharge isting at the location in the line I! where the side of the compressor, the value of “C” is the pulsation is to be arrested. velocity of the gas in line l3 plus the velocity While; the factor “78.6711” represents substan of sound in that gas. On the other hand, if the tially the value to. be used, it is stated in- a spe apparatus. isv installed at the suction or intake ci?c valuation to a particular unit and three side of the compressor, the value of "C” becomes decimal places, simply because its theoretical den the velocity of sound in the gas in line [3,, minus ivation gives that specific value. the. velocity of the gas flow in that line. Accord A value for ingly, the expression “net velocity” is understood to mean the velocity of sound in the gas,_ plus or minus the velocity of the gas in the line 13, depending upon whether the apparatus is in stalled respectively at the discharge or suction A R2 is arbitrarily taken to be as large as can be tol erated with regard to pressure loss in the line 13. sides of the compressor. Inasmuch as the velocity 55 In other words, knowing the gas pressure at cham of the gas is very low as compared with, the ber I2 and the rate of gas flow to occur through velocity of sound in the gas, it is apparent that line l3, the latter may arbitrarily be given length the velocity condition of importance is the ve and radial dimensions permitting passage of the locity of sound in the gas. To cite an example gas through the line Within a suitable or limiting of conditions encountered in practice Where 60 range of pressure drop. Having thus determined fairly high pressure gas is ?owing through an the values for "C” and eight inch line pipe, the velocity of sound in the 13. gas may be in order of 100,000, feet per minute, R2 or above, and the gas velocity around 300 to 400 feet per minute. Accordingly, the value of “C,” 65 the value of each chamber volume, or “V,” be whether or not the gas velocity is taken into comes directly determinable. It will be under account, represents substantially the velocity of stood of course that the determined value for “V” sound in the gas. is substantially a minimum value, and that the When a reciprocating compressor is a source chamber volume may be increased beyond that of pulsation, it is possible to determine the fun 70 value without impairing performance, although damental frequency (F) of the pulsations in in practice it is ordinarily desirable to make the accordance with the R. P. M. of the compressor, chamber of a size close to its calculated volume in as previously explained. All harmonics of this order to economize on materials and avoid unnec frequency naturally will be at a higher frequency essarily large equipment. With the volume of the than this fundamental. Referring to Fig. 2 chambers and the length and radius of the inter 2,405,100 connecting line thus established, it is only nec essary to interconnect the parts in a manner most feasible for the particular installation. Expe rience with diiferent installations indicates that in those instances it has been possible to keep 6 3. In combination with a gas compressor, ap paratus for dampening pulsations in a gas stream having pulsating ?ow created by the compressor, comprising a pair of relatively large pulsation absorbing chambers connected in series with the compressor, and means forming variable size rel atively restricted acoustical inductance passage one-fourth the Wave length of sound in the gas. means interconnecting said chambers. It may happen that in a given installation, the 4. In combination with a gas compressor, ap fundamental frequency of the compressor may be subject to variation, as where the compressor is 10 paratus for dampening pulsations in a gas stream having pulsating ?ow created‘ by the compressor, convertible for operation either as a single-acting comprising a pair of relatively large pulsation or double-acting type. In such situations, it may absorbing chambers connected in series with the be desirable to render the apparatus capable of compressor, a plurality of conduits interconnect effectively eliminating pulsations despite such variation of the fundamental compressor fre 15 ing said chambers and forming relatively re stricted acoustical inductance passages, and quency. Assuming, for example, the apparatus to means for selectively maintaining gas ?ow be designed for use in conjunction with a single through one or more of said conduits. acting compressor, conversion of the compressor 5. In combination with a gas compressor, ap operation to double-acting would of course result in an increased and excessive pressure drop in a 20 paratus for dampening pulsations in a gas stream having pulsating ?ow created by the compressor, single interconnecting line l3. Normally the ca comprising a pair of relatively large pulsation pacities of the chambers l2 and I4 would be ade absorbing chambers connected in series with the quate for effective pulsation dampening at the in compressor, a pair of conduits interconnecting creased rate of gas flow and at the changed fun damental compressor frequency, but a limitation 25 said chambers and forming relatively restricted acoustical inductance passages, and valve means would exist by reason of the restricted ?ow in at least one of said conduits. through a single line 13. It is apparent from the 6. In combination with a gas compressor, ap equation given above that when the frequency is paratus for dampening pulsations in a gas stream doubled upon change from single-acting to the length of the connecting pipe l3 well under double-acting compressor operation, and with the ‘‘ volumes of chambers l2 and I4 remaining the same, the value of L can be greatly reduced and proper pulsation elim- ' ination still obtained. Accordingly, to render the apparatus adaptable to pulsation elimination un der the changed condition, chambers I2 and I 4 having pulsating ?ow created by the compressor, comprising a pair of relatively large pulsation absorbing chambers connected in series with the compressor so that the gas ?ows through both chambers continuously and at a substantially constant rate, and means forming relatively re stricted acoustical inductance gas passage means may be interconnected by one or more additional pipes I5 containing a valve I6 which is closed under the ?rst described conditions of operation. When additional ?ow capacity then is needed un der the last assumed conditions of operation, valve Hi may be opened to permit gas ?ow through interconnecting said chambers. '7. In combination with a gas compressor, ap paratus for dampening pulsations in a gas stream having pulsating ?ow created by the compressor, comprising a pair of relatively large, substan tially equal volume pulsation absorbing chambers connected in series with the compressor so that the gas ?ows through both chambers continuous ly and at a substantially constant rate, and 45 line I5 and thereby add its ?ow capacity to that means forming relatively restricted acoustical of line I 3. inductance gas passage means interconnecting I claim: said chambers. 1. In combination with a gas compressor, ap 8. In combination with a gas compressor, ap paratus for dampening pulsations in a gas stream paratus for dampening pulsations in a gas stream 60 having pulsating flow created by the compressor, having pulsating ?ow created by the compressor, comprising a pair of relatively large pulsation comprising a pair of relatively large pulsation absorbing chambers having corresponding mini absorbing chambers connected in series with the mum. volumes as de?ned in the equation below compressor so that the gas flows through both and connected in series with the compressor, and chambers continuously and at a substantially a circular cross-section conduit forming an acous constant rate, means forming relatively re tical inductance passage interconnecting said stricted acoustical inductance gas passage means chambers, the volumes of said chambers and the interconnecting said chamber, and a valve in said dimensions of said passage having predetermined gas passage means, the volumes of said chambers values substantially in accordance with the fol 60 and the dimensions of said inductance passage lowing equation: L _ means being such as to cause substantial elimi cz nation in the gas ?owing therethrough of pres sure pulsations at the fundamental frequency created by the compressor. REX V_ substantially 7 8.674F’ wherein L=length of said passage in inches, R=radius of said passage in inches, 9. In combination with a gas compressor, ap \ V=minimum volume of each chamber in cubic inches, C=substantially the velocity in feet per minute of sound in the gas, F=a selected value for the fundamental fre quency per second of pulsations created in said gas stream by the compressor. 2. Apparatus as claimed in claim 1, in which “F” has a value within the range of. 85% to 100% To of said fundamental frequency. paratus for dampening pulsations in a gas stream having pulsating ?ow created by the compressor, comprising a pair of relatively large pulsation absorbing chambers connected in series with the compressor so that the gas ?ows through both chambers continuously and at a substantially constant rate, and means forming relatively re stricted acoustical inductance gas passage means interconnecting said chambers, the volumes of said chambers and the dimensions of said in 2,405,100 ‘7 ductance vpassage means ‘being such as to cause substantial elimination in the gas ?owing there through ‘of pressure pulsations at the funda mental frequency created by the compressor and ‘at the higher harmonics of that frequency. 10. The combination comprising a piston-type vcompressor, a pipe line connecting with the com pressor and within ‘which pressure pulsations are created in ages stream by the compressor opera tion, and a pair of relatively large pulsation ab sorbing chambers connected in series in said line so that the gas ?ows through both chambers continuously and at a substantially constant rate, 8 tinuously and at a substantially constant rate, and pipe means interconnecting said chambers and forming a relatively restricted acoustical in ductance passage means, the volumes of said chambers and the dimensions of said passage being predetermined to cause substantial elimi nation in ‘said gas stream of pressure pulsations in the frequency range of from about 85% to 100% of the fundamental frequency created by the compressor. 12. In combination ‘with a gas compressor, ap paratus for dampening pulsations in a gas stream having pulsating ?ow created by the compressor, and pipe ‘means interconnecting said chambers comprising a pair of relatively large pulsation and forming relatively restricted acoustical in- a: absorbing chambers connected in series with the ductance gas passage means, ‘the volumes of said compressor so that the gas flows through both chambers and the dimensions of said passage be chambers continuously and at a substantially ing predetermined to cause substantial elimina constant rate, and means forming relatively re~ tion in said gas stream of pressure pulsations at stricted acoustical inductance gas passage ‘means the fundamental frequency created by the com CO interconnecting said chambers, the volumes of pressor and at the higher harmonics of that fre said chambers and the dimensions of said induc quency. 11. The combination comprising a piston-type tance passage means being such as to cause ‘sub stantial elimination in the gas ?owing there compressor, a pipe line connecting with the com through of pressure pulsations in the frequency pressor and within which pressure pulsations are 25 range of from about 85% to 100% of the funda created in a gas stream by the compressor opera mental frequency created by the compressor and tion, a pair of relatively large pulsation absorb .ing chambers connected in series in said line so that the gas ?ows through both chambers con also at the higher harmonics at that frequency. FOSTER M. STEPHENS.