US2570241A - Pulsation dampener - Google Patents

Description

Oct. 9, 1951 u c so 2,570,241

PULSATION DAMPENER Filed Oct. s, 1948 3 Sheets-Sheet 1 FIG.|

FIG. 2

FIG. 3

INVENTOR. ARTHURJ.L. Hurc-HmsoN ATTORNEYS 1951 A. J. 1.. HUTCHINSON 2,

PULSATION DAMPENER Filed Oct. 9, 1948 3 Sheets-Sheet 2 5| FIG.4

FIG. 5

FIG.6

ATTO R NEYS O 9, 1951 A. J. L. HUTCHINSON 2,570,241

PULSATION DAMPENER Filed Oct. 9. 1948 3 Sheets-Sheet 5 INVENTOR A RTH U R J. L. 'Hu-rcumsou wfimrs.

ATORNEYS Patented Oct. 9, 1951 PULSATION DAMPENER Arthur J. L. Hutchinson, Houston, Tex., assignor to Fish Engineering Corporation,

Houston,

Tex., a corporation of Delaware Application October 9, 1948, Serial No. 53,725

8 Claims. 1

Thi invention relates to the control of pulsations in compressible fluids, and more particularly it relates to an improved form of the generally employed apparatus and method of pulsation control in which fluid flow characterized by pulsation effects therein is directed into acoustical capacitance chambers connected in combination with an acoustical inductance line. It can be specifically difierentiated from presently employed arrangements, such as disclosed in Patent No. 2,405,100 issued July 30, 1946, to Foster M. Stephens, in which acoustical capacitance chamber are connected with acoustical inductance lines in a manner that the flow of pulsating fluid passes in series from element to element, since the special benefits obtained by this invention are derived by connecting acoustical capacitance chambers and acoustical inductance lines in a manner to insure that at least part of the fluid flow therethrough passes back out of a capacitance chamber over the same path by which it enters.

The arrangement of directing fluids under pulsation into acoustical capacitance chambers in combination with acoustical inductance lines has been employed, for example, innatural gas compressor plants, both on the inlet side of the compressor in order to control pulsations in the flow which the compressor i taking from the supply header, and more generally on the discharge side of the compressor in order to control pulsations in the discharge line, the pulsation frequency in either case being a function of compressor R. P. M.

In general theory, fluid, as gas, under the impact of forces which are vibratory in character responsive to transmission cycles, is conducted into an acoustical chamber, and therein pressure is built up. The pulsation or pressure waves, which are impelled in cycles through the inlet to the chamber, pass therethrough at considerable velocity, with the consequence that the waves are of relatively large amplitude.

However, it can be seen that, as pressure builds up in the chamber, the pulsations therein will become more feeble, or of lesser amplitude. It then follows that, since the outlet from the capacitance chamber is of limited size, it will take a volume of gas at pulsation amplitudes which are a function of the size of the chamber.

An extreme condition may be considered wherein a chamber may be provided of such a large volume that the pulsations of the inrushing fluid will be substantially dampened out in amplitude by the expanse of the chamber, with the result that the fluid will depart from the chamber with a substantially steady, non-pulsating flow almost entirely responsive to the pressure built up Within the chamber rather than in response to the incoming pulsations. However, as such a large chamber would be an impractical installation, it has been found practicable to employ capacitance chambers Within the size limitations of the installation on which they are to be employed, with the result that a limited pulsation effect Will pass out from a first capacitance chamber into an acoustical inductance line to which it may be connected.

As the mass of a fluid, as a gas, is transferred into a line or pipe of considerable length, as compared to the diameter thereof, inertia to any change in the rate of flow is built up, so that the amplitude of pulsations therealong are dampened in response to this tendency of the pipe to pass therethrough a steady, rather than a pulsating flow of fluid. conceivably, a pipe of such length could be connected directly to a source of transmission of pulsating fluid, and at the end of the pipe the pulsations would be dampened to a negligible amplitude. However, such a length would be highly impracticable due to the practical necessity of substantially dampening pulsations in the pipes between pulsation source, asthe compressor, and the headers, which must run not too remotely in space from such source.

In view of the impracticability of excessively large volume chambers or of extremely long pipes, it has been found necessary to connect these two elements in combinations to obtain the dampening efiects essential to successful operation.

It i therefore an object of this invention to control pulsations in fluid systems by providing an arrangement of acoustical inductance lines and acoustical capacitance chambers which may variably require smaller capacitance "chambers, shorter inductance lines, or larger diameter inductance pipes. I

It is a further object of this invention t control pulsations in fluid systems by providing an arrangement of acoustical inductance lines and acoustical capacitance chambers characterized by the ease with which such elements may be installed on an existing fluid line subject to excessive fluid pulsations therein.

It is still a further object of this invention to controlpulsations in fluid systems by providing an arrangement of acoustical inductance lines and acoustical capacitance chambers connected in such a manner that at least part of the flow of fluid therethrough passes into and out of a capacitance chamber over the same path.

It is yet a further object of this invention to control pulsations in fluid systems by arrangements characterized by the fact that elements insuring that at least part of the pulsating fluid passes into and out of a capacitance chamber by the same path are also elements which add acoustical inductance to the system.

It is still another object of this invention to increase horsepower delivered by a compressor through providing a pulsation control system in which effective inductance may be increased per unit of pipe, so that under a given set of conditions, a shorter length or larger inner diameter of pipe will be required, with the result that pressure drop will be decreased through the system.

Other and further objects will be obvious when the specification is considered in connection with the drawings, in which like elements are given the same reference numeral in the several figures herein described:

'Fig. 1' shows diagrammatically an arrangement of pulsation control elements in which the compressor discharges into a chamber, and the inductance pipe has an outlet to a header.

"Fig. 2 shows diagrammatically a second arrangement of pulsation control elements in which the compressor discharges through part of the inductance passage. into a chamber, and the inductance has an outlet to a header.

Fig. 3 shows diagrammatically still a third arrangement of pulsation control elements in which the compressor discharges through part of the inductance passage into a chamber, and the other chamber is connected to a header.

Fig. 4 shows diagrammatically an arrangement of pulsation control elements in which a header feeds into a chamber, and the inductance pipe has an outlet to the compressor.

Fig. 5 shows diagrammatically an arrangement of pulsation control elements in which a header feeds through part of the inductance passage into a chamber, and the inductance pipe has an outlet to the compressor.

Fig. 6 shows diagrammatically an arrangement of pulsation control elements on the intake f side 'Of a compressor in which a header feeds through part of the inductance passage into a chamber, and the other chamber is connected to a compressor.

'-Fig. 7 shows the elements of Figs. 2 and 5 connected, respectively, to the discharge and intake side of a compressor in the manner in which they may be employed in practice.

Fig. 8 shows diagrammatically pulsation curves explanatory of the invention, the wave lengths thereof being greatly shortened for illustrative purposes.

In the diagram of Fig. 1 the compressor I, which may beeither a single acting or double acting compressor, discharges fluid, as natural gas, through the discharge line 2, and such fluid pulsates at the fundamental frequency of the compressor; such frequency being a function of the compressor R. P. M. The fluid discharged into the discharge line 2 passes therethrough at a relatively high velocity due to the impulse of ejection from the compressor, and passes into the inlet 4 of the acoustical capacitance chamber 3. The inertia of the fluid, as gas, carries it against the chamber bottom 5, and it rebounds therefrom and in doing so reacts against the successive incoming waves. The discharging of the compressor into the capacitance chamber 3 builds up pressure therein, and this forces the fluid out the side outlet 6 into the pipe 1. The waves rebound off the chamber bottom 5 theoretically 180 out of phase with the incoming waves, with the result that the resultant hypothetical wave which travels from the chamber bottom 5 to the side outlet 6 is further considerably attenuated since this resultant wave is of the difference in amplitude between incoming and rebounding wave amplitudes.

In practice the pipe 1 is of a length necessary to carry the compressed fluid from the compressor to return header location, and is of comparatively small cross-sectional area as compared to the cross-sectional area of the chamber 3. The mass of gas, which flows from the side outlet 6 into this pipe 1, resists any change in the rate of flow therethrough, due to its inertia, and as a consequence the amplitude of the pressure wave passing through the pipe 1 is further attenuated.

From the pipe 1 the waves pass through the straight section 9 of the T 8 and into the inlet I2 of the second capacitance chamber II, to rebound off of the end l4 thereof. The same effeet then occurs as has been described as occurring in chamber 3, that is, the rebounding wave amplitude is subtracted from the incoming wave amplitude, with the consequence that the resultant wave which passes back out through the leg l5 of the T 8 has undergone substantially further attenuation to the extent that practically all pulsations have been dampened out of the fluid which passes out the connection pipe [6 to the return header, not shown.

In the arrangement of Fig. 2, the T H is inserted in the discharge line 2 between compressor and capacitance chamber, with the result that 5 the waves rebounding off of the chamber bottom 5 react against the incoming waves, not only within the capacitance chamber 3 but in the inlet 4 thereof and in the straight section I8 of the T before the pressure within the capacitance chamber forces them out through the T-leg 20 into the inductance pipe I.

In the arrangement of Fig. 3, waves, attenuated as. described in the foregoing paragraph, pass down the inductance pipe I through the inlet |2 of the chamber H and out through the end 2| thereof into the return line [6 and on to the return header, not shown. The waves coming into the chamber ll rebound to some extent from the bottom 2l thereof, due to the inertia of the mass of the gas, and there is a degree of further Wave attenuation due to this rebounding. This attenuation is obviously less marked than that occurring in the examples of Figs. 1 and 2 because the inertia of the gas tends to carry it straight through the chamber I l, thereby quickly reducing the attenuating effect of the rebounding waves to negligible factors. 7

Figures 4, 5, and 6 show arrangements for con trolling pulsations between supply header and compressor intake so that the vibratory efiect set up in the ordinary intake line may be minimized. Such pulsations as hereinabove described are functions of compressor R. P. M., and result from the cyclic taking of fluid from the supply line on each successive intake stroke of the compressor, whereas during the remainder of compressor stroke no gas or fluid is taken, with the result that the intake line pulsates similarly as does the discharge line. By controlling pulsations inthis line so as to dampen incoming wave amplitude, thereby assuring a steady flow in the incoming line, compressor efficiency may be appreciably increased.

In Fig. 4 the pulsating gas comes from the supply header, not shown, through the line 22 into the inlet of capacitance chamber 25, rebounds off the bottom thereof, and is discharged through side outlet 12 into inductance pipe 29. From in ductance pipe 29 the attenuated pulsations go through the straight section 3! of the T 30 into the inlet 33 of capacitance chamber 32, rebound from the chamber end 34, and pass through the T-leg 35 into the inlet pipe 35 to the compressor I.

In the arrangement of Fig. 5, the pulsating waves entering line 22 from the supply header are subjected to the same steps of attenuation as they pass through to the compressor I as are the waves of Fig. 2 in their course from compressor to return header.

In Fig. 6 the waves pass from the supply header into the line 22 and chamber 25; rebound back to be discharged out into line 29; pass from there into chamber 32, and out from this chamber through line 38 to the compressor.

Fig. 7 shows the piping arrangement by which a typical compressor employed in the compressing of natural gas may have both the intake and discharge connected within pulsation control equipment to insure a substantially steady gas flow, both into the compressor and into the outlet header. In this arrangement the compressor l is shown installed within a building so that the inductance pipes I and 29 of the pulsation control system pass through building 45 and out to return header ll and supply header 4!), res ectively. Such arrangement permits the capacitance chamber 32 of the pulsation control system for the intake to be located within the building and in close proximity to the compressor inlet 41; and it also permits the second capacitance chamber l l of the discharge pulsation control system to be located outside of the building and in close proximity to the return header ii. The valves 39 and 52 in the supply and output line, respectively, should have flow passages therethrough of substantially the same inner cross-sectional area as the respective pipes 29 and i.

In Fig. 8 exaggerated curves showing the attenuation of pulsation amplitude through a control system are plotted, the wave lengths being shown of disproportionate brevity as compared with actual length of a pressure wave, and with the actual length of the control system. For illustrative purposes these curves may be applied to the diagram of 'Fig. 2, and to the piping system of Fig. 7 in which the elements of Fig. 2 are shown on the discharge side of the compressor.

At the compressor discharge 2-8, a pressure Wave enters the line 2 at plotted point 49 at the velocity of discharge, and successive crests 50 and 5! are at successively smaller, plotted amplitude distances from the base line 52. At point 53 the wave has passed into the T H, and as it passes on through to the chamber bottom 5 due to the inertia of the mass of the gas, its successive hypothetical crests 54 and 55 are attenuated to successively smaller amplitude distances from the base line 52.

Upon contacting the chamber bottom 5 at the point 56 the waves rebound approximately 180 out of phase with the inrushing waves, and such a hypothetical wave may be assumed rebounding to the point 53, with the crests 5'! and 58 thereof also of successively smaller amplitudes due to the pressure within the chamber 3 and due to the inductance effects within the inlet 4 and lower half of the straight section N3 of the T IT.

As the rebounding hypothetical wave 59 is approximately 180 out of phase with the successive inrushing wave 60, the two waves react against each other. The hypothetical resultant wave 63 is plotted with the crest 6| representing the difference in amplitude between crest 55 and crest 51, and with the crest 62 representing the difference in. amplitude betwen the crest 54 and the crest 58.

The actual wave 15 which passes out through the T-leg 28 is defined in amplitude by the hypothetical resultant wave 63, but undergoes further attenuation in thus passing out through the T 28, and undergoes still further attenuation in its passage down the inductance pipe 29, as shown by the successive crests 64, 65, 65, 61.

At the point 68 the wave, as attenuated in the inductance pipe, has passed into the T 30, and the inertia of the mass of the gas causes it to pass on into the capacitance chamber II and against the end [4 thereof. The hypothetical incoming wave 69, the hypothetical rebounding wave '50, and the resultant hypothetical wave H are delined by the same theories herein above described for corresponding occurrences in capacitance chamber 3.

The actual wave '12, defined by resultant wave H and further attenuated in passage through the T 8 out into the line [5, is shown by the crests l3 and '14 thereof as being attenuated to such an extent that the gas may arrive at the return header 4| dampened down to substantially a steady flow.

The basis by which chamber volume, pipe length, and pipe inner diameter may be calculated is the well known equation:

R substantially 78.6741 wherein L=calculated length of passage in inches, passage sections of above normal inductance per unit length of the passage being included at their equivalent inductance length value;

V=minimum volume of each chamber in cubic inches;

R=radius of the passage in inches;

C=substantia1ly the velocity in feet per minute Of sound in the gas;

F=a selected value for the fundamental frequency per second of pulsations created in the fluid by the compressor.

The net velocity C is the velocity of sound in the gas minus the velocity of the gas in the line 35 in cases where the pulsation control equipment is on the intake side ofv the compressor since obviously the sound travels opposite tothe direction of gas flow. However, when the pulsation control equipment is installed on the discharge line 2 from the compressor, the net velocity C is the sum of the velocity of sound in the gas and the velocity of the gas in the line, since in this case both gas and sound travel in the same direction.

It should be pointed out however that the velocity of sound is so much greater than the velocity with which gas may be impelled through a line, as exemplified by sample velocities of 100,000 feet per minute for sound travel in a gas line wherein the gas travels at 400 feet per minute, that the value of C represents substantially the velocity of sound in the gas. Existing tables give sound velocities in gases under standard conditions and from these, velocities for conditions under consideration may be approximated and then corrected for pressure and temperatures to be encountered in operation.

As set forth herein above, the pulsation frequency is a function of compressor R. P. M. In the case of a single-acting compressor this fundamental frequency is substantially equal to the compressor R. P, M. while in the case of a double-acting compressor the fundamental frequency is twice the compressor R. P. M. Such fundamental frequencies may be, and usually are within audio frequency range, although the harmonics thereof may be above such range. The fact that the pulsation waves set in motion by a compressor in a gas line are pressure waves, as are sound waves, is therefore the basis for applying the term acoustical capacitance and acoustical inductance to the pulsation control elements employed to dampen such Waves.

In practice the value of F employed in the equation set forth herein above is usually taken at about 85% or 90% of the fundamental compressor frequency, since by sizing the pulsation control equipment to dampen out frequencies less than the fundamental frequency, the dampening out of this fundamental compressor frequency and its harmonics will be assured.

The factor 78.674 obtained in the derivation of the equation is only carried out to three decimal places since the equation is employed in sizing equipment in which considerable variation obtains so that such a constant need only be substantially accurate.

As the values of the right hand factors of the equation are determinable at outset, it is only necessary to arrive at values of the left hand side of the equation which will equal the right hand side. When there is a limited space available between compressor and header, this limitation will affect the factors of pipe length, pipe inner diameter, and chamber volume which comprise the left hand side of the equation. In the absence of such limitation the next limiting factor becomes the pressure drop through the pulsation control system. This is obvious since in the absence of pressure drop considerations it would be possible to select comparatively large values for and low values for V, thereby obtaining a desired saving in materials and space required by the capacitance chambers.

Since experience with different installations indicatesthat the length of pipe between capacitance chambers should be kept well under onefourth of the wave length of sound in the gas, this consideration also enters to limit selected pipe length. In this regard it should be pointed out that the Wave lengths plotted in Fig. 8 are shown shortened to less than one-eighth the actual length of these waves as compared to inductance pipe length employed in practice; such exaggeratedly shortened waves having been plotted to better illustrate the steps of wave attenuation, as herein above stated.

In calculating the length of inductance pipe required between two capacitance chambers of known volume, all fittings, as those causing change of direction, like Ts and elbows, are computed as equivalent lengths of straight pipe, as in the case of prior pulsation control systems, as those in which inductance pipes and capacitance chambers are connected in 'series so that pressure waves depart from the chambers by 8 other than the paths by which they enter the chamber.

It is pointed out however that this equivalency of length, as applied to fittings, as where direction is changed, is not calculated on the actual equivalent length of the passage through such fittings in inches, but such equivalency is rather based on the equivalent inductive length of each fitting, it being well known in theory that a change of direction in a line is equivalent to an increase in the acoustical inductance of the line. The pressure drop in a fitting, especially where direction is changed, works in opposition to any increase in inductance per inch of passage through such fitting, but such opposition is not suflicient to affect the result that actual increase in acoustical inductance does occur per unit length of passage through such a fitting. As a consequence such fittings in an acoustical inductance line ar equivalent to the addition of inductive length to the line in excess of the actual length of the passage through the fittings.

Additionally, the superimposition of rebounding hypothetical waves from the capacitance chamber upon the hypothetically plotted incoming waves, as set forth in description of the cycles of Fig. 8, results in wave attenuation due to additional acoustical inductance imparted to the straight length of passage between the chamber inlet and the hypothetical point in the fitting where the rebounding hypothetical wave and the resultant hypothetical wave terminate, and the actual resultant wave 6| passes down the acoustical inductance pipe to the next chamber, as plotted in Fig. 8. By the same theory the straight length of passage between second chamber inlet and the point where the resultant attenuated Wave 12 passes out the direction-changing fitting toward the header, has built up, by virtue of this superimposition of waves, more acoustical inductance therein than occurs in an equivalent length of acoustical inductance pipe down which waves pass in only one direction.

It thus results that the arrangement of pulsation control systems on either side of a compressor, after any one of the connection methods shown in Figs. 1 through 6, will obtain greater acoustical inductance per length of pipe required, than in systems heretofore known in which none of the gas passing through the system is ever diverted back over part of an acoustical inductance line by which it enters a capacitance chamber. Conversely, where a stated inductance may be required, such may be obtained with less pipe,

and with consequently less pressure drop, so that the horsepower efiiciency of the compressor may be hereby increased.

Stated in another manner, the arrangement of this invention will supply additional inductance over that supplied by presently employed systems, and thus, under conditions where space and distance from compressor to header may determine that a certain length of pipe should be employed, this additional inductance will permit the advantages of either a larger inner diameter of pipe or else a smaller volume capacitance chambers.

In the case of the use of a larger inner diameter inductive pipe, lower pressure drop in the a line also results, with an attendant increase of horsepower efliciency at the compressor.

As regards the size of the acoustical capacitance chambers, it is pointed out that whereas in theory both tanks are calculated to be of minimum volume within the computation of the equa 9 tion herein above set forth, and also of equal volume, no undesired effects result when either or both of the chambers are of volumes greater than these minimum volumes.

Other obvious advantages are obtained since in any of the disclosed arrangements at least one capacitance chamber may be cut out of the line for replacement or repair without necessitating cutting out the transfer of gas between compressor and header. Such arrangements also have general advantages in the ease and flexibility of connection as compared with systems where inductance pipes and acoustical chambers following each other without any of the flow therethrough being forced back upon itself.

Broadly this invention considers arrangements of pulsation control systems for fluids, such as gases which are taken into compressors, compressed, and transferred, characterized by the distinctive features wher by change of direction of the fluid flow is imparted to it after it has just rebounded back to the point of direction change over the same path by which it has previously entered a capacitance chamber.

What is claimed is:

1. In combination with a compressor and a header, pulsation control apparatus for dampening pulsating fluid flow caused bythe compressor, said apparatus comprising a pair of acoustical capacitance chambers and a circular cross-section conduit forming an acoustical inductance passage interconnecting the chambers, flow connection means of substantially uniform diameter between the compressor and the apparatus, flow connection means between the header and the apparatus, one of the flow connection means being connected to the inductance passage adjacent a chamber and at a point in the passage to which fluid flow from said last mentioned chamber must return by the same path by which it has entered said last mentioned chamber, the volumes of the chambers and the dimensions of the passage having predetermined values substantially in accordance with the following equation:

E X V substantially 78.6741

wherein L=calculated length of passage in inches, passage sections of above normal inductance per unit length of the passage being included at their equivalent inductance length value;

V=minimum volume of each chamber in cubic inches;

R=radius of the passage in inches;

C=substantially the velocity in feet per minute of sound in the gas;

F=a selected value for the fundamental frequency per second of pulsations created in the fluid by the compressor.

2. In combination with a compressor and a header, pulsation control apparatus for dampening pulsating fluid flow caused by the compressor, said apparatu comprising a pair of acoustical capacitance chambers and a circular cross-section conduit forming an acoustical inductance passage interconnecting the chambers, flow connection means of substantially uniform diameter between the compressor and the apparatus, flow connection means between the header and the apparatus, one of the flow connection means being connected to the inductance passage adjacent a chamber and at a point in the passage to which fluid flow from said last mentioned chamber must return by the same path by which it has entered said last mentioned chamber, the volumes of the chambers and the dimensions of the passage having predetermined values substantially in accordance with the following equation:

L c F substantially 78.6741

wherein L calculated length of passage in inches, passage sections of above normal inductance per unit length of the passage being included at their equivalent inductance length value;

V=minimum volume of each chamber in cubic inches;

R=radius of the passage in inches;

C=substantially the velocity in feet per minute of sound in the gas;

F=a selected value for the fundamental frequency per second of pulsations created in the fluid by the compressor, said selected value being within the range of to of the fundamental frequency.

3. In combination with a compressor and a header, pulsation control apparatus for dampening pulsating fluid flow caused by the compressor, said apparatus comprising a pair of acoustical capacitance chambers and a circular cross-section conduit forming an acoustical inductance passage interconnecting the chambers, flow connection means of substantially uniform diameter between the compressor and a chamber, flow connection means for connecting the header to the inductance passage adjacent the other chamber and at a point in the passage to which fluid flow from said other chamber must return by the same path by which it has entered the chamber, the volumes of the chambers and the dimensions of the passage having predetermined values substantially in accordance with the following equation:

2 substantially 78.674F wherein L=calculated length of passage in inches, passage sections of above normal inductance per unit length of the passage being included at their equivalent inductance length value;

V=minimum volume of each chamber in cubic inches;

R radius of the passage in inches;

C =substantially the velocity in feet per minute of sound in the gas;

F= a selected value for the fundamental frequency per second of pulsations created in the fluid by the compressor.

4. In combination with a compressor and a header, pulsation control apparatus for dampening pulsating fluid flow caused by the compressor, said apparatus comprising a pair of acoustical capacitance chambers and a circular cross-section conduit forming an acoustical inductance passage interconnecting the chambers, flow connection means of substantially uniform diameter connecting the compressor to the inductance passage adjacent a chamber and at a point in the passage to which fluid flow from the chamber must return by the same path by which it has entered the chamber, and flow connection means connecting the header to the inductance passage adjacent the other chamber and at a point in the passage to which fluid flow from the chamber must return by the same path by which it has entered said other chamber, the volumes of the I I 1 chambers and the dimensions of the passage having predetermined values substantially in accordance with the following equation:

XV- R substantia1ly 78.6741 wherein L=calculated length of passage in inches, passage sections of above normal inductance per unit length of the passage being included at their equivalent inductance length value;

V=minimum volume of each chamber in cubic inches;

R=radius of the passage in inches;

C=substantially the velocity in feet per minute of sound in the gas;

F=a selected value for the fundamental frequency per second-of pulsations created in the fluid by the compressor.

5; In combination with a compressor and a header, pulsation control apparatus for dampening pulsating fluid flow caused by the compressor, said apparatus comprising a pair of acoustical capacitance chambers and a circular cross-section conduit forming an acoustical inductance passage interconnecting the chambers, flow connection means between the header and a chamber, flow connection means of substantially uniform diameter for connecting the compressor to the inductance passage adjacent the other chamber and at a point in the passage to which fluid flow from said other chamber must return by the same path by which it has entered the chamber, the volumes of the chambers and the dimensions of the passage having predetermined values substantially in accordance with the following equation:

L C' E X substantial1y 7 8.67 4F wherein L=ca1culated length of passage in inches, passage sections of above normal inductance per unit length of the passage being included at their equivalent inductance length value;

V=minimum volume ofeach chamber in cubic inches; 7

R=radius of the passage in inches;

C=substantially the velocity in feet per minute of sound in the gas; 1

F=a selected value for the fundamental frequency per second of pulsations created in the fluid by the compressor.

6. A pulsation control system for dampening vibrations set up in a fluid flow line connected 'to a compressor, said system comprising, 'a pair of equal minimum volume acoustical capacitance chambers, an acoustical inductance conduit interconnecting the chambers, means of substantially uniform diameter connecting one chamber to a compressor, means connecting a header to the conduit at a point adjacent the other chamber to which fluid from the said other chamber must return by the same path over which it'enters said other chamber.

7.-'A pulsation control system for dampening vibrations set up in a fluid flow line connected to a compressor, said system comprising, a pair of equal minimum volume acoustical capacitance chambers, an acoustical inductance conduit interconnecting the chambers, means of substantially uniform diameter connecting one chamber to a header, means connecting a compressor to the conduit at a point adjacent the other chamber to which fluid from the said other chamber must return by the same path over which it enters said other chamber.

' 8. In combination with a compressor and a header, pulsation control apparatus for dampening pulsating fluid flow caused by the compressor, said apparatus comprising a pair of acoustical capacitance chambers and a circular cross-section conduit fdrming an acoustical inductance passage interconnecting the chambers, flow connection means of substantially uniform diameter connecting the compressor to the inductance passage adjacent a chamber and at a point in the passage to which fluid flow from the chamber must return by the same path by which it has entered the chamber, and flow connection means connecting theheader to the inductance passage adjacent the other chamber and at a point in the passage to which fluid flow from the chamber must return by the same path by which it has entered said other chamber.

ARTHUR J. L. HUTCHINSON.

REFERENCES CITED The following references are ,of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 2,405,100 Stephens July 30, 1946 2,474,553 Stephens June 28, 1949 2,474,555 Stephens June 28, 1949 OTHER REFERENCES A Text Book of Sound, A. B. Wood, London,

"G. Bell and Sons, Ltd., 1946, pages 502-507.

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