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Патент USA US2405100

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jug? 3%; 1946“
PULSATION
‘F.ELIMINATION
M.
IN GAS LINES
Filed Jan. 11, 1944
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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.
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