Abstract:
A flexible diaphragm is disposed in a housing between a working fluid and a gas-charged chamber to damp pulsations in the working fluid. The diaphragm has a flat base that, when fully distended by pressure in the gas chamber, lies against a flat, perforated circular metal sheet. The perforated metal sheet is closely spaced from a planar backing surface that prevents the sheet from permanently deforming under the force exerted by the pressurized diaphragm. An annular channel formed in the backing surface places the working fluid in contact with the perforated metal sheet. Pressure in the working fluid displaces the diaphragm away from the perforated metal sheet. A flat retaining wall in the gas chamber limits the travel of the diaphragm away from the metal sheet. Pressure pulsations in the working fluid move the diaphragm back and forth between the retaining walls. Back and forth flow of the pulsing fluid through the perforations and the compression of the gas in the gas chamber dissipates the energy of the pulses to achieve the damping effect. Multiple pulsation dampers operating at different charge pressures may be used to increase the range of high damping ratios for wider working fluid pressure ranges.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the damping of pressure pulsations in a fluid system. More particularly, the present invention relates to a gas charged pulsation damping assembly for damping pressure pulsations in power, transmission or control systems. 
     2. Setting of the Invention 
     Working fluid used in power, transmission and control systems may be subjected to periodic, rapid pressure increases and decreases. As used herein, the term “working fluid” is intended to refer to liquids and gases, both flowing and static, used to monitor, power or regulate machinery or to the fluids moving through a pipeline, or to other fluids that are the effective or active fluids in a static or dynamic system. 
     These pressure fluctuations in working fluids, referred to generally as “pulsations,” can damage and interfere with the operation of the systems. Pressure pulsations are frequently induced by positive displacement pumps associated with systems. A wide variety of devices have been developed to dampen the pulsations. A common pulsation damping technique allows the working fluid pressure to be exerted against an energy-absorbing device that tends to diminish the amplitude of the pulsations. 
     A common “tubular” design used for pulsation damping of flowing fluids employs a perforated tube section extending centrally through an annular, gas-pressurized diaphragm contained within a section of a system fluid flow line. One such design is illustrated in U.S. Pat. No. 4,759,387. Pulsations in the working fluid (usually a liquid) flowing through the perforated tube are damped by distending the diaphragm radially outwardly. This action forces the working fluid within the tube to flow radially through the perforations in the tube, thereby dissipating a portion of the pulsation energy with no system loss of flow or drop in pressure of the working fluid. 
     Pulsation damping systems using the described prior art design are usually intended to operate within a relatively narrow pressure range within which the diaphragm is substantially unstressed. If the system is operated outside its optimum pressure range, the pressurizing gas and the pressure surges caused by pulsations in the working fluid can stretch and thereby stress the resilient diaphragm. By virtue of their design, these prior art pulsation damping systems are relatively large and the performance and efficiency of such systems vary as a function of the gas pressure charges acting against the diaphragm. One prior art pulsation damping arrangement of the described “tubular” design exhibits a significant decrease in damping ratio as the gas charge (determined as a percentage of working fluid pressure) is increased toward the operating pressure of the working fluid. 
     These “tubular” pulsation damping systems require the fabrication of a perforated tubular section that underlies and supports the inflatable diaphragm. Some of such systems require additional structural supporting materials to prevent the perforated tube from collapsing under the compressive force exerted by the pressurized diaphragm. These perforated tubes and associated structural supporting members can be large and expensive to fabricate, particularly when it is necessary to use exotic metals and alloys and other corrosion resistant or specialty strength-enhancing materials. 
     Another prior art pulsation damping design uses a bellows or a piston-cylinder arrangement disposed in a surge chamber that communicates with the working fluid being damped. U.S. Pat. No. 5,205,326 illustrates pulsation dampers of this type. The bellows compresses, or the piston is driven into the cylinder, as the pressure of the working fluid in the surge chamber increases during pulsation. Compressed gas or mechanical springs are used to resist the compressive force exerted by the fluid pulsation. As with the tubular pulsation damping systems, the damping efficiency of the bellows and piston-cylinder arrangements varies over the range of the internal gas charge or spring force exerted against the pressure responsive element. The bellows and piston-cylinder members of these prior art systems require relatively large components and are also expensive to fabricate. 
     The prior art also teaches a pulsation damper design employing a relatively thick, flexible diaphragm that rests against a domed, perforated support when the gas pressure charging the diaphragm is sufficiently greater than that of the pressure of the working fluid. The design protects the diaphragm from rupturing when a large pressure differential exists between the pressure of the working fluid and the gas charge pressure. An example of such a design may be seen in U.S. Pat. No. 2,563,257, which employs a perforated plate having a cup or dish shape to support the gas charged diaphragm. The diaphragm is movable in a large chamber between its extreme pressured and unpressured positions without stretching or stressing the diaphragm. Because the diaphragm can move its entire length in either direction from its central mounting point, the pulsation absorber described in the patent requires a chamber that is substantially twice the unstressed axial displacement height of the diaphragm. The cup or dish shape is said in the patent to be preferable to a flat perforated plate in that it acts as an arch and provides a greater area for perforations. 
     As with the previously described pulsation damping systems employing tubular diaphragms and bellows or piston-cylinder arrangements, the dome-shaped cup or dish design can be relatively large and expensive to fabricate, particularly when it must be constructed of metal alloys or other specialty, strength-enhancing materials. The damping efficiency of the systems can also be widely variable over the range of the pressure variations in the working fluid. 
     SUMMARY OF THE INVENTION 
     A flexible diaphragm is disposed between a working fluid and a gas-charged chamber to form a pulsation damper. The diaphragm has a flat base that, when fully distended by pressure in the gas chamber, lies against a flat, perforated circular metal sheet. The perforated metal sheet is closely spaced from a planar backing surface that prevents the sheet from permanently deforming under the force exerted by the pressurized diaphragm. An annular channel formed in the backing surface places the working fluid in contact with the perforated metal sheet and permits fluid flow through the assembly when the perforated sheet is engaging the planar backing surface. Pressure pulsations in the working fluid displace the diaphragm away from the perforated metal sheet. A flat retaining wall in the gas chamber limits the travel of the diaphragm away from the metal sheet. Back and forth flow of the pulsing working fluid through the perforations and the compression of the gas in the gas chamber dissipate the energy of the pulses to achieve the damping effect. 
     The diaphragm is maintained in a non-stressed condition during its movement between the flat metal sheet and the flat retaining wall. The diaphragm moves only in a single direction from its mounting within the body of the damper assembly, which reduces wear of the diaphragm and contributes to reducing the total height of the damping assembly. The lateral walls of the cup-shaped diaphragm are relatively thin compared to the diaphragm base. The thin wall construction enhances the response of the diaphragm to pressure fluctuations in the working fluid while the thicker base protects the diaphragm from damage caused by engagement with, and movement over, the perforated disk. 
     The design of the components of the present invention coupled with the limited movement, non-stressed operating range of the diaphragm produce a low cost, long-lived assembly that exhibits a linear relationship between its damping ratio verses the gas chamber charge as a percentage of the working fluid pressure, even at percentages approaching 100 percent of the working fluid pressure. 
     The components of a pulsation damper of the present invention may be easily and inexpensively fabricated from readily available materials. The use of planar surfaces for the perforated metal sheet, the backing surface behind the sheet and the retaining wall in the gas chamber reduces fabrication costs of both the retaining members and the conforming diaphragm. The flat backing surface behind the perforated metal sheet is easily machined or milled to provide a desired fluid course that is maintained in close contact with the sheet. The limited displacement and absence of stress in the diaphragm, over the full operating range of the system, combined with the system design, enables long-lived, efficient operation even at gas pressure charges approaching the design operating pressure of the working fluid. 
     The design of the pressure damper of the present invention also permits fabrication of a relatively small assembly that can be easily associated with control elements in pressure regulating systems. 
     The improved operating efficiency and small size of the pressure damping assembly of the present invention enhances its suitability for use in pressure sensitive control systems and other pressure sensitive devices, such as pilot operated pressure relief valves. Pilot operated pressure relief valves are set to open and closed automatically as required to maintain operating pressure levels by relieving excess system pressure. The “set pressure” of the relief valve is typically set at some percentage below the maximum allowable working pressure of the piping and equipment associated with the relief valve. 
     In many commercial systems, such as may be found for example at a chemical plant, it is desirable to operate a “process” at as high a pressure as possible, within safe operating levels of the piping and associated equipment. Operating at higher pressures permits higher efficiencies and better yields from the process. A pilot operated pressure relief valve protects the piping and attached equipment by relieving excess pressure in the system once the “set point” of the pilot has been exceeded. Without damping, the peaks of the pressure pulsations in the working fluid are typically high enough to activate the pilot and pressure relief valve and/or cause excessive wear in the pilot. To keep from activating the relief valve and reducing the life of the pilot, the plants must reduce the pressure of the process, thus reducing efficiency and yield. Adding a pulsation damper of the present invention allows the process working pressure to be raised closer to the set pressure of the relief valve. The pulsation damper of the present invention achieves a high degree of damping efficiency at gas charge pressures approaching 100 percent of the process working pressure. 
     In the method of the present invention, multiple pulsation dampers are simultaneously exposed to the working fluid. The pulsation dampers are provided with different gas charges to more effectively dampen pulsations in wider pressure ranges of the working fluid. 
     In view of the foregoing, it will be appreciated that an important object of the present invention is to provide an efficient pulsation damper having relatively small dimensions, which is inexpensively fabricated from readily available materials. 
     An important object of the present invention is to provide a small-bodied pulsation damper for damping pressure pulses in a working fluid wherein the pulsation damper exhibits an increasing damping ratio as the gas charge pressure in the damper approaches the pressure of the fluid being damped. 
     An object of the present invention is to provide an assembly to dampen the pulsations in a monitored fluid in which the damping ratio of the assembly increases linearly as the gas charge in the damper approaches the pressure of the monitored fluid. 
     A related object of the present invention is to provide an apparatus for damping pressure pulsations in a monitored fluid wherein the damping ratio of the apparatus increases linearly over a range of gas charges that extends beyond a gas charge of 90 percent of the monitored fluid pressure. 
     Yet another object of the present invention is to provide a small, inexpensively fabricated, damping apparatus that may be used in a pressure sensitive system whereby operation of the pressure sensitive system is optimized. 
     A specific object of the present invention is to provide a small, inexpensively fabricated, efficient damping apparatus that may be used with a pilot operated pressure relief valve to permit improved efficiency and yield of the process system being protected by the pressure relief valve. 
    
    
     The foregoing objects, features and advantages of the present invention, as well as others, will be better understood and more fully appreciated by reference to the following drawings, specification, and claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional view of a pulsation damper of the present invention; 
     FIG. 2 is a sectional view taken along the line  2 — 2  of FIG. 1; 
     FIG. 3 is an enlarged cross sectional view of a small area of FIG. 1 illustrating details in the construction of the damping of the present invention; 
     FIG. 4 is an elevation view, partially in section, illustrating a modified form of the pulsation damper of the present invention; 
     FIG. 5 is a perspective view of a pilot operated pressure valve equipped with the pulsation damper of the present invention; and 
     FIG. 6 is a graphical representation comparing the operating efficiency of a pulsation damper of the present invention with a prior art pulsation damper. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A pulsation dampening assembly of the present invention is indicated generally at  10  in FIG.  1 . The working fluid to be damped enters the assembly through an inlet port  15  and exits through an outlet port  17 . The ports are formed in a cylindrical steel coupling  20  and are equipped with internally threaded receptacles  15   a  and  17   a , respectively, for connection with threaded fittings connecting to a pressure system. 
     As best illustrated by joint reference to FIGS. 1,  2  and  3 , the coupling  20  is an axially extending cylindrical body having a flat recessed axial end surface  22 . An annular groove  23  formed in the planar end surface  22  connects with the ports  15  and  17  to permit fluid communication between the inlet port  15  and the outlet port  17 . 
     A circular metal disk  25  having multiple perforations  27  is mounted on an annular ridge  29  formed around the flat recessed space  22  of the steel coupling  20 . The mounting of the disk  25  on the ridge  29  produces an axially and radially extending space  30  between the disk  25  and the recessed surface  22  through which the working fluid flows during operation of the pulsation damper. As will be further explained, fluid in the space  30  is forced to flow back and forth through the perforations  27  between the space  30  and a second axially and radially extending space  31  formed on the opposite side of the disk  25 . 
     A flexible flat-bottomed diaphragm  33  is positioned with its flat bottom  34  engageable with the metal disk  25 . The diaphragm  33  has a reduced thickness, annular wall section  36  that extends between the relatively thick flat bottom  34  and an enlarged annular mounting lip  37  at the mouth of the diaphragm. The reduced thickness, annular wall section  36  is supported against an annular steel ring  40  positioned on the rim  29  of the coupling  20 . An annular, elastomeric O-ring seal  41  positioned between the ring  40  and the ridge  29  maintains a pressure seal between the two components. 
     A thin flat ring  45  of Teflon® (polytetrafluoroethylene “PTFE”) is clamped between the steel ring  40  and the metal disk  25  to provide a smooth, low friction surface for the diaphragm  33  to move along as the diaphragm pushes the perforated disk  25  into the annular groove  23  in the coupling  20 , keeping the diaphragm from extruding into the perforations or being cut on the edges of the perforations. 
     The coupling  20  is received within an internally threaded cylindrical opening  47  in a steel main body  50 . An externally threaded, steel retaining ring  51  is positioned in the cylindrical opening  47  to retain the coupling  20  in firm engagement with the main body  50 . Wrench recesses  52  are provided at an end of the ring  51  for engagement with a torque wrench (not illustrated) that may be used to rotate the ring  51  to make up the threads between the ring and the body  50  to firmly seat the coupling  20  in the recess  47  of the body  50 . A radial opening  53  extends through the sidewall of the body  50  into the recess  47  and acts a “weep hole” for easy, visible indication of a diaphragm or O-ring failure. 
     The cylindrical body  50  is provided with a flat retaining wall  55  that extends laterally from the central axis of the body  50 . The wall  55  cooperates with the flexible diaphragm  33  to form a retention surface to enclose a gas pressure chamber  56 . A gas pressure charge is supplied to the gas chamber  56  via a gas chamber charging valve  60 . Dry nitrogen, or other suitable gas, may be used to charge the chamber  56 . The valve  60  operates conventionally to permit the one-way application of a high-pressure charging gas into the confined area of the pressure chamber  56 . A round top poppet  61  covers the entry port extending through the retaining wall  55  into the chamber  56  to prevent displacement of the diaphragm  34  into the port when the pressure of the monitored fluid collapses the diaphragm against the retaining wall  55 . Bent legs  61   a  of the poppet  61  hold the poppet in place while permitting sufficient movement of the poppet head to allow the gas charge to flow from the valve  60  into the chamber  56 . 
     The detail drawing of FIG. 3 illustrates the axially and radially extending space  30  formed between the flat bottom  22  and the perforated disk  25 . During operation of the pulsation damper, fluid flows from the inlet  15  to the outlet  17  of the assembly along a course indicated by the arrow A. In following the course between the inlet and outlet, the fluid is forced to flow through the perforations  27  in the disk  25  between the axial spaces  30  and  31 . The back and forth flow of the fluid through the perforations  27  and the compression of the diaphragm  33  damps the pressure pulsations in the fluid. 
     In the operation of the damping apparatus of the present invention, the various backing and support surfaces afforded on either side of the diaphragm  33  are effective in protecting the diaphragm from damage regardless of the direction or the size of the pressure differential acting across the diaphragm. When the damping assembly  10  is initially provided with a gas charge through the charging valve  60 , the absence of pressure in the spaces  30  and  31  allows the diaphragm  33  to be expanded fully against the annular ring  40 , Teflon® ring  45  and the perforated disk  25 . The annular disk  25  may be pushed against the backing surface  22  when the pressure in the chamber  56  is sufficiently high. Full distension of the diaphragm may also occur during operation at any time the pressure in the chamber  56  is sufficiently greater than that of the fluid being damped. 
     The design of the assembly  10  prevents damage to the perforated disk during these periods of relatively high pressures in the gas chamber  56 . To this end, the small spacing between the backing surface  22  and the disk  25  limits the axial travel of the perforated disk below the yielding stress of the disk material and prevents the disk from being permanently deformed when it is pushed against the backing surface. The annular ring  45  provides additional backing support above the annular groove  23  to prevent the material of the diaphragm  33  from being cut or extruded through the perforations  27 . 
     When the pressure of the working fluid sufficiently exceeds the pressure in the gas chamber  56 , which may occur during abnormal working pressures or because of a loss of pressure in the chamber  56 , the diaphragm  33  is forced against the retaining wall  55 . The retaining wall  55  limits the axial movement and distension of the diaphragm  33  to protect it from damage. During such periods of high working fluid pressures acting on the diaphragm, the roundheaded poppet  61  prevents the material of the diaphragm from extruding into the charging port. 
     Under normal operating conditions, the gas chamber  56  is charged to a pressure that is determined by the operating pressure of the working fluid to be damped. An initial gas chamber charge may be 60 to 90 percent, or more, of the expected operating pressure of the fluid to be damped. During normal operation, when exposed to the system fluids, the diaphragm  33  is displaced away from the perforated disk  25  into the area between the backing surface  22  and the retaining wall  55  such that the average gas charge pressure and the average pressure of the fluid being damped are substantially equal. 
     Pressure pulsations of the working fluid cause the diaphragm to move back and forth in the area between the retaining wall  55  and the perforated disk  25 , alternately compressing and decompressing the gas charge in the chamber  56 . This action forces the working fluid to flow back and forth through the perforations  27  in the disk  25 , dissipating the energy of the pulsations. The working fluid is exposed to a large area of perforations by the combined action of the annular groove  23  and the large surface area formed in the space  30  between the perforated disk and the backing surface  22 . The system design permits fluid damping with the diaphragm  33  having to move only the length of the axial height of its annular wall section  36 . The diaphragm  33  may not travel axially beyond its point of mounting with the main body, thus preventing reverse flexing of the diaphragm. 
     FIG. 6 of the drawings is a graphical representation of the operating efficiency of the pulsation damper of the present invention and a prior art pulsation damper illustrating the relationship between damping ratio and the gas charge in the gas chamber as a percentage of the pressure of the working fluid. The curves of FIG. 6 were developed using a triplex pump operating at a speed of 150 revolutions per minute and a working or “line pressure” of 1000 pounds per square inch (psi). The damping ratio, depicted on the vertical axis, is the ratio of the pulsation amplitude in the working fluid before and after damping. The horizontal axis depicts the pressure charge in the gas chamber as a percentage of the working line pressure. 
     The curve  70  in FIG. 6 was obtained using a damping assembly  10  of the present invention in which all the metal components were constructed of 316 stainless steel. The perforated disk  25  has a thickness of 0.015 in. and the perforations have a diameter of 0.033 in. The diaphragm  33  and O-ring  41  were constructed of Viton®, a flexible fluorocarbon material. The thin portion  36  of the diaphragm  33  was 0.017 in. thick and the thicker base  34  had a thickness of 0.033 in. The flat PTFE ring  45  had a thickness of 0.010 in. Dry nitrogen at pressures ranging between 200 psi and 900 psi was employed to charge the chamber  56 . The outside diameter of the main body  50  was 3.25 in. and the axial length of the assembly, as measured centrally across the main body  50  and coupling  20 , was 2.7 in. The total dimension laterally across the main body  50 , including the charging valve  60 , was 4.9 in. The prototype pulsation damping assembly operating with the design, materials of construction and dimensions given for the assembly  10  weighs 6 lbs. and is rated at a maximum operating pressure of 5000 psi and a maximum temperature of 400 degrees Fahrenheit. 
     The curve  71  in FIG. 6 was obtained using a prior art “tubular” pulsation absorber (suppressor) device manufactured by Wilkes-McLean, Ltd. The Wilkes-McLean suppressor, employing a design such as described in detail in U.S. Pat. No. 4,759,387, was operated with a dry nitrogen gas charge pressure ranging between 200 psi and a 900 psi. The prior art suppressor had a tubular diameter of 2.5 inches, a tubular length of 6.875 inches and a combined tubular diameter and charge valve height of 4.25 in. The device weighed approximately 6.5 lbs. 
     An important feature of the damping assembly  10  is that the damping ratio of the assembly continues to increase linearly as the gas charge in the gas chamber  56  approaches the operating pressure of the line containing the working fluid. This feature is readily apparent from the straight-line curve  70  in FIG.  6 . As may be seen by reference to the curve  71 , a conventional prior art dampening assembly exhibits a decreasing damping ratio in the upper operating ranges as the assembly gas charge approaches that of the line pressure. If desired, the damper assembly  10  of the present invention may be used to damp pressure pulses in a static fluid system by simply blocking the outlet port and applying the static working fluid to the inlet port  15 . Such a system would have use, for example, in damping pressure fluctuations in a pressure gauge. 
     FIG. 5 of the drawings illustrates the pressure damper  10  of the present invention installed in the pilot operating system of a pilot operated, pressure relief valve indicated generally at  100 . A pressurized working fluid in a regulated or monitored system  101  is provided to an inlet  102  of the valve  100 . Excess pressure in the system  101  is vented through the valve  100  to an outlet  105 . 
     The damper assembly  10  is secured to the valve  100  with an accessory bracket  107 . The damper assembly  10  is plumbed between pilot sense line sections  109   a  and  109   b  so that pressure at the inlet  102  of the valve  100  communicates through the damper assembly  10  to the sensing input of a pilot control  111 . A discharge pressure line  112  discharges fluid flowing through the pilot control  111  into the outlet  105 . A pilot control line  115  extends from the pilot  111  to the relief control  100  to regulate the opening and closing of the valve  100 . When opened under the direction of the pilot control  111 , the valve  100  permits fluid from the system  101  to flow through the valve  100  and out through the outlet  105 . 
     A Pressure verses Time chart  120  in FIG. 5 illustrates pressure fluctuations in the working fluid contained within the system  101 . A similar chart  125  in FIG. 5 illustrates the damped fluctuations in the system working fluid after the pulsation damper  10  has processed the fluid. As may be noted by comparing the difference in the amplitudes of the pressure pulsations in the charts  120  and  125 , the pulsations in the pressure fluid in the sensing line  109   b  have been substantially reduced. The reduction in the pulsation amplitudes permits the operating pressure of the fluid in the system  101  to be raised closer to the opening or set point of the pilot operated, pressure relief valve  100 . 
     A modified pulsation damper of the present invention is indicated generally at  210  in FIG. 4 of the drawings. The system  210  permits the range of high damping of the working fluid to be efficiently extended over wider pressure ratios. The pulsation damper  210  includes two symmetrically arranged pulsation damper sections  211  and  212 , each similar in operation to the pulsation damper  10 . The sections  211  and  212  are combined to effectively increase the damping effect of pulsations in a working fluid flowing through the damper. An important feature of the system  210  is that each of its dual gas charge chambers may be charged to different gas charge pressures to accommodate and more efficiently dampen pressure pulsations over larger pressure ranges of fluids as compared with the system  10 . 
     The pulsation dampener section  211 , which is identical in construction to its symmetrical section  212 , is identified with reference characters that are higher by  200  than corresponding components in the pulsation damper  10 . Because of the similarity in construction and operation of the two damper sections  211  and  212 , only the section  211  will be described in detail. It will be understood that components of the damper section  212  operate in a manner symmetrically consistent with their corresponding components in the damper section  211 . 
     Working fluid to be damped by the system  200  enters an inlet port  215  formed in one end of a main body  250 . The working fluid flows through the dampener  200  and exits through an outlet port  217  formed in the opposite side of the main body  250 . A steel coupling  220 , held in position on the main body  250  with a steel retaining ring  251 , forms a gas charge chamber  256   a  in the damper section  211 . A symmetrically corresponding gas chamber  256   b  is formed in the adjoining pulsation damper section  212 . 
     Gas is supplied to the chamber  256   a  through a gas charge valve  260 . A spring loaded poppet  261  covers the access opening from the charging valve to the chamber  256 . The poppet  261  cooperates with a flat retaining wall  255  to limit displacement of a diaphragm  233 . The diaphragm  233  isolates the gas chamber  256   a  from a space  231  that communicates with the working fluid. A perforated disk  225  in the space  231  communicates with an annular groove  223  machined into a flat backing surface  222  formed on the main body  250 . The backing surface  222  limits displacement of the diaphragm  233  when the gas charge greatly exceeds the pressure of the fluid at the inlet  215 . As with the assembly  10 , compression of the gas charged chamber  256   a  by the working fluid in the assembly  210  causes fluid entering the port  215  to flow back and forth through perforations in the perforated disk  225  to dampen pressure pulsations in the fluid. 
     In operation, the chambers  256   a  and  256   b  are each charged to a different pressure. The chamber charge with the lower pressure dampens pulsations of lower average pressure efficiently whereas the damper with a higher charge dampens the pulsations of higher average pressure more efficiently. The dual chamber design also provides a working back up that continues pulsation damping even if one of the chambers should fail. It will be appreciated that the pulsation damping effect provided by the charged chambers  256   a  and  256   b  can be provided by equivalent devices such as spring loaded piston-cylinder force absorbing devices or other equivalent devices that absorb the energy of the pressure pulsations. 
     While preferred embodiments of the pulsation damper of the present invention have been described in detail herein, it will be appreciated that other forms of the invention may be made without departing from the spirit and scope of the invention, as set forth in the following claims.