US2934093A

US2934093A - Accumulator

Info

Publication number: US2934093A
Application number: US586997A
Authority: US
Inventors: William J Bleasdale
Original assignee: Superior Pipe Specialties Co
Current assignee: Superior Pipe Specialties Co
Priority date: 1956-05-24
Filing date: 1956-05-24
Publication date: 1960-04-26
Anticipated expiration: 1977-04-26

Description

April 26, 1960 w. J. BLEASDALE ACCUMULATOR Filed May 24. 1956 Unite States Patent ACCUMULATOR William J. Bleasdale, Cleveland, Ohio, assignor to Superior Pipe Specialties Co., Cicero, Ill., a corporation of Illinois Application May 24, 1956, Serial No. 586,997

' s claims. (ci. 13s- 31) The present invention relates to an accumulator for the storage of mechanical energy, and more particularly to an accumulator of the gas-liquid type capable of storing potential energy to be later delivered as kinetic energy.

Many different types of gas-liquid accumulators have been proposed in the prior art. For relatively high pressure applications, one common type of such accumulator utilizes nesting, generally cylindrical, radially spaced inner and outer shells, the inner shell having disposed therein a freely oating piston which separates the inner shell in to a gas compartment on one side of the piston and a liquid compartment on the other side of the piston. the gas compartment is in free communication with the annular space between the two shells and surrounding the outer periphery of the inner shell. The gas compartment and the annular space are charged with a gas, usually nitrogen, under pressure, and then the gas compartment is sealed. The liquid compartment is adapted to receive a liquid, such a hydraulic oil, under pressure which forces the piston against the gas pressure to compress the gas to the liquid pressure. rIhe compressed gas provides a source of potential energy which can be converted to kinetic energy upon subsequent release of the liquid from the liquid compartment. The liquid is forced from the liquid compartment under the pressure of the compressed gas to provide a charge of pressurized hydraulic liquid, when needed.

ln the conventional or prior accumulators of this type, the gas pressure is the same within the gas compartment of the inner sleeve and within the annular space between the inner and outer shells, so that the inner shell is not subjected to any diierential pressure which would tend to distort the inner shell. Thus, the outer shell is subjected to. a bursting force which is dependent upon and directly proportional to the pressure of the compressed gas. This type of accumulator is widely utilized for working at pressures of up to about 3000 pounds per square inch. The standard safety requirements for hydraulic accumulators of this type require a safety factor of 3 to 1, which means that the outer shell must withstand a maximum burst pressure of about 9000 pounds per square inch. This burst pressure can be attained by the use of a drawn or forged steel casing of such thickness that the wall thickness of the outer shell is retained within reasonable limits and the weight of the accumulator is within reason.

However, in attempting to adapt this type of accumulator construction to higher working pressures, on the order of 5000 pounds per square inch or greater, the minimum burst strength of the outer shell must be increased to at least 15,000 pounds, which either requires a drawn or forged steel cylinder of such wall thickness as to be impossibly heavy and bulky for eiiicient installation or use, or the utilization of a hardened steel which becomes so brittle as to fragmentate upon actual bursting of the cylinder. Thus, one is given the choice of forming the outer cylinder of a brittle steel which poses an actual and considerable safety hazard during use, or forming vthe outer cylinder of greatly increased thickness with the resultant impractical weight and size of the accumulator. Consequently, there is not available today a satisfactory, safe, practically usable accumulator of this type which is operable at higher pressures on the order of 5000 pounds per square inch or greater.

The present invention now proposes a modified type of accumulator which is novel in its construction and unc tion and in which the outer shell is subjected to less than the actual working pressure, so that the shell thickness and weight may be reduced, while still retaiing an adequate safety factor, and while eliminating the possibility of shell fragmentation upon bursting.

The accumulator of the present invention comprises inner and outer, generally cylindrical, radially spaced shells, the inner shell or sleeve containing a freely floating piston. However, the inner and outer shells are iso-4 lated from one another so that a sealed, annular gas chamber substantially surrounds the outer periphery of the inner shell, and this gas chamber is completely isolated from the Working gas-liquid chamber within the inner sleeve. The inner and outer sleeves are thus isolated from one another and may be subjected to a differential uid pressure.

In charging the accumulator of the present invention with a gas and prior to its subjection to liquid pressure, the gas chamber between the two sleeves is charged to a pressure appreciably less than the nal working pressure to which the gas in the working chamber will be subjected, i.e. the pressure to which the gas in the working chamber will be compressed by liquid during working of the accumulator. Of course, the gas compartment of the working chamber is also charged with gas under pressure, this initial charging of the gas compartment being at a pressure considerably less than the final working pressure of this compartment. The initial charging of the gas chamber and the gas compartment of the working chamber may be at the same pressure or at different pressures, depending upon the nal working gas pressure which is desired in the gas compartment.

After the gas chamber and the gas compartment of the working chamber have been separately charged initially, the chamber and the compartment are sealed, as by the utilization of conventional one-way check valves, and the accumulator is now ready to receive a working liquid exerting pressure on the liquid side of the oating piston in the working compartment. The introduction of such liquid under pressure into the working chamber will move the piston so as to compress the gas within the working chamber.

Assuming that the working pressure of the accumulator is 5000 pounds, the entry of liquid under this pressure will compress the gas within the working chamber to 5000 pounds. The working chamber thus is iilled with liquid and gas at the same pressure, namely 5000 pounds, while the gas chamber between the two shells is subjected to a lesser gas pressure, say on the order of 3000 pounds.

Thus, there is a burst pressure upon the outer shell ofV differential pressure will result in the inner sleeve being.

subjected to a burst pressure of 2000 pounds per square inch. Thus, although the accumulator is operating ata working pressure of 5000 pounds per square inch, neither of the shells is subjected to this extremeburst pressure. Each of the shells is subjected to a pressure,-

which is substantially less than the working pressure,

3 Y and Vthe actual pressures to which the shells are subjected may be readily accommodated by shells formed of drawn or forged steel and of reasonable thickness.

It is, therefore, an important object of the present invention'rto'provide an accumulator of the Ygas-liquid type capable of .operating at relatively high Working pressures. Another importantV object is the provision of an accumulator of the double shell, floating pistont'ype capable of operating at a relatively high working pressurexwith both of the Tshells being subjected to a burst pressure which is substantially less than the working pressure of the accumulator.V

It is a further object of this invention to provide an improved gas-liquid accumulator wherein a working chamber is enclosed by a sleeve subjected to a differential pressure substantially less than the accumulator working pressure and an outer structural shell is subjected to a burst pressure substantially less than the working pressure of the accumulator. Still another important object of this invention is the provision of a gas-liquid accumulator having nested, spaced inner and outer shells isolated from one another and adapted to contain fluid at different pressures, the inner shell defining a working chamber adapted to be charged with fluid under pressure Yfor subsequent discharge and a space between the shells containing uid at a pressure substantially less than the working pressure of the accumulator.

It is a still further object of this invention to provide animproved liquid-gas accumulator having concentric, isolated working and gas storage chambers, the working chamber being subjected toa relatively high Yworking pressure and the surrounding gas chamber being subjected toa lesser pressure, thereby reducing the burst pressure of the accumulator shell to a pressure substan-Y tially less than the working pressure of the accumulator.

These and other objects will be more apparent from the following detailed description of a preferred embodiv ment of my invention and byreference to the drawings forming a part hereof wherein:

On theA drawings:

The single figure of the drawing is a broken axial section of anv accumulator of the present invention and illustrating the'manner of filling isolated gas and working chambers with a duid under pressure.

As shown on the drawings:

In the single figure of the drawings, reference numeral 10 refers generally to an accumulator of the present invention. yThe accumulator 10 comprises an outer, generally cylindrical shell 11 formedv of forged or drawn structural steel or the like material and having itsropposite ends interiorly threaded, as at 12 and 13. p

Spaced inwardly from the threaded open ends of the outer shell 11 are a pair of end plugs indicated generally at 14 and 15, respectively, the plug 14 beingrprovided with a radially venlarged flange 16 snugly received within the shell 11 axially inwardly beyond rthe threaded portion V12 thereof and havingv a peripheral groove 17 with# in which is seated an 0 ring or similar sealV 18. Prof jecting axially inwardly from the flange 16 is an axial boss 19 of lesser diameter than the flange 16 and having a cylindrical radially outward surface 22' which is provided with a peripheral groove 21 within which is seated a second 0 ring or similar seal 20. YProjecting axially outwardly from the flange 16 is a reduced diameter em# hossnrent 23 which is further reduced, as at 24, and interiorly threaded, as at 25, for the reception of the threaded end of an hydraulic tting or the like.

' The other end plug 15 is provided with a radially enlarged flange 26 which snugly contacts the inner periphery of the shell 11 axially inwardly from the threaded portion 13, this ange 26 merging through a shoulder 27 witha reduceddiameter embossment 28. The flange 26 is provided with an annular peripheral recess 29 withiiwhich is seated an O ring or similar seal 30, and the boss 28 has its outer peripheral surface 31 similarly provided with a recess 32 within which is seated an O ring or similar seal 33. Y

Located within the outer shell or casing 11 is an inner shell or sleeve indicated generally at 35, this inner sleeve 35 having its opposite axial ends 36 and 37 abutting the shoulders 16a and 27 of the plugs 14 and 15, respectively. The inner peripheral surface 38Yof the inner sleeve 35 contacts the seal rings 20 and 33, respectively, so that the interior annular gas chamber 40 dened between the outer shell 11 and the inner shell 35 is completelyisolated from the interior of the inner shell 35. The interior of the inner shell 35 defines a working chamber indicated generally at 41.

The plugs 14 and 15 are retained in positionfwith the shoulders 16a and 27 abutting the ends 36 and 37, respectively, of the inner sleeves 35 by means of annular threaded locking rings 42 and 43V having their exterior peripheries threaded, as at 42a and 43a, respectively, for threaded engagement with the

threads

12 and 13 of the outer sleeve. Thus, the

locking rings

42 and 43 retain all of the fixed parts of the accumulator, namely, the exterior shell 11, theinterior shell 35, Vand the end plugs 14 and 15 in assembled relation. The seal rings ,18 and 30 interposed between the plugs 14 and Y15, respectively, and the outer shell 11 prevent any leakage of gas from the chamber 40 through the threads 12-42a and 13-43a. To facilitate assembly of the locking rings, each'ring is provided with a peripherally spaced series of Spanner wrench holes 44.

Disposed within the working chamber 41 is a free floating piston, indicated generally at 45. This piston is provided with a medial, generally cylindrical portion 46 which is of substantially the same exterior diameter as the interior diameter of the sleeve 35. This medial portion; 46 is provided with a pair of axially spaced, annular, peripheral grooves 47 within which are seated rings or similar seals 48. Intermediate the two seals, the cylindrical portion 46 is provided with an axially elongated, annular, exterior peripheral groove 49, for a purpose to be hereinafter more fully described.

It will be noted that the plug 14 is provided with a generally cylindrical annular interior surface 50V defined by the axially extending boss 19 and that end of the piston adjacent the plug 14 is provided with a reduced diameter embossment 51 loosely enterable into the space enclosed by the surface 50. The surface 50, in combination with the remainder of the plug 14, defines an annular shoulder 52 concentric with the sleeves 11 and 35 and the adjacent radial face of the piston 45 is provided with an annular embossment 53 which is adapted to abut this face 42to limit movement of the piston toward that end of the accumulator closed by the plug 14. The' threaded aperture 25 communicates with a cylindrical opening 54 Which is in full communication with the working chamber 41, and the piston is provided with a concentric, axially extending boss 55 guidingly insertable in, but in radially spaced relation to, the cylindrical opening 54. The free end of the boss 55 is chamfered as at 56, for a purpose to be hereinafter more fully described.

To reduce the weight of the piston, and to increase the fluid capacity of the working'chamber 41, the piston is provided with an interior bore 57 within the cylindrical portion 46, a reduced diameter bore 58 within the embossmentSS, and a generally frusta-conical bore section 59 joining the bores 57 and 58.

The annular groove 49 formed in the cylindrical peripheral portion46 of the piston is utilized to equalize the pressures upon Vthe piston seal rings 48, through the communication of this groove, via a slot 60 and a passage 61, With the cylindrical opening 54. Of course, in the drawings, the piston 45 is shown in .its fully discharged position in which the piston boss 53 abutsthe shoulder 52 of the plug 14. When the piston is in this position, it will be appreciated that the groove 49 is subected to any uid pressure within the opening 54 tending to move the piston to the left, as shown in the drawings, or toward its charged position at which potential energy 1s stored within the accumulator. The provision of the passage 60 will insure that the groove 49 is subjected to any piston-displacing liquid pressures at all operative positrons of the piston, and the seal rings 48 are thus both subjected to the same pressure, so that there is no tendency toward extrusion of the O rings or similar seals from the seal recesses 47.

To charge the accumulator with a gas, such as nitrogen, under pressure, the gas chamber 40 and the working chamber 41 are individually filled. It will be noted that the piston 45 divides the working chamber 41 into a gas compartment 65 and a liquid compartment 66, the liquid compartment being at its minimum dimension, and the gas compartment being at its maximum dimension, when the accumulator is fully discharged and the piston occupies the position illustrated in the drawings.

To charge the gas chamber 40, the plug 15 is provided with an axially extending recess 67 extending only partially through the plug 15 and communicating with a radially extending passage 68 extending radially beyond the confines of the inner shell 35 and communicating through an axial passage 69 with the gas chamber 40. The axially outward end of the recess 67 is interiorly threaded to receive a lling valve 68 of conventional one- Way design which will accommodate the passage of fluid under pressure into the recess 67 and the passages 68 and 69, but which will prevent the back-flow of fluid under pressure through these passages from the gas chamber 40. The gas compartment 65 of the working chamber 41 is precharged with gas under pressure through a straight, generally cylindrical passage 71 extending cornpletely through the plug 15 and threadedly receiving at its outer end a valve 72 identical with the valve 70 heretofore described.

During the filling operation, the filling

valves

70 and 72 are connected to a tank 73 or similar source of gas under pressure. A typical filling installation includes the tank 73, a regulating valve 74 located at the outfed line 75 of the tank and eective to regulate the pressurevof gas from the tank to some predetermined filling pressure, say 3000 pounds per square inch. A iilling line 76 runs directly from the regulator valve to the valve 70, so that the gas chamber 40 is iilled with gas at the pressure determined by the regulating valve, 3000 pounds per square inch, in the chosen example. A branch line 77 has interposed therein a reducing valve 78 for reducing the pressure in the line 77 which is connected to the valve 72. The gas compartment 65 of the working chamber 41 therefore is filled at the pressure determined by the reducing valve, for example on the order of 2500 pounds.

Thus, the annular gas chamber 40 is filled to a pressure of 3000 pounds, while the gas compartment 65 is filled to a pressure of 2500 pounds. As initially filled, there is a collapsing force which is radially inwardly directed acting upon the outer periphery of the sleeve 35 which is equivalent to the differential pressure of the gas chamber, 3000 pounds per square inch, and the pressure in the gas compartment 65, namely 2500 pounds per square inch. The net or differential collapsing force acting upon the sleeve 35 is thus 500 pounds per square inch.

The filling lines 76 and 77 `are now removed from the

valves

70 and 72, respectively, and the valves act to seal the chambers 40 and 41 from one another. The threads 25 are not utilized to connect the accumulator into its hydraulic actuating circuit, and upon the entry of hydraulic uid under pressure greater than the gas pressure in the compartment 65, the piston 45 will be moved to the left to its charged position. Assuming that the hydraulic pressure acting upon the piston is 5000 pounds, the piston will be moved to the left until the gas pressure within the compartment 65 equals the hywill be 5000 pounds per square inch of gas pressure in the gas compartment 65 and the 5000 pounds per square inch of hydraulic pressure acting on the piston in the liquid compartment 65. Thus, the interior periphery of the sleeve 35 will be subjected to a radially acting bursting pressure of 5000 pounds per square inch.

However, the exterior periphery of this sleeve is subjected to a collapsing pressure which is equivalent tothe pressure in the gas chamber 40, which is 3000 pounds per square inch. Accordingly, there will be a net bursting pressure upon the sleeve 35 of 2000 pounds per square inch. This bursting pressure may be readily accommodated by a sleeve of moderate or reasonable thickness and formed of a drawn or forged steel.

During this change in the pressure Within the working chamber 41, there has been no change in the pressure in the gas chamber 40. The pressure in the gas chamber remains at its initial filled pressure of 3000 pounds per square inch, and this pressure constitutes the sole bursting force exerted upon the outer sleeve. This burst ing force remains constant throughout the entire worling cycle, and this pressure can be readily accommodated by a sleeve of reasonable thickness and of conventional drawn or forged steel.

Thus, it will be seen that the present invention accommodates the generation of a high working pressure within the working chamber of the accumulator without subjecting either the inner sleeve or the outer sleeve to a burst pressure n excess of that which can be readily accommodated by a casing or shell of practical size and construction. A constant burst force is exerted upon the outer shell during all working positions of the piston. The sleeve is subjected to a net burst pressure considerably less than the actual working pressure within the Working chamber, and the burst load actually generated by the high working pressure is distributed or allocated between the two sleeves or easing parts.

The many practical advantages and the commercial advantages of utilizing this type of construction ywill be readily appreciated by those skilled in the art.

While preferred embodiments have been described above in detail, it will be understood that numerous modiications might be resorted to without departing from the scope of my invention as defined in the following claims.

I claim:

l. An accumulator comprising nesting, spaced inner and outer shells isolated from fluid communication with one another and adapted to contain uid at different pressures and a uid pressure displaceable element disposed inside said inner shell, the inner shell being adapted to be charged with uid under. pressure for subsequent tiuid discharge, and the space between said inner shell and the outer shell being adapted to contain lluid at a pressure substantially less than a pressure of uid in said inner shell when charged, whereby neither of said shells is subjected to a burst load commensurate with the pressure generated within said inner shell.

2,. An accumulator comprising a generally tubular outer casing closed at each end, an inner generally tubular sleeve axially nested within said outer casing and radially spaced therefrom to define therewith a sealed gas chamber surrounding the periphery of said sleeve, an axially movable piston disposed in said sleeve and sealingly engaging the inner periphery thereof to divide the interior of said sleeve into a sealed gas compartment and a liquid compartment, and means communicating with said liquid compartment for admitting liquid under pressure thereinto, said sealed gas chamber being adapted to contain a gas under pressure, and said gas compartment being adapted to contain a gas under pressure determined by the pressure of any liquid in said liquid compartment and normally substantially greater than the pressure in said chamber.

3. A gas-liquid accumulator comprising an outer shell 7 and an inner shell separated lby a sealed gas` chamber substantially surrounding said inner shell, said inner shell enclosingl a working chamber containing both a liquid Y and a gas under pressure, a piston disposed in said inner shell and interposed between the liquid and the gas therein and freely movable axially of the shell in accordance with any `differential liquid and gas pressures acting thereon, said sealed gaschainber containing a gas 'under pressure substantially less than the pressure in said working chamber, said outer shell being subjected to a substantially constant burst pressure .which is substantially less than the Working pressures obtainable in said working chamber. Y

4. In an accumulator for the storage of mechanical energy in `the form of a compressed gas, nesting structural elements dening a plurality of substantially concentric chambers each containing a uid under pressure, said chambers being isolated from uid communication with one another, an outer one of said chambersbeinglled with a uid under a constant pressure, an inner o'ne of said lchambers being filled with a fluid ata fluctuating pressure normally substantially greater than the constant pressure in said outer chamber, and a free oating piston disposed in said inner one of said chambers for movement therein in accordance `with said uctuatingworking pressure, the differential pressure between said chambers being exerted upon one of said chamber deining elements common to said chambers, and a constant burst pressure being exerted upon a second of said chamber dening elements enclosing said outer chamber.

5. A gas-liquid accumulator comprising an open-ended outer shell and an open-ended, cylindrical shell nested in vsaid outer'shell,` end plugs closing the ends of both shells and said shells being circumferentially separated by a sealed gas chamber surrounding said inner shell and isolated from uid communication with the interior there of, said inner shell enclosing a wor/king chamber containing both a liquid and a gas under pressure,ra Afree oating piston disposed in said working chamber toV separate the liquid and gas therein, means in one of said end plugs dening a passage for introducing liquid under pressure into said working chamber to charge the `ac'- cumulator by compressing the gas in said worling chamber so thatv the compressed gas can later discharge said liquid under pressure, and means in the other of said end plugs for introducing into said sealed gas chamber a gas under a pressure less than the pressure of the compressed gas in the working chamber when the accumulator is charged, the outer shell being subjected to a burst load determined by the lesser pressure in said sealed chamber and the inner shell being subjected to a maximum burst load determined by the differential pressure between the pressure in said sealed'chamber and the pressure of the compressed gas and the liquid in said working chamber.

References Cited in the ile of this patent UNTED STATES PATENTS Germany Jian. 31, 1925