US2708949A - Hydraulic accumulators - Google Patents

Description

May 24, 1955 J. A. KRAPF HYDRAULIC ACCUMULATORS Filed Nov. 2, 1954 |NVENTOR okn Albert Krapf BY uw f- ATTORNEYS United States Patent O HYDRAULIC ACCUMULATORS John Albert Krapf, Cleveland Heights, Ohio Application November 2, 1954, Serial No. 466,260

'7 Claims. (Cl. 13S-31) This invention relates to accumulators for hydraulic pressure lines which may be used as storage vessels for hydraulic iiuid under pressure and as cushions to absorb pressure shocks. The accumulator of the present invention may be made in a large variety of sizes, the larger sizes being generally used as storage vessels andthe smaller sizes as shock cushions. When used as a storage vessel the accumulator is placed in a pressure line directly connected to the hydraulic pumps or other pressure source, so that when the demand for the pressure iluid is less than the output of the pressure source, a reserve supply will be forced into the accumulator until it is full and, when the demand is greater than the output of the pressure source, a portion of the reserve supply of liquid will be forced into the pressure line to supplement the supply of liquid from the pressure source.

The accumulator of the present invention is of the precharged pneumatic pressure type employing a closed pneumatic system the volumetric capacity of which is greater than the reserve supply capacity of the accumulator, and which may bear any desired ratio to the said reserve supply capacity such as l to l or 20 to l, so that the entire reserve supply of the accumulator may be forced into the pressure line with a relatively small drop in the pressure of the closed pneumatic system, there being a correspondingly slight differential in the pressure that resists entry of hydraulic fluid into the accumulator.

The accumulator has a liquid displacement chamber in open communication with the liquid pressure line, a gas pressure chamber separate from but alined with the displacement chamber, and a liquid displacing plunger that has one end in the displacement chamberand its opposite end in the gas pressure chamber and that extends through guiding and sealing sleeves in the proximate ends of the liquid and gas chambers. The plunger is' of a length such that it can have a stroke in which the end thereof in the displacement chamber can move far enough to displace the desired volume of liquid while the opposite end remains in the gas pressure chamber, and the chambers and plungers are preferably of lengths such that the portion or" the plunger in one chamber or the other at the ends of its stroke is of greater'length than the portion thereof extending through the heads.

Each accumulator will be designed about a. definite volume. of fluid which it may retain or expel into the pressure line. This volume is determined by the diameter of the plunger and the length of its stroke in the liquid displacement chamber. An important feature of this accumulator is in the volumetric differential between the gas pressure chamber and the displacement volume of the plunger. This will be a predetermined ratio which may be anything desired within very wide limits. The volumetric capacity of the gas chamber is preferably large as compared to the volume of liquid that can be displaced by the plunger so that-the difference in gas pressure at the ends of the plunger stroke will be relatively small.

At each end of the plunger stroke the gas pressure will ICC have no etlect on the liquid pressure but at any point of plunger travel between the two extremities the gas pressure will tend to equal the liquid pressure. Upon the slightest drop or rise of pressure in the pressure line the plunger will be moved correspondingly by this action of the gas pressure to expel liquid into the pressure line to reinforce the supply source or absorb liquid for storage. The gas chamber will be precharged, with no luid pressure in the liquid displacement chamber, to a pressure equal to the desired minimum liquid pressure. The liquid displacement chamber is then filled with liquid from the pressure line to create a pressure in the gas chamber which is recognized as the maximum liquid pressure. External means of control will be used to hold the line pressure within these minimum and maximum pressures. This accumulator will act as a cushion for shock when the plunger is at any intermediate position or when the plunger is at the end after expelling all liquid.

The liquid displacing plunger is preferably hollow and closed at the end thereof that is within the liquid displacement chamber, the interior of the plunger being at all times in communication with the gas pressure of the chamber. The thin-walled tubular plunger is of light weight and is quickly responsive to changes in pressure in the hydraulic circuit and, by providing a hollow plunger with its interior in communication with the gas chamber, the volumetric capacity of the gas chamber is increased.

The gas pressure and liquid displacement chambers are so supported that the liquid displacing chamber can be readily detached from the pressure line and from the air chamber to permit removal of the plunger and replacement of the seals in the heads of the two chambers. The gas and liquid chambers are connected by means of Va supporting and spacing structure which serves to accurately position the two chambers with a portion of the plunger exposed between the heads. The supporting structure is open on at least one side thereof to provide accessibility to the gas chamber head for lubrication of the seals and for replacement of the seal in the gas chamber head and also to expose to view the heads through which the plunger passes and the portion of the plunger between them, so that fluid or gas leakage can be quickly detected and movements of the plunger due to actuations of the control valve or valves can be observed.

Since the pneumatic pressure system is entirely disconnected from the hydraulic pressure line and there is no possibility of leakage of gas from the pneumatic pressure chamber into the hydraulic line, air may be employed in the pneumatic system without danger of creating an explosive mixture in the hydraulic system, making it unnecessary to charge the accumulator with an inert gas such as nitrogen.

Objects of the invention are to provide an accumulator ofthe gas pressure chamber type in which the volume of liquid which the accumulator can be depended upon to supply to the pressure line can be accurately predetermined, to provide an accumulator in which the maximum pressure drop in the gas chamber due to flow in the pressure line can be accurately predetermined and limited to a relatively small percentage of the maximum pressure, to provide an accumulator of the movable plunger type which can be quickly and easily assembled and which can be readily disassembled for replacement of seals, and to eliminate the expense incident to the charging of the accumulator with an inert gas.

Further objects of the invention are to provide an accumulator of the plunger type which is of simple construction and in which the cost of manufacture is low because of the few machining operations required, which can readily be installed close to the control valve or valves.

With the above and other objects in view, attention is directed to the accompanying drawings forming a part of this specification, in which:

Figure 1 is a side elevation of the accumulator with portions broken away and shown in central, vertical section;

Fig. 2 is a horizontal section taken on the line indicated at 2 2 in Fig. 1; and

Fig. 3 is a foreshortened longitudinal section showing a modified form of accumulator.

The accumulator of the present invention has a gas pressure chamber A, a liquid displacement chamber B that is in open communication with a hydraulic pressure line C, and a liquid displacement plunger D that is slidably mounted in proximate heads of the chambers A and B with one end thereof in the chamber A and the other end thereof in the chamber B.

Since the liquid displacement plunger D is guided only in the heads of the chambers A and B, these chambers can be of any desired shape. In the accompanying drawings the chambers are shown in cylindrical form and this construction is preferred because of the pressure resisting capacity of cylindrical walls. The accumulator is preferably mounted in upright position with the gas chamber A above the liquid displacement chamber B, but may be mounted in other positions in installations where the vertical mounting is not convenient.

As herein shown, the chamber A is provided with an elongated cylindrical Wall 1, an upper head 2 and a lower head 3 that is provided with a downwardly projecting plunger guiding sleeve portion 4. Any suitable means may be provided for charging the chamber A with gas at the desired pressure, such as a fitting 5 adapted to be connected to a suitable source of pressure and having a valve 6 for closing the passages through the tting.

The gas chamber A is attached to a supporting structure which has parallel vertically disposed side plates 7 and 8 which engage the cylindrical wall 1 at opposite sides thereof. Vertical connecting plates 9 and 10 are welded to the inner faces of the plates 7 and 8 and are disposed perpendicularly to the plates 7 and 8 and radially with respect to the axis of the chamber A, the plates 9 and 10 being welded at their upper ends to the head 3 and at the upper portions of their inner edges to diametrically opposite portions of the sleeve 4. The bottom edges of the plates 7, 8, 9 and 10 are welded to a horizontal bottom plate 11 which is provided with a central opening 12 in axial alinement with the sleeve portion 4 of thc head 3.

The liquid displacement chamber B has an elongated cylindrical wall 13 which may be of considerably smaller diameter than the wall 1 of the chamber A. The lower end of the chamber B is closed by a head 14 and the upper end thereof has a head 15 which has a f sleeve portion 16 that is received in the opening 12 of the plate 11 and a circumferential ange 17 that engages the under side of the plate 11. The ange 17 is detachably secured to the under side of the plate 11 by bolts 18 and has a boss 11a that lits in the opening 12 to position the sleeve 16 in axial alinement with the sleeve 4. The plates 9 and 10 which space the plate 11 from the head 3 are of a length such that the sleeve portions 4 and 16 of the heads 3 and 15 are spaced a short distance apart, exposing a portion of the plunger between them.

The plunger D is tubular, having a cylindrical wall 19 and a closure disk 20 secured in the lower end thereof. The upper end of the plunger is reinforced by a disk 21 secured therein a short distance below the upper end of the tubular wall 19, the disk 21 being provided with a central aperture 22 and the adjacent edge of the wall 19 being provided with notches 23 so that the interior of the plunger is in communication with the interior of the gas pressure chamber A when the plunger is in engagement with the head 2.

The chambers A and B are preferably of substantially the same length and the plunger D is of a length such that when in its uppermost position in engagement with the head 2 of the chamber A, its lower end is in the upper end portion of the chamber B, and when in its lowermost position in engagement with the head 14 of the chamber B, its upper end will be in the lower end portion of the chamber A. In order to enable the liquid under pressure in the chamber B to exert an upward thrust on the plunger D when it is in its lowermost position, the head 14 is provided with a central stop lug or projection 24 with which the closure member 2!) engages and which serves to space the major portion of the member from the head 14. In order to permit detachment of the chamber B from the supporting structure to obtain access to the seals, connection between the chamber B and the hydraulic pressure line C is through a pipe line 25 that has a detachable connection 26 between portions of the line connected to the chamber and pressure line, and a valve 27 between the detachable connection 26 and the line C which can be closed when it is desired to detach the chamber B.

Any suitable guiding and sealing means may be provided in the space between the exterior of the plunger and the interiors of the sleeve portions 4 and 16 of the heads. As herein shown, bearing sleeves 28 and 29 are provided in the sleeve portions 4 and 16 and packings 30 and 31 of the V-ring type are provided at the inner ends of the bearing sleeves. Annular retaining anges 32 and 33 are bolted to the lower end of the sleeve portion 4 and at the upper end of the sleeve portion 16.

As shown in Fig. 2 of the drawings, the supporting and spacing structure has two open sides affording access to the space between the heads 3 and 15 of the chambers A and B. Where the liquid of the hydraulic system is an oil, the seal for the liquid displacement chamber B will usually be adequately lubricated by oil carried on the plunger during its upward movements and the seal in the head 3 of the gas chamber A may also be lubricated to some extent by oil carried on the plunger surface from the chamber B. However, conventional lubricant fittings may be provided on the exposed portions of the heads if desired. Lubrication of the seals may also be effected by applying lubricant to the exposed portion of the plunger during its reciprocating movements. Oil thus applied may also facilitate the observation of the plunger movements upon actuation of the control valves and detection of leakage past the seals.

The chambers A and B are preferably constructed from sections of steel tubing of the desired diameter with heads in the form of disks of the proper size welded to the ends thereof. The plunger is also formed of cylindrical steel tubing with disks welded in the ends thereof.

Precision machining is required only on the exterior surface of the plunger and the interior surfaces of the guiding and bearing members. The exterior of the plunger' is accurately machined and highly polished and the bearing sleeves are accurately machined to lit the plunger. Suitable means may be provided for gauging the pressure in the gas chamber A when desired, and the gauging device may be in the pressure supply line, as is common practice in the art'.

When it is desired to provide a pneumatic system of a volumetric capacity quite large as compared to the capacity of the liquid displacement chamber, it is advantageous to provide a pressure tank separate from the air pressure chamber into which the plunger extends that communicates with the pressure chamber. When such a pressure supply tank is provided the air pressure chamber of the accumulator may be identical with the liquid displacement chamber, both chambers being but slightly greater in diameter than the plunger.

ln Fig. 3 an accumulator is shown which is substantially like that shown in Figs. l and 2 except that it has an air pressure chamber A', is of the same size and shape as the liquid displacement chamber B' and is in communication with a pressure tank E which may be of any desired volumetric capacity. The chamber B' is substantially identical with the chamber B above described and the plunger D' moves from a position engaging the upper end of the chamber A' to a position engaging the lower end of the chamber B. The chambers A and B are supported in axial alinement with their adjacent ends spaced apart in a structure having apertured walls within which are located parallel supporting plates 36 and 37 having alined central openings 33 and 39 to receive the ends of the chambers A' and B. The chamber A' has a tubular wall 40 and an upper end closure 41 that has a central internal boss 42. The chamber B which is substantially identical with the chamber A, has a cylindrical wall 4.3 and a lower end closure 44 provided with a central internal boss 45. The chambers A and B have heads 46 and 47 `with sleeve portions 48 and 49 which receive guiding and sealing means for the plunger D' which are substantially the same as the guidf ing and sealing means in the modification first described. The heads 46 and 47 are provided with flanges 50 and 51 that engage the plates 36 and 37 and that are provided with positioning bosses 53 that fit in the openings 38 and 39.

The plunger D' has a tubular body 54 and upper and lower heads and 56. The head 55 is in the form of a disk secured within the upper end of the tubular body 54 and has openings 57 which admit gas from the chamber A' to the interior of the plunger. The head 56 is in the form of an imperforate disk secured in and closing the lower end of the hollow plunger. The heads 55 and 56 have external bosses 5S and 59 that engage with the bosses 42 and 45 to space the plunger from the closures 41 and 44 at the ends of its stroke, so that the gas pressure within the plunger and acting on the head 56 is always connected to the pressure in the chamber A and the head 56 is exposed to the hydraulic pressure in the chamber B when in its lowermost position.

The chamber B' may be detachably connected to the hydraulic pressure line as in the modification previously described and the chamber A will be maintained in constant communication with the tank E.

By making both the gas pressure chamber and the liquid displacing chamber of the same size, tubing of relatively small diameter may be used, thereby reducing the cost of manufacture of the accumulator, and by providing a gas storage tank of the proper size the desired ratio may be provided between the liquid displacement and the volumetric capacity of the pneumatic system. If desired, two or more accumulators may be connected to a single gas storage tank, thereby effecting a further economy in the cost of installation.

Accumulators embodying the present invention may be conveniently connected to the pressure line close to individual control valves and such accumulators may be designed to supply the volume of liquid necessary for the particular mechanism served by the valve and a pressure drop that will provide adequate shock absorption.

In the accumulator of the present invention the volume of liquid supplied to the pressure line is determined by the size of the plunger D and the length of its stroke and the drop in pressure in the gas chamber is inversely proportional to the volumetric capacity of the Vchamber which is varied by movements of the plunger. It will be apparent that for any given liquid supplying capacity any desired pressure drop within wide limits may be obtained by providing a gas chamber of the proper size.

It is to be understood that in accordance with the provisions of the patent statutes, variations and modifications of the specific device herein shown and described may be made without departing from the spirit of the invention.

What I claim is:

l. An accumulator for hydraulic pressure lines comprising a liquid displacement chamber for connection to a hydraulic pressure line and aV gas pressure chamber disposed end to end and spaced apart, said chambers having heads at their proximate ends that are provided with axially alined sleeve portions, a plunger extending through said sleeve portions and movable in response to variations in line pressure, said plunger being of a length to extend from said gas pressure chamber through said heads and through the major portion of the length of said displacement chamber, a seal in the space between the interior of each of said sleeve portions and said plunger, and stop means limiting the movement of said plunger in each direction and permitting movement of said plunger between positions in which the end thereof in said displacement chamber is adjacent one end or the other of said chamber.

2. An accumulator for hydraulic pressure lines comprising a liquid displacement chamber for connection to a hydraulic pressure line and a gas pressure chamber disposed end to end and spaced apart, said chambers having heads at their proximate ends that are provided with axially alined sleeve portions, a plunger extending through said sleeve portions and movable in response to variations in line pressure, said plunger being of a length to extend from said gas pressure chamber through said heads and through the major portion of the length of said displacement chamber, said plunger being hollow, closed at the end thereof in said displacement chamber and open to said gas pressure chamber, a seal in the space between the interior of each of said sleeve portions and said plunger, and means for limiting the movements of the plunger at extreme positions in which the closed end of said piunger is adjacent one end or the other of said displacement chamber.

3. An accumulator for hydraulic presusre lines comprising an elongated liquid displacement chamber for connection to a hydraulic pressure line and a gas pressure chamber of substantially the same length as said displacement chamber, said chambers being disposed end to end and having heads at their proximate ends that have axially alined sleeve portions, a hollow cylindrical plunger extending through said sleeve portions and movable in response to variations in line pressure, said plunger being of a length to extend through said heads and into engagement with either of the remote ends of said chambers, said plunger having a closure at the end thereof in said displacement chamber, a seal in the space between the interior of each sleeve and said plunger, and means for subjecting said closure to the gas chamber pressure and to the displacement chamber pressure in all positions of the plunger.

4. An accumulator for hydraulic pressure lines comprising an elongated liquid displacement chamber for connection to a hydraulic pressure line and a gas pressure chamber of substantially the same length as said displacement chamber, said chambers being disposed end to end and having heads at their proximate ends that have axially alined sleeve portions, a hollow cylindrical plunger extending through said sleeve portions and movable in response to variations in line pressure, said plunger being of a length to extend through said heads and into engagement with either of the remote ends of said chambers, said plunger having a closure at the end thereof in said displacement chamber, said plunger having an apertured disk spaced slightly from the end thereof within said gas chamber, and a notched end that provides communication between the interior of the plunger and the gas chamber when the plunger engages the end wall of the gas chamber, and a lug projecting from the end wall of said displacement chamber for engagement with said end closure to provide a space between the end wall and closure to which the liquid in said chamber has access.

5. An accumulator for hydraulic pressure lines comprising a gas pressure chamber having a head provided with a projecting sleeve, a spacing and supporting structure attached to said head and including a plate parallel to and spaced from said head, said plate having an opening in alinement with said sleeve, a liquid displacement chamber having a head provided with a projecting sleeve received in said opening and a flange engaging said plate around the opening, means for detachably securing said flange to said plate to attach said displacement chamber to said structure and position sai-d sleeves in axial alinement, a cylindrical plunger of uniform diameter from end to end extending through said sleeves, said plunger' being of a length to extend through said heads with the major portion thereof in one of said chambers, said plunger being removable with said displacement chamber when the displacement chamber is detached, a seal be tween the interior of each sleeve and said plunger and means for limiting the movements of said piston in each direction.

6. An accumulator such as deiined in claim 5 in which the ends of said sleeves are spaced apart and in which said supporting and spacing structure is open at one side lil thereof to permit inspection of said seals and to expose to view the portion of the plunger between said sleeves.

7. An accumulator for hydraulic lines comprising a liquid displacement chamber for connection to a hydraulic pressure line and a gas pressure chamber disposed end to end, said chambers 1being elongated and of substantially the same length and diameter, said chambers having heads at their proximate ends that are provided with axially alined sieeve portions of but slightly less diameter than said chambers, a plunger slidably .fitting in said sleeve portions and movable in response to variations in line pressure, said plunger being of a length to extend through said sleeve portions and through the major portion of the length of either of said chambers, a seal in the space between the interior of each of said sleeve portions and said plunger, stop means limiting the movement of the plunger in each direction, and a gas pressure tank in communication with said gas pressure chamber.

No references cited.

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