FR2563584A1 - Improved hydraulic accumulator for a high-pressure hydraulic fluid system - Google Patents

Abstract

Abstract of the technical content of the invention. In this accumulator comprising a cylindrical tubular wall 10 having a stainless steel sheathing 24 and end caps 14a, 14b, one 14a of the said caps comprises an internal sheathing 26, the peripheral edge of which is welded to the peripheral edge of the sheathing 24, the parts of the sheathings 24, 26 facing each other being in addition clamped between surfaces of the tubular wall 10 and of the end cap 14a. The opposite end cap 14b comprises a central flow orifice 20 the internal end 22 of which forms a valve seat. A piston 34 is installed in a sliding manner in the cylindrical tubular part and has a part 39 in the shape of an inverted dome which is adapted so that it may be applied onto the seat 22 in case a bellows 40, with moulded undulations, which is placed between the periphery of the piston and that of the end cap 14b, breaks.

Description

 The present invention relates to accumulators, flushing tanks and in general to systems in which an inflatable member constituted by a metal bellows disposed in a chamber is adapted to undergo elastic deformation When a gas under pressure in the end of the chamber is applied to one side of the bellows to resist the pressure of a hydraulic fluid system acting at the other end of the chamber, on the other face of the bellows, and it relates more particularly to accumulators high pressure hydraulics intended to operate in pressure ranges of the order of 20,680 to 41,360 kPa.

 Until now, commercially available standard accumulators have included a large piston with conventional circular rings which were expensive to maintain. I1 appeared i; more recently, accumulators in which the circular ring device has been replaced by a metal bellows with welded edges which has been found to have inherent undesirable operating characteristics and to cause problems due to contamination and high stress concentrations. .

 Failure of a welded-type metal bellows is usually limited to the weld that holds all of the corrugations and normally results in the separation of one complete corrugation from another and instantaneous loss of air or other compressed actuation gas in the system. hydraulic, and therefore the bellows of the welded corrugation type has not usually been accepted in particular for use. under operating conditions under high pressure.

 The prior art is represented by US Pat. Nos. 2,411,315, 2,682,893, 3,230,975, 3,456,673, 3,695,297, 3,862,646, 3,935,882, 3,939,872, 4,064,911, 4,129,025, 4,177,023 and 4,213,545 ..

 It has been found according to the invention that most of the problems posed by bellows in accumulators, and in particular those having to operate under relatively high pressures, can be reduced and in most cases largely eliminated by using an element inflatable constituted by a metal bellows of the type comprising deformed corrugated corrugations.

 US Patent No. 3,862,646 describes a hydraulic accumulator comprising a tank which is in its cylindrical assembly with an end wall made of material and a bottom welded on the other end of the tank and comprising a central orifice which communicates with the inside the tank. A piston having a circular shape is arranged inside the tank so as to move therein with an axial longitudinal movement, this piston comprising a central portion in the form of a plate which is movable as it approaches and s away from a closed position with respect to said orifice.A metal bellows of the welded type is fixed by welding to the external periphery of the piston and to the internal surface of the bottom and guide means are provided on the periphery of the piston to bear against the internal surfaces of the tank and to guide the movements of the piston when the bellows expands and contracts. As described in this way, the bellows is subject to the aforementioned inherent problems and operational failures, which are for the most part corrected by the invention by the use of a bellows of the type comprising deformed corrugations. molded.

 This document also describes a pressure indicator intended to indicate the absence or the existence of a pressure in the chamber previously charged with air or another gas, in which a charging rod has an end inside. of the pressure chamber and an end opposite to the outside of this chamber, which is closed by pinching after the loading operation.

The load rod is biased in one direction by a spring and can move in response to pressures in the chamber to provide a signal visible from the outside indicating the presence or absence of pressure in the chamber. According to the present invention, the constricted filling tube or the rod is newly formed so as to produce a Bourdon tube, which will be deformed in a well-known characteristic manner in the event of a loss of the gas pressure in the chamber, thus providing an external visual indication.

 US Patent No. 4,213,545 describes an expandable bellows for a flush tank, in which the metal bellows is of the type comprising deformed molded corrugations. This document discusses in detail the advantages of this type of molded bellows and its ease of adaptation in particular for arrangements in which the extension of the bellows extends beyond the usually limited mode of extension. In the present invention, the bellows is contracted in order to evacuate the hydraulic fluid from the chamber of the accumulator and thus has a different operating mode from that described in this aforementioned patent.

The invention includes a number of improved form and function characteristics which distinguish it from the prior art, these characteristics being the following:
1) An important characteristic consists in the use of bellows comprising molded corrugations instead of corrugations which are welded together by their internal and external edges. A main advantage of the molded bellows compared to the welded type bellows is that a failure in the molded bellows is usually limited to a small region in the minor root of one of the corrugations of the bellows and produces a small leak which gives time for replacement or repair; otherwise, a bellows failure usually occurs in the weld that holds the corrugations together and normally results in one complete corrugation separating from another, causing instant loss gas in the hydraulic system.

 2) The accumulator according to the invention is manufactured so as to produce an airtight chamber previously filled with gas, which provides the energy to move the piston in a desired direction to eject the hydraulic fluid when the system pressure drops.

3) The gas chamber of the accumulator is previously charged by means of a filling tube which is permanently closed at its external end and in which the external part: of this tube is shaped so as to produce in made a tube of
Bumblebee which provides a visual indication in the event of a loss of gas pressure.

 4) The closed container of the invention uses a housing which is provided with a stainless steel liner to which the stainless steel bellows can be welded, thus making it possible to produce the housing in a suitable light material such as high-strength titanium .

 5) In the gas chamber, the lining of the end cap and the side wall are tightly connected by means of a new combination of a welded joint and with compression, in which the peripheral edge of the cap joint is welded on the adjacent end edge of the wall liner, the welded edges then being clamped between opposing surfaces respectively on the threaded end cap and on the adjacent end of the enclosure casing.

 6) The reciprocating guided piston of the accumulator is designed so as to produce a suspended dome which rests on a valve seat formed at the internal end of a flow fitting in the end cap for the fluid from the hydraulic system of the accumulator chamber, and which functions as a mushroom valve to close the accumulator in the event that there is a significant pressure drop in the hydraulic system, and thus prevents air or gas to pass into the hydraulic system which is connected.

 7) The piston is shaped so as to have a guide ring of its periphery adapted to come into sliding contact on the internal face of the lining of the side wall in order to ensure a uniform movement of the piston and to prevent any misalignment or tipping over which would result in seizure or excessive overload.

 The invention relates more particularly to improvements to hydraulic accumulators and in particular to accumulators intended to operate with high pressure hydraulic systems.

The aims of the invention are to produce an accumulator:
- intended to be used with a hydraulic fluid system and which uses a metal bellows having molded corrugations and which is connected to a piston - mobile in order to operate in contraction mode in order to expel the fluid from the hydraulic system when the pressure of this system falls;
- intended for use with a high pressure hydraulic fluid system in which a piston is guided to move axially in a chamber of a casing and divides the chamber into a part containing a gas under pressure and into a part belonging to the System hydraulic fluid under high pressure, and in which a metal bellows is connected by one end to the periphery of the piston and is welded by its other end to a stainless steel chamber liner which surrounds it;
- intended to be used with a high pressure hydraulic fluid system, which comprises a chamber containing a gas formed by an outer casing wall which surrounds it, and a threaded end cap, and in which the chamber containing the gas is hermetically sealed by the new combination of a welded joint and a compression, in which the peripheral edge of a jacket of the end cap, made of stainless steel, is welded to the associated peripheral end edge of a outer wall liner of stainless steel which surrounds it, and in which the welded edges are gripped and tightened circumferentially between annular tightening surfaces cooperating together provided respectively on the end cap and the adjacent end of the wall of the outer casing related to it ;;
- in which a reciprocating piston and a metal bellows connected to it and having molded corrugations, separate an internal chamber into a part containing a pressurized gas and into a part having a flow orifice connected to a system with hydraulic fluid, this connection comprising at its internal end an annular valve seat, and the piston having a cup part which can cooperate with the seat to shut off the flow of gas coming from the chamber in the hydraulic system, in the case of a leak in the bellows.

 Another object of the invention is to produce a simple and new pressure indicator for a chamber of an accumulator, previously filled with gas, in which the closed external end part of a filling tube for the chamber containing the gas is shaped so as to produce a Bourdon tube sensitive to pressure in order to provide an external visible indication in the event of a loss of pressure in the chamber containing the gas.

Other characteristics and advantages of the invention will appear during the description which follows, made with reference to the appended drawing given solely by way of example and in which:
Fig.l is a side elevational view of an accumulator according to the invention, some parts being cut away in a diametrical axial section in order to show important details of the construction and the relative arrangement of the members cooperating together;
Fig.2 is a partial sectional view on a larger scale of the part surrounded by line 2-2 of Fig.l in order to show the details of the sealing combination by welding and compression for the linings of the walls d external end of the chamber containing the gas;
Fig.3 is a partial sectional view on a larger scale of the region surrounded by line 3-3 of Fig.l to show the details of the welded connection between one end of the metal bellows and the steel liner stainless of the external wall;
Fig.4 is an enlarged sectional view of the region surrounded by line 4-4 of Fig.l to show the details of the welded connection of the metal bellows with the piston;
Fig.5 is a partial plan view on a larger scale of the Bourdon tube of the device visibly indicating outside a loss of pressure occurring in the chamber of the accumulator containing the gas, along line 5 5 of Fig. L.

 Referring more particularly to the drawing, the high pressure hydraulic accumulator according to the invention is shown in FIG. 1 and comprises an elongated cylindrical enclosure C which is preferably made of a light and high resistance material such as titanium in order to produce a tubular wall 10 which is connected at its opposite ends respectively by screw connections 12a, 12b to end caps 14a and 14b which are also made of titanium. The innermost end of the screw connections 12a, 12b is preferably sealed by means of an annular sealing ring 16a, 16b respectively. Preferably the end cap 14a is shaped so as to produce a wall d the end 18a in the shape of an inverted bowl, while the end cap 14b is shaped so as to produce a frustoconical end wall 18b curved inwards which has in its center a connector 20 for a flow orifice, the inner end of which is shaped so as to produce an annular valve seat 22.

 The wall 10 and the internal surface of the end wall 18 are lined with a stainless steel liner 24, 26 respectively. As best seen in Fig. 2, a marginal portion 24a is covered by a peripheral marginal portion 26a of the liner 26 of the end cap, and the marginal portions are then welded together and then clamped in a manner that will be explained in order to achieve a new sealing combination by welding and compression. For this purpose, the welded marginal portions 24a, 26a of the liner ge are arranged between annular chamfered surfaces 28a and 28b facing each other, which are formed respectively on the adjacent end of the tubular wall 10 and on a clamping ring. 30 which is rotatably mounted in support in a circumferential groove 32 of the end cap 14a which extends in the periphery thereof. Thanks to this arrangement, it is understood that when the end cap 14a is screwed onto the adjacent end of the tubular wall 10, the surfaces 28a and 28b which face each other tighten and compress the welded marginal parts 24a and 26A.

 A reciprocating piston 34 is mounted inside the enclosure and is shaped so as to present a peripheral groove 36 open towards the outside which is arranged so as to carry a ring 38 for guiding the piston in sliding contact. with the internal surface of the lining 24 of the wall in order to ensure a uniform movement of the piston and to prevent it from offsetting, or tipping over, which would result in seizure or overload. The piston also comprises a part 39 made of material, extending downwards and in the form of a cup or dome, which fulfills the function of valve shutter when it is moved axially in contact with the annular seat 22, under the operating conditions which will be described more fully below.

 Although it is generally known in the prior art to connect a piston with a metal bellows comprising welded corrugations, according to a characteristic of the invention, a bellows of the type comprising molded corrugations is used for the reason that found that this type of bellows ensures considerably improved and more reliable operation, in particular in the case of high pressure accumulators.

Consequently, a bellows 40 of the molded type is arranged so as to surround the dome-shaped part 39 of the piston 34, one end of this bellows being welded by its periphery, as indicated at 42 in FIG. 4, on the part 39 in the shape of a dome of the piston, in the vicinity of its junction with the peripheral part of the piston having a groove 36, the other end of the bellows being welded as indicated at 44 in FIG. 3 on the end of the lining 24 of the wall adjacent to the end cap 14b.

 With this arrangement the piston 34 and the sou-.

flounder 40 cooperate to divide the interior of the enclosure
C in a chamber 46 containing a gas and in a chamber 48 containing a hydraulic fluid. The chamber 46 containing the gas is arranged so as to be previously filled with a compressed gas by means of a small filling tube 50 (FIGS. 1 and 5) which is fixed to the end cap 14a with a end extending through the end wall 18a thereof and the internal end of which is welded to the liner 26 in order to communicate with the interior of the chamber 46. The external end of the tube 50, after the filling of the chamber, is closed permanently as indicated by the reference 52 in Fig. 5. According to another characteristic of the invention, the external end part of this filling tube is shaped so as to produce a tube Bumblebee to provide an external visual indication in the event of loss of gas pressure in chamber 26.

 In operation, it is understood that the gas under pressure in the chamber 46 provides the energy to force the piston 34 in the desired direction to drive the hydraulic fluid through the flow fitting 20 when the pressure of this fluid drops, and that when the pressure drops enough or when the bellows can be broken, the part 39 of the dome-shaped piston acts as a valve plug to come into contact with the seat 22 and thus isolate the hydraulic fluid from the system and prevent it from receiving gas from the accumulator enclosure.

 It appears from the foregoing description and from the drawings that the aims of the invention are thus achieved.

 Of course, the invention is not limited to the embodiment shown and described which has been chosen only by way of example, numerous modifications being able to be made to it without departing from its scope or its mind.

Claims (10)

 1- High pressure hydraulic accumulator  characterized in that it comprises an enclosure (C) comprising an elongated tubular wall (10) with an internal cylindrical surface, end caps (14a, 14b) respectively fixed by screwing in the opposite ends of the tubular wall and cooperating with these to make an interior chamber, one of said end caps (14b) having a central connector (20) with a flow orifice in said chamber for a hydraulic fluid system, a piston (34) mounted so as to perform an axial reciprocating movement guided in said tubular wall and cooperating with said internal surface to separate said chamber into a - part f previously filled with a gas under pressure and in a part communicating with said fitting (20) for the hydraulic fluid system, and a bellows (40) of metal of the type having corrugated molds under pressure in order to reduce the risk of leakage in operation, said bellows having one end fixed by its perip inherited on the surface of the internal wall contiguous to the end cap (14b) comprising said connector (20) in order to allow a longitudinal expansion of the bellows when the piston (34) is moved away from said connector (20) and a longitudinal contraction of the bellows when the piston is moved closer to said fitting.  2- hydraulic accumulator according to claim 1, characterized in that said tubular wall is made of a light material with high resistance, said internal surface being constituted by a lining (24) of stainless steel and said opposite end of the bellows (40) being welded by its periphery to said liner (24).  3- Hydraulic accumulator as claimed in claim 2, characterized in that the internal surface of the other of said end caps (14a) comprises a lining (26) made of stainless steel, this lining comprising a peripheral edge welded circumferentially to an edge adjacent to the liner (24) of the tubular wall, which covers it.  4- hydraulic accumulator according to claim 3, characterized in that the edges of the liner (26) of the end cap and of the liner (24) of the tubular wall, which overlap and are welded are also hermetically sealed by circumferential clamping between annular surfaces facing the threaded end cap and the adjacent end of the tubular wall (10) respectively.  5- hydraulic accumulator according to claim 1, characterized in that said first end cap (14b) is shaped so as to produce a frustoconical end wall (18b) curved inward, said connector (20) of the the flow port having an inner end shaped to provide an annular valve seat (22).  6- hydraulic accumulator according to claim 5, characterized in that the piston (34) has a peripheral groove (36) open inward and a guide ring (38) disposed in said groove and in sliding contact with said surface of the cylindrical internal wall in order to prevent the piston from offsetting had to seize during its axial displacements.  7- Hydraulic accumulator according to claim 6, characterized in that the piston (34) further comprises a part (39) in the form of a bowl or dome, extending downward and moving so as to come into contact with said annular seat (22), to prevent  the gas flow in the hydraulic fluid system in the event of a significant rupture of the bellows (40).  8- Hydraulic accumulator according to claim 1, characterized in that the other (14a) of the end caps is shaped so as to produce an end wall (18a) curved inward, a liner (26) made of stainless steel being fixed so as to cover the internal surface of said wall of the end cap.  9- Hydraulic accumulator according to claim 8, characterized in that a tube (50) for filling the chamber with a gas under pressure is mounted in said end wall (18a) curved inwards, its internal end being welded to said stainless steel liner (26), the outer end of said filler tube (50) being closed definitively after filling and the end portion of said tube (50) being deformable to provide an external indication of loss of gas pressure in said chamber.  10- Hydraulic accumulator according to claim 9, characterized in that the outer drextrême part of said filling tube (50) constitutes a Bourdon tube.