Device Supplying A Working Fluid Under A Determined Pressure

Abstract

Device for supplying a working fluid under a determined pressure with the use, as pressure source, of an accumulator delivering to a jack an auxiliary fluid under a pressure varying with the displacement of one element (piston or cylinder) of said jack, comprising at least two jacks, one of which has one element articulated to a fixed point and the other element articulated to one element of another jack through a movable articulation member compelled to be displaced along a predetermined path when one of the elements of a jack is displaced with respect to the other.

Description

The present invention relates to a device for supplying a working fluid under a determined pressure.

Attention will particularly be drawn in the following to devices for keeping a working fluid under a substantially constant pressure using at least one gas accumulator, such as an oleopneumatic (oil-and-gas) accumulator, suitable for use in apparatuses designed for maintaining at a substantially constant value the tension applied to an elongated member.

There will be contemplated, by way of non limitative example, operations such as off-shore drilling, preformed from a floating installation from which is suspended, for example, an elongated member, such as a drill-string.

During these operations the drill string has to be kept under a substantially constant tension, so as to be unaffected by the vertical movements of the floating installation.

The upper end of the drill string is generally connected to a hook carried by a travelling block which is suspended, by a cable used for handling the drill string, from a stationary crown block, located at the top of a derrick carried by the floating installation.

In order to automatically compensate for the vertical movements of the floating installation, it has been proposed to make use of a hydraulic jack fixed at one of its ends to the top of the derrick and supporting the stationary crown block, this jack extending with its longitudinal axis along the direction of displacement of the floating installation, i.e., along a substantially vertical direction.

An automatic compensation for the movements of the floating installation is obtained by supplying the jack with fluid under pressure delivered by an oleopneumatic accumulator.

When, as a result of the vertical movements, the piston is displaced within the cylinder of the jack, the pressure in the accumulator varies according to a polytropic law : P V .sup.k = constant.

It can be shown that, as a first approximation, the volume variations .DELTA. V.sub.o and pressure variations .DELTA. P.sub.o of the mass of gas contained in the accumulator, resulting from the vertical movements of the floating installation, are defined by the relationship :

.DELTA.P.sub.o /P.sub. o = K (.DELTA.V.sub.o /V.sub. o)

In the above formulae P.sub.o is the initial gas pressure in the accumulator which is the same as that of the fluid contained in the jack, whereby a tension force can be exerted on the drill string, V.sub.o is the volume of gas at the pressure of the accumulator and K a coefficient which depends on the type of gas housed in the accumulator, its value being from 1.1 to 1.5.

For a maximum acceptable variation of 10 percent for example, in the tension exerted on the drill string, corresponding to a variation of 10 percent of the pressure in the jack, there must be used an accumulator having a volume V.sub.o such that

V.sub.o .gtoreq. 10 K .DELTA.V.sub.o

In practice, since the choice of the pressure P.sub.o is determined by the design requirements for the accumulator and the jack and by the amplitude of the vertical movement of the floating installation, there must be used accumulators of great volume V.sub.o which are very expensive and bulky on the floating installation.

It has therefore been proposed to add to the vertical jack, or to substitute for this vertical jack, one or several inclined jacks, each having one end articulated on the derrick and the other end supporting the stationary crown block. By using such jacks inclined with respect to the travel path of the stationary crown block (path relative to the floating installation) there can be obtained a better regulation in the tension exerted on the drill string and it becomes possible to substantially reduce the overall volume V.sub.o of the accumulators.

The drawbacks of such devices consist, on the one hand, in the fact that the volumes V.sub.o required for the accumulators are still rather great and, on the other hand, that the heavy weight of the jacks fixed at the top of the derrick is detrimental to the stability of the floating installation and creates high dynamic stresses in the derrick.

An object of the present invention is accordingly to suppress or at least, to reduce the drawbacks of the prior devices, by providing a device for keeping a working fluid under a determined pressure, this device being, in particular, suitable for use in apparatuses for keeping an elongated member under a substantially constant tension.

The device according to the invention supplying a working fluid under a determined pressure, comprises in combination a source of at least one pressurized fluid, said source containing a gas whose pressure varies with the volume occupied by the gas, and at least one group of jacks, an element of at least one jack of said group being connected through a moveable articulation to an element of at least another jack of said group, the element of at least one jack of said group which is not connected to said moveable articulation being rotatably mounted on a fixed point of the installation, said moveable articulation being compelled to move along a predetermined path, fixed with respect to the installation, said fixed point being so located that the axis of said rotatable jack remains inclined on said path during the rotation of said rotatable jack, at least one jack of said group being fed with pressurized fluid from said source, and at least one jack of said group supplying the working fluid.

One of the main advantages of the device according to the invention is to make possible the use of an accumulator of very small volume and of reduced weight and bulk, this accumulator delivering an auxiliary fluid under a variable pressure.

Other advantages will appear from the following description, illustrated by the appended drawings showing non-limitative embodiments of the device and apparatus according to the invention wherein :

FIG. 1 diagrammatically shows an apparatus for keeping substantially constant the tension exerted on a drill string suspended from a floating installation, used in offshore drilling operations, this apparatus being equipped with the device according to the invention,

FIG. 2 illustrates a preferred embodiment of the device according to the invention.

FIG. 3 diagrammatically illustrates an alternative embodiment of the device of FIG. 2.

FIG. 4 diagrammatically shows another embodiment of the apparatus using the device illustrated in FIG. 2, and

FIG. 5 diagrammatically illustrates another type of hydraulic accumulator which can be used in the device of the invention and

FIGS. 6 and 7 respectively show the variation in the pressure supplied to the main jack and in the tension exerted on the drill column, as a function of the displacements of the piston of this jack, under the action of the vertical movements of the floating installation.

FIG. 1 diagrammatically shows an apparatus for keeping substantially constant the tension applied to an elongated element, such as a drill string suspended from a floating installation, for off-shore drilling operations, this apparatus being equipped with a device according to the invention.

Reference numeral 1 indicates the floating installation topped by a derrick 2. A drill string (not shown) is suspended from the floating installation through handling means constituted, in this particular embodiment, by a hook 3 integral with a travelling block 4 suspended by a cable 5 from a crown block 6. The cable 5, used for handling the drill string, passes over a device, which forms no part of the invention, constituted by articulated arms 7 and 8, and pulleys 9 and 10, for preventing the wear of the cable which might result from friction on the crown block 6.

The crown block 6 is suspended from the end of the rod of a main jack or supporting jack 11 fixed to the derrick 2 and constituting the means for supporting the drill string.

This jack is placed substantially in line with the direction of the vertical movements of the floating installation, i.e. along a substantially vertical direction. The jack 11 is connected through a pipe 12 to the device of the invention, indicated as a whole by reference numeral 13. The device 13 keeps under a determined pressure, in the manner indicated hereinafter, the working fluid supplied to the jack 11.

The device 13 is connected through a pipe 20a to a pressure accumulator 20 which delivers an auxiliary fluid under a variable pressure, such as an accumulator housing an invariable or constant mass of gas. This accumulator is, for example, as diagrammatically illustrated in FIG. 1, an oleopneumatic accumulator of small capacity.

The operation of the apparatus will now be described.

The pressure in the jack 11 having a determined value, the latter applies the desired tension T to the drill string.

When the floating installation moves toward the water bottom, the tension in the drill string tends to decrease, but the pressure in the jack 11 having a determined value, the piston of the jack moves in the direction toward the top of the drawing with respect to the cylinder of the jack, driving the block 6, whereby the tension of the drill string remains substantially constant.

When the floating installation moves away from the water bottom, the tension applied to the drill string tends to increase, but the pressure in the jack 11 having a determined value, the piston of the jack moves toward the bottom of the drawing with respect to the cylinder of the jack, driving the block 6, whereby the tension of the drill string remains substantially constant.

This apparatus exhibits, among others, the advantage of requiring only one supporting jack 11 at the top of the derrick for supporting the means for handling the drill string, so that it is possible, in contrast to the previously used apparatuses, to reduce the top heaviness of the floating installation which reduce the stability of the floating installation, due to the important weight of the jacks which must support very heavy loads.

Such an embodiment of apparatus for maintaining constant with sufficient accuracy the tension exerted on an elongated member requires the use of the device 13 maintaining under a determined pressure, the working fluid supplied to the supporting jack 11.

In FIG. 1, the elements constituting the device 13 have been shown in a vertical position for the clarity of the drawing, but this arrangement is not limitative. The device 13 comprises a first jack 14 having one of its constituting elements, for example its cylinder, articulated at one of its ends about a fixed point 15 on the floating installation, a second jack 16 having one of its constituting elements, for example its cylinder, articulated at one of its ends about a fixed point 17 on the floating installation, the two points 15 and 17 being remote from each other.

The other elements constituting the jacks 14 and 16, i.e. the rods of their pistons are interconnected and articulated through a movable member 18 which constitutes a common articulating member displaceable along a guiding way 19 determining the path of the movable member 18.

The path of the movable member 18 defined by the guiding way 19 has been so determined, with consideration of the locations of the fixed articulation points 15 and 17 of the jacks 14 and 16, that the jacks 14 and 16 are inclined on the guiding way 19, so that at any moment the smaller or acute angles formed by the direction of the guiding way 19 and the directions of each of the jacks 14 and 16 (these angles being respectively indicated as .alpha. and .beta. ) vary in opposite directions relative to each other, when the movable member 18 is displaced along the guiding way 19.

The jack 16 is connected through pipe 12 to the supporting jack 11, the cylinders of the jacks 11 and 16 and the pipe 12 being filled by a fluid which may be for example incompressible, such as oil or water, kept under a determined pressure by the device 13.

The jack 14 is connected to an accumulator of hydraulic energy 20, which, in this embodiment is an oleopneumatic accumulator having an initial pressure P.sub.o with a volume V.sub.0 , the pressure in this accumulator varying as a function of the relative movements of the elements constituing the jack 14.

The device works as follows :

The jacks 14 and 16 being in a determined position, for example that illustrated in FIG. 1, the pressure P.sub.u applied by the piston of the jack 16 to the hydraulic working fluid is :

P.sub.u = P(s/S) (cos.alpha./cos.beta.) (1)

P.sub.u, .alpha. and .beta. having the above indicated meanings, s being the cross-sectional area of the piston of the jack 14 and S the cross-sectional area of the jack 16, P being the pressure of the auxiliary fluid of the accumulator 20 for the considered position of the movable member 18.

When the movable member 18 is displaced, the pressure of the auxiliary fluid of the accumulator varies between a maximum value P.sub.B =P.sub.o, for which the movable member 18 is located at point B on the guide way 19 and a minimum value P.sub.H, for which the movable member is located at point H.

Due to the selected arrangement for the jacks 14 and 16, the angles .alpha. and .beta. vary in opposite directions, the ratio cos .alpha./cos .beta. varies in inverse proportion to the pressure P, so that the product P.sup.. (cos .alpha./cos.beta.), and thus the pressure P.sub.u in the jack 11, undergoes only small variations. It is consequently possible to make use of an accumulator of reduced volume V.sub.o whose fluid is subjected to a substantial pressure variation P.sub..sub..beta. - P.sub.H.

When the floating installation moves toward the water bottom, the pressure of the working fluid in the jack 11 tends to decrease and, under the action of the jack 14, the movable member 18 is displaced toward point H along the guide way 19, thus tending to increase the pressure of the working fluid contained in the jack 16 by displacement of its piston.

If the installation moves away from the water bottom, the pressure of the working fluid in the jack 16 tends to increase thereby producing, against the antagonistic action of the jack 14, the displacement of the movable member 18, the movable member 18 being displaced in the direction of point B.

The advantages resulting from the use of the device according to the invention are principally the following ones:

it is possible to make use of an accumulator 20 having a volume considerably smaller than those used in prior devices. For the same performance it is possible to make use of an accumulator having an initial volume V.sub.o which is about one third of those required in prior art devices for compensating the same vertical movements of a floating installation.

In addition to the reduction in bulkiness, it should be noted that, since the cost of the accumulators increases with their volume, a non negligible saving is obtained, in the cost of the accumulators;

the weight of the devices located at the top of the derrick is simultaneously reduced by 30 to 60 percent, so that it does not affect the stability of the floating installation, this being an important factor when this installation is for example a ship, and does not induce dynamic stresses in the derrick.

Obviously, the characteristics of the device 13, i.e. the limit-values of the angles .alpha. and .beta. , the volume of the accumulator etc., have to be determined in accordance with the conditions of use.

For example, in order to maintain in a drill string a tension of about 200 tons, there can be used an accumulator having a pressure P.sub.o of 300 bars with a gas volume of 2m.sup.3, the angle .alpha. varying between 20.degree. and 45.degree., the angle .beta. varying between 45.degree. and 20.degree., the variation in the pressure of the auxiliary fluid being 70 bars for an amplitude of the vertical displacements of the floating installation of 4.5 m, the tension in the drill string being kept substantially constant with small variations not exceeding 1.5 percent with respect to a preselected value.

FIG. 2 diagrammatically shows a preferred embodiment of the device according to the invention.

In this embodiment, the forces applied by the jacks 14 and 16 to the movable member, in a direction at right angles to the path T are substantially compensated by two additional jacks 14a and 16a. Each of these jacks has one of its ends articulated about a point on the floating installation (points 15a and 17a) said jacks being respectively placed in a position symmetrical to that of the jacks 14 and 16 with respect to the path T. The other ends of these jacks are interconnected and articulated to a movable point 18.

The jacks 14 and 14a are connected to the accumulator 20, while the jacks 16 and 16a are connected to the pipe 12.

Such an arrangement provides for an increased performance of the device 13.

FIG. 3 illustrates an alternative embodiment of the device of FIG. 2, wherein the jacks 14, 14a, 16 and 16a are located in two substantially parallel planes, so as to minimize the bulkiness of the device 13.

FIG. 4 diagrammatically illustrates an arrangement in series of a number n of devices according to the invention, whereby the volume V.sub.o required for the accumulator 20 can be considerably decreased, n devices such as the device 13 illustrated by FIG. 2 have been connected in series, each device being identified by an index (devices 13.sub.1, 13.sub.2 . . . 13.sub.n.sub.-1, 13.sub.n).

The jacks 14 and 14a of the device 13.sub.1 are connected to the accumulator 20 while the jacks 16 and 16a are connected to the jacks 14 and 14a of the device 13.sub.n.sub.-14 etc.

In this way the pressure P.sub.n at the outlet of the device 13.sub.n will be : ##SPC1##

and in the case where the devices are identical :

P.sub.u = P (s/S).sup.n .times. (cos .alpha./cos .beta.).sup.n

so that it is possible to obtain a determined pressure P.sub.u which is substantially constant by using an accumulator 20 adaptable to very large pressure variations and hence a very small volume.

As it is apparent from the foregoing description, the device according to the invention may be used with an accumulator of hydraulic energy whose pressure varies in inverse proportion to its volume. The above description contemplates the utilization of oleopneumatic accumulators, but it will be possible to make use of an accumulator of the type illustrated in FIG. 5. This accumulator consists of a cylinder 21, having a piston 22 slidably mounted therein which delimits two spaces 23 and 24.

The first of these spaces 23 is filled with an incompressible auxiliary fluid, such as oil, whereas in the second space is housed a resilient element, for example helical spring 25 which transmits to the fluid, through the intermediary of the piston 22 a pressure which is proportional to its compression rate.

Such an accumulator has the advantage of being less expensive than oleopneumatic accumulators.

Changes may be made without departing from the scope of the present invention.

It will, for example, be possible to use gas accumulators whose pressure and volume vary in opposite directions.

It is also possible to articulate the cylinders of the jacks at any point thereof and not necessarily at their ends, and the guide way of the travel path of the movable point may have any configuration, provided that the ratio of the cosines of the angles .alpha. and .beta. varies in inverse proportion to the pressure of the auxiliary fluid when the movable point moves along its path.

One of the jacks 14 or 16 might be not articulated about its point of fixation, this jack being then placed in line with the axis of the path of the movable point, provided that the other jack be inclined with respect to the path of this movable point, so that the above-defined ratio cos .alpha./cos .beta. varies in inverse proportion to the pressure of the auxiliary fluid, when the movable point is displaced along its path.

Through geometrical adaptations, those skilled in the art can modify the device of the invention in order to obtain in the pipe 12 a pressure value complying with a predetermined law, selected according to the conditions of use.

The pressure Pu supplied by the jack 16 and the pressure P in the accumulator 20 are interrelated through the relationship :

Pu = P (s/ S) (Cos .alpha./Cos .beta.) (1)

The values of this pressure which correspond to the limit positions (B and H) of the moveable articulation 18 in the guideway 19 (FIG. 1) are respectively :

Pu.sub.B = P.sub.B (s/ S)(Cos .alpha..sub.B /Cos .beta..sub.B) (2)

and

Pu.sub.H = P.sub.H (s/S)(Cos .alpha..sub.H /Cos .beta..sub.H) (3)

wherein the indexes B and H indicate the particular values of the different parameters Pu, P, .alpha. and .beta. of the relation (1), corresponding to the respective positions B and H of the moveable articulation 18.

In practice, it is sufficient to choose the limit values Pu.sub.B and Pu.sub.H of the desired working pressure Pu which has to be supplied by the jack 11 for the limit positions of the moveable element of the jack 11 (these values Pu.sub.B and Pu.sub.H being, or not, different).

The values Pu.sub.B and Pu.sub.H will be selected as a function of the particular conditions of each considered case of utilization.

In the contemplated embodiment wherein this pressure is used in a main or supporting jack 11 in order to control the tension T applied to a drill column, the values of Pu.sub.B and Pu.sub.H will for example be determined with consideration of the influence of a system of pulleys interposed between the drill column and the supporting jack 11.

Test values are selected for the construction parameters of the regulating system, these parameters being (FIG. 1) the values of d.sub.14 and d.sub.16 (respective distances of the articulation points 15 and 17 from the axis of the guideway 19), the limit values .alpha..sub.H, .alpha..sub.B and .beta..sub.H, .beta..sub.B of the angles .alpha. and .beta. and the values of the respective cross-sections s and S of the jacks 14 and 16 respectively.

By application of the relationships (2) and (3) it can be deduced from the values selected for Pu.sub.B and Pu.sub.H the values P.sub.B and P.sub.H of the pressure of the auxiliary fluid in the accumulator 20, as a function of the values .alpha..sub.B, .alpha..sub.H, .beta..sub.B and .beta..sub.H (FIG. 1) which have been selected.

The determination of the values of P.sub.B and P.sub.H makes it possible to calculate the volume which is necessary for the accumulator 20.

As a matter of fact, the pressure P in this accumulator varies substantially according to a physical law having the form : PV.sup.K = constant, wherein K is a coefficient whose value depends, in particular, on the nature of the pressurized gas and V is the volume of gas at the pressure P in the accumulator 20, applied to the piston of the jack 14.

There results therefrom the relationship :

P.sub.H V.sub.H.sup. K = P.sub.B V.sub.B.sup. K (5)

wherein V.sub.B and V.sub.H are the values of the volume of pressurized gas when the position of the moveable articulation 18 is respectively at point B and point H of the guideway 19.

Letting V.sub.H - V.sub.B be defined as .DELTA.V ; there results from the relation (5) : ##SPC2##

The value of .DELTA.V is known, since it is equal to the product of the cross-section s of the jack 14 by the stroke of its piston when the moveable articulation 18 is displaced between points B and H, V.sub.B being the minimum value of the volume of pressurized gas.

The nominal volume of the accumulator 20 can thus be determined since the values of P.sub.B and P.sub.H have already been determined (the calibrating pressure of this accumulator is substantially equal to P.sub.B).

Thereafter can be plotted, in the manner to be indicated hereinunder, the curve

T =F (h) (6)

representing the variations in the tension T applied to the drill column, as a function of the displacement h of the main jack 11 from its lowermost position.

To each value of h corresponds a well defined position of the moveable articulation 16 along the guideway 19, i.e. well defined values for the angles .alpha. and .beta., when the values .beta..sub.H, .beta..sub.B, d.sub.16 and S have been fixed.

As a matter of fact, the displacement of the piston of jack 11 from its lowermost position corresponds to a determined variation of the volume of hydraulic fluid in the cylinder of jack 16 through the pipe 12 (at any moment the displacements of the pistons of the jacks 11 and 16 from their initial position (lowest position), represent the same percentage of their maximal stroke).

In this position of the moveable articulation 18, to which corresponds a determined position of the piston of the jack 14, the gas at the pressure of the accumulator 20 occupies the volume V.sub.B + .delta.V and its pressure P is defined by the relation :

P.sub.B V.sub.B.sup.K = P(V.sub.B + .delta. V).sup.K

hence

P = P.sub.B [ V.sub.B /CV.sub.B + .delta. V)].sup.K (7)

it is thus possible to determine the pressure P for each value of h to which corresponds a well-defined value of each of the angles .alpha. and .beta..

For each so-obtained value of P is determined the corresponding value of Pu using the above-indicated relation :

Pu = P (s/S) (Cos .alpha./Cos .beta.)

and there is deduced the corresponding value of the tension T which, in the embodiment illustrated by way of example, depends on the influence of the pulley or block system.

The graphs of FIGS. 6 and 7 show respectively the variations of Pu (expressed in kg/cm.sup.2) and T (expressed in tons), as a function of the stroke h (expressed in meters) of the piston of jack 11, obtained in accordance with the following data :

horizontal distance between the axes of pulleys 9 and 10 and the axis of pulley 6 when the latter is in its lowermost position = 3.3 meters,

vertical distance between the axes of pulleys 9 and 10 and the axis of pulley 6 when the latter is in its lowermost position = 1.8 meters,

The cable 5 forms 12 turns between the pulley 6 and the moveable block or pulley system 4.

maximum stroke h.sub.M (FIG. 1) of the main jack 11 determined by the amplitude of the vertical movements of the floating installation = 4.6 meters.

Moreover the following data have been selected :

d.sub.14 = 3.30 meters

d.sub.16 = 3.90 meters

.beta..sub.H = 41.degree.

.beta..sub.b = 20.degree.

in the graphs of FIGS. 6 and 7 the curves in dotted lines show the varations obtained for Pu and T respectively when choosing :

.alpha..sub.H = 23.degree.

.alpha..sub.b = 45.degree.

the curves in solid lines show the results which are obtained with the following newly selected values :

.alpha..sub.H = 26.degree.

.alpha..sub.b = 50.degree.

the curves in dot and dash lines are the ideal curves to which the actual curves have to be brought as near as possible.

It is thus possible to optimize the system by selecting for the parameters of construction : .alpha..sub.H, .beta..sub.B, d.sub.14, s and .beta..sub.H, .beta..sub.B, d.sub.16 and S, the values corresponding to the test curve of the pressure Pu which is nearer the curve in dot and dash line representing the desired values of this pressure Pu, in this particular embodiment, chosen in order to obtain the variations of the force exerted by the jack 11 which makes it possible to keep substantially constant the tension T applied to the drill column.

It should be noted that on the graph of FIG. 7 the scale of the ordinates has been considerably amplified, the relative variations in the tension T of the drill column not exceeding .+-. 1.5 percent.

It will obviously be possible to select differently the limit values Pu.sub.B and Pu.sub.H of the pressure, to comply with different conditions of use and for example as a consequence of a different value of the tension T.

This can be achieved by a modification of the mass of fluid in the accumulator 20, for example by activating the valve 20b (FIG. 1).

Claims

What we claim is:

1. A device for supplying a working fluid under a determined pressure to a chamber means of variable volume comprising in combination a source of at least one pressurized fluid, said source containing a gas whose pressure varies with the volume occupied by the gas, and at least one group of jacks, an element of at least one jack of said group being connected through a moveable articulation to an element of at least another jack of said group, an element of at least one jack of said group which is not connected to said moveable articulation being rotatably mounted on a fixed point of an installation, said moveable articulation being compelled to move along a predetermined path, fixed with respect to the installation, said fixed point being so located that the axis of said jack having the rotatably mounted element remains inclined on said path during the rotation of the rotatably mounted element of said jack, at least one jack of said group being fed with pressurized fluid from said source, and at least one jack of said group supplying the working fluid to the chamber means of variable volume under a pressure different from that of said source.

2. A device for supply supplying working fluid under a determined pressure to a chamber means of variable volume comprising in combination a source of at least one pressurized fluid, said source containing a gas whose pressure varies with the volume occupied by the gas, and at least one group of jacks, an element of at least one jack of said group being connected through a moveable articulation to an element of at least another jack of said group, an element of at least one jack of said group which is not connected to said moveable articulation being rotatably mounted on a fixed point of an installation, said moveable articulation being compelled to move along a predetermined path, fixed with respect to the installation, said fixed point being so located that the axis of said jack having the rotatably mounted element remains inclined on said path during the rotation of the rotatably mounted element of said jack, at least one jack of said group being fed with pressurized fluid from said source, and at least one jack of said group supplying the working fluid to the chamber means of variable volume under a pressure different from that of said source, said group of jacks consisting of at least one pair of jacks, a first jack of said pair being fed with pressurized fluid from said source, the second jack of said pair supplying the working fluid to the chamber means of variable volume and in which said path is so determined that the ratio of the values of the cosines of the acute angles formed respectively by the first and second jacks with said path, varies in inverse proportion to the value of the pressure of the fluid of said source when said moveable articulation moves along the path.

3. A device according to claim 2, wherein said path is rectilinear.

4. A device according to claim 1, comprising at least one jack having one element connected at one end to said moveable articulation and another element connected at one end to a fixed point of the installation.

5. A device according to claim 4, wherein said moveable articulation is slidable along a fixed guide way defining said path.

6. A device according to claim 1, wherein said source is constituted by a gas accumulator.

7. A device according to claim 1, wherein said source consists of an oleopneumatic accumulator housing a constant mass of gas.

8. A device for compressing an hydraulic working fluid under a determined pressure in a chamber means having a variable volume, comprising at least one accumulator containing a gas under pressure and connected to a regulating system including at least one regulating jack mounted for pivotal movement about a fixed point and connected to an articulated member moveable along a predetermined path, said pivotable regulating jack remaining inclined with respect to said path during its pivotal movement in which the regulating system supplies the chamber means through an auxiliary system, said auxiliary system having at least one jack connected to the chamber means through a duct containing the compressed working fluid, said jack of said auxiliary system being connected to said pivotable regulating jack via said articulated member and providing a relative positional arrangement of said pivotable regulating jack and said jack of said auxiliary system with respect to said predetermined path such that the ratio cos .alpha./cos .beta. of the values of the cosines of the acute angles .alpha. and .beta. of said pivotable regulating jack and said jack of said auxiliary system, respectively, with respect to said predetermined path varies in a direction inverse to the pressure of the gas in the accumulator when said articulated member is displaced along said predetermined path.