WO2023016840A1

WO2023016840A1 - Fluid-operated control device, for double-acting actuators

Info

Publication number: WO2023016840A1
Application number: PCT/EP2022/071552
Authority: WO
Inventors: Fiorenzo CHIARI
Original assignee: Omt Group S.P.A.
Priority date: 2021-08-10
Filing date: 2022-08-01
Publication date: 2023-02-16
Also published as: IT202100021647A1

Abstract

A fluid-operated control device for double-acting actuators includes a valve body which integrates a first overcenter valve in which the inlet is connected to a distribution device by means of a first connecting branch and the outlet is connectable to a first chamber of at least one fluid-operated cylinder, the valve body further integrating a second overcenter valve in which the inlet is connected to the distribution device by means of a second connecting branch and the outlet is connectable to a second chamber of the fluid-operated cylinder, the first overcenter valve being actuatable by means of a first control branch which is connected to the second connecting branch and being provided with particular fluid throttling, check and drainage elements connected to the first connecting branch, the second overcenter valve being actuatable by means of a second control branch connected to the first connecting branch, the distribution device being provided with a control chamber and being automatically switchable between a first operating condition, in which the first connecting branch is connected to a delivery branch of a working fluid and the second connecting branch is connected to a return branch of the working fluid and the control chamber of the distribution device is connected to the return branch of the working fluid by means of a unidirectional throttle valve, and a second operating condition, in which the first connecting branch is connected to the return branch by means of the unidirectional throttle valve and the second connecting branch is connected to the delivery branch, the switching between the first operating condition and the second operating condition being controlled by an overpressure valve integrated in the valve body and having the inlet connected to the first connecting branch by means of a third control branch and the outlet connected to the control chamber of the distribution device.

Description

FLUID-OPERATED CONTROL DEVICE, FOR DOUBLE-ACTING ACTUATORS

The present invention relates to a fluid-operated control device adapted in particular for double-acting actuators.

More precisely, the fluid-operated control device according to the invention is capable of performing automatically a single cycle of opposite strokes of a fluid-operated actuator, or of a cylinder, which is repeated in a noncontinuous manner, with the switching occurring in the intermediate reversal point of the strokes and being actuated by overpressure.

As is known, oil-hydraulics is a field of fluid dynamics which deals with the study of the transmission of energy by means of pressurized working fluids, particularly hydraulic oil.

GB2224081A discloses an arrangement for operating hydraulic actuating means provided with overcenter valves in a rock drilling boom, wherein the overcenter valves are connected to pressure fluid conduits of the actuating means and to control conduits for the valves in such a manner that the valves stop the flow of the pressure fluid in the conduits in a direction away from the actuating means, when no pressure fluid is supplied to the actuating means, and when pressure fluid is supplied to one of the conduits. The overcenter valve connected to the other conduit opens when the pressure of the supplied pressure fluid acts on its control conduit, allowing the flow of the pressure fluid therethrough away from the actuating means. The arrangement further comprising hoses for pressure fluid extending from the carrier of a rock drilling apparatus in the longitudinal direction of the boom for supplying pressure fluid to the actuating means in the boom and for removing it therefrom, and regulating valves for controlling each one of the actuating means.

US10969801 B1 discloses a proportional flow control and counterbalance valve having a single seat configuration. The valve includes a first port configured to be fluidly coupled to an actuator, a second port configured to be fluidly coupled to a reservoir, a third port configured to provide an output pilot fluid signal and receive an input pilot fluid signal, a fourth port configured to be fluidly coupled to a source of fluid, a pilot poppet configured to be subjected to a first fluid force of fluid received at the first port and configured to be subjected to a second fluid force of the input pilot fluid signal. A solenoid actuator sleeve is axially movable between an unactuated state and an actuated state. A setting spring is configured to apply a biasing force on the pilot poppet.

US5490441A discloses an automatic reciprocation of a reversible fluid pressure unit and switching valve therefor. The fluid pressure piston-cylinder drive unit is reciprocated automatically by coupling the opposite ends of the cylinder through delivery conduits to a source of fluid pressure and exhaust through a switching valve in which a longitudinally reciprocative spool has a pair of passageways which reversibly couple one end of the cylinder to the source of fluid pressure and the other end of the cylinder to an exhaust conduit. The opposite ends of the switching valve contain shift pistons each of which engages an end of the spool through a coil spring. The shift pistons abut the opposite ends of an elongated rod which extends freely through a bore in the spool. Bypass conduits couple the opposite ends of the cylinder through the delivery conduits one to each end of the valve body such that fluid pressure in one delivery conduit from the source is coupled to one end of the valve body, while exhaust fluid pressure from the other delivery conduit is coupled to the other end of the valve body. The exhaust conduit communicates with a detent conduit in which a detent pin is moved by exhaust fluid pressure into a selected detent in the spool to secure the spool against movement. When the piston-cylinder unit is a high volume drive unit, a secondary switching valve is interposed between the cylinder and the primary switching valve to supply high volume fluid pressure to the cylinder by control from the primary switching valve.

US1952690A discloses an automatic reverse valve for stokers, for furnaces and the like, having a reverse mechanism for the piston of the stoker ram.

A typical oil-hydraulics system, according to the prior art, essentially includes a generation unit, a control unit and a user unit.

In the generation unit, constituted by one or more pumps, mechanical energy is converted into hydraulic energy which the user unit, formed by actuators of various kinds, transforms back into mechanical energy.

In the control unit, the working fluid is conditioned by making it assume certain pressure and flow-rate values and distributing it where necessary. Generally, control units consist of valve assemblies that allow to distribute the pressurized fluid to all user devices, allowing in particular the repetition, interruption and reversal of the work movements.

The need is felt to have a fluid-operated control device that is capable of performing a complete single cycle of strokes for the extraction and retraction, or vice versa, of the stem of a fluid-operated cylinder, with a single delivery of working fluid from the pump with free return to the reservoir.

At the same time, this fluid-operated control device must allow control of the load, whether fixed or variable, that is applied to the fluid-operated cylinder, in both directions of travel and in any angular position of the load, as well as limitation of the maximum pressure induced by the load to the chambers of the cylinder.

This is required in order to protect the hydraulic circuit against mechanical damage due to the fact that during work the user device applied to the cylinder receives excessive stress from the outside environment and therefore unwanted pressure peaks.

While the prior art control units may satisfy some specific requirements, none of them is able to compound all the requirements listed above, in an optimal manner.

The aim of the present invention is therefore to provide a fluid-operated control device, for double-acting actuators, that overcomes the drawbacks of the prior art and has such characteristics as to compound the requirements listed above, in the best way.

Within the scope of this aim, a particular object of the invention is to provide a fluid-operated control device that is compact, lightweight and easy to install with standard hydraulic connections.

A further object of the invention is to provide a fluid-operated control device that has a good resistance with respect to the external atmospheric environment and with respect to possible contaminants of the hydraulic working fluid.

A further object of the invention is to provide a fluid-operated control device that is capable of performing the cycle for switching the direction of flow of the oil from the delivery to the chambers of the fluid-operated cylinder gradually and smoothly, without sudden variations which would affect the structure of the load.

A further object of the invention is to provide a fluid-operated control device that is capable of performing the locking and the release of the stem of the fluid-operated cylinder, which correspond to the starting and stopping of the movement of the load, in a manner that is gradual and with a speed that is suitable to avoid triggering oscillations of the structure of the load.

A further object of the invention is to provide a fluid-operated control device that has a good durability over time.

This aim and these objects, as well as others which will become better apparent hereinafter, are achieved by a fluid-operated control device for double-acting actuators, as claimed in the appended claims.

Further characteristics and advantages will become better apparent from the description of a preferred but not exclusive embodiment of a fluid-operated control device according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a detailed hydraulic diagram of a fluid-operated control device according to the invention;

Figure 2 is a perspective view of the fluid-operated control device according to the invention;

Figure 3 is a side view of the fluid-operated control device of Figure 2;

Figure 4 is a top view of the fluid-operated control device of Figures 2 and 3;

Figure 5 is a hydraulic diagram and a partial sectional view, taken along the plane V-V of Figure 4, of the fluid-operated control device according to the invention in an inactive position;

Figure 6 is a hydraulic diagram and a partial sectional view, taken along the plane V-V of Figure 4, of the fluid-operated control device according to the invention during an outgoing stroke;

Figure 7 is a hydraulic diagram and a partial sectional view, taken along the plane V-V of Figure 4, of the fluid-operated control device according to the invention during a switching step;

Figure 8 is a hydraulic diagram and a partial sectional view, taken along the plane V-V of Figure 4, of the fluid-operated control device according to the invention during a return stroke;

Figure 9 is a simplified hydraulic diagram of a fluid-operated control device according to the invention;

Figure 10 is another top view of the fluid-operated control device according to the invention.

With reference to the cited figures, a fluid-operated control device according to the invention is generally designated by the reference numeral 1.

The fluid-operated control device 1 includes a valve body 2 which is formed by a single part, preferably having the shape of a parallelepiped and preferably made of metallic material.

Through holes 3 are provided in the valve body 2 for fastening the valve to a structure, for example; the structure is not shown in the figures.

A delivery port 4, a return port 5, a first outlet port 6 and a second outlet port 7 are provided in the valve body 2, in compliance with the statutory standards, and are preset to fluidically connect the fluid-operated control device 1 to an oil-hydraulics system.

The delivery port 4 allows to connect the fluid-operated control device 1 to a pump P, not shown in the figures, which on command of an operator feeds a working fluid into the oil-hydraulic system, typically a hydraulic oil.

The return port 5 allows to connect the fluid-operated control device 1 to a reservoir T, not shown, which collects the working fluid that returns from the oil-hydraulic system.

Preferably, the connection between the delivery port 4 and pump, and the connection between the return port 5 and the reservoir, occur by means of a valve 100, for example a four-way three-position valve, which is per se known and not here described in detail.

The first outlet port 6 and the second outlet port 7 are configured to be connected respectively to a first chamber 111 and to a second chamber 112 of a fluid-operated cylinder 110.

At each individual delivery of working fluid from the pump, on command of the operator, the fluid-operated control device 1 is configured to repeat a set cycle of strokes of the fluid-operated cylinder 110.

Namely, the fluid-operated cylinder 110 can repeat a "START-EXTRACTION- RETRACTION-STOP" cycle, or a "START-RETRACTION-EXTRACTION-STOP" cycle.

In this context, the first chamber 111 is the chamber of the fluid-operated cylinder 110 that must be pressurized first, on the basis of the cycle to be performed, while the second chamber 112 is the one that must be pressurized second in the same cycle.

In the example shown in Figure 1 and in Figures 5 to 8, for example, in which the fluid-operated cylinder 110 is preset to repeat a "START-RETRACTION-EXTRACTION- STOP" working cycle, the first chamber 111 is the one on the right, with reference to the figures, while the second chamber 112 is the left one; however, it is apparent to the person skilled in the art that in an oil-hydraulic system, that is different from the one described here by way of example, the first chamber 111 and the second chamber 112 might be arranged in a reversed position.

According to the present invention, the valve body 2 integrates multiple components which are functionally mutually connected, among which, in particular, a first overcenter valve 10 and a second overcenter valve 20, also known as balancing valves, a distribution device 30, an overpressure valve 50, and a unidirectional choke valve 60.

In greater detail, the inlet of the first overcenter valve 10 is connected to the distribution device 30 by means of a first connecting branch 11, while the outlet of the first overcenter valve 10 is designed to be connected to the first chamber 111 of the fluid-operated cylinder 110 by means of the first outlet port 6.

Also, the inlet of the second overcenter valve 20 is connected to the distribution device 30 by means of a second connecting branch 21 , while the outlet of the second overcenter valve 20 is designed to be connected to the second chamber 112 of the fluid- operated cylinder 110 by means of the second outlet port 7.

The first overcenter valve 10 essentially consists of a first pressure control valve 12, of the controlled type, and of a first check valve 13, which are accommodated in a first seat 14 provided in the valve body 2. The first pressure control valve 12 can be controlled by means of a first control branch 15 which connects the first seat 14 to the second connecting branch 21.

Advantageously, the first control branch 15 integrates a check valve 8, a first choke 18 arranged in series thereto and a drain, essentially constituted by a second choke 19, toward the first connecting branch 11.

This allows to perform a particular dynamic control of the first overcenter valve 10, which is already known from oil-hydraulics technology.

The first seat 14 has an end closed axially by a first closure body 16, which is provided with means for calibrating the first pressure control valve 12, which are not shown.

Advantageously, the calibration means of the first pressure control valve 12 can be adjusted from the outside by means of a screw 17 which, once tightened, is protected against tampering.

Also, the second overcenter valve 20 essentially consists of a second pressure control valve 22 of the controlled type and of a second check valve 23, which are accommodated in a second seat 24 provided in the valve body 2.

The second pressure control valve 22 is controlled by means of a second control branch 25 which connects the second seat 24 to the first connecting branch 11.

The second seat 24 has an end which is closed axially by a second closure body 26, which is provided with means, not shown, for calibrating the second pressure control valve 22.

Advantageously, the means for calibrating the second pressure control valve 22 can be adjusted from the outside by means of a screw 27 which, once tightened, is protected against tampering.

The first seat 14 and the second seat 24 have a predominantly longitudinal extension and are substantially mutually parallel.

As mentioned, the first and second overcenter valves 10, 20 are connected to the distribution device 30, which essentially consists of a slider 31 which is slidingly and hermetically engaged in a tubular casing 32 having a plurality of through channels 33a, 33a', 33b, 33b', 33c, 33c', 33d, 33d', 33e and 33e'. The tubular casing 32 is accommodated in a third seat 34 formed to pass through the valve body 2 and axially closed by third closure bodies 35a and 35b.

The slider 31 is a substantially cylindrical body from which four annular partitions 36a, 36b, 36c and 36d protrude and, together with the tubular casing 32, form three annular chambers 37a, 37b and 37c.

The annular chambers 37a, 37b and 37c allow to connect the various branches of the fluid-operated control device 1, in various combinations.

The distribution device 30 is in fact capable of switching automatically between a first operating condition, in which it connects the first connecting branch 11 to a delivery branch 38 of the working fluid and the second connecting branch 21 to a return branch 39 of the working fluid, and a second operating condition, in which it connects the first connecting branch 11 to the return branch 39 and the second connecting branch 21 to the delivery branch 38.

In the first operating condition, the slider 31 is in an inactive position, as shown schematically in Figures 5 and 6. The slider 31 is arranged so that the first annular chamber 37a connects the through channels 33a and 33a', through which the return branch 39 leads into the tubular casing 32, to the through channels 33b and 33b', through which the second connecting branch 21 leads into the tubular casing 32.

At the same time, the second annular chamber 37b connects the through channels 33c and 33c', through which the delivery branch 38 leads into the tubular casing 32, to the through channels 33d and 33d', through which the first connecting branch 11 leads into the tubular casing 32.

At the same time, the third chamber 37c is arranged in communication with the return branch 39 by means of a third connecting branch 41 which integrates a unidirectional choke valve 60, which includes a spring-loaded check valve 61 connected in parallel to a third choke 62.

Advantageously, the third chamber 37c is connected by means of through holes 42 and 43 to a control chamber 40 of the distribution device 30, which is extended axially into the slider 31.

In the second operating condition, shown schematically in Figure 8, the slider 31 is arranged so that the second annular chamber 37b connects the through channels 33b and 33b', through which the second connecting branch 21 leads into the tubular casing 32, to the through channels 33c and 33c', through which the delivery branch 38 leads into the tubular casing 32.

At the same time, the third annular chamber 37c connects the through channels 33d and 33d', through which the first connecting branch 11 leads into the tubular casing 32, to the through channels 33e and 33e', through which the third connecting branch 41 leads into the tubular casing 32 in order to connect to the control chamber 40.

Advantageously, the third connecting branch 41 is connected to the return branch 39 with the interposition of the unidirectional choke valve 60, the inlet of which is connected to the control chamber 40.

Preferably, the unidirectional choke valve 60 is mounted in a fifth seat 63.

The switching between the first operating condition and the second operating condition, shown schematically in Figure 7, is actuated by the overpressure valve 50, wherein the inlet of the overpressure valve 50 is connected to the first connecting branch 11 by means of a third control branch 51 and the outlet of which is connected to the control chamber 40.

The overpressure valve 50 is arranged in a fourth seat 52 provided in the valve body 2.

The fourth seat 52 has an end which is closed axially by a fourth closure body 53 which has means for calibrating the overpressure valve 50, not shown.

Advantageously, the means for calibrating the overpressure valve 50 can be adjusted from the outside by means of a screw 54 which, once tightened, is protected against tampering.

The action of the overpressure valve 50 is contrasted by elastic preloading means 44, which are constituted for example by a spring and are interposed between the third closure body 35a and the slider 31 so as to keep in the latter normally in the first operating condition.

In practice, the branches cited above are formed by ducts that extend into the valve body 2. The operation of the fluid-operated control device according to the present invention is as follows.

The fluid-operated control device 1 is initially in an inactive position with the slider 31, as schematically shown in Figure 5, when the operator begins the cycle with the delivery of working fluid from the pump, as schematically shown in Figure 6.

The inactive position of the slider 31 substantially corresponds to the first active condition of the distribution device 30.

The fluid, propelled through the delivery branch 38, reaches the second annular chamber 37b of the distribution device 30, which is in the first operating condition, and from there it reaches and passes through the first overcenter valve 10 by means of the first connecting branch 11 and enters, with the first outlet port 6, the first chamber 111 of the fluid-operated cylinder 110.

At the same time, the working fluid pressurizes the second control branch 25 of the second overcenter valve 20 to the value of the release pressure.

Accordingly, the second overcenter valve 20 opens and the fluid-operated cylinder 110 begins the maneuver.

During its stroke, the fluid-operated cylinder 110 expels working fluid from the second chamber 112, and the fluid, through the second outlet port 7, reaches and passes through the second overcenter valve 20, which controls its flow, applying the balancing function.

Then, through the second connecting branch 21 , the working fluid reaches the first annular chamber 37a of the distribution device 30, which is still in the first operating condition, and from there reaches the reservoir T by means of the return branch 39.

During this maneuver, any seepage of working fluid originating from the system, which might pressurize the control chamber 40 and therefore might entail an incorrect operation of the operating cycle, is conveniently drained via the return branch 39, by means of the already mentioned unidirectional choke valve 60 arranged along the third connecting branch 41.

When the stem of the fluid-operated cylinder 110 reaches the end of its stroke, the pressure in the first connecting branch 11 rises up to the calibration value of the overpressure valve 50, which by opening sends part of the working fluid into the control chamber 40 of the distribution device 30, as shown schematically in Figure 7.

Accordingly, the slider 31 reaches the second operating condition, overcoming the action of the elastic preloading means 44, as shown schematically in Figure 8.

Therefore, the working fluid, which always arrives from the delivery branch 38, reaches the second annular chamber 37b of the distribution device 30, which is now in the second operating condition, and from there it reaches and passes through the second overcenter valve 20 via the second connecting branch 21 and enters with the second outlet port 7 the second chamber 112 of the fluid-operated cylinder 110.

At the same time, the working fluid, after passing through the first choke 18 and opening the check valve 8, pressurizes the first control branch 15 of the first overcenter valve 10 to the release pressure value.

In the meantime, the working fluid of the first control branch 15 is partly drained through the first connecting branch 11 , by means of the second choke 19, converting the control of the first overcenter valve 10 from a static condition to a dynamic condition, in order to create a damping and delay effect on the command to open the first overcenter valve 10, as already known from oil-dynamics methods.

Accordingly, the first overcenter valve 10 opens and the fluid-operated cylinder 110 begins the maneuver with a motion in the opposite direction.

During its stroke, in this step, the fluid-operated cylinder 110 expels working fluid from the first chamber 111 and the fluid, through the first outlet port 6, reaches and passes through the first overcenter valve 10, which controls its flow, applying the balancing function.

Then, through the first connecting branch 11, the working fluid reaches the third annular chamber 37c of the distribution device 30, which is in the second operating condition, and from there passes through the unidirectional choke valve 60 to then reach the reservoir T by means of the third connecting branch 41 and the return branch 39.

The working fluid that passes through the unidirectional choke valve 60 keeps the distribution device 30 and the slider 31 in the second operating condition up to the end of the maneuver. At the end of the maneuver, the stem of the fluid-operated cylinder 110 reaches the end of its stroke, returning to the initial position and thus in practice ending the preset cycle.

It should be noted that in this step, while the operator continues to act on the delivery of fluid to the system, the fluid-operated cylinder 110 remains in the final position without automatically restarting the maneuver.

This is made possible by the working fluid that is introduced by the delivery duct 38, passes through the second annular chamber 37b and pressurizes the second connecting branch 21, passing through the elements of the first control branch 15, is introduced in the first connecting branch 11, reaches the third annular chamber 37c of the distribution device 30 and, by passing through the unidirectional choke valve 60, keeps the distribution device 30 and the slider 31 in the second operating condition before reaching the reservoir T by means of the return branch 39.

Then, by acting on the valve 100 upstream of the circuit, the operator ends the delivery of working fluid, arranging the fluid-operated system for discharge, with an appropriate distribution unit installed in the control region.

At this point, the stem of the fluid-operated cylinder 110 is locked, since the first and second overcenter valves 10, 20 are closed.

It remains in any case possible to release the stem of the fluid-operated cylinder 110 at a maximum peak pressure value, by means of the relief function of the first and second overcenter valves 10, 20, when the fluid-operated system receives an overload from the outside work environment, in order to avoid damaging the structure of the apparatus.

In this circumstance, the fluid-operated control device 1 is depressurized and, through internal drainage orifices, all the annular chambers 37a, 37b and 37c of the distribution device 30 are also depressurized, and the elastic preloading means 44 return the slider 31 to the first operating condition.

All the elements of the fluid-operated control device 1 are in the starting position for a new work cycle.

It has been found in practice that the invention achieves the intended aim and objects, providing a fluid-operated control device for double-acting actuators that at each delivery of oil with the commands by the operator is capable of repeating a set cycle of strokes of the cylinder, which can be in particular "START-EXTRACTION- RETRACTION-STOP" or "START-RETRACTION-EXTRACTION-STOP".

Namely, the fluid-operated control device according to the invention can automatically perform a single cycle of opposite strokes of a fluid-operated actuator, or of a cylinder, which is repeated in a non-continuous manner, the switching occurring in the intermediate reversal point of the strokes and being actuated by overpressure.

Also, the fluid-operated control device according to the invention allows to perform safe locking, release for the start of motion and control of the movement speed of the loads applied to a fluid-operated actuator or a cylinder during the execution of the set automatic cycle of strokes.

A further advantage of the fluid-operated control device according to the invention is that it allows to perform the movement of the load at reduced pressures when the operator acts on the oil delivery and the load is being lifted; this allows a considerable energy saving.

Also, the fluid-operated control device according to the invention allows to safely lock the load that bears on the fluid-operated cylinder when the operator interrupts the delivery of oil in any position of the stroke.

The fluid-operated control device according to the invention is in fact capable of safely limiting the overpressure that is induced by the loads applied and acts in the chambers of the fluid-operated cylinder during the step of locking in the working position.

In the fluid-operated control device according to the invention, the speed of motion of the load during descent is kept constant, avoiding jamming or escape of the load.

It should be noted that the fluid-operated control device according to the invention is constituted by a body shaped like a parallelepiped, which is lightweight and resistant to corrosion and inside which all the details that operate are made of steel that is thermally treated to have the maximum resistance to compression stresses, plastic deformations and wear due to sliding. The materials used, as well as the dimensions and shapes, may of course be any according to the requirements and the state of the art.

This application claims the priority of Italian Patent Application No. 102021000021647, filed on August 10, 2022 the subject matter of which is incorporated herein by reference.

Claims

1. A fluid-operated control device for double-acting actuators, characterized in that it comprises a valve body which integrates a first overcenter valve in which the inlet is connected to a distribution device by means of a first connecting branch and the outlet is connectable to a first chamber of at least one fluid-operated cylinder, said valve body further integrating a second overcenter valve in which the inlet is connected to said distribution device by means of a second connecting branch and the outlet is connectable to a second chamber of said fluid-operated cylinder, said first overcenter valve being actuatable by means of a first control branch which is connected to said second connecting branch with the interposition of a check valve and of a first choke and to said first connecting branch with the interposition of a second choke, said second overcenter valve being actuatable by means of a second control branch connected to said first connecting branch, said distribution device being provided with a control chamber and being automatically switchable between a first operating condition, in which said first connecting branch is connected to a delivery branch of a working fluid and said second connecting branch is connected to a return branch of said working fluid and said control chamber is connected to said return branch by means of a unidirectional throttle valve, and a second operating condition, in which said first connecting branch is connected to said return branch by means of said unidirectional throttle valve and said second connecting branch is connected to said delivery branch, the switching between said first operating condition and said second operating condition being controlled by an overpressure valve integrated in said valve body and having the inlet connected to said first connecting branch by means of a third control branch and the outlet connected to said control chamber.

2. The fluid-operated control device according to claim 1 , characterized in that said unidirectional throttle valve comprises a spring-loaded check valve connected in parallel to a third choke.

3. The fluid-operated control device according to one or more of the preceding claims, characterized in that said first overcenter valve comprises a first controlled pressure control valve and a first check valve which are accommodated in a first seat provided in said valve body.

4. The fluid-operated control device according to one or more of the preceding claims, characterized in that said second overcenter valve comprises a second controlled pressure control valve and a second check valve, which are accommodated in a second seat formed in said valve body.

5. The fluid-operated control device according to claims 3 and 4, characterized in that each one of said first and second seats has an end which is axially closed, respectively by a first closure body and by a second closure body, which support means for the calibration of said first and second pressure control valves respectively, said calibration means being protected against tampering.

6. The fluid-operated control device according to one or more of the preceding claims, characterized in that said distribution device comprises a slider which is slidingly and hermetically engaged in a tubular casing having a plurality of through channels; said tubular casing being accommodated in a third through seat formed in said valve body and closed axially by third closure bodies.

7. The fluid-operated control device according to claim 6, characterized in that said distribution device comprises elastic preloading means interposed between said slider and one of said third closure bodies; said slider being normally kept in said first operating condition by said elastic preloading means.

8. The fluid-operated control device according to claims 6 or 7, characterized in that said slider comprises a substantially cylindrical body, from which four annular partitions protrude which are adapted to form three annular chambers together with said tubular casing, said three annular chambers being adapted to connect, in multiple combinations, said first connecting branch, said input branch, said second connecting branch, said return branch, said third control branch and said third connecting branch in said first and second operating conditions.

9. The fluid-operated control device according to one or more of the preceding claims, characterized in that said overpressure valve is arranged in a fourth seat formed in said valve body.

10. The fluid-operated control device according to claim 9, characterized in that 17 said fourth seat has an end which is dosed axially by a fourth closure body which supports calibration adjustment means adapted to interact respectively with said fourth movable element, said calibration adjustment means being protected against tampering.