FR2729720A1 - Safety valve for hydraulic power cylinder - Google Patents

Abstract

The safety valve (1) situated on the inlet side of the receiver (15) comprises a housing (5) containing a piston or slide valve (7) operated by the fluid pressure. The housing has at least one first aperture (18) connected to the distributor, and a second aperture (13) linked to the receiver (15). The slide valve (7) can occupy two main positions - a first or safety position, in which it is held against a seat (10) by a spring (9) and prevents the flow of hydraulic fluid between the first and second apertures and a second or operating position, in which allows such a flow.

Description

 The present invention relates to a safety device, and in particular a retaining device intended to ensure the blocking of a load moved by a hydraulic receiver, such as a jack, in the event of rupture of the fluid supply piping. The present invention also relates to a safety valve intended to implement said device.

 The hydraulic cylinders used for moving loads consist of a piston slidably mounted in a cylinder, this piston separating said cylinder into two chambers. Distributor means supply the cylinder with a pressurized hydraulic fluid which is admitted into one of the chambers, so as to push back the piston and the load to be displaced (configuration of working fluid, ie in which the fluid moves from the distributor means to the cylinder). The load can be locked in any determined position by interrupting the distribution of hydraulic fluid.

 To move the load in the opposite direction (driving load configuration, that is to say in which the fluid moves from the jack to the distributor means), the fluid previously admitted to the chamber is allowed to flow through an orifice. the passage section of which is controlled so as to adjust the speed of movement of the piston to a desired value.

 It is understood that the rupture of the pipe joining the distributor means to the jack has the effect of putting in communication the fluid contained in the chamber thereof directly with the atmosphere, without interposition of the orifice of controlled section, so that the load is immediately released, which can be the cause of particularly serious damage, in particular when this rupture occurs on a lifting device whose load is in the high position.

 In order to avoid this type of drawback, it has been proposed to use a safety valve, known as a "parachute valve", which is interposed between the distributor means and the inlet of the jack. We know that such a safety valve usually consists of a cylindrical body in which is disposed a valve which is maintained at a given distance from a valve seat by a spring which exerts on it an opening force. given, possibly adjustable. In the configuration of working fluid, in particular for lifting a load, hydraulic fluid is admitted via supply channels which pass through the body of the valve to arrive in the space between the valve seat and the valve. The spring thus ensures the opening of the valve and the hydraulic fluid passes through the safety valve to supply the actuator.

 In the drive load configuration, in particular for lowering the load, the hydraulic fluid is passed through the safety valve in the opposite direction and exerts on the valve a closing force antagonistic to that of the spring. This closing force follows the laws of flow of fluids through small orifices and is proportional to the square of the flow of fluid passing through the safety valve. Thus, in the case of a sudden pressure drop, due for example to a rupture channel, the return flow increases quickly and the pressure drop created at the valve, between the valve and its seat, increases in significant proportions and exceeds the force of the opening spring, so that the valve is applied on the valve seat, thus ensuring the stopping of the flow of the fluid and, consequently, the stopping of the piston of the jack. It is therefore necessary, for each acceptable fluid limit speed for such a determined safety valve, to adjust the distance existing between the valve and its seat to a value large enough so that the valve remains open under the force of the spring when the fluid hydraulic flow back through the safety valve (drive load configuration) but also small enough, however, so that, in the event of a break in the pipe connecting the distributor means to the jack, the pressure drop caused by the increased flow rate of the hydraulic fluid can close the valve.

 Such a safety valve also has a major drawback, namely, in the event of a rupture of the pipe connecting the distributor means to the jack, of not ensuring immediate immobilization of the piston of the latter. Indeed, on the one hand when the system is in the configuration of working fluid, that is to say when the fluid moves from the distributor means towards the jack, which corresponds in particular to the case where a load is lifted, it it is necessary that the piston of the jack moves over a certain distance so that the flow of fluid is reversed and generates a sufficient pressure drop to ensure the closing of the valve. Such a reversal of movement ensures a sudden stop of the load during an accelerated movement, which subjects the mechanical elements to significant stresses.

 On the other hand, when the system is in the drive load configuration, that is to say when the fluid moves from the jack to the distributor means, which corresponds in particular to the case where a load is lowered, it is necessary that a certain flow of fluid crosses the valve so that the pressure drop created reaches a value greater than the force of the valve opening spring in order to ensure the closure of the valve, so that the load is thus brought to make a significant movement before being stopped, which can be particularly dangerous.

 The object of the present invention is to propose a safety device for a hydraulic receiver intended to move a load which does not require complex adjustment and which is able to ensure, almost immediately, the blocking of the load. in the case of a rupture of the pipe connecting the means for distributing hydraulic fluid to said receiver.

The present invention thus relates to a safety device for a hydraulic receiver and in particular for a hydraulic cylinder, supplied by means for distributing pressurized hydraulic fluid, this device comprising a safety valve disposed at the inlet of said receiver, characterized in that
the safety valve essentially consists of a body in which a piston or drawer moves under the action of the hydraulic fluid under pressure, the body comprising at least a first orifice connected to the dispensing means and a second orifice connected to the receiver, the drawer being able to occupy two main positions, namely a first position, or safety position, in which it is in abutment against a seat under the effect of elastic means and thus blocks the circulation of the hydraulic fluid between the first and second orifices, and a second position, or operating position, in which it allows a circulation of the fluid between the above-mentioned orifices,
- It includes a return valve capable of creating a "pilot pressure" applied to the drawer against the elastic means, which is greater than the force exerted by the latter when the hydraulic fluid circulates between the first and second orifices of the valve , so that this pilot pressure keeps the slide in the open position against the restoring force of said elastic means.

 The present invention also relates to a safety valve for a hydraulic receiver, and in particular for a hydraulic cylinder, supplied by means for distributing pressurized hydraulic fluid, characterized in that it comprises a body in which a piston or drawer moves. , under the action of the hydraulic fluid under pressure, the body comprising at least a first orifice intended to be connected to means for distributing said fluid and a second orifice intended to be connected to the receiver, the drawer being able to occupy two main positions, namely a first position, or safety position, in which it is in abutment against a seat under the effect of elastic means and thus blocks the circulation of hydraulic fluid between the first and second orifices, and a second position, or position operating, in which it allows a circulation of the fluid between the aforesaid orifices, the first orifice being in communication with a volume provided between the seat of the drawer and the latter.

Various embodiments of the present invention will be described below, by way of non-limiting examples, with reference to the appended drawings in which
Figure 1 is a schematic view of an embodiment of a safety device according to the invention.

 Figure 2 is a partial sectional view of a first variant of a safety valve used in the safety device according to the invention.

 Figure 3 is a partial sectional view of a second variant of a safety valve.

Figure 4 is a sectional view of the alternative embodiment shown in Figure 3 along the line
IV-IV thereof.

 Figure 5 is a schematic view of an alternative embodiment of the invention.

 The safety device according to the invention described in FIG. 1 is intended to lift a load 2. It essentially comprises a safety valve 1 and a valve called the return valve 3. The valve 1 consists of a tubular body 5 to the interior of which is slidably mounted a drawer 7 urged by a calibrated spring 9 against a seat 10, into which opens an orifice 11. The drawer 7 is hollowed out so as to constitute with the internal walls of the body 5 an annular chamber 20. The body 5 has a lateral orifice 13 which is closed by the drawer 7 when the latter is in abutment against the seat 10 (FIG. 1).

The orifice 13 is connected by a rigid pipe 14 to a hydraulic cylinder 15 whose piston 16 is intended to move the load 2. The body 5 has another orifice 18 which opens into the chamber 20 of the drawer 7.

 The device comprises means for distributing the hydraulic fluid essentially consisting of a distributor 24 and a source of supply of pressurized fluid consisting of a pump 30 in suction with a tank 32 containing the hydraulic fluid. The distributor 24 has three positions, namely a position A, or rest position, a position B, or configuration of working fluid, corresponding in FIG. 1 to a position for raising the piston 16, and a position C, or configuration of engine load, corresponding in this same figure to a descent position of the piston 16. The distributor 24 is provided with an inlet orifice 28, an outlet orifice 26 and an orifice 29 for entry or The inlet port 28 is connected to the pump 30, and the outlet 26 is connected to the tank 32 containing the hydraulic fluid, by means of the return valve 3. The latter is designed so as to present, in normal operation, a pressure drop making it possible to maintain in the circuit a slight residual pressure, or pilot pressure, which is slightly greater than the force exerted by the spring 9 on the slide 7 when the hydraulic fluid moves towards the tank 32, and which is closed otherwise.

 The orifice 29 is joined to the valve 1 by a pipe 12, usually a flexible pipe.

This pipe, in the present embodiment, is in communication both with the orifice 11 and with the orifice 18 of the body 5 by a pipe 17.

 Under these conditions, the operation of the safety device according to the invention is carried out as described below.

 When it is desired to lift the load 2 by means of the piston 16, the distributor 24 is placed in the position B or configuration of working fluid, which corresponds to a position for raising the piston 16 in FIG. 1, so that the pressurized fluid supplied by the pump 30 arrives at the inlet 28, passes through the distributor 24, leaves it through the orifice 29, then borrows the flexible pipe 12 to enter the valve 1 both through the orifices li and 18. The fluid admitted through the orifice 11 thus pushes the drawer 7 upwards, against the force exerted by the spring 9, which has the effect of releasing the orifice 13, so that the fluid under pressure arriving through the orifice 18 can flow freely through the said orifice 13, take the rigid pipe 14 and push up the piston 16, as well as the load 2.

 If, during the displacement of the piston 16, the flexible pipe 12 breaks, the supply of fluid to the orifice 11 is interrupted, so that the spring 9 immediately brings the drawer 7 back into contact with the seat 10, which has the immediate effect of closing the orifice 13, so that the flow of hydraulic fluid is immediately stopped as well as the movement of the piston 16.

 When it is desired to lower the load 2 held by the piston 16, the distributor 24 is placed in position C, or configuration of driving load, which corresponds to a lowering position of the piston 16 in FIG. 1. In this position, the orifice 11 is in communication with the tank 32 via the return valve 3. Due to the pressure drop created by the latter, the pilot pressure keeps the slide 7 in the open position, so that the hydraulic fluid coming from the jack 15 can pass through the line 14, the orifice 13 and the annular chamber 20 to exit the valve 1 through the orifice 18 and reach, through the flexible line 12, the orifice 29 of the distributor 24, the orifice 26 thereof, the return valve 3 and the tank 32.

 When, during this phase, a circuit break occurs at the flexible pipe 12, the pilot pressure keeping the slide 7 spaced from its seat 10, against the action exerted by the spring 9 disappears, if although the latter brings the drawer 7 into contact with its seat 10, which has the effect of closing the orifice 13. Therefore, any movement of the piston 16, both in the direction of the rise and in the direction from the descent, is thus stopped almost instantaneously.

 The present safety device therefore makes it possible to avoid any sudden descent of the load 2, both during ascent and during descent.

 In an alternative embodiment of the invention shown in FIG. 2, the valve body 5 does not have an orifice 11 connecting the seat 10 of the drawer 7 to a fluid circulation pipe, but the base of the drawer 7 is hollowed out by a recess 34 which is in communication by a conduit 36 hollowed out in the drawer 7, with the chamber 20.

Under these conditions, when the fluid is admitted through the orifice 18 into the annular chamber 20, it is also admitted through the conduit 36 into the recess 34, so that it can, as in the previous embodiment, push the drawer 7 against the return force of the spring 9, without requiring the presence of an orifice 11 in the valve seat 10.

 In another alternative embodiment of the invention shown in FIGS. 3 and 4, communication is ensured between the annular chamber 20 and the base surface of the drawer 7 by producing two diametrically opposite flats 38 on the base of it this. In this embodiment, the fluid is admitted between the seat 10 and the base of the drawer 7 by microchannels formed therein, in particular by sanding with scratches, etc.

 The device according to the invention can be easily adapted on existing equipment which uses safety valves.

 In another embodiment of the invention, shown in FIG. 5, the application of a pilot pressure was carried out externally. It is known in fact that in certain installations numerous pressure drops are created on the pipe which connects the distributor means to the jack. These pressure losses are due most of the time to more or less defective connections and connections as well as to commands from various devices which are connected to this pipe.

 According to the present variant, the valve seat 10 comprises, as in the embodiment described with reference to FIG. 1, an orifice 11 which is placed directly in communication with the orifice 29 of the distributor 24 by means of a line 12 ′ free of any element which can cause a significant pressure drop. The orifice 18 is also connected to this same orifice 29 by the line 12, the latter being able on the other hand to include elements capable of introducing pressure losses such as fittings 37, elbows 37 ′ as well as connections 40 and 40 'to various hydraulic devices.

 This variant is particularly advantageous in that it makes it possible to have an installation which tolerates pressure drops on the pipe connecting the distributor 24 to the safety valve 1, without the latter disturbing the operating reliability of the device. security.

Claims (10)

 1.- Safety device for a hydraulic receiver, and in particular for a hydraulic cylinder, supplied by means of distributing hydraulic fluid under pressure, this device comprising a safety valve (1) disposed at the inlet of said receiver (15), characterized in what  the safety valve (1) essentially consists (18, 13) of a body (5) in which a piston or drawer (7) moves, under the action of the hydraulic fluid under pressure, the body ( 5) comprising at least a first orifice (18) connected to the dispensing means and a second orifice (13) connected to the receiver (15), the drawer (7) being able to occupy two main positions, namely a first position, or position safety, in which it is in abutment against a seat (10) under the effect of elastic means (9) and thus blocks the circulation of hydraulic fluid between the first and second orifices (18,13), and a second position , or operating position, in which it allows a circulation of the fluid between the aforesaid orifices,  - It includes a return valve (3) capable of creating a "pilot pressure" applied to the slide (7) against the elastic means (9), which is greater than the force exerted by the latter when the hydraulic fluid circulates between the first and second orifices (18,13) of the valve (1), so that this pilot pressure keeps the slide (7) in the open position against the restoring force of said elastic means (9 ).  2.- Device according to claim 1 characterized in that the drawer (7) is hollowed out of a cavity which defines with the internal wall of the valve (1) an annular chamber (20) which is in communication with the first orifice (18 ) and with the second orifice (13) when the drawer (7) is in the operating position, the second orifice (13) being closed by the drawer (7) when the latter is in the safety position.  3.- Device according to claim 2 characterized in that the chamber (20) is in communication with a volume (34) provided between the seat (10) of the drawer (7) and the latter.  4.- Device according to claim 3 characterized in that said communication is provided by at least one channel (36).  5.- Device according to claim 3 characterized in that said communication is provided by at least one chamfer (38) made at the base of the drawer (7).  6.- Device according to one of the preceding claims characterized in that the seat (10) of the drawer (7) is provided with an orifice (11) in direct communication with the dispensing means, by a control pipe (12 ' ), the first orifice (18) being in communication with the dispensing means by another pipe (12).  7.- Safety valve for hydraulic receiver, and in particular for hydraulic cylinder, supplied by means for distributing pressurized hydraulic fluid, characterized in that it comprises a body (5) in which a piston or drawer (7) moves , under the action of the hydraulic fluid under pressure, the body (5) comprising at least a first orifice (18) intended to be connected to means for distributing said fluid and a second orifice (13) intended to be connected to the receiver (15 ), the drawer (7) being able to occupy two main positions, namely a first position, or safety position, in which it is in abutment against a seat (10) under the effect of elastic means (9) and thus blocks the circulation of the hydraulic fluid between the first and second orifices (18, 13), and a second position, or operating position, in which it authorizes a circulation of the fluid between the aforesaid orifices, the first orifice being in communication with a volume (34) provided between the seat (10) of the drawer (7) and the latter.  8. Safety valve according to claim 7 characterized in that the drawer (7) is hollowed out of a cavity which defines with the internal wall of the valve (1) an annular chamber (20) which is in communication with the first orifice ( 18) and with the second orifice (13) when the drawer (7) is in the operating position, the second orifice (13) being closed by the drawer (7) when the latter is in the safety position.  9. Safety valve according to one of claims 7 or 8 characterized in that said communication is provided by at least one channel (36).  10. Safety valve according to one of claims 7 or 8 characterized in that said communication is provided by at least one chamfer (38) formed at the base of the drawer (7).