JPS6336087B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydraulic operating circuit for a high-voltage, large-current breaker having a self-holding mechanism in its operating valve.

In general, this type of hydraulic operation circuit includes a hydraulic cylinder that operates the breaker, a main valve that sends pressure oil for operation to the hydraulic cylinder, an operation valve that sends pressure oil for operation to the main valve, and a control valve that drives the operation valve. It consists of a closing solenoid valve and a closing solenoid valve.

The hydraulic operation circuit is provided with a self-holding mechanism.

The self-holding mechanism maintains the closed state of the hydraulic cylinder using pressure oil flowing through the hydraulic circuit, and prevents the contact of the shingle breaker from inadvertently moving from its closed position.

FIG. 1 shows a self-holding mechanism provided on the side of the operating valve 4. In this case, the operating valve 4 that sends pressure oil with a total pressure of 17 to the main valve 3 is connected to the P port, the A port, the R port, and the R port.
It is mainly composed of first and second hydraulically operated switching valves 12 ₁ and 12 2, which are a type of 3-port 2-position switching valve, and the first hydraulically operated switching valve _{12 1 has} two operation chambers. 16 ₁ and 16 ₂ are provided.

That is, the first hydraulically operated switching valve 12 ₁ has one operation chamber 16 ₁ connected to the conduit from the closing solenoid valve 5 , and the other operation chamber 16 ₂ connected to the A
A branch pipe of the pipeline connecting the port and the main valve 3 is connected via a second hydraulically operated switching valve 12 ₂ driven by the solenoid valve 6 for cutting off.

Then, when the closing solenoid valve 5 is energized, pressure oil flows into the operation chamber ₁₆₁ , the operation piston 15 moves to the left, the ball valve 13 opens between the P port and the A port, and the pressure oil is sent out from the pressure source 17. Pressure oil is sent to the main valve 3 and the P port of the second hydraulically operated switching valve 12 ₂ .

The main valve 3 receives the pressure oil and operates a hydraulic cylinder (not shown) to set the contactor (not shown) of the shingle breaker in the closing position.

On the other hand, the pressure oil sent to the P port of the second hydraulically operated switching valve ₁₂₂ passes through the P port and the A port to the first
enters the operating chamber 16 ₂ of the hydraulically operated switching valve 12 ₁ and continues to press the operating piston 15 to the left.

Therefore, even if the closing solenoid valve 5 is demagnetized and the pressure oil in the operation chamber ₁₆₁ is released to the tank, the operation chamber 1
Since the pressure oil in 6 ₂ is maintained as it is, the operating piston 15 remains moved to the left, and as a result, the pressure oil is also maintained in the main valve 3, and the breaker is closed. It will be self-preserving.

However, in such a self-holding mechanism, the pressure source 1
As long as the pressure in step 7 (hereinafter referred to as system pressure) is always normal, no problem will occur.
If the system pressure drops for some reason, such as an oil leak from the pressure source, in the above-mentioned closed state, and the cause is removed and the system pressure is raised again, the breaker will close before the system pressure drops. The problem arises in that as the system pressure gradually recovers, the disconnector gradually shifts to the shattered state without giving a shrivel command.

That is, when the system pressure decreases, the pressure in the operation chamber 16 ₂ for self-holding of the first hydraulically operated switching valve 12 ₁ also decreases, so the operation piston 1
5 returns to the right, and the ball valve 13 closes between the P port and the A port. For this reason, pressure oil is not supplied to the main valve 3 even if the system pressure is increased again.

Conventionally, two methods have been proposed as solutions to this problem.

The first method is to mechanically clamp the operating piston 15 to prevent it from returning to the right when the system pressure decreases, and to supply pressure oil to the main valve when the system pressure increases again. The second method is to mechanically clamp the piston rod of the hydraulic cylinder that directly operates the shear breaker to maintain the closed state of the shear breaker when the system pressure decreases. It is.

However, all of these methods require the installation of a sturdy and complex clamping device to clamp the operating piston 15 or piston rod against the hydraulic pressure generated when the system pressure rises again. There were also problems with the reliability of the clamping device.

The present invention was developed in view of the above-mentioned circumstances, and is designed to release pressure oil into a tank when the system pressure abnormally drops below the set pressure _P1 in the middle of the pipeline that directly connects the operating valve 4 and the pressure source 17. , a first pressure control valve is provided that causes pressure oil to flow when the pressure is recovered to P ₁ or more, and a third operation chamber for the self-holding piston 15 is provided in the first hydraulic operation switching valve 12 ₁ of the operation valve 4, A new conduit is provided that directly connects the operation chamber of No. 3 and the pressure source 17, and pressure oil is flowed in the middle of this conduit in conjunction with the piston rod of the hydraulic cylinder 2 when the shear breaker 1 is in the closed state. The set pressure P ₁ of the switching valve that releases pressure oil to the tank in the disconnected state and the first pressure control valve.
By installing a second pressure control valve that allows pressure oil to flow when the system pressure abnormally drops below a higher set pressure _P2 , and releases the pressure oil to the tank when the system pressure recovers to _P2 or higher. Only when the disconnector 1 is in the closed state and the system pressure is abnormally low, pressure oil flows into the new pipe and is supplied to the third operation chamber of the self-holding piston 15, and the system pressure is restored. A self-retaining piston 15 by the system pressure itself delivered to said third operating chamber on rising.
The above-mentioned conventional problem can be solved by providing a hydraulic operation circuit for the valve breaker which is pressed leftward, opens the gap between the P port and the A port, and supplies the recovered system pressure to the main valve 3. This is an attempt to eliminate them all at once.

Hereinafter, the present invention will be explained in detail based on the accompanying drawings.

In Fig. 2, 1 is a power cutter, 2 is a hydraulic cylinder that operates the cutter 1, 3 is a main valve that sends operating pressure oil to the hydraulic cylinder 2, and 4 is a main valve 3. An operating valve that sends pressure oil for operation; 5 and 6 are closing solenoid valves and sheath-off solenoid valves that drive the operating valve 4; 11 is an accumulator. In addition, a first pressure control valve 25 provided in the middle of a pipe connecting the above-mentioned parts, that is, a pipe connecting an operating circuit and a pressure source 17 that supplies pressure oil to the operating circuit, is a first pressure control valve of the operating valve 4. Hydraulic operation switching valve 12 ₁ operation chamber 29
26 and 27 respectively represent a second pressure control valve and a switching valve provided in the middle of the pipe lines 32 and 33 directly connecting the pressure source 17 and the pressure source 17.

The main valve 3 is a type of 3-port 2-position switching valve that has a P port, an A port, and an R port.
A poppet valve 7 that controls opening and closing between ports, an operating piston 8 for the poppet valve 7, and an operating chamber 1 for the operating piston 8.
It is composed of a poppet valve 9 that controls opening and closing between the 0 and A ports and the R port. The P port is connected to the rod side of the hydraulic cylinder 2 and the accumulator 11, and the A port is connected to the bore side of the hydraulic cylinder 2.

The operating valve 4 is mainly composed of first and second hydraulically operated switching valves 12 ₁ and 12 ₂ which are a type of three-port two-position switching valve having a P port, an A port, and an R port.

The first hydraulically operated switching valve ₁₂₁ includes a poppet valve 23 that controls opening and closing between the P port and the A port, a poppet valve 24 that controls the opening and closing between the A port and the R port, and a self-holding piston for operating the poppet valves 23 and 24. 1
5. Two operation chambers 16 ₁ of the self-retaining piston 15,
16 ₂ , a third operation chamber 29 equipped with a pressing piston 30 for the self-holding piston 15, and the like.

The P port of this valve ₁₂₁ is connected to the first pressure control valve 2.
5 to a pressure source 17, and the A port is connected to an operation chamber 10 of the main valve 3. A pipe line connecting this A port and the operation chamber 10 of the main valve 3 is branched in the middle and connected to the P port of the second hydraulically operated switching valve 12 ₂ . The R port is connected to the tank. The control room 16 ₁ has a closing solenoid valve 5
The operation chamber 16 ₂ is connected to the A port of the second hydraulically operated switching valve 12 ₂ , and the operation chamber 29 is connected to the pressure source via the switching valve 27 and the second pressure control valve 26 . 17.

The second hydraulically operated switching valve ₁₂₂ includes a poppet valve 28 that controls opening and closing between the P port and the A port and opening and closing between the A port and the R port, an operating piston 19 of the poppet valve 28, an operating chamber 20 of the operating piston 19, etc. has. The R port of this valve 12 ₂ is connected to the tank, and a pipe line from the solenoid valve 6 for cutting off the shield is connected to the operation chamber 20 .

The first pressure control valve 25 is provided in the middle of a pipe line connecting the pressure source 17 and a pipe line (operation circuit) connecting each part of the operation valve 4, both solenoid valves 5 and 6, and the accumulator 11, so that the system pressure can be controlled. Setting pressure
When P drops to ₁ or less, it becomes the E position and releases the pressure oil in the operating circuit to the tank, reducing the system pressure.
When the pressure is restored to _P1 or more, the pressure oil from the pilot pipe line 34 switches to the F position and operates to supply pressure oil to the operating circuit.

The second pressure control valve 26 and the switching valve 27 are connected to the pressure source 1
7 and the operation chamber 29 of the first hydraulically operated switching valve 12 ₁ are provided in the middle of pipes 32 and 33 that directly connect the control chamber 29 of the first hydraulically operated switching valve 12 1 .

That is, the second pressure control valve 26 is connected to the pressure source 17
is branched from the middle of the pipe line connecting the first pressure control valve 25 and is provided in the middle of the pipe line 32 connected to the primary side port of the switching valve 27. When the system pressure drops below the set pressure _P2 , which is higher than the set pressure _P1 , the system enters the C position and pressure oil flows into the pipe 32, and when the system pressure recovers to _P2 or higher, the pressure oil flows from the pilot pipe 35. Therefore, it switches to the D position and operates to release pressure oil to the tank.

The secondary port of the switching valve 27 is connected to the operation chamber 29 of the first hydraulically operated switching valve 12 ₁ via a conduit 33 . The switching valve 27 switches in conjunction with the piston rod of the hydraulic cylinder 2, and is in the A position when the piston rod is extended, that is, when the shield disconnector 1 is in the closed state, and supplies pressure oil to the operation chamber 29, and when the piston rod is retracted, that is, in the closed state. When the shroud breaker 1 is in the shunt-off state, it is in the B position, and pressurized oil in the operation chamber 29 is released to the tank through the pipe line 33.

Next, the operation of this hydraulic operation circuit will be explained.

FIG. 2 shows the case where the shingle breaker 1 is in the shingled state. In this state, when the pressure oil from the pressure source 17, that is, the system pressure is normal, the first pressure control valve 25 and the second pressure control valve 26 are switched to the F position and the D position, respectively, by hydraulic pressure. The switching valve 27 is switched to the B position by the hydraulic cylinder 2, and the system pressure is between the P port of the first hydraulically operated switching valve ₁₂₁ , both solenoid valves 5 and 6, the accumulator 11, the hydraulic cylinder 2, and the P port of the main valve 3. Supplied to ports, etc.

Therefore, when the closing solenoid valve 5 is energized now, pressure oil is supplied to the operating chamber 16 ₁ of the first hydraulically operated switching valve 12 ₁ through this valve 5, and the self-holding piston 15 and the poppet valves 23 and 24 are spring-loaded. The poppet valve 24 closes the connection between the A port and the R port, and at the same time the poppet valve 23 connects the P port and the A port to transfer the system pressure between the operation chamber 10 of the main valve 3 and the second port. Hydraulic operation switching valve 12
₂ P port.

The system pressure supplied to the operating chamber 10 of the main valve 3 pushes the operating piston 8 to the left, moves the poppet valve 7 to the left against the spring 21, and connects the P port and A port of the main valve 3. do.

By opening between the P port and the A port of the main valve 3, the pressure oil of the accumulator 11 is transferred to the hydraulic cylinder 2.
However, since the pressure receiving area of the hydraulic cylinder 2 is larger on the bore side than on the rod side, this pressure difference causes the piston of the cylinder 2 to move to the left, causing the piston connected to the tip of the piston rod to 1 is set to the closed state. At this time, the switching valve 27 is switched to the A position by the spring.

When the piston of the hydraulic cylinder 2 moves to the left end, the pressure on the bore side of the hydraulic cylinder 2 becomes almost the same as the pressure in the accumulator 11 and the operating chamber 10 of the main valve 3, the flow of pressure oil stops, and the operating piston 8 and poppet valve 7 are spring 2
It returns to the right end with a force of 1, and the space between the P port and the A port is closed. In this case, since the poppet valve 9 remains held at the left end by the spring 22, the hydraulic circuit is not connected to the low pressure side (tank) while the hydraulic cylinder 2 is in operation.

Further, the system pressure branched from the A port of the first hydraulically operated switching valve 12 ₁ to the P port of the second hydraulically operated switching valve 12 ₂ passes through the A port of the valve 12 ₂ to the first hydraulically operated switching valve 12 2 . Control room 1 for valve 12 ₁
6 ₂ , and presses the self-holding piston 15 further to the left to maintain the closed state.

Through this series of operations, the breaker 1 completes the closing operation, but the closing solenoid valve 5 is demagnetized during the closing operation. Due to this demagnetization, the valve 5 returns to the position shown on the right side by the spring, and the pressure oil in the operation chamber 16 ₁ of the first hydraulically operated switching valve 12 ₁ returns to the tank via the solenoid valve 5, but the pressure in the operation chamber 16 ₂ Self-retaining piston 1 because the oil is retained
5 remains moved to the left end. That is, even though the closing solenoid valve 5 is demagnetized, the shield breaker 1 continues to maintain the closed state.

Next, the operation of the circuit when the system pressure decreases in the closed state of the shield breaker 1 will be described.

For example, if an oil leak or the like occurs in the pressure source 17 and the system pressure decreases, the pressure in the entire operation circuit decreases, and the pressure in the operation chamber 10 of the main valve 3 also decreases.
Since the poppet valve 9 remains held at the left end by the force of the spring 22, the piston of the hydraulic cylinder 2 also remains closed.

When the system pressure further decreases to below the _P2 pressure, the second pressure control valve 26 is spring operated and the C
The position is changed and pressure oil flows into the pipe line 32. The switching valve 27 is switched to the A position by the spring because the piston moves to the left end when the hydraulic cylinder 2 is closed.
The pressure oil flowing through the switching valve 27 is supplied to the operating chamber 29 of the first hydraulically operated switching valve 12 ₁ via the pipe 33 , and pushes the piston 30 in the operating chamber 29 to the left against the spring 31 . Then, push the self-holding piston 15 further to the left.

When the system pressure further decreases to below _P1 , the first pressure control valve 25 is spring operated to switch to the E position, blocking the supply of pressure oil to the operating circuit and opening the circuit to the tank. At this time,
If there is any remaining pressure oil in the pressure source 17, that pressure oil is led to the operation chamber 29 via the pipes 32 and 33, so the operation of the piston 30 is not affected in any way, and the piston rod of the hydraulic cylinder 2 is It remains in the closed state.

When the cause of the system pressure drop is resolved and the system pressure begins to rise again, the pressure oil will flow through the pipes 32 and 3.
3 into the operation chamber 29, the piston 30 moves to the left, and the self-retaining piston 15 is pushed to the left to configure the closed state function. At this time, since the first pressure control valve 25 remains in the E position, no pressure oil is supplied to the operating circuit.

When the system pressure increases and exceeds the _P1 pressure, the first pressure control valve 25 switches to the F position,
Pressure oil is supplied to the operating circuit. At this time, the self-holding piston 15 has already moved to the left and the closed function has been configured, so the pressure oil flowing into the operation circuit is transferred to the hydraulic cylinder 2, the operation chamber 10 of the main valve 3, and the first hydraulically operated switching valve. 12 ₁ and is simultaneously supplied to the self-holding operation chamber 16 ₂ . Therefore, the piston rod of the hydraulic cylinder 2 does not move in the opposite direction.

When the system pressure increases further and exceeds the P ₂ pressure, the second pressure control valve 26 switches to the D position, blocking the pressure oil flowing to the pipes 32 and 33 and opening it to the tank. As a result, the piston 30 in the operation chamber 29 is pushed back to the right by the force of the spring 31, but the self-holding piston 15 is strongly pushed to the left by the pressure oil supplied to the operation chamber ₁₆₂ and has already activated its self-holding function. It consists of

Therefore, even if the system pressure drops abnormally with the shroud breaker 1 in the closed state, the shredder breaker will not shift to the shattered state, and the self-holding function will be restored as the system pressure recovers. The breaker 1 continues to maintain the closed state from beginning to end.

Next, when changing the closed state of the shear breaker 1 to the shear off state, the sheath breaker solenoid valve 6 is energized. When the shear cutoff solenoid valve 6 is energized, pressure oil from the pressure source 17 is applied to the second hydraulically operated switching valve 12 ₂
Pressure oil is supplied to the operation chamber 20 of. The operation piston 19 moves to the left by the pressure oil supplied to the operation chamber 20, opens the poppet valve 28, and communicates between the A port and the R port, so that the operation chamber of the first hydraulically operated switching valve ₁₂₁ The pressure oil in 16 ₂ is collected into the tank via the A port and R port of the second hydraulically operated switching valve 12 ₂ . Then, the self-holding piston 15 and the poppet valve 24 move to the right by the spring force, closing the P port and communicating the A port with the R port, so that the pressure oil in the operation chamber 10 of the main valve 3 is released. It is collected into the tank via the A port and R port of the first hydraulically operated switching valve 12 ₁ . Along with this, the poppet valve 9 of the main valve 3 rapidly moves to the right side against the force of the spring 22 due to the force of the pressure oil stored in the bore side of the hydraulic cylinder 2, opening the R port and causing the hydraulic pressure to increase. Collect the pressure oil on the bore side of cylinder 2 into the tank. Pressure oil from the accumulator 11 is constantly supplied to the rod side of the hydraulic cylinder 2, so when the pressure oil on the bore side is collected into the tank and the pressure decreases, the piston of the hydraulic cylinder 2 rapidly moves to the right due to the pressure difference. In conjunction with this, the contactor of the sheath breaker 1 shifts from the on state to the shear off state. At the same time, the switching valve 27 is switched to the B position, and the pressure oil in the operation chamber 29 of the first hydraulically operated switching valve 12 ₁ is recovered into the tank. The shearing operation is thus completed.

When the cutting operation is completed, the bore side of the hydraulic cylinder 2 becomes atmospheric pressure, and the poppet valve 9 of the main valve 3 returns to the left side by the force of the spring 22, closing between the A port and the R port, and the next Prepare for the launch order.

Next, the operation when the system pressure decreases in this shrunken state will be described.

When the system pressure decreases in the damped state and becomes less than _P2 pressure, the second pressure control valve 26 switches to the C position and pressurized oil is supplied to the pipe line 32, but the switching valve 27 is in the B position. , here the pressure oil is blocked, and the pipe line 33 and the first hydraulically operated switching valve 12 ₁
is not supplied to the operation room 29. Therefore, the piston 30 in the operation chamber 29 is pressed to the right by the spring 31, and the self-retaining piston 15 also remains moved to the right by the force of the spring, that is, remains in the sheared state.

When the system pressure further decreases to below _P1 pressure, the first pressure control valve 25 switches to the E position and the pressure oil supply to the operating circuit is blocked.
The shrunken state is maintained as is.

When the pressure source 17 is restored and the system pressure begins to rise, the pressure oil first flows into the pipe line 32, but since the switching valve 27 is in the B position,
It is blocked here. At this time, the first pressure control valve 2
5 remains in the E position, so the supply of pressure oil to the operating circuit is blocked. Therefore, the self-retaining piston 15 continues to move to the right and is in a sheared state.

When the system pressure increases above P ₁ pressure,
The first pressure control valve 25 is switched to the F position and pressure oil is supplied to the operating circuit, but the pressure oil to the operating valve 4 is blocked by the poppet valve 23 of the first hydraulically operated switching valve 12 ₁ . It is not supplied to the operation chamber 10 of the main valve 3. Therefore, the cylinder 2 does not operate and remains in the damped state.

When the system pressure further increases to _P2 pressure or higher, the second pressure control valve 26 switches to the D position, and the pressure oil to the line 32 is blocked, and at the same time, the line 32 is opened to the tank. , hereafter switching valve 2
7 is in either position A or B, pressure oil is not supplied to the operation chamber 29 of the first hydraulically operated switching valve 12 ₁ , and the piston 30 in the operation chamber 29 is moved to the right by the force of the spring 31. Continue to hold the pressed state. Therefore, the self-holding piston 15 does not move to the left, and remains in the disconnected state from beginning to end until the system pressure is restored to normal and the next closing command is received.

As explained above, the present invention provides that the hydraulic operating circuit of the breaker, which is equipped with a self-holding mechanism on the operating valve side, loses its self-holding function when the system pressure decreases while the breaker is closed. , the problem that it is impossible to supply pressure oil from the operation valve to the main valve even if the system pressure rises again can be solved by installing a piston 30 for pushing the self-holding piston on the back of the self-holding piston 15. A chamber 29 is provided, and the operation chamber 29
New branch pipes 32, 33 connecting the pressure source 17 and
is provided with a second pressure control valve 26 and a switching valve 27,
When the system pressure is less than the set pressure _P2 in the closed state, pressure oil is supplied to the operation chamber 29 to maintain the self-holding function, and in the cut-off state, pressure oil is supplied to the operation chamber 29 regardless of the system pressure. A first pipe that is closed and maintains a shrunken state, and supplies pressure oil to the operating circuit at a set pressure P1 or higher, where the system pressure is lower than _P2 , in the middle of the pipe connecting the pressure source ₁₇ and the operating circuit. A pressure control valve 25 is provided so that pressure oil is supplied to the operating circuit after the self-holding piston completes the closing movement to the left when the system pressure drops and rises again in the closed state. 2 can be prevented from malfunctioning from the closed state to the closed state, and there is no need to incorporate a complicated clamping device into the circuit as in the conventional case. Therefore, the overall structure of the hydraulic circuit is simplified, reliability is increased, and excellent effects such as cost reduction can be expected.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram illustrating a conventional hydraulic operating circuit in which an operating valve is provided with a self-holding mechanism, and FIG. 2 is a circuit diagram illustrating a hydraulic operating circuit according to the present invention. 1: Shutoff switch, 2: Hydraulic cylinder, 3: Main valve, 4: Operation valve, 5: Closing solenoid valve, 6:
Solenoid valve for shielding, 7, 9, 23, 24, 2
8: Poppet valve, 8, 19: Operation piston, 1
0, 16 ₁ , 16 ₂ , 20, 29: Operation room, 11:
Accumulator, 12 ₁ : First hydraulically operated switching valve,
12 ₂ : Second hydraulically operated switching valve, 13, 14, 1
8: Ball valve, 15: Self-holding piston, 17:
Pressure source, 21, 22, 31: Spring, 25:
First pressure control valve, 26: Second pressure control valve, 27:
Switching valve, 30: Piston, 32, 33: Pipe line, 3
4, 35: Pilot pipe.

Claims (1)

[Claims] 1 a hydraulic cylinder 2 that operates the breaker 1;
A main valve 3 that sends operating pressure oil to the hydraulic cylinder 2
and an operating valve 4 that sends operating pressure oil to the main valve 3, the operating valve 4 is connected to a first hydraulically operated switching valve 121 and a second hydraulically operated switching valve ₁₂₁ . _The first hydraulically operated switching valve 12 ₁ has three operation chambers 16 ₁ , 16 ₂ ,
29, the pipe line from the input solenoid valve 5 is connected to the first operation chamber ₁₆₁ , and the second operation chamber 162 is connected to the first operation chamber _161.
A branch pipe is connected to the pipe that branches from the pipe that supplies operating pressure oil to the main valve 3 and is opened and closed by a second hydraulically operated switching valve 12 ₂ that is operated by the cutoff solenoid valve 6 . It is attached to the hydraulic cylinder 2 in the third operation room 29, and is linked to the piston rod of the cylinder to flow pressure oil when the shatter breaker 1 is in the closed state, and to flow the pressure oil into the tank when the shatter breaker 1 is in the closed state. A pipe line is connected from the secondary side port of the two-position switching valve 27 that opens to A _first pressure control valve 25 is provided which operates to release the pressure oil to the tank when the pressure drops to P1 or less, and to supply the pressure oil to the pipe when the pressure recovers to _P1 or more, and the first pressure control valve 25 The pipe line connecting the pressure source 17 and the pressure source 17 is branched from the middle, and the
When the system pressure drops below the set pressure _P2 , which is higher than _P1 , pressure oil is supplied to the pipe line connecting to the primary port of the position switching valve 27, and when the pressure recovers to _P2 or higher, pressure oil is supplied to the tank. 1. A hydraulic control circuit for a shear breaker, characterized in that it is provided with a second pressure control valve 26 that operates to open when the valve is open.