GB1582491A

GB1582491A - Hydraulic apparatus

Info

Publication number: GB1582491A
Application number: GB23922/77A
Authority: GB
Original assignee: Brodr Soyland A S
Current assignee: Brodr Soyland A S
Priority date: 1976-06-09
Filing date: 1977-06-08
Publication date: 1981-01-07
Also published as: DK170677A; DE2712076A1; FR2354466A1; SE7703508L; IT1071866B; NO761983L

Description

(54) HYDRAULIC APPARATUS (71) We, BRDR. SYLAND A/S, a Norwegian Body Corporate, of 4340 Bryne, Norway, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to hydraulic apparatus including a device to safeguard against fractures in pressurized pipes, tubing and hoses in hydraulic systems, such as elevating plants, construction machinery, 'forest machinery and the like. In addition to reducing the possibility of a fracture occurring, the purpose of the invention is also to minimize the possible consequences of a line fracture by permitting the controlled member to remain under full control even after a fracture has occurred. Moreover, the device according to the invention also comprises a relief mechanism which eliminates the danger of the controlled member being overloaded.

Various types of safeguards to prevent accidents and injuries resulting from a fracture in a pressure line are known. On hoisting cranes and the like, for example, a type of pressure-operated braking valve is used which opens when pressure is applied on the opposite side of the piston in a cylinder. Pressure must thus be used in order to lower a suspended load. Such valves however, are difficult to control.

Other known devices include a valve which closes if the flow velocity becomes abnormally great, as is generally the case with a line fracture. Another solution has been to mount a direction control valve directly on the controlled member. thereby eliminating pressure lines completely.

However, this solution is difficult to apply in many cases, owing to requirements of the space and weight limitations of the embodiment. ' The invention provides hydraulic apparatus comprising a piston and cylinder device and a safety device mounted on the cylinder, the cylinder having a port opening on to a compression chamber in the cylinder, the safety device comprising a one way valve, an inlet port for pressure medium to pass via the one way valve and then to leave the safety device through a further port communicating with the cylinder port, a return valve for allowing pressure medium to leave the compression chamber of the cylinder, which return valve is biassed to the closed position and communicates with the downstream side of the one way valve, an outlet port for the return valve, a pilot valve biassed to the closed position and controlling the return valve, an inlet control port for pressure medium to control the pilot valve, and an outlet port for the pilot valve.

The pilot valve may include a slide biassed into a position closing a passage communicating the downstream side of the return valve with the outlet port of the pilot valve, and pressure medium entering the control port urges the slide to a position opening the passage and allowing pressure medium to flow from the downstream side of the return valve so causing the return valve to open to allow pressure medium to flow from the cylinder and out through the outlet port of the return valve.

A passage may communicate the cylinder port with the pilot valve when the return valve is in the closed position and the pilot valve may be arranged to allow pressure medium to flow from the cylinder port along the passage to the outlet port of the pilot valve whilst the return valve is in the closed position when the pressure of the pressure medium exceeds a pre-derermined level.

The passage may include an aperture and the pilot valve may include a cone biassed by a spring to a position closing the aperture, and a set screw for adjusting the biassing force of the spring on the cone.

Specific embodiments of the invention will now be described by way of example and with reference to the accompanying drawings: Figure 1 depicts a hydraulic system provided with the safety device; and Figure 2 shows one practical embodiment of the invention.

On Figure 1 the safety device 1 comprises the components lying within the dotted dashed lines. The working member in this example is a cylinder 2 on which a load P is applied, which causes a pressure in chamber A of the cylinder 2. The safety device 1 is rigidly mounted on the cylinder such that the cylinder port 3 is connected to the safety device via inlet port 41. The pressure from the load P is transmitted via the ports 3 and 41, and a channel 4 to a one-way valve 5 and a pilot-operated valve 6 which are both normally closed.

In this condition, the pressure from the load P is borne by these two valves and the pressure in line 7 can be completely relieved. The direction control valve 8 will normally be a type of slide valve, so that a small leakage will result in the prompt and complete relief of the pressure in line 7.

Should the leak in the valve 8 be significant, the safety device 1 will maiptain the fluid in the cylinder and prevent the load P from falling.

When the load P is to be raised, control pressure from a control valve (not shown) will be supplied to a line 9, and the slide in the valve 8 will be displaced such that route 10 becomes operative. This causes the connection between a prcssure line 12 and a return line 15 to be closed, and the pressure medium will flow through a one-way valve 13 and a channel 14 to the pressure line 7, and further through one-way valve 5, the channel 4, the port 3 and to the chamber A.

When the piston in the cylinder moves, the return medium from cylinder chamber B will flow through a line 16 to directional valve 8 and further to the system's oil tank through a tank line 17. A fracture in pressure line 7 will cause one-way valve5 to close promptly, thus preventing the loach from falling. When the load is to be lowered, the control valve is regulated so as to effect a pressure in a control line 18. The control pressure from the line 18 pushes the slide in valve 8 over and route 11 becomes operative, so that the pressure medium from the pump F can now flow through line 16 to chamber B. (In reality, pressure is not needed in chamber B. but merely a replenishment of the fluid when the load moves the piston toward chamber A.) The control pressure in line 18 simultaneously affects a pilot valve 19 such that it opens and connects a control channel 20 with a line 21 and hence a return port 44.

and further to a non-pressurized tank.

As the pressure in control line 18 increases the pilot valve 19 gradually opens more and the pilot pressures in channel 20 decreases.

As a result, the pilot operated valve 6 opens and permits the passage of pressure medium from chamber A to a return channel 22, through the port 3 and channel 4.

Thus it can be seen that the pressure line 7 is not pressurized either when the load is being held or when it is being lowered. Even if the line 7 were to be torn off, one still has full control over the descent of the working member and can manoeuvre it even if the line 7 is missing and/or if the directional control valve 8 malfunctions.

The pilot valve 19 is further provided with a control line 23. If unusually high pressure is present in chamber A as a result of overloading, .this excessive pressure will be transmitted through the channel 4 to the valve 6. The control pressure in the control channel 20 will increase correspondingly and will be transmitted over the control line 23 to the pilot valve 19. When the control pressure exceeds a predetermined level, pilot valve 19 opens and relieves the pilotoperated valve 6 so that the latter permits the passage of pressure medium to the tank.

As soon as the pressure comes down to the preset level, pilot valve 19 and valve 6 close once more.

An example of the construction of the safety device 1 in practice js shown on Figure 2. A pilot-operated valve 6 is mounted in an outer housing 24. The valve 6 consists of a valve body 27 containing seals against the housing 24 and a guide for a valve cone 28. The valve cone 28 is provided with a choke opening 29 and is held in position against its seat in the housing by a spring 30 which lies in its own housing 31.

The safety device also comprises a pilot valve 19 for controlling the valve 6. The pilot valve consists of a pilot housing 33 contaning seals against the outer housing 24, a guide for the pilot slide 34, a pilot cone 35, spring 36, set screw 37 further spring 38 and a spring housing 39. In the housing 24 there is also a one-way valve 5 which is held against its seat by a spring 40. The housing 24 also has an intake port 41, outlet port 42, pilot channel 20, control port 43, drainage port 44. and cylinder port 3. The safety device functions as follows: When the load P (Figure 1) is being raised. pressure medium is supplied through the one-way valve 5 to the intake 41 (Figure 2), and flows to the cylinder port 3. The pressure medium from the cylinder port 3 is transmitted to the front end of the valve cone 28 of the pilot-operated valve 6, through the choke opening 29 to the back end (spring side) of the valve cone, holding the cone closed against the seat 45 in a known manner. The pressure medium is further transmitted through a hole 46 to the pilot channel 20 and pilot valve 19. The pressure flows further through a hole 47 in the pilot housing 33 and a channel 48 in the pilot slide 34 to the pilot cone 35. The pilot cone 35 is held sealed against the seat by means of a spring 36. The spring force against the pilot cone 35 is regulated via the set screw 37, and this determines the maximum limit of the pilot pressure. When the preset level is exceeded, the pilot cone 35 lifts from its seat and allows pressure medium to flow to the tank via the drainage port 44. The pilot-operated valve 6 is held closed as long as the pressure in the cylinder port 3 does not exceed a maximum limit.

When the hoisting operation ends, one-way valve 5 closes, and the pressure caused by the load P is stopped by valve 5 and the pilot-operated valve 6. The tubing and hoses which carry pressure medium to the safety device are thus completely relieved.

When the load is to be lowered, control pressure from line 18 (Figure 1) is supplied to the control port 43. This control pressure exerts force to the end of the pilot cone 35, and when this force exceeds the spring force from the spring 38, the pilot slide will be displaced toward the spring as the spring effect is overcome. A seal shoulder 49 will thereby be pushed back from a choke groove 50, providing a connection from the pilot channel 20 to the drainage outlet 44 through the hole 47 in the pilot slide.

Gradually, as the opening over the choke grooves 50 increases, the connection between the pilot channel 20 and the drainage port 44 to the non-pressurized tank will be freer, so that the pilot pressure on the pilot-operated valve 6 decreases. At sufficiently low pilot pressure, the valve 6 gradually opens and permits pressure medium to flow from the cylinder port 3 to the outlet port 42 over the seat 45. By regulating the pilot pressure and thereby the opening of the pilot-operated valve 6, the flow of pressure medium from the cylinder port 3 and thereby the movement of the load P are also regulated. Thus it can also be seen that one has full control over the load P, independent of which connection exists between the outlet port 42 and the tank.

Even if this connection should be broken, one still retains full control over the load.

During raising as well as during lowering operations, the pilot cone 35 is under constant spring force and safeguards against overloading. This is achieved because the pilot cone and spring are integral parts of the pilot slide and follow along with it during load manoeuvering.

WHAT WE CLAIM IS: 1. Hydraulic apparatus comprising a piston and cylinder device and a safety device mounted on the cylinder, the cylinder having a port opening on to a compression chamber in the cylinder, the safety device comprising a one way valve, an inlet port for pressure medium to pass via the one way valve and then to leave the safety device through a further port communicating with the cylinder port, a return valve for allowing pressure medium to leave the compression chamber of the cylinder, which return valve is biassed to the closed position and communicates with the downstream side of the one way valve, an outlet port for the return valve, a pilot valve biassed to the closed position and controlling the return valve, an inlet control port for pressure medium to control the pilot valve, and an outlet port for the pilot valve.

2. Hydraulic apparatus as claimed in claim 1, wherein the pilot valve includes a slide biassed into a position closing a passage communicating the downstream side of the return valve with the outlet port of the pilot valve, and pressure medium entering the control port urges the slide to a position opening the passage and allowing pressure medium to flow from the downstream side of the return valve so causing the return valve to open to allow pressure medium to flow from the cylinder and out through the outlet port of the return valve.

3. Hydraulic apparatus as claimed in claim 1 or 2, wherein a passage communicates the cylinder port with the pilot valve when the return valve is in the closed position and the pilot valve is arranged to allow pressure medium to flow from the cylinder port along the passage to the outlet port of the pilot valve whilst the return valve is in the closed position when the pressure of the pressure medium exceeds a predetermined level.

4. Hydraulic apparatus as claimed in claim 3, wherein the passage includes an aperture, and the pilot valve includes a cone biassed by a spring to a position closing the aperture, and a set screw for adjusting the biassing force of the spring on the cone.

5. Hydraulic apparatus substantially as herein described with reference to and as shown in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. known manner. The pressure medium is further transmitted through a hole 46 to the pilot channel 20 and pilot valve 19. The pressure flows further through a hole 47 in the pilot housing 33 and a channel 48 in the pilot slide 34 to the pilot cone 35. The pilot cone 35 is held sealed against the seat by means of a spring 36. The spring force against the pilot cone 35 is regulated via the set screw 37, and this determines the maximum limit of the pilot pressure. When the preset level is exceeded, the pilot cone 35 lifts from its seat and allows pressure medium to flow to the tank via the drainage port 44. The pilot-operated valve 6 is held closed as long as the pressure in the cylinder port 3 does not exceed a maximum limit. When the hoisting operation ends, one-way valve 5 closes, and the pressure caused by the load P is stopped by valve 5 and the pilot-operated valve 6. The tubing and hoses which carry pressure medium to the safety device are thus completely relieved. When the load is to be lowered, control pressure from line 18 (Figure 1) is supplied to the control port 43. This control pressure exerts force to the end of the pilot cone 35, and when this force exceeds the spring force from the spring 38, the pilot slide will be displaced toward the spring as the spring effect is overcome. A seal shoulder 49 will thereby be pushed back from a choke groove 50, providing a connection from the pilot channel 20 to the drainage outlet 44 through the hole 47 in the pilot slide. Gradually, as the opening over the choke grooves 50 increases, the connection between the pilot channel 20 and the drainage port 44 to the non-pressurized tank will be freer, so that the pilot pressure on the pilot-operated valve 6 decreases. At sufficiently low pilot pressure, the valve 6 gradually opens and permits pressure medium to flow from the cylinder port 3 to the outlet port 42 over the seat 45. By regulating the pilot pressure and thereby the opening of the pilot-operated valve 6, the flow of pressure medium from the cylinder port 3 and thereby the movement of the load P are also regulated. Thus it can also be seen that one has full control over the load P, independent of which connection exists between the outlet port 42 and the tank. Even if this connection should be broken, one still retains full control over the load. During raising as well as during lowering operations, the pilot cone 35 is under constant spring force and safeguards against overloading. This is achieved because the pilot cone and spring are integral parts of the pilot slide and follow along with it during load manoeuvering. WHAT WE CLAIM IS:

1. Hydraulic apparatus comprising a piston and cylinder device and a safety device mounted on the cylinder, the cylinder having a port opening on to a compression chamber in the cylinder, the safety device comprising a one way valve, an inlet port for pressure medium to pass via the one way valve and then to leave the safety device through a further port communicating with the cylinder port, a return valve for allowing pressure medium to leave the compression chamber of the cylinder, which return valve is biassed to the closed position and communicates with the downstream side of the one way valve, an outlet port for the return valve, a pilot valve biassed to the closed position and controlling the return valve, an inlet control port for pressure medium to control the pilot valve, and an outlet port for the pilot valve.