GB2162979A

GB2162979A - Controlling flow of hydraulic fluid

Info

Publication number: GB2162979A
Application number: GB08420207A
Authority: GB
Inventors: John Talbot; John F W Griffiths
Original assignee: Edbro Ltd
Current assignee: Edbro Ltd
Priority date: 1984-08-09
Filing date: 1984-08-09
Publication date: 1986-02-12
Also published as: GB2162979B; GB8420207D0

Abstract

Uncontrolled loss of hydraulic fluid, in the event of rupture of a flow line, is avoided by the use of apparatus comprising, at the downstream end of the flow line, a sensor (31) of the rate of downstream flow of hydraulic fluid and, at the upstream end of the flow line, a protection valve (36) with a valve member movable, in response to a sensed downstream flow reduction consequent upon said rupture, from an open flow disposition (B) to a restricted flow disposition (A). The apparatus is useful as part of the tipping gear of a tipping body goods vehicle. <IMAGE>

Description

SPECIFICATION Controlling flow of hydraulic fluid This invention relates to controlling flow of hydraulic fluid and more particularly, but not exclusively, is concerned with controlling flow of hydraulic fluid out of a damaged high pressure flexible pipe connecting a source of hydraulic fluid with a hydraulic ram hoist tipping gear of a tipping goods vehicle.

Conventionally, controlled lowering of the load body of a tipping goods vehicle by a hydrau!ic hoist tipping gear is accomplished by the provision of a suitable flow restriction in the RAISE/NEUTRAL/LOWER control valve of the hydraulic tipping system. In a case where the control valve is connected to the tipping gear by a flexible pipe, however, there is a danger consequent upon rupture of the flexible pipe of uncontrolled nesting of the tipping gear under the weight of the load body of the vehicle so that it crashes down in an uncontrolled manner.

It is one object of the present proposal to avoid or mitigate this danger.

The present Applicant first investigated the possibility of closing off the flow of hydraulic fluid out of the tipping gear in response to a loss of pressure in the supply pipe adjacent the control valve. Such a possibility proved impracticable, however, because the difference in fluid pressure when lowering the load body, on the one hand when fully loaded, and on the other when carrying load, is larger than the difference between lowering with no load and lowering when the pipe has ruptured.

According to the present invention there is provided apparatus for preventing uncontrolled loss of hydraulic fluid in the event of rupture of a flow line of said fluid, the apparatus comprising at the downstream end of the flow line a sensor of the rate of downstream flow of hydraulic fluid and at the upstream end of the flow line a protection valve with a valve member movable, in response to a sensed downstream flow reduction consequent upon said rupture, from an open flow disposition to a restricted flow disposition.

Preferably, the hydraulic fluid flow valve is biased to the restricted flow disposition and moves to the open flow disposition only when actuated by the sensing of a downstream flow of fluid which is greater than a preselected critical value. In cases where the apparatus is part-of the tipping gear of a vehicle, the said flow is in a direction from the hoist to the tipping control valve. For flow in the other direction, to raise the vehicle load, any substantial restriction of flow through the protec tion-valve is- avoided by the provision, in parallel with the path of restricted flow, of a check valve which allows unimpeded flow to the hoist (while preventing flow from the hoist).

For a better understanding of the invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic diagram of a previously proposed hydraulic supply apparatus to a hydraulic hoist tipping gear for a goods vehicle; Figure 2 is a similar diagram of apparatus which is substantially similar to that shown in Figure 1, but is in accordance with the present invention; and Figure 3 is a logitudinal, axial section of a flow sensor device of the apparatus of Figure 2.

Referring first to Figure 1, a hydraulic hoist 10 is connected, by a quick-detach coupling 11, high pressure flexible flow line 1 2 and a control valve generally referenced 13, to a pump 1 4 which establishes the high pressure required for extending the hoist 1 0. The valve 1 3 has three dispositions, indicated on the drawing by RAISE, NEUTRAL and LOWER.

Hydraulic fluid drains to a tank 1 5 and, to protect the various components of the flow circuit, the output side of the pump 1 6 is connected to the tank 1 5 through a pressure relief valve 17.

In the LOWER disposition of the control valve 13, the output side 16 of the pump 14 is connected to the high pressure pipe 1 2 through a check valve 18. Fluid supplied by the pump 14 flows to the tank 1 5 along a line 19, and fluid from the hoist 10 flows to the tank 1 5 through the pipe 12 and an open, spring-biased shut-off valve 20, which is provided with a manual actuator 21 for displacing the biased valve member 22 off its seat to allow a controlled flow of hydraulic fluid from the pipe 1 2 to the tank 15, so as to provide whatever rate of fall of the load body is required.

In the NEUTRAL disposition of the control valve 13, in which the valve is located in Figure 1, any flow of fluid from the pump 14 flows to the tank 1 5 along line 19. There is, however, no connection between the flexible pipe 1 2 and the tank 1 5 except through the closed check valve 1 8 and the shut-off valve 20, which thus prevents the load body from dropping.

In the RAISE disposition of the control valve 13, the connection 1 9 between the pump 14 and the tank 15 is opened, so that fluid from the pump 1 4 is delivered through the check valve 1 8 to the tipping hoist 10, to raise the load body of the vehicle.

Turning now to Figure 2, the apparatus is substantially similar and equivalent components of it have been given the same reference numerals as have been used in Figure 1.

The control valve 1 3 is identical to that of Figure 1 but a flow sensor device 31 is located. between the control valve 1 3 and the flexible pipe 1 2. The flow sensor device 31 is arranged to provide an output signal along the leads 32 to control circuit 33 only when flow of fluid through the device 31 is in a direction from left to right in Figure 2 and of more than a preselected critical value (which is substantially lower than occurs during low ering of the load body).

The control circuit 33 generates an output signal which is fed along lines 34 to a sole noid 35 of- a solenoid protection valve 36, to move the valve member from the restricted flow position A, as shown, to the alternative full flow position B A pressure monitor 37 generates an- output signal whenever the fluid in the hoist 10 is at working pressure. The signal is fed along leads 38 to a klaxon 39 which accordingly is actuated for as long as the load body is raised above its rest disposition.

When the body is to be raised, the valve 1 3 is moved to the RAISE disposition and fluid flows through the flow sensor 31 and a check valve 40 in the protection valve 36 in its free flow disposition.

When the body is to be lowered, the valve 1 3 is moved from the RAISE or NEUTRAL disposition to the LOWER disposition, permit ting fluid to flow through the flow sensor 31 from left to right. This flow gives rise to actuation of the solenoid 35 to move the protection valve 36 to the full flow disposition B.

But in the event of rupture X of the pipe 1 2 flow of fluid from left to right in the sensor device 31 ceases and so the protection valve 36 reverts to the restricted flow disposition A.

With reference now to Figure 3, the flow sensor device 31 comprises a spring-biased spool 50 which is magnetic. Movement of the spool 50 from left to right in Figure 3, against the biasing force of the spring 51, thus dis places within the spool housing 52 a mag netic field which is present around the spool.

A reed switch 53 is responsive to the change in magnetic field and so is actuated when there is a sufficient flow of fluid i.e. one in excess of the above-mentioned critical value through the device in the return direction from the hoist 10, i.e. from left to right in Figures 2 and -3. The actuation of the reed switch generates the output signal to the control circuit 33. Preferably a visual indication, such as an LED 54, is actuated whenever the output signal is present.

Some further description of the construction of the flow sensor 31 is appropriate. -The mild steel housing 52 has at a pump end 60 thereof a threaded (1" B.S.P.) aperture 61 which receives a mild steel adaptor 62.

Bonded to the adaptor 62 is an aluminium spacer 63 and sealing it to the housing 52 is a so-called "Dowty" washer 64.

The spool 50 slides in a bore 65 of the housing 52 and is biased to an end surface of an aluminium spacer 66 at the left hand end of the bore 65 by a helical compression spring 67 which reacts against a shoulder 68 in the adaptor 62. The spool comprises an annular magnet 69 captivated on a two-part magnet holder of aluminium comprising a spindle 70 and a retaining ring 71.

The reed switch 53 is located in a bore 72 in the -housing 52. It is in series circuit with a 2 K ohm resistor 73.

In use, the adaptor is connected to the control valve 1 3 by an externally threaded (1 B.S.P.) connection ?4 and the housing 52 is connected to the line 1 2 by an internally threaded (3/4" B.S.P.) connection 75. The biasing force of the spring 51 is weak enough to be overcome by a strong flow of hydraulic fluid from left to right in Figure 3, to move the right hand end 76 of the spool 50 towards the spacer 63, and away from the spacer 66.

Claims

1. Apparatus for preventing uncontrolled loss of hydraulic fluid in the event of rupture of a flow line of said fluid, the apparatus comprising at the downstream end of the flow line a sensor of the rate of downstream flow of hydraulic fluid and at the upstream end of the flow line a protection valve with a valve member movable, in response to a sensed downstream flow reduction consequent upon said rupture, from an open flow disposition to a restricted flow disposition.

2. Apparatus as claimed in claim 1 being part of the tipping gear of a vehicle, wherein said downstream flow of fluid is in a direction from a tipping hoist of the tipping gear to a tipping control valve of the gear.

3. Apparatus as claimed in claim 2 including a path of unimpeded flow of hydraulic fluid from the tipping control valve to the hoist, in parallel with the flow line in which the protection valve is included, the path of unimpeded flow including a check valve which prevents return flow of fluid from the hoist-to the tipping control valve.

4. Apparatus as claimed in any one of the preceding claims wherein the protection valve includes means to bias it to the restricted flow disposition, the apparatus including a sensor of downstream flow of fluid greater than a preselected critical value, operatively con nected to the protection valve so as to move it, against its bias, to the open flow disposition when the downstream flow of fluid is sensed to be greater than the critical value.

5. Apparatus for preventing loss of hydrau lic fluid substantially as hereinbefore described with reference to, and as shown in, Figures 2 and 3 of the accompanying drawings.