GB2194293A

GB2194293A - Improvements in hydraulic lift systems

Info

Publication number: GB2194293A
Application number: GB08620296A
Authority: GB
Inventors: Gerald Arthur Needham
Original assignee: British Nuclear Fuels PLC
Current assignee: Sellafield Ltd
Priority date: 1986-08-20
Filing date: 1986-08-20
Publication date: 1988-03-02
Also published as: GB8620296D0

Abstract

In an hydraulic system for lifting and lowering loads a balancing valve (11) is included in a fluid flow conduit (9) between a double-acting piston and cylinder assembly (2,3) and a directional control valve (7). The balancing valve comprises first and second oppositely acting, normally closed, non-return valves (A,B) arranged in parallel. The non-return valve which opens to permit lowering of a load is urged into its closed position by adjustable spring means set to oppose and balance the hydraulic pressure exerted by the load. <IMAGE>

Description

SPECIFICATION Improvements in hydraulic lift systems The present invention concerns hydraulic systems for lifting and lowering loads.

According to one aspect of the present invention an hydraulic system for lifting and lowering loads comprises an hydraulic circuit including a double-acting piston and cylinder assembly, fluid flow conduits connecting opposite ends of the assembly to a selectively operable valve member, the valve member in a first position directing flow in the circuit to enter the piston and cylinder assembly at one end to lift a load and in a second position reversing the direction of flow to lower the load and in which a balancing valve is included in the circuit between the selectively operable valve member and said one end of the piston and cylinder assembly, the balancing valve functioning to resist flow from the assembly when the selectively operable valve member is in said second position.

Preferabiy the balancing valve comprises first and second oppositely acting non-return valves mounted in parallel, the non-return valve which opens to permit flow from said one end of the piston and cylinder assembly to the selectively operable valve member to lower the load being urged into its closed position by adjustable spring means set to oppose and balance the pressure exerted by the load.

According to another aspect of the present invention a valve assembly for inclusion in an hydraulic flow conduit comprises a pair of oppositely acting non-return valves arranged in parallel in the flow line, spring means for urging the valves into normally closed positions and means for selectively adjusting the pressure exerted by at least one of the springs whereby the valve associated therewith can only open when the pressure in the flow conduit exceeds a predetermined value.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of an hydraulic system; and Figure 2 is a sectional view of a balancing valve employed in the system.

An hydraulic system for lifting and lowering loads comprises a double acting cylinder 1 with a piston 2 in sliding, seaiing engagement in the bore of the cylinder. A piston rod 3 extends in sealing engagement through an end wall of the cylinder and a load 4 is releasably attached to the protruding end of the piston rod 3. An hydraulic pump 5 deiivers hydraulic fluid from a reservoir (not shown) through conduit 6 to a slide valve 7 movable between two positions. The valve 7 establishes communication between the conduit 6 and either of conduits 8 or 9 leading to opposite ends of the cylinder 1 The position of the valve determines the direction of flow of fluid in the system and hence the lifting or lowering of the load attached to the piston rod 3.In the position shown in Fig. 1 the valve 7 directs fluid from the pump along conduit 8 to the upper end of the cylinder 1 and the return conduit 9 is connected to a drain outlet 10 through the valve 7. In the alternative position of the valve 7 the flow is pumped along conduit 9 to the lower end of the cylinder 1 and the conduit 8 is connected to the drain outlet 10.

In the absence of a positive resistance to the lowering of the piston the load 4 can fall under its own weight resulting in a dangerous situation. Thus in the position of the valve 7 as shown in Fig. 1 and in the absence of a resistance in the conduit 9, the pump 5 is not required to push fluid into the cylider 1 in order to lower the load 4. As a result air can be drawn into the system and it is not possible to control the fall of the load.

To avoid this problem a balancing valve assembly 11 is included in the conduit 9. This valve assembly 11, as shown in detail in Fig.

2, comprises two oppositely acting non-return valves A and B. Valve A allows hydraulic fluid to flow into the cylinder 1 when raising the load 4. With flow in the opposite direction to lower the load the valve A is closed and flow can pass through valve B. Both valves A and B are urged against their seats by springs 12 and 13 respectively. Valve B is a variable pressure control valve and the spring 13 is selectively adjustable by a manually operable screw 14.

In use, the spring 13 is set to balance the pressure in the conduit 9 resulting from the load on the piston and to prevent the valve B from lifting off its seat with the pump inoperative. The load 4 is thereby prevented from falling. The load can only be lowered by operating the pump 5 to pump fluid through conduit 8 into the top of the cylinder 1 and to force fluid in the conduit 9 to lift the valve B off its seat. The valve B is closed immediately on stopping the pump 5.

1. An hydraulic system for lifting and lowering loads comprising an hydraulic circuit including a double-acting piston and cylinder assembly, fluid flow conduits connecting opposite ends of the assembly to a selectively operable valve member, the valve member in a first position directing flow in the circuit to enter the piston and cylinder assembly at one end to lift a load and in a second position reversing the direction of flow to lower the load and in which a balancing valve is included in the flow conduit between the selectively operable valve member and said one end of the piston and cylinder assembly, the balancing valve having first and second oppositely

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

Claims

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

SPECIFICATION Improvements in hydraulic lift systems The present invention concerns hydraulic systems for lifting and lowering loads.

According to one aspect of the present invention an hydraulic system for lifting and lowering loads comprises an hydraulic circuit including a double-acting piston and cylinder assembly, fluid flow conduits connecting opposite ends of the assembly to a selectively operable valve member, the valve member in a first position directing flow in the circuit to enter the piston and cylinder assembly at one end to lift a load and in a second position reversing the direction of flow to lower the load and in which a balancing valve is included in the circuit between the selectively operable valve member and said one end of the piston and cylinder assembly, the balancing valve functioning to resist flow from the assembly when the selectively operable valve member is in said second position.

Preferabiy the balancing valve comprises first and second oppositely acting non-return valves mounted in parallel, the non-return valve which opens to permit flow from said one end of the piston and cylinder assembly to the selectively operable valve member to lower the load being urged into its closed position by adjustable spring means set to oppose and balance the pressure exerted by the load.

According to another aspect of the present invention a valve assembly for inclusion in an hydraulic flow conduit comprises a pair of oppositely acting non-return valves arranged in parallel in the flow line, spring means for urging the valves into normally closed positions and means for selectively adjusting the pressure exerted by at least one of the springs whereby the valve associated therewith can only open when the pressure in the flow conduit exceeds a predetermined value.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic circuit diagram of an hydraulic system; and Figure 2 is a sectional view of a balancing valve employed in the system.

An hydraulic system for lifting and lowering loads comprises a double acting cylinder 1 with a piston 2 in sliding, seaiing engagement in the bore of the cylinder. A piston rod 3 extends in sealing engagement through an end wall of the cylinder and a load 4 is releasably attached to the protruding end of the piston rod 3. An hydraulic pump 5 deiivers hydraulic fluid from a reservoir (not shown) through conduit 6 to a slide valve 7 movable between two positions. The valve 7 establishes communication between the conduit 6 and either of conduits 8 or 9 leading to opposite ends of the cylinder 1 The position of the valve determines the direction of flow of fluid in the system and hence the lifting or lowering of the load attached to the piston rod 3.In the position shown in Fig. 1 the valve 7 directs fluid from the pump along conduit 8 to the upper end of the cylinder 1 and the return conduit 9 is connected to a drain outlet 10 through the valve 7. In the alternative position of the valve 7 the flow is pumped along conduit 9 to the lower end of the cylinder 1 and the conduit 8 is connected to the drain outlet 10.

In the absence of a positive resistance to the lowering of the piston the load 4 can fall under its own weight resulting in a dangerous situation. Thus in the position of the valve 7 as shown in Fig. 1 and in the absence of a resistance in the conduit 9, the pump 5 is not required to push fluid into the cylider 1 in order to lower the load 4. As a result air can be drawn into the system and it is not possible to control the fall of the load.

To avoid this problem a balancing valve assembly 11 is included in the conduit 9. This valve assembly 11, as shown in detail in Fig.
2. An hydraulic system for lifting and lowering loads substantially as herein described with reference to and as illustrated in the accompanying drawings.

2, comprises two oppositely acting non-return valves A and B. Valve A allows hydraulic fluid to flow into the cylinder 1 when raising the load 4. With flow in the opposite direction to lower the load the valve A is closed and flow can pass through valve B. Both valves A and B are urged against their seats by springs 12 and 13 respectively. Valve B is a variable pressure control valve and the spring 13 is selectively adjustable by a manually operable screw 14.

In use, the spring 13 is set to balance the pressure in the conduit 9 resulting from the load on the piston and to prevent the valve B from lifting off its seat with the pump inoperative. The load 4 is thereby prevented from falling. The load can only be lowered by operating the pump 5 to pump fluid through conduit 8 into the top of the cylinder 1 and to force fluid in the conduit 9 to lift the valve B off its seat. The valve B is closed immediately on stopping the pump 5.

1. An hydraulic system for lifting and lowering loads comprising an hydraulic circuit including a double-acting piston and cylinder assembly, fluid flow conduits connecting opposite ends of the assembly to a selectively operable valve member, the valve member in a first position directing flow in the circuit to enter the piston and cylinder assembly at one end to lift a load and in a second position reversing the direction of flow to lower the load and in which a balancing valve is included in the flow conduit between the selectively operable valve member and said one end of the piston and cylinder assembly, the balancing valve having first and second oppositely acting normally closed non-return valves arranged in parallel in the flow conduit, with the non-return valve which opens to permit flow from said one end of the piston and cylinder assembly to the selectively operable valve member to lower the load being urged into its closed position by adjustable spring means set to oppose and balance the hydraulic pressure exerted by the load.