GB2160950A

GB2160950A - Hydraulic damper valves

Info

Publication number: GB2160950A
Application number: GB08416260A
Authority: GB
Inventors: James Malcolm Agnew; Richard James Wooton
Original assignee: Coal Industry Patents Ltd
Current assignee: Coal Industry Patents Ltd
Priority date: 1984-06-26
Filing date: 1984-06-26
Publication date: 1986-01-02
Also published as: GB8416260D0

Abstract

A damper valve for smoothing out pressure pulses in a hydraulic line has an inlet port (2) through which fluid enters and forces hollow damper piston (4) to retreat, so causing fluid between piston (4) and end cap (16) to be forced slowly into outlet port (5,6) through cross-bored holes (13,14). When piston has retreated far enough from its seating at the end of inlet port (2) fluid flows direct from inlet port (2) via bore (3) to the outlet port (5,6). When flow ceases a coil spring between the piston (4) and end cap (16) returns the piston to its seating in readiness for the next pulse. The valve may be used in cyclic hydraulic circuits, e.g. in mining equipment. <IMAGE>

Description

SPECIFICATION Improvements in or relating to hydraulic damper valves This invention relates to improvements in hydraulic damper valves. In particular this invention relates to a damper valve for use in hydraulic circuits, for example hydraulic mining equipment.

In deep-mine coal mining operations it is common practice to operate longwall faces. In this technique once the coal has been removed the overburden behind the hydraulic roof supports is allowed to collapse. in some operations debris from the road headings at either end of the face is used as in fill behind the hydraulic roof supports to minimise the collapse of the overburden. One method of packing the debris behind the hydraulic roof supports is to use a cam packer on the back of each packhole hydraulic roof support. The cam packer, in common with many other cyclic hydraulic appliances, is hydraulically operated via a spool valve which operates in a conventional manner.The spool valve and cam packer are connected to a remote high pressure hydraulic supply by a service (high) pressure line which delivers a hydraulic fluid to the spool valve, and a return (low pressure) line which returns hydraulic fluid to the hydraulic supply. The lines used for delivery and return of hydraulic fluid are of flexible hose type. The operation of the spool type control valve can generate transient pressure peaks.

These peaks (pulses of energy) have the most marked effect in the return line. When the spool valve is closed to the service line and opened to the return line, a high pressure fluid pulse travels rapidly down the low pressure return line. This causes the line to flex and snake thus constituting a hazard to local personnel and damaging the flexible hose by impact and abrasion with surrounding objects.

It is an object of the present invention to minimise the pressure pulses in hydraulic return lines to extend the working life of return hoses.

Accordingly a first aspect of the present invention provides a hydraulic damper valve, comprising a body having; a fluid inlet port communicating witha first end of a cylindrical bore, and a fluid outlet port communicating, radially with said cylindrical bore, said cylindrical bore having therein a hollow damping piston, whose crown faces the first end of said cylindrical bore and whose skirt forms a damper fluid chamber with a second end of the cylindrical bore, said damper fluid chamber containing bias means which bias the damping piston to the first end of the cylindrical bore, and said skirt having a number of crossbored holes therein communicating with the fluid outlet port.

The bias means may be a coil compression spring.

The damping piston may have a plurality of cutaways in the circumference of its crown.

Conveniently there are four cutaways equispaced about the circumference of the crown.

Conveniently there are two cross-bored holes in the damper piston skirt.

Conveniently the second end of the cylindrical bore is defined by a screw-in end cap.

A second aspect of the present invention provides a hydraulic circuit incorporating a hydraulic damper valve according to the first aspect of the present invention.

The present invention will now be described by way of example only with reference to the accompanying drawings in which, Figure 1 shows a cross section of a damper valve, according to the present invention, with the damper piston in the closed position; Figure 2 shows the same section as Fig. 1 but with the damper piston in the open position; Figure 3 shows a side view of the damper piston and Figure 4 shows a cross section through the damper piston Referring to Figs. 1 and 2 the damper valve consists of a body 1 having a fluid inlet port 2 communicating with a cylindrical bore 3 in which is housed a damper piston 4. A section of the cylindrical bore 3 has a larger diameter than the damper piston 4 and forms a radially disposed annular chamber 5 which communicates with a fluid outlet port 6. Referring now to all the Figures; the damper piston 4 has a crown 7 and a skirt 8.Four cutaways 10, 11 and 1 2 (only 3 shown) are equi-spaced about the circumference of the crown 7. The skirt 8 has a pair of cross bored ports 1 3 and 14. A compression return spring 1 5 sits behind the damper piston 4 and bears on a screw-in end cap 1 6 which fits a threaded hole 1 7 being concentric with and of larger diameter than the cylindrical bore 3. In operation the valve is fitted in the return line adjacent the spool valve and works as follows; A pressure pulse within the hydraulic fluid on the return line of the spool valve enters the damper valve via fluid inlet port 2 where it meets the crown 7 of the damper piston 4 which seals the fluid inlet port 2 (as in Fig. 1).The pressure pulse forces the damper piston 4 to retreat towards the end cap 1 6. The motion of the damper piston 4 is controlled by the rate at which hydraulic fluid, in a damper chamber defined between the damper piston 4 and the end cap 16, can escape to the fluid outlet port via the annular chamber 5 and the cross-bored ports 1 3 and 1 4. The size of the cross-bored ports is chosen to provide a suitable motion of the damper piston 4 (viz damping characteristic) for a particular viscosity of hydraulic fluid.

After the initial retreat of the damper piston 4 the cutaways 10, 11 and 1 2 in the piston crown 7 allow a direct passage of input hy draulic fluid from the fluid inlet port 2 to the fluid outlet port 6 via the cylindrical bore 3 and the annular chamber 5 (see Fig. 2). Upon further operations of the direction control spool valve to stop flow into the return line the return spring 1 5 forces the damper piston 4 back towards the fluid inlet port 2 thus closing the valve (As in Fig. 1). This valve effectively "flattens" a pressure pulse thus allowing the pressure change in the return hose down stream of the damper valve to be much slower and less violent than the incident pressure pulse. The damper valve could be used to damp such pressure pulses in any hydraulic line but will find most use in hydraulic systems operating on a cyclic basis.

Claims

1. A hydraulic damper valve, comprising a body having a Fluid inlet port communicating with a first end of a cylindrical bore and a fluid outlet port communicating radially with said cylindrical bore, the cylindrical bore having therein a hollow damping piston, whose crown faces the first end of the cylindrical bore and whose skirt forms a damper fluid chamber with a second end of the cylindrical bore, said damper fluid chamber containing bias means which biases the damping piston to the first end of the cylindrical bore, and said skirt having a number of cross-bored holes therein communicating with the fluid outlet port.

2. A hydraulic damper valve according to Claim 1, wherein the bias means is a coilcompression spring.

3. A hydraulic damper valve according to Claim 1 or 2, wherein the damping piston has a plurality of cutaways in the circumference of its crown.

4. A hydraulic damper valve according to claim 3, wherein there are four cutaways equispaced about the circumference of the crown.

5. A hydraulic damper valve according to any of the preceding claims, wherein there are two cross-bored holes in the damper piston's skirt.

6. A hydraulic damper valve according to any of the preceding claims, wherein the second end of the cylindrical bore is defined by a screw-in end cap.

7. A hydraulic damper valve substantially as hereinbefore described with reference to the accompanying drawings.

8. A hydraulic circuit incorporating a hydraulic damper valve according to any of the preceding claims.