GB2254658A

GB2254658A - Hydraulic actuator

Info

Publication number: GB2254658A
Application number: GB9107545A
Authority: GB
Inventors: Michael Arnold Calvert
Original assignee: Prime Actuator Control Systems Ltd
Current assignee: Prime Actuator Control Systems Ltd
Priority date: 1991-04-10
Filing date: 1991-04-10
Publication date: 1992-10-14
Also published as: GB9107545D0

Abstract

A linear actuator comprises a rod (10) slidable in a housing (6), the rod being biased to a rest position by spring means (20) provided within the housing (6) and movable from the rest position by the application of hydraulic pressure via associated means for supplying hydraulic fluid. A portion of the rod (10) defines a pot (18), which provides the reaction surface against which hydraulic pressure is applied. The means for applying hydraulic pressure includes a hydraulic fluid inlet spigot (19) penetrating the pot (18), and having seals arranged between the outer side of the spigot (19) and the inner side of the pot whereby sediment from the hydraulic fluid is confined within the pot (18) assuming the actuator is mounted in a vertical position. <IMAGE>

Description

HYDRAULICALLY OPERATED LINEAR ACTUATOR Description This invention related to a hydraulically-operated linear actuator. The invention is intended particularly for actuating a linearly-movable valve member, eg in a gate valve.

An object of the invention is to minimise damage to seals and finely-machined surfaces of movable parts from sedimentation in hydraulic fluids.

According to the invention there is provided a linear actuator having a housing adapted to be mounted on a unit casing from which extends a shaft to be moved linearly, the linear actuator also including a rod slidably mounted in the housing, one end of the rod being adapted to be connected end-to-end with the shaft and the other end of the rod being extended in the form of a cylindrically shaped pot slidably receiving a fixed tubular spigot extending inwardly from an end plate of the housing, seals being arranged between the outer side of the spigot and the inner side of the pot and a connection for a hydraulic pressure line being provided in the end plate and opening into the spigot, and coiled return spring means within the housing and surrounding the rod and the pot and confined between a flange on the pot and a second plate of the housing in the vicinity of the slidable mounting of the rod.

With such an arrangement, particularly with the actuator upright and the end plate of the housing at the top, any sediment in the hydraulic fluid is collected at the bottom of the pot and away from the seals.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing showing an axial section through a linear actuater.

In the drawing a linear actuater has a housing mounted on a unit (eg a gate valve) casing having a flange 1. The housing comprises a bottom ring 2 bolted to the flange 1. A lower tube 3 upstands from and is welded to the ring 2. An intermediate ring 4 is welded to the upper edge of the tube 3 and is bolted to a lower end plate 5. An upper tube 6 upstands from and is welded to the plate 5. An upper ring 7 is welded to the upper edge of the tube 6. An upper end plate 8 is bolted to the ring 7.

A shaft 9 extends from the flange 1 and is intended to be moved linearly. The linear actuater also includes a rod 10 slidably mounted in the housing. The rod 10 is connected end-to-end with the shaft 9 by means of an internally-screwthreaded sleeve 11 screwed onto a screw-threaded neck 12 terminating the shaft 9 so that a flanged upper end 13 of the sleeve 11 confronts a flanged lower end 14 of the rod 10 and the ends 13 and 14 are clamped together by a manacletype clamp 15. Other forms of end-to-end connections between the shaft 9 and the rod 10 may be provided instead.

The rod 9 is slidably received in a bearing sleeve 16 screwthreadedly received at 17 in a central opening through the plate 5. The upper end of the rod 10 is extended in the form of a cylindrically-shaped pot 18 which is welded to the rod 10. The pot 18 is slidably receives a fixed tubular spigot 19 depending from the plate 8. Seals and bearings are provided between the pot 18 and spigot 19 and also between the rod 10 and the sleeve 16.

Coiled return spring means in the form of a single spring 20 within the tube 6 surrounds the rod 10 and the pot 18 and is confined between a flange 21 on the pot 18 and the plate 5. In order to minimise galvanic action between the spring 20 and the items 5 and 21 insulating rings 22 are provided as beds for the ends of the spring 20. Between the clamps 15 and the sleeve 16 an anti-torque yoke 23 is clamped to the rod 10 and is slidable along a guide 24 mounted in the tube 3 between the plate 5 and an insert 25 welded to the ring 2. A plurality of springs could replace the single spring 20 in a modification.

Adjustment stops for the movement of the rod 10 are provided as follows. A collar 26 screw-threadedly received the rod 10 below the sleeve 16 and is anchored to the rod 10 by a grub-screw 27. A spring clip 28 mounted on the underside of the plate 5 is received in a selected one of a number of circumferentially-spaced axially-extending grooves in the sleeve 16. A further adjustment is provided in the form of annular shims 29 inserted between shoulders on the pot 18 and the flange 21. A connection 30 for a hydraulic pressure line (not shown) is provided in the end plate 8 and opens into the spigot 19.

Instead of the rings 2 and 4 being welded to the tube 3 and instead of the plate 5 and the ring 7 being welded to the tube 6 they made be held together by long bolts or screw-threaded rods and nuts. Indeed, the plate 8 and the ring 7 may be replaced by an end plate releasably secured to the upper end of the tube 6.

Claims

1. A linear actuator comprising a rod slidable in a housing, the rod being biased to a rest position by spring means provided within the housing and movable from the rest position by the application of hydraulic pressure via associated means for supplying hydraulic fluid; a portion of the rod defining a pot, wherein the reaction surface against which hydraulic pressure is applied is within the pot; the means for applying hydraulic pressure including a hydraulic fluid inlet spigot penetrating the pot, and having seals arranged between the outer side of the spigot and the inner side of the pot whereby sediment from the hydraulic fluid is confined within the pot.

2. A linear actuator according to claim 1, wherein one end of the rod is adapted to be connected end-to-end with a shaft which extends from a unit casing mounted on the housing.

3. A linear actuator according to claim 2, wherein the rod is connected to the shaft by means of an internally threaded sleeve screwed onto a threaded end portion of the shaft and clamping means clamping the shaft to the rod.

4. A linear actuator according to claim 2 or 3, wherein the pot is welded to the other end of the rod.

5. A linear actuator according to any one of claims 1 to 4, wherein the spring means acts between a flange on the pot and a bearing surface within the housing.

6. A linear actuator according to claim 5, wherein the spring means surround the rod.

7. A linear actuator according to claim 5 or 6, wherein the spring means comprises a plurality of coiled springs.

8. A linear actuator according to any one of the preceding claims, wherein the hydraulic fluid inlet spigot is cylindrical and depends from an end plate of the housing.

9. A linear actuator substantially as hereinbefore described with reference to and as shown in the drawing.