GB2219833A - Hydraulic nut or bolt seal - Google Patents

Abstract

A high temperature piston seal 8 comprises an annulus of elastically deformable material with upstanding walls 21,22 extending from its inner and outer margins, the central region 25 of the annulus having an annular deformation effective to bias apart the distal edges of the walls. <IMAGE>

Description

Hydraulic-nuts/bolts This invention relates to hydraulic nuts and/or bolts.

Such devices are very well-known indeed; they are used for developing stress in bolted connections. A typical hydraulic nut has an annular piston and cylinder device built into it, so that when screwed down the shank of a bolt, or a stud, against some associated hardware, the piston and cylinder device can be operated to stress the bolt or stud. After stressing to a pre-chosen level, the stress is retained by inserting shims or by use of a locking ring. The hydraulic pressure is thereafter removed. Removal of the nut is carried out by re-pressurising the annular piston and cylinder device until the locking ring can be unscrewed, or the shims withdrawn.It will be appreciated that once the bolted connection has been suitably stressed, the hydraulic nut thereafter remains in place although the hydraulic connections are of course removed, until such time as it is necessary to break the bolted connection, for example for maintenance purposes. In a case of a hydraulic bolt, the piston and cylinder device is built into the underside of the bolt head. The operation is otherwise the same as with a hydraulic nut.

Further references in this specification to hydraulic nuts should be taken as including hydraulic bolts and all other types of fastener using the same jacking principle.

The internal construction of hydraulic nuts varies considerably, particularly in relation to the method used for containing the hydaulic fluid. Very substantial pressures are used and accordingly, the method of containing the fluid is very important. Apart from conventional annular rubber seals it is common practice to use a tubular tyre resembling a car tyre inner tube to contain the hydraulic fluid.

Some of the applications for which hydraulic nuts are potentially useful are in situations where the bolted connection and the associated hardware is sustained at high temperature in use. This is especially true of bolted connections in turbine casings. It is commonplace for the working temperature to be in excess of 150 C and indeed in some applications it may rise as high as 400 or 5000C. At these temperatures, the conventional rubber seal is useless. The practical temperature limit for nitrile rubber seals is around 1300C and for long term use probably lower than this. One solution to this problem has been proposed in published specification EP-A 0129440, in which the substitution of a metal capsule for the conventional rubber tyre of, for example, specification GB-A-991 783.However, such metal capsules although effective are expensive to manufacture. It is an object of the present invention to provide a seal which is easier to manufacture and less costly.

According to the present invention a seal for use in a hydraulic nut, or in the head of a hydraulic bolt, comprises a generally planar annulus of an elastically deformable material having upstanding, generally parallel walls extending from its radially inner and outer edges, characterised in that the central region of the annulus contains an annular deformation effective to biass apart the distal edges of said walls.

The deformable material is preferably metal and more preferably copper or an alloy thereof. The annular deformation is preferably slightly convex as seen in section, to constitute with the walls a W-like shape.

In use, the seal replaces the conventional tyre, or other rubber seal. The planar annulus seats against the piston (inside the cylinder) with those portions of the annulus lying radially inwardly and outwardly of the central region (the deformation) in contact with the piston face. The upstanding walls are directed generally towards the oil entry point. The distal edges of the walls seat against the cylinder bore, providing an initial seal. The annular deformation contributes towards the establishment of this initial seal, by biassing outwards the distal edges of the walls of the seal.

When fluid pressure is applied to operate the piston and cylinder device, the fluid pressure is applied to the whole of the seal, forcing the distal edges against the walls of the cylinder and at the same time flattening the annular deformation. However, because annular regions of the annulus are already seated against the piston, by which they are therefore fully supported, increasing pressure serves only to increase the contact pressure between these parts of the annulus and the piston top, thereby restricting the extent to which the annular deformation can be flattened. The greater the pressure, the greater the friction which will be developed between the annulur regions and the piston head.Accordingly although the walls can be plastically deformed against the walls of the cylinder the annular deformation itself is subject only to elastic deformation, the applied pressure serving to minimise creep into the walls. Because of this, when the hydraulic pressure is relieved following insertion of shims or use of a locking ring to retain the developed stress in the bolted connection, the annular deformation will still be effective to biass apart the distal edges of the walls of the seal. When at some future date it is desired to release the bolted connection, hydraulic fluid can be injected into the piston cylinder device without significant risk of uncontrolled leakage, because the initial seal created or developed by the annular deformation biassing apart the distal edges of the seal walls will still have some effect.Accordingly the piston and cylinder device can be energised in the usual manner to enable the nut to be removed, even if, by virtue of long term loading due to differential expansion for example, the distal-edges are not in contact with the side walls of the cylinder. The shape of the seal is such that the upstanding side walls present a divergent gap to the potential leakage path.

It is this divergence and consequent hydrodynamic instability that tends to close the seal edge on to the wall almost instantaneously, thereby minimising leakage.

In order that the invention be better understood an embodiment of it will now be described by way of example with reference to the accompanying drawing which is a schematic side view in section through a hydraulic nut including a seal constructed in accordance with this invention.

In the figure, only half of the hydraulic nut is shown; the other half is substantially identical and need not be further discussed here. The nut is shown sectioned through the axis of a stud bolt on which it is installed. Referring now to the figure, the hydraulic nut comprises a body portion 1. An annular piston 2 is engaged in an annular cylinder 3 machined into one face of the nut. The nut is internally screw-threaded, 26, and as shown in the figure has been screwed down a stud bolt 4 until the lowermost face of the piston 2 abuts against hardware 5, the latter having a clearance bore therein 6 for the stud bolt 4. An annular chamber 9 is defined between the inner end of the piston 2 and the base of the recess 3. A bore 10 and associated pipe connection 11 enable hydraulic fluid to be applied to the chamber 9. To prevent leakage of fluid past the sides of the piston an annular seal 8 is provided. The seal is in this case made from -copper and has piston face-contacting regions 30 and 31 together with side walls 21 and 22. The tips 23 and 24 of the side walls abut against the sides of the cylinder. Between the piston face-contacting regions 30 and 31 there is a domed or slightly convex region 25.

Around the outside of the nut body there is an internally screw-threaded collar 40 which can be screwed down the body 1 to abut against the face of the hardware 5.

The operation of the device is as follows.

Firstly, with the annular piston 2 pushed as far back into the body 1 as possible, and with the ring 40 screwed upwards as far possible away from the hardware 5, the nut is run down the stud bolt 4 until it seats against the hardware. Hydraulic fluid is now admitted via bore 10. The initial pressure shock causes the side wall tips 23 and 24 to seal firmly against the walls of the cylinder 3. As the pressure increases the side walls themselves 21, 22 are forced against the cylinder walls.

At the same time the central part of the annulus 10 is flattened down against the piston top. The hydraulic pressure is of course applied through the seal to the piston and when the outer face of the latter has moved into abutting relation with the hardware 5, the same pressure is also applied to the hardware. The reaction to this is against the retaining means for the opposite end of the stud bolt 4. This is progressively drawn through the bore 6 until any slack has been taken up.

From then on,. as the pressure increases the stud bolt is stretched. As it stretches, the underside of the nut body 1 rises away from the hardware 5. As soon as a desired stress has been developed in the stud bolt, the locking ring 40 may be run down the outside of the nut body until its lower edge abuts against the hardware.

Alternatively, shims may be introduced into the gap.

At this point the hydraulic pressure may be progressively reduced to zero. The hydraulic fluid source may now be disconnected and the nut can be left in situ, possibly for a considerable period of time and quite possibly at elevated temperature. When it is desired to remove the nut, for example during routine periodic maintenance of the associated hardware, hydraulic fluid may be again applied to the chamber 9 through the bore 10 and connector 11.The original application of pressure may have caused plastic deformation of the side walls 21 and 22 of the seal 8, and in the region of transition from side wall to annulus base regions 30 and 31, but the enormous friction developed by face-to-face contact in these latter annular regions should- ensure that plastic deformation of the central region of the annulus following flattening of the domed region 25 will still leave sufficient residual elastic recovery for the seal to function again when it is desired to remove the nut.

To assist in this the piston crown may be itself correspondingly domed, to provide support for the central region of the seal.

Ideally sufficient elasticity will be retained in the seal to ensure that the side walls 21 and 22 are still biassed outwardly towards the wall of the cylinder 3.

Accordingly, on re-pressurising the chamber 9, the seal will still function effectively and enable the piston to be forced against the hardware 5 sufficiently to enable the locking collar 40 to be withdrawn. Once the locking ring 40 has been unscrewed, the hydraulic pressure may be progressively released and the stud bolt 4 allowed to relax towards its original unstressed length. The nut may then be removed in conventional manner.

Claims (6)

1. A seal for use in a hydraulic nut, or in the head of a hydraulic bolt or the like, comprising a generally planar annulus of an elastically deformable material having upstanding, generally parallel walls extending from its radially inner and outer edges, characterised in that the central region of the annulus contains an annular deformation effective to biass the apart the distal edges of said walls.

2. The seal of claim 1, characterised in that the deformable material is a metal.

3. The seal of claim 2, characterised in that the metal is copper or an alloy thereof.

4. The seal of any preceding claim characterised in that the deformation is slightly convex, as seen in section, to constitute with said walls a W-like shape.

5. A hydraulic bolt stressing device having an annular piston and cylinder therein, characterised in that the sealing means within said cylinder is a seal according to any preceding claim.

6. A hydraulic nut substantially as herein described with reference to and as illustrated by the accompanying drawing.