GB2295433A - Hydraulic bolt or stud tensioning apparatus - Google Patents

Abstract

Retraction of an extended bolt-tensioner piston 17 (Figure 1) into its cylinder 16 when a load is removed, against the resistance of seals 26 and residual fluid in chamber 19, is effected by withdrawal of the fluid by suction means creating a sub-environmental pressure in the chamber. The suction means comprises a suction pump 32 and a control valve 37 which controls an air compressor 25 to drive either the supply pump 23 or the suction pump 32. Alternatively, the suction means is one or several vacuum bottles evacuated by pump or chemical reaction, or a rigid container having an internal wall or diaphragm displaceable to produce suction. Additional seals may be included in tandem with main seals 261, 262 to prevent environmental fluid from being drawn into the chamber by the suction. <IMAGE>

Description

Hydraulic Tensionina Apparatus This invention relates to hydraulic tensioning apparatus for inducing longitudinal stress in threaded bolts, studs or like bodies to permit a fastening nut to be positioned, and in particular relates to subsequent removal of such apparatus.

In such hydraulic tensioning devices for bolts or the like one end of a bolt shank is displaced relatively to its other by attachment of a piston, itself displaceable with respect to a cylinder body by the supply of hydraulic oil at superenvironmental pressure to a driving chamber defined between the piston and cylinder and retained in the cylinder by sealing means between cooperating walls of the cylinder and piston. The separating force exerted on the piston and cylinder body by the fluid pressure overcomes any reaction force due to a load formed by tension induced in the bolt, and environmental pressure acting on the piston, to displace the bolt end to the desired extent.

Upon such extension, the extended bolt is secured by a fastening nut or the like to retain the tension therein and the piston of the bolt tensioning device in retracted relative to the cylinder body and the device removed.

Such hydraulic tensioning apparatus is well known per se, such as from patent specifications Nos GB 1,321,398 or GB 1,590,131.

Such apparatus may be required to operate within an environment that is gaseous or liquid and which has a significant effect in respect of the absolute pressure exerted on parts thereof by the environment. Within this specification the pressure from the immediately surrounding environment is considered as ambient and pressures positive and negative with respect thereto are herein termed 'super-environmental' and ' sub-environmental' pressures respectively.

Similarly, it is convenient to refer to 'bolt tensioning apparatus' as including also apparatus for tensioning analogous threaded elongate studs or fixed shanks which are other than bolts per se.

It is well understood in the field of bolt tensioning apparatus that retraction of the piston with respect to the cylinder in the absence of any reaction from the load displaced may cause operational difficulties.

It is found, for example, in existing hydraulic bolt tensioning devices designed to have overall minimal size that to develop an adequate load displacing pressure in a chamber the fluid is supplied at high pressure (of the order of 1300-1500 Bar) and low flow rate by fluid lines and couplings designed to withstand high internal pressures and with small orifice areas to minimise joint sealing problems.

Furthermore, in order to withstand the high load bearing pressures, the sealing means tend to be actuated by the pressure to create a considerable degree of sliding friction against motion between the piston and cylinder, notwithstanding the use of materials in the sealing means having low coefficient of friction per se.

It may also be necessary to displace the end of a bolt, in order to induce a required tension therein, by more than the stroke length of the piston and cylinder arrangement, that is, by more than the piston can be extended with respect to the cylinder.

In such circumstances, it is usual to stretch the bolt to the limit of piston extension by said fluid pressure, temporarily restrain the bolt tension by way of the fastening nut, retract the piston into the cylinder, displacing fluid in the process, attach the piston to a new position on the bolt shank and resupply fluid at said high pressure to repeat said extension.

Thus when it is required to retract the piston, whether as an intermediate step in tensioning a bolt shank by multiple piston extensions or to remove such a tensioning device after displacing the bolt end, the source of driving chamber fluid pressure is removed and fluid permitted to flow out of the chamber; that is, the chamber is vented, and the piston either is caused to retract by the force of its own weight, if the device is orientated such that the weight act in an appropriate direction, against resistance to motion due to friction caused by the sealing means and resistance to the flow of fluid by way of the restricted supply orifices, or is forced to retract by the operator manually augmenting such force.In practice, the nature of the sealing means required to withstand the high driving fluid pressures imposes a level of friction that can only be overcome in retracting the piston by substantial manual augmentation effort.

It will be appreciated that such a bolt tensioning device may be employed singly, or in a group coupled by means of a common supply, in hazardous environments and/or confined dispositions that make removal, and manual intervention instrumental to such removal, a disadvantage that distracts from their use. For example, such devices may be employed under water for tightening an array of bolts disposed about a pipe flange and before any device or set of linked devices can be used with any other bolts of the flange every piston must be retracted on site, using up limited dive time of the operator, or returned to the surface.

It is known where ease of piston retraction is an operational requirement and the forces involved are significant to provide a double acting piston arrangement, whereby a further driving chamber is created between the piston and cylinder to move the piston in the reverse direction by admitting fluid thereto from the, or a separate, supply, or to provide a return spring arrangement, compressed by the load forcing stroke of the piston, having the strength to overcome any resistance to retraction.

In certain circumstances, such in the illustrative bolt tensioning arrangement, where there is usually a requirement for minimal dimensions it may be considered undesirable to employ piston return techniques which require a considerable increase on size and complexity of the piston or cylinder arrangement.

Notwithstanding constructional details and limitations dependent upon precise utilisation, it is an object of the present invention to provide a hydraulic bolt tensioning apparatus with piston retraction assistance and a method of operating such apparatus to effect improved retraction.

According to a first aspect of the present invention hydraulic bolt tensioning apparatus comprises an annular piston adapted to surround, and be releasably engaged with, one end of a bolt to be tensioned contained within a cylinder space defined by a cylinder body adapted to bear against a body to which the other end of the bolt is anchored against motion with the piston, a fluid chamber defined in said cylinder space by co-operating walls of the piston and cylinder body, a replenishable source of hydraulic fluid at super-environmental pressure, connectable to the chamber in an actuation mode to provide fluid thereto to displace the piston with respect to the cylinder in an actuation stroke, suction means arranged, in a retraction mode, to be coupled to the chamber instead of the source and operable to develop a pressure difference between the environment acting on the piston and a region of the suction means to effect flow of fluid, supplied to the chamber by the source, from the chamber to said region of the suction means.

According to a second aspect of the present invention a method of operating a bolt tensioning device as defined in the preceding paragraph comprises releasably attaching the piston directly or indirectly to one end of a bolt, seating the cylinder directly or indirectly on a body with respect to which the other end of the bolt is anchored, tensioning the bolt by driving the piston with respect to the cylinder by supplying hydraulic fluid at super-environmental pressure to the chamber defined between the piston and cylinder to derive a predetermined level of tension in, and extension of, the bolt, fixing the bolt in its tensioned state by means of a fastening nut carried adjacent said one end bearing on the body, detaching the piston from said one end of the bolt, removing the supply of hydraulic fluid to the chamber and withdrawing fluid from the chamber at such a rate as to draw the piston into the cylinder space defined by the cylinder body.

According to a third aspect of the present invention a method of facilitating retraction of a piston of hydraulic bolt tensioning apparatus pushed from a cylinder space, defined by a cylinder body, by super-environmental pressure of fluid supplied to a chamber, defined between the piston and cylinder body and sealed by seal means to prevent leakage of super-environmental pressure fluid, comprises isolating the chamber from a source of superenvironmental pressure, exposing the chamber to a source of subenvironmental pressure and withdrawing fluid from the chamber.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a schematic arrangement of hydraulic bolt tensioning apparatus according to the present invention showing a sectional elevation through one half thereof and hydraulic fluid withdrawal means having suction means in the form of a suction pump and control means therefor incorporating a change-over valve, Figure 2 is a sectional elevation through part of an annular hydraulic bolt tensioning device similar to that of Figure 1 but incorporating in addition to the main seal arrangement depicted in Figure 1 an auxiliary seal arrangement, Figure 3 is a schematic arrangement, including a fragmentary sectional elevation, similar to Figure 1 but illustrating a modified disposition of the valve means of the control means, Figure 4 is a schematic arrangement, including a fragmentary sectional elevation, similar to Figure 1 but illustrating separate valves in the control means, Figure 5 is a schematic arrangement, including a fragmentary sectional elevation, of a bolt tensioning device similar to Figure 1 but having separate withdrawal and supply means without valve means, Figure 6 is a schematic bolt tensioning device based upon that of Figure 1 showing a plurality of piston and cylinder body parts disposed in an array corresponding to an array of bolts to be tensioned simultaneously.

Figure 7 is a schematic arrangement of hydraulic bolt tensioning apparatus similar to Figure 1 but in which the hydraulic fluid means has suction means in the form of a closed fluid receiver bottle containing, at least in operation, a gaseous atmosphere at sub-environmental pressure, Figure 8 is a schematic arrangement similar to Figure 8 but having separate supply and withdrawal means, Figure 9 is a schematic arrangement of an alternative form of suction means comprising a plurality of reservoir bottles and distribution valve means to select one for use, and Figures 10(a) and 10(b) illustrate alternative forms of suction means.

Referring to Figure 1 a bolt tensioning device in accordance with the present invention, is indicated generally at 10 and shown in operational disposition with respect to a bolt 11 (shown ghosted), extending through a body 12. The bolt 11 is intended to be held under tension with respect to the body by a nut 13 in order to apply compressive force to the body. The part 14 of the tensioning device is annular and surrounds the bolt 11 and nut 13 but only one half of the arrangement, symmetrical about longitudinal axis 15 of the bolt, is shown in sectional elevation.

The portion 14 comprises a cylinder body 16 defining a cylinder space in which is movable a piston 17 releasably engageable with the end of bolt 11 by means of a puller 18, attachable to the end of bolt 11 by co-operating threads or the like, loosely supported on the piston.

The bolt 12 may be disposed under water or on land, that is within a liquid or gaseous environment, and the part 14 must be similarly disposed and operable within an appropriate environment and under the forces and pressures imposed thereon by its operating environment.

The piston 17 and cylinder body 16 define, by co-operating walls thereof, a fluid chamber 19 to receive fluid at superenvironmental pressure by way of duct 20 and coupling arrangement 20, from a source 21, connected to the coupling arrangement by line 22.

The source 21 of pressurised fluid may comprise a pump 23 taking hydraulic oil from a sump 24 and operated by compressed gas from a source 25, and the pump 23 and/or gas source 25 does not need to share the environment of part 14, particularly if hostile. The source of compressed gas 25 may, for example, be an air compressor remote from the pump 23 and the part 14 if either is in a liquid or explosive gaseous environment.

Seal means 26 comprises outer and inner seal elements 26X, and 262 disposed between co-operating relatively sliding surfaces of the piston and cylinder to prevent leakage of fluid from the chamber at super-environmental pressure. It is usual, and preferable, for the seal means to comprise seal elements which increase the sealing effect in accordance with the magnitude of superenvironmental pressure in the chamber 19, that is, which are pressurised by the fluid. For example, such seal elements may be provided by a glass reinforced PTFE ring exposed to the chamber pressure.

The form of tensioning device thus far described is conventional in its general structure and function; the tensioning device may be used with one part 14 for a single bolt or with an array of parts 14 disposed to tension array of bolts simultaneously, as shown in Figure 6 described more fully below.

Fluid supplied at super-environmental pressure of the order of 1,400 Bar (20,000 PSI) by source 23, line 22 and duct 20 to chamber 19 causes displacement of the piston with respect to the cylinder body against frictional resistance of seal means 26, the reaction of the bolt 12 against being tensioned, and possibly the weight of the piston and/or the effect of environmental pressure on the piston. Clearly, at such a supply fluid pressure the resistance to motion by all sources other than bolt tension reaction is negligible.

When the bolt 12 has been stretched sufficiently to define therein a predetermined tension the nut 13 is brought into contact with the body 12 and the tensioning device is ready for removal.

However, it may be necessary to stretch the bolt to a greater extend than the stroke of the tensioning device, in which case it is necessary to temporarily restrain the bolt tension by means of nut 13, and retract the piston into the cylinder, adjusting its position with respect to the bolt, before supplying fluid to the chamber 19.

The supply of pressurised fluid by pump 23 is stopped by an operator and retraction of the piston 17 into the cylinder collapses chamber 19 and returns fluid displaced therefrom into sump 24. Such retraction may be required numerous times, each followed by piston extension, and/or possibly at the end of operation to retract the piston for removal of the tensioning device.

In accordance with the present invention the bolt tensioning device also includes piston retracting means 30 to ease return of the piston to the cylinder. As shown in Figure 1 the retracting means 30 comprises fluid withdrawal means shown by broken line boundary 31 operable in the absence of supply of fluid to the chamber at super-environmental pressure to produce a sub-environmental pressure in the chamber, whereby resistance to retraction forces on the piston is diminished to the extent that little force augmentation is required to retract the piston or, preferably, the piston is retracted by the difference between environmental and chamber pressures alone (with any gravitational assistance).

To this end the withdrawal means 31 comprises suction means arranged to effect a pressure differential between the environment acting on the piston and the fluid in the chamber in order to effect a flow of fluid from the chamber to the suction means. In this embodiment the suction means comprises a suction pump 32, which may also be operated by compressed gas from source 25, and control means, shown generally by dotted boundary line 33, which is operable to inhibit operation of the suction pump during supply of fluid to the chamber 19. That is, the control means can define alternatively a piston actuation mode in which the pump 23 is operable and a piston retraction mode in which pump 32 is operable. The term 'suction pump' is employed for convenience to distinguish from pump 23 by principal function, notwithstanding that the pump 32 is a positive displacement pump.

The control means 33 conveniently includes controller 34 and a gas valve 35 by which the controller enables the compressed gas source 25 to supply alternatively pump 23 or suction pump 32.

The suction pump 32 is connected by fluid line 36 to the cylinder to withdraw fluid therefrom. As shown in Figure 1 this line does not make a separate and direct connection to part 14 but shares a part 222 of line 22 which permits bidirectional flow and the control means 33 includes valve means 37 under control of controller 34 to define in the piston actuation mode, when pump 23 is operating, a fluid path including source 21 and chamber 19 but excluding the suction pump 32 and operable, in a piston retracting mode, when suction pump 32 is operating a fluid path including chamber 19 and the suction pump but excluding fluid source 21.In the embodiment shown the valve means 37 comprises a three-port change-over valve having a common port 371 connected by line 22 to the chamber and alternatively opened ports 372 and 373 connected to fluid source 21 by part 222 of line 22 and connected to suction pump 32 by line 36, respectively.

It will be appreciated that in implementing such fluid withdrawal by creating sub-environmental pressure in the chamber, piston retraction is still dependant on the rate at which fluid can be withdrawn from the chamber by way of flow restrictions caused by any coupling, such as 20,, designed principally to supply fluid safely to the cylinder at high pressure. If the withdrawal rate is too low then any diminished retraction resistance intended to ease manually augmented retraction may be too slow to be of practical benefit whereas to effect automatic piston retraction, a fluid withdrawal rate that is too slow may permit the piston and/or cylinder to become stationary with respect to the seal elements whereby an additional resistance of static friction has to be overcome in addition to the dynamic of friction continuously moving seal elements.

Furthermore, as the seal means 26 is designed to respond to super-environmental chamber pressure to prevent fluid leaking to the environment, it may not be as effective a seal at subenvironmental chamber pressure and, at least over a prolonged retraction period, may permit environmental fluid to be drawn past the seal elements to reduce the pressure differential essential for piston retraction and also contaminate the system fluid. Similar consideration is required in respect of any coupling 20, or line 22 which is designed primarily to contain and retain contents at super-environmental pressures and must be adapted if necessary to mitigate leakage or collapse with contents at sub-environmental pressures.

To mitigate such effects the suction pump 32 may be caused to develop a high flow rate and a large sub-environmental pressure so that fluid is withdrawn from the chamber 19, or each of several connected chambers in linked device parts, at such a rate that automatic or augmented retraction is effective.

To further mitigate any negative behaviour of the seal means 26 in accommodating sub-environmental pressure in the chamber 14, auxiliary seal means 40 may be provided between the piston and cylinder body as shown in the device in 101 in Figure 2, in which items identical to those described above and shown in Figure 1 are given the same reference numbers.

The auxiliary seal means 40 comprises outer and inner seal elements 40, and 402 disposed on tandem with the main seal elements 26, and 262 respectively, between the main seal elements and the environment.

The auxiliary elements work oppositely to the main seal elements to prevent environmental fluid at higher pressure entering the chamber at sub-environmental pressure. The auxiliary seal elements may be pressure activated by such pressure difference or, in view of the smaller pressure differences involved, may be conventional resilient 'o'-ring types. It will be understood that the presence of such auxiliary seal means will introduce additional frictional resistance but the benefit of excluding environmental fluid and thus developing a better subenvironmental pressure in chamber 14 compensates for this.

Nevertheless, the frictional behaviour of any seal material or design may taken into account in providing such auxiliary seal means.

It will be appreciated that a number of variations may be made to the above described actuator without departing from the invention.

Referring to Figure 3 this shown a bolt tensioning device 50 somewhat similar to the device 10 or 10' except that the valve means 37 is carried by, or formed integrally with, the coupling 20 (of Figure 1) to form a modified valve/coupling 51. This valve/coupling may be a direct replacement to a known coupling and single supply line 22, requiring only a single additional line 36 to the suction pump 32 and a single valve control line 52 from controller 34 extending to the part 14; that is, minimal disturbance to an existing supply arrangement. In such an arrangement the lines 22 and 36 are only required to carry fluid unidirectionally and tolerate pressures which are always positive or negative respectively with respect to the environment, and the coupling 51 may be engineered to prevent leakage at both superenvironmental and sub-environmental pressures.

Referring to Figure 4 this shows a bolt tensioning arrangement 60, also similar to 10 and with analogous elements analogously referenced.

The valve means 37 is shown as two valves 61, 62, one each in the supply line part 222 and withdrawal line 36, and under control of controller 34 are opened or closed in such a manner that only one valve is open at any time according to whether the device is in piston actuation or piston retracting mode. As is also shown in this Figure the source 25 of compressed gas to the pump 23 and 32 may also be supplied by way of separate valves 63, 64 likewise controlled by controller 34.Referring to Figure 5 this arrangement of a bolt tensioning device 70 according to the invention has no valve means 37 but the modified withdrawal means 31' comprises, in addition to suction pump 32 and control means 33 for connecting compressed gas source 25 to either supply pump 23 or suction pump 32, a separate coupling 71 between withdrawal line 36 and the part 14 wherein an additional internal duct 72 is connected to the duct 20 and chamber 19. Clearly, in the actuation mode the coupling 71, line 36 and inoperative suction pump must withstand exposure to super-environmental pressure whereas in the piston retracting mode the coupling 20l, line 22 and inoperative supply pump 23 must withstand exposure to subenvironmental pressure.

In all of the above described embodiments the source of fluid at super-environmental pressure has been pump 23 and source of fluid withdrawal at sub-environmental pressure has been suction pump 32 with both pumps operated by compressed gas from source 25.

As indicated, the gas may be air compressed by a compressor located with, or remote from, the pumps although it will be understood that a more portable and less environment-dependant source, such as compressed gas bottle, may be used. The control means 33 may actuate fluid control valve means 37 and pump gas distributing valve means 35 by electrical, hydraulic or pneumatic signals as appropriate, but it is considered convenient to employ compressed gas made available for driving pumps 23 and 32.

As indicated above, any single actuator, particularly of a bolt tensioning device part such as 14, may be coupled in respect of fluid flow to and from the part to a plurality of other similar parts. Referring to Figure 6 a bolt tensioning device 90 is shown for the simultaneous tensioning of a plurality of bolts 1all, 112, 113, arranged around a flange of a body 92 and shown in plan view. The device includes a corresponding plurality of cylinder body parts 14,, 142, 143... each associated with a different bolt. Fluid couplings 93,, 932 933 ... associated with corresponding cylinder body parts each have two connections and fluid lines 94 connecting with their immediate neighbours.One of the couplings, say 932, has an additional coupling 95 to which the supply line 22X, of the fluid supply/withdrawal part (described in relation to Figure 1) is connected. It will be seen that in the actuation mode each of the cylinder parts 141, 14 . . . has fluid supplied thereto at super-environmental pressure simultaneously and in the piston retracting mode fluid is withdrawn from each of the cylinder parts simultaneously. It will be appreciated that any augmentation to, or automatic effecting of, piston retraction will be advantageous to the operator and may be achieved with only minor modifications to the cylinder parts that do not increase their dimensions to affect packing density or require controls other than may be mounted remotely if appropriate.

In some environments, particularly underwater where environmental pressures are greater and the environment is more difficult to work in, the arrangement of Figures 1 to 6 may be costly to implement either in the requirement for having complex pump arrangements disposed in the underwater environment or having long supply lines and possible couplings therefor able to withstand both super- and sub-environmental pressures whilst coupled to a surface pumping station.

Figure 7 shows the tensioner portion 14 of Figure 1 with source 21 of pressurised fluid in the form of pump 23 and sump 24 but with fluid withdrawal means 100. The withdrawal means 100 comprises a controller 34, compressed gas source 25, gas valve 35, three-port changeover valve 37, all as shown in Figure 1 and described hereinbefore, and suction means in the form of a closed fluid receiver bottle 101.

The pump 23, sump 24, controller 24 and gas source 25 and gas valve 35 are all disposed at the surface of the water in the atmosphere, the fluid supply line 22 extending from the pump to the valve 37 disposed underwater with the receiver bottle 101 in the vicinity of the tensioner device body part 14.

Initially the bottle 101 contains a gaseous atmosphere of subenvironmental pressure, preferably below surface atmospheric pressure, and is deployed by a diver or remotely operated vehicle (ROV) with the line 22 coupled by way of valve 37 and coupling 20 to the tensioner cylinder body 16. Conveniently the bottle is at least partially evacuated of air which forms the receiving atmosphere therein.

As described above in relation to Figure 1, the part 221 of the line and coupling 20, are required to support both super- and sub-environmental pressures without leakage, whereas the major part 222 is required only to support super-atmospheric pressure.

Thus in operation and in the actuation mode, pump 23 supplies hydraulic fluid at super-environmental pressure to the tensioner chamber 19 to extend the piston with respect to the cylinder against the resistance of the environmental pressure, the valve 37 closing off the receiver bottle 101. When it is required to retract the piston, the pump 23 is stopped and the valve 37 operated to enter the retraction mode, whereupon the fluid in the chamber 19 is exposed to a pressure difference between the piston and the atmosphere in the receiver bottle and the fluid is displaced from the chamber by collapse under the said pressure difference.

The valve 37 may be operated again to seal the receiver bottle from the chamber and expose the latter to more fluid at superenvironmental pressure from the pump 23 to re-extend the piston, followed by a retraction in which the chamber fluid is displaced into the receiver bottle to add to the fluid contained from the preceding retraction. Thus the receiver bottle may operate to receive fluid from a plurality of sequential retractions provided of course that it has sufficient capacity and adequate pressure difference remains between the instantaneous atmosphere with respect to the environment at that depth to overcome any resistances to piston retraction. When tensioning is finished the receiver bottle is returned to the surface and the fluid disposed of or returned to sump 24 for further use.

It will be appreciated that a number of variations may be effected in embodying such a suction means 100 that are analogous to those described hereinbefore for suction pump 32, in terms of separately operated valve arrangements or direct connection of the receiver bottle to the cylinder body 16.

It will be appreciated that a receiver bottle which has the capacity and/or initial pressure differential to support a plurality of sequential piston retractions may be too unwieldy for space available in the vicinity of the bolt to be tensioned or for handling and manipulation by a diver or ROV. If desired, a plurality of small receiver bottles, each having the capacity to effect one piston retraction may be employed, a new receiver bottle being connected prior to each piston retraction.

It will be appreciated that where a receiver bottle is capable of efficient connection and disconnection in the underwater environment by virtue of self-sealing couplings, such coupling may permit the various valve means described above to be simplified or omitted, the self-sealing valves of the couplings providing isolation in actuation and retraction modes, as illustrated in Figure 8 which is analogous to Figure 5.

Where it is inappropriate to have a single receiver bottle to receive fluid from a plurality of piston retractions and inappropriate to physically install a fresh receiver bottle for each retraction of a sequence, then the suction means may take a form indicated schematically at 100' in Figure 9 comprising a plurality of receiver bottles 101, . . 1012, 1013 each initially charged with an atmosphere at sub-environmental pressure and each connected to distribution valve means, indicated generally at 102 and comprising respective valves 102X, 1022, 102 , and by way thereof to a common supply line 103.

Thus for a sequence of retractions a different valve is operated for each retraction, either manually or remotely and a different bottle receives the expelled fluid.

Clearly such a suction means in the form of a receiver bottle is not limited to underwater applications when the environmental pressure is naturally high, but may be used in normal gaseous atmospheres provided the, or each, receiver bottle used can provide a sufficiently sub-environmental pressure.

However, for such underwater operation at depth where the ambient environmental pressure is significantly above atmospheric pressure at the surface a fluid receiver bottle which is merely sealed at the surface containing atmospheric air or other gas may present an adequately sub-environmental pressure to be useful at operational depth. For greater efficiency at both great and modest depths, or for operating in a gaseous environment, the receiver bottle may be evacuated in part or as totally as is practicable prior to use. Conveniently such evacuation is performed by a pump at the surface removing atmospheric gas from the bottle, but if desired such evacuation may be effected by chemical or physical effects acting upon the atmosphere in the bottle after it is sealed at the surface.Chemically, such evacuation may be effected by the the bottle containing means operable by chemical reaction to provide the appropriate degree of sub-environmental pressure.

The reactive means may comprise a solid, liquid or gaseous component caused to react with a similar component or the bottle atmosphere such that the atmosphere is consumed totally or in part by the reaction. Such reaction may be effected at the surface before the receiver bottle is used or may be initiated by the diver or ROV at the time of use if appropriate.

In such an arrangement it may be desirable for any reaction products remaining in the bottle to be isolated from fluid drawn into the bottle by a diaphragm of some form, such as a flexible and possibly expansible sac coupled to the bottle operative to receive and contain the fluid as shown ghosted at 104 in Figure 7.

Physically, the atmosphere within the bottle may be raised to an elevated temperature prior to sealing the bottle at the surface, a reduced environmental temperature, particularly underwater, at the time of use effecting a cooling of the contents and reduced atmospheric pressure within the bottle.

An alternative form of suction means is shown in Figures 10(a) and 10(b), comprising in each case a fluid receiver 120 in the form of a rigid walled container which has an internal wall 121 thereof defining a receiving volume 122 for fluid from the chamber 19. The internal wall 121 is displaceable with respect to the external container walls by drive means indicated generally at 123 which is operable in said retraction mode to increase the receiving volume 122 from its initial value by the volume of fluid in the chamber for the last actuation stroke.

In Figure 10 (a) it will be seen that the internal wall comprises a rigid wall 121, sealed with respect to the fixed container walls and connected by an actuation rod 124 to drive means 1231 which may comprise a linear actuator, possibly hydraulic or pneumatic or a gear or friction drive by a shaft rotating about an axis orthogonal to the axis of the rod. Alternatively (not shown) the actuator rod or internal wall could be formed with a helical thread and be displaced along its longitudinal axis by rotation about it through co-operation with some nut device.

In Figure 10(b) it will be seen that the internal wall comprises a flexible membrane 1212 which separates the receiving volume from the remainder 125 of the container containing a gas or liquid (possibly the environment). The drive means 1232 comprises a pump for displacing the gas as liquid in order to expand the receiving volume.

In both of the above described forms, it will be appreciated that the receiving volume and drive means may be arranged to operate to produce a plurality of successive internal wall displacements, each related to the volume of hydraulic fluid in the chamber 19, such that the piston may be subjected to a plurality of successive actuation strokes (which may be necessary to provide accumulated tension in a bolt) or to withdraw fluid from a plurality of different chambers.

In all of the above descriptions the piston has been shown as executing a rectilinear displacement with respect to a cylinder when in a actuation and retraction mode. It will be understood that the inventive principles apply equally in respect of angular displacement if appropriate and the terms extension and retraction should be construed accordingly in relation to the original home disposition of the piston relative to the cylinder.

Although shown in the Figures with a puller 14 forming part of the tensioner device and removable therewith, the tension device piston may be attachable directly to a bolt shank by thread engagement or other abutment forms or may be attachable by way of a puller which comprises an adapter nut which forms an extension of a short bolt and which remains in place after removal of the tensioner device.

Similarly the terms piston and cylinder are used according to convention and the description relates to the piston movement as being in relation to a usually static piston. Clearly the roles may be reversed with such relative movement being by a moveable cylinder with respect to a stationary piston.

Claims (36)

1. Hydraulic bolt tensioning apparatus comprising an annular piston contained within a cylinder space defined by a cylinder body adapted to bear against a body to which the other end of the bolt is anchored against motion with the piston, a fluid chamber defined in said cylinder space by co-operating walls of the piston and cylinder body, a replenishable source of hydraulic fluid at super environmental pressure, connectable to the chamber in an actuation mode to provide fluid thereto to displace the piston with respect to the cylinder in an actuation stroke, suction means arranged, in a retraction mode, to be coupled to the chamber instead of the source and operable to develop a pressure difference between the environment acting on the piston and a region of the suction means to effect flow of fluid, supplied to the chamber by the source, from the chamber to said region of the suction means.

2. Apparatus as claimed in claim 1 in which the suction means comprises a suction pump operable to withdraw fluid from the chamber by way of the pump.

3. Apparatus as claimed in claim 2 in which the source of super-environmental pressure fluid comprises a compressed gas-operated pump and the suction pump comprises a compressed-gas-operated pump operable by the same compressed gas source.

4. Apparatus as claimed in claim 2 or claim 3 in which the suction pump comprises a compressed-gas-operated reciprocating pump.

5. Apparatus as claimed in claim 1 in which the suction means comprises a closed fluid receiver bottle arranged to contain a gaseous atmosphere at sub-environmental pressure and operable in said retraction mode to receive fluid displaced from said chamber by the pressure difference between said environments and the bottle.

6. Apparatus as claimed in claim 5 in which the receiver bottle is arranged to contain air at a low pressure with respect to the atmosphere.

7. Apparatus as claimed in claim 5 or claim 6 in which the receiver bottle has such a volume, and is arranged to have such initial internal pressure, as to effect withdrawal of fluid for a plurality of sequential piston retractions.

8. Apparatus as claimed in any one of claims 5 to 7 in which the suction means include a plurality of closed receiver bottles and withdrawal distribution valve means operable to connect a different receiver bottle to said chamber for each retraction of the piston.

9. Apparatus as claimed in any one of claims 5 to 8 in which the withdrawal means includes connection means having closure means arranged to make connection between the chamber and a closed receiver bottle by connecting the receiver bottle thereto.

10. Apparatus as claimed in any one of claims 5 to 9 in which the fluid receiver bottle contains means operable by chemical reaction to provide a sub-environmental pressure therein.

11. Apparatus as claimed in claim 10 in which the receiver bottle contains a diaphragm operable to separate the fluid from the means providing said sub-environmental pressure.

12. Apparatus as claimed in claim 11 in which the withdrawal diaphragm comprises a closed flexible walled sac.

13. Apparatus as claimed in any one of claims 10 to 12 in which the means operable by chemical reaction comprises at least one component operable to react chemically with another and consume atmospheric gas within the bottle.

14. Apparatus as claimed in claim 2 in which the suction pump comprises a fluid receiver, comprising a container having substantially rigid fixed external walls and defining therein a fluid receiving volume by an internal wall displaceable with respect thereto, and drive means operable to displace the internal wall at least to the extent necessary to increase the receiving volume of fluid supplied by the source to the chamber.

15. Apparatus as claimed in claim 14 in which the drive means is operable to displace the internal wall by a plurality of successive displacements to increase by each displacement the receiving volume by the volume of fluid in the chamber for the preceding actuation stroke.

16. Apparatus as claimed in claim 14 or claim 15 in which the internal wall is substantially rigid and connected to an actuation rod extending from the container and displaceable along its longitudinal axis by the drive means.

17. Apparatus as claimed in clam 14 or claim 15 in which the internal wall is a flexible diaphragm and the drive means is operable to displace fluid from the side of the diaphragm received from the receiving volume.

18. Apparatus as claimed in any one of claims 1 to 17 in which the suction means is arranged to withdraw fluid at such a rate that the force on the piston due to the pressure difference between the environment and the chamber, and any force on the piston due to gravity, effect retraction of the piston with respect to the cylinder at a rate to avoid or overcome frictional effects between the piston, cylinder and seal means.

19. Apparatus as claimed in any one of claims 1 to 18 in which the withdrawal means includes control means comprising valve means operable in said actuation mode to define a fluid flow system including the source and chamber but excluding the suction means and operable in said retraction mode to define a fluid flow system including the chamber and the suction means but excluding the source.

20. Apparatus as claimed in claim 19 in which the valve means comprises a three port change-over valve having a common port connected to the chamber and alternatively opened ports connected to the fluid source and the suction means.

21. Apparatus as claimed in claim 19 or claim 20 in which the cylinder body is remote from the valve means and connected thereto by a common bidirectional fluid line.

22. Apparatus as claimed in any one of the preceding claims in which the seal means is adapted also to prevent the leakage of environmental fluid into the chamber when at sub environmental pressure.

23. Apparatus as claimed in claim 22 in which the seal means includes a main seal arrangement having one or more main seal elements actuated by super-environmental pressure in the chamber to define sealing between the piston and cylinder that impedes leakage of fluid to the environment and an auxiliary seal arrangement comprising one or more auxiliary seal elements each in tandem with a main seal element between the main seal element and the environment.

24. Apparatus as claimed in 23 in which each element of the auxiliary seal arrangement comprises a pressure-actuated seal actuated by the environmental pressure against a sub environmental pressure within the chamber.

25. Apparatus as claimed in claim 23 in which each element of the auxiliary seal arrangement comprises an elastomeric 'O'-ring.

26. Hydraulic tensioning apparatus substantially as herein described with reference to, and as shown in, any one of the accompanying drawings.

27. A method of facilitating retraction of a piston of hydraulic bolt tensioning apparatus pushed from a cylinder space, defined by a cylinder body, by super-environmental pressure of fluid supplied to a chamber, defined between the piston and cylinder body and sealed by seal means to prevent leakage of super-environmental pressure fluid, the method comprising isolating the chamber from a source of super-environmental pressure, exposing the chamber to a source of sub-environmental pressure and withdrawing fluid from the chamber.

28. A method as claimed in claim 27 comprising exposing the chamber to a fluid receiver bottle containing a gaseous atmosphere at sub-environmental pressure.

29. A method as claimed in claim 28 comprising coupling a fluid receiver bottle empty of fluid to the chamber for each piston retraction.

30. A method as claimed in claim 28 for effecting multiple sequential retractions of said piston comprising exposing the chamber to a fluid receiver bottle of such volume and initial internal pressure that fluid from the chamber is received into the bottle for each of said retractions of the sequence.

31. A method of facilitating retraction of a piston of hydraulic bolt tensioning apparatus pushed from a cylinder, substantially as herein described with reference to, and as shown in, the accompanying drawings.

32. A method of operating a bolt tensioning device as claimed in any one of claims 1 to 26, the method comprising releasably attaching the piston directly or indirectly to one end of a bolt, seating the cylinder directly or indirectly on a body with respect to which the other end of the bolt is anchored, tensioning the bolt by driving the piston with respect to the cylinder by supplying hydraulic fluid at super-environmental pressure to the chamber defined between the piston and cylinder to derive a predetermined level of tension in the bolt, fixing the bolt in its tensioned state by means of a fastening nut carried adjacent said one end bearing on the body, detaching the piston from said one end of the bolt, removing the supply of hydraulic fluid to the chamber and withdrawing fluid from the chamber at such a rate as to draw the piston into the cylinder space defined by the cylinder body.

33. A method as claimed in claim 32 comprising withdrawing fluid from the chamber by exposing the chamber to a sub environmental pressure defined by the gaseous atmosphere of a closed fluid receiver bottle.

34. A method as claimed in claim 33 comprising, at least once, re-attaching the piston directly or indirectly to said one end of the bolt, tensioning the bolt further by resupplying hydraulic fluid to the chamber, fixing the bolt in its tensioned state, detaching the piston from the bolt and withdrawing fluid from the chamber into the fluid receiver bottle by exposing the chamber to sub-environmental pressure defined by the gaseous atmosphere of the fluid receiver bottle.

35. A method as claimed in claim 32 comprising, at least once, re-attaching the piston directly or indirectly to said one end of the bolt, tensioning the bolt further by resupplying hydraulic fluid to the chamber, fixing the bolt in its tensioned state, detaching the piston from the bolt, coupling a closed fluid receiver bottle containing only a gaseous atmosphere at sub-environmental pressure to the chamber and withdrawing fluid from the chamber into the fluid receiver bottle by exposing the chamber to sub environmental pressure defined by the gaseous atmosphere of the fluid receiver bottle.

36. A method of operating a bolt tensioning device substantially as herein described with reference to any of Figures 1 to 6 or any one of Figures 7 to 10 of the accompanying drawings.