GB2072145A - Liquid core sampler - Google Patents

Abstract

This invention relates to an interface sampling device for determining the thickness of the water layer in a water-oil mixture. The device makes use of a trigger mechanism 7, 8, 9 to which the valves 35, 38 of a sample chamber 1 respond. That is, when the trigger is loaded and the device immersed in the mixture, the valves are open allowing free flow of the sample in and out of the chamber enabling the sample in the chamber to attain equilibrium with the surrounding oil/water mixture. Upon unloading the trigger 7, 8, 9, the valves 35, 38 snap shut rapidly, trapping the sample within the chamber. The device ensures that samples collected are representative and is particularly suitable for measuring thickness of a water layer in tanker bottoms. <IMAGE>

Description

SPECIFICATION Liquid core sampler The present invention relates to an interface sampling device, in particular to a device for determining the thickness of the water layer in a water-oil mixture at the bottom of a storage tank, and a method of retrieving a representative sample of the water from the bottoms of storage tanks.

Several methods and devices have been used to determine the level of water in water-oil mixtures stored in tanks. The most commonly used is a water-level detecting probe coated with a paste which responds by discolouration upon contact with water. This technique is satisfactory where the oil in the water-oil mixture is relatively light and where the object is only to detect the level of water in such mixtures stored in tanks. The technique, however, gives inconsistent results when such mixtures contain relatively heavier oils.

Other methods used include those which employ bell-shaped sampling devices and waisted tubes.

The probiem with the former is that these have to be evacuated before being lowered into the liquid to be sampled, the valves have to be shut rapidly once the sample is collected and usually the samples collected are non-representative due to the inevitable disturbarre of the interface during the lowering and sampling operations. The waisted tube technique claimed and described in our British Patent Specification No. 1496505 has been found to be unsatisfactory for sampling bottoms layers although it has been very useful for recovering core samples of surface layers.

It has now been found that the problems encountered with prior art devices may be mitigated by using a modified design for the sampler.

Accordingly, the present invention is a liquid core sampling device which comprises: A) an outer tube provided with: (a) a first valve seat spaced from one end thereof by means of a hollow perforated collar, (b) means at the opposite end thereof for suspending the tube, (c) a second valve seat located between the first valve seat and the suspending means, (d) an internal over-centred trigger located between the second valve seat and the suspending means, and (e) openings on the walls of the tube between the second valve seat and the trigger to allow egress of fluid from the outer tube; B) an elongated inner member axially oriented with respect to and slideably mounted within the tube and extending from the first valve seat to beyond the trigger, said member being provided with:: (a) a first valve at the collar end thereof capable of sealing engagement with the first valve seat and having an outer diameter substantially less than the inner diameter of the collar, and (b) a second valve capable of sealing engagement with the second valve seat, said member being responsive to the trigger such that loading the trigger opens the valves allowing free ingress of liquid into the tube and unloading the trigger closes the valves trapping the sample in the space between the two valves; and C) means for loading and unloading the trigger.

The outer tube is suitably of a corrosion resistant material which may be of a rigid poiymer or metal, preferably brass.

One end of this tube is provided with a hollow perforated collar. The perforations are sufficiently large to allow free flow of the liquid being sampled. The perforations are suitably spaced around the periphery of the collar at the end of the tube.

The outer tube is provided with two valve seats on the inside which are cooperable and capable of sealing engagement with the valves which each comprise a valve plate and a stem. The first valve seat is spaced just above the perforated collar and the second valve seat positioned at a point which is intermediate between the perforated collar and the point from which the tube is suspended at the opposite end thereof.

The means for suspending the tube may be one or more hooks or holes on the side of the tube through which a suspension wire or cord may be connected to the tube. The connection may be achieved by fastening the wire or cord to the hook(s) or hole(s). The function of the suspension means is to lower the device into the liquid to be sampled and to recover the device after the sample has been collected in the tube. It will be understood by those skilled in the art that other conventional suspension means which serve this purpose may be used.

The outer tube is also provided with an overcentred trigger to enable the valves to be opened or closed as desired.

The over-centred trigger comprises two sets of lever mechanisms which are pivotally connected to opposite sides of a central annular boss thereby enabling the two lever mechanisms to act in parallel. Each mechanism consists of two opposing slotted cross heads spaced from each other, two links and a spring. One end of each link is slideably mounted into the respective slot of each cross head. The slideably mounted ends of each link are also mutually connected by the spring under tension. The free ends of the two links are pivoted to the same point on one side of the central boss. On the opposite side of the boss the second lever mechanism of the set of two is similarly pivotally connected.In the absence of applied force on the boss, the tensioned spring urges together the slideably mounted ends of each set of the links, moving the pivoted ends and the central boss away from an imaginary central horizontal plane of the opposing set of cross heads thus causing the links in each set to collapse.

By applying a force on the boss in the collapsed position of the links it is possible to force the boss and hence the links to either side of the central plane of the cross heads. However, if by applying a force, the boss is forced fractionally beyond one side of the central plane the natural bias of the tensioned spring ensures that the movement of the boss continues rapidly in that direction even after the applied force is withdrawn. This characteristic of the trigger is used to load and unload the trigger. For example, a force maybe applied on the boss to move it fractionally past the central plane and the extent of vertical movement of the boss in the same direction, especially towards the perforated collar, can be prevented by using some stopping means which may simply be a catch.The boss of course cannot revert to its original position on the other-side of the central plane without applying further force in the opposite direction.

Therefore, the boss and hence the trigger is maintained in this, its loaded position. The stopping means may also be used to adjust the sensitivity of response af the trigger apart from merely controlling the distance through which the boss is caused to move by the tensioned spring.

Both these functions may, for example, be achieved by a stop screw acting on the boss. From the loaded position, the trigger may be unloaded or released by applying only that much force which is necessary to move the boss fractionally to the other side of the central plane. Thereafter the force for the rapid collapse of the links and the further continued movement of the boss in that direction is supplied by the tension in the spring.

The trigger is mounted inside the outer tube by means of the four cross-heads (two sets of two each) which are suitably integral with and extend radially inwards from the walls of the outer tube.

The central boss of the over-centred trigger is so positioned that it is capable of transmitting any force applied to the trigger whether it is for loading or unloading the trigger.

The outer tube also has openings along its side between the second valve seat and the trigger to allow free flow of fluid through the tube during lowering of the device into the liquid to be sampled and during collection of the sample whilst both the valves are open. The openings reduce the effects of turbulance during these operations which may be carried out without any substantial disturbance of the interface.

The elongated inner member may be a solid rod or a hollow tube and is suitably coaxial with the outer tube. The inner tube may be retained in a coaxial position with respect to the outer tube by means of centralising radial lugs provided on the latter. The inner member has two valves cooperable with the valve seats in the outer tube so as to be able to form a sealing engagement therewith. Each valve comprises a valve plate and a stem, the stems being integral with or, if detachable, being aligned with the axis of the inner member. The stems may also be hollow or solid. The valve plate and/or the stems are preferably detachable from the inner member because this will facilitate the assembly of the device. The first valve is preferably provided with O-ring seals so as to improve the sealing contact with the first valve seat.The outer diameter of the first valve plate is substantially smaller than the inner diameter of the perforated collar so that when the device rests on its collar e.g. on lowering the device to the bottom of a tank, the valve remains open and is therefore capable of allowing free flow of liquid in and out of the device across the perforations. This enables liquid within the tube to attain equilibrium during sampling.

The second valve has a valve plate preferably smaller in diameter relative to that of the first valve and may simply form a metal to metal seal with the second valve seat. The second valve plate is preferably supported by a compression spring.

The position of the two valves, the respective valve seats and the strength of this compression spring on the second valve seat are suitably adjusted to allow the second valve to close fractionally before the first valve. The subsequent closure of the first valve will simply compress the spring on the second valve seat and close the second valve more firmly. The valves are thereafter snapped closed by the action of the trigger thereby trapping the sample.

The elongated inner member is connected at its other end to the trigger in such a manner that it is responsive to the trigger. That is, when the trigger is loaded, the inner member is pushed towards the perforated collar thereby opening the valves and when the trigger is unloaded, the valve plates are snapped shut against the valve seats to form a liquid-tight chamber between the two valves. The connection between the elongated inner member and the trigger may be achieved in several ways.

For example, they may be rigidly connected through the boss on the over-centred trigger.

Alternatively, the inner member may be provided with a retaining flange and slideably mounted through but in abutment with the boss and the trigger such that the member and hence the valves respond to the loading or unloading of the trigger as before.

The means for loading and unloading the trigger may be any means which enables a force to be applied on the trigger. The means in this respect may be any of a simple wire or cord, a rigid rod or shaft or a sprung lever, which may be hydraulic, which may be connected either directly or indirectly to the trigger.

In this embodiment the means for suspending the device and the means for operating the trigger are separate and independent. Under certain circumstances the use of two such means is not satisfactory. This is particularly the case if the means of suspension and operation of the trigger are cords or wires because the two are liable to get twisted, especially if the storage tank from which the liquid is to be sampled is either deep or is on a moving vessel. With this contingency in mind, a modified embodiment of the above invention has been devised.

Thus, according to a further embodiment, the present invention is a liquid core sampling device which comprises: A. an outer tube provided with (a) a first valve seat spaced from one end thereof by means of a hollow perforated collar, (b) a collet at the opposite end thereof, (c) a second valve seat located between the first valve seat and the collet, (d) an internal over-centred trigger comprising a boss located between the second valve seat and the collet, and (e) openings on the walls of the tube between the second valve seat and the trigger to allow egress of fluid from the tube;; B. an inner member provided with (a) a first valve at the collar end thereof capable of sealing engagement with the first valve seat and having an outer diameter substantially less than the inner diameter of the collar, (b) a second valve capable of sealing engagement with the second valve seat, (c) a flange at the trigger end thereof situated above and adapted to rest on the boss of the overcentred trigger, and (d) a longitudinal slot extending from above the second valve to beyond the boss and adapted to receive and allow longitudinal movement of a pin therethrough, said inner member extending from the first valve to beyond the trigger; and C. a suspended shaft capable of longitudinal movement through the collet in its open position, the boss and the inner member, said shaft being provided with (a) a rectangular recess at which the collet closes around the shaft to form an integral unit therewith enabling the device to be suspended by the shaft, and (b) an integral transversely oriented pin which projects through the slot to restrict the movement of the shaft within the inner member to the length of the slot, such that when the pin abuts against the valve end of the slot it enables the trigger to be loaded under applied force thereby opening the valves and allowing ingress of the sample into the outer tube, and when the pin abuts against the boss it enables the trigger to be unloaded, thereby snapping shut the first and second valves against the respective valve seats to form a liquid-tight chamber for retaining the sample.

In this embodiment the first and second valve seats and the perforated collar are the same as that for the previous embodiment. However, the means for suspending the device and the means for operating the trigger are both combined into a single unit which comprises a collet, a shaft with a rectangular axial recess, a transversely oriented pin, and a slotted tube. In particular, the collet is a split coned sleeve capable of holding the shaft at its rectangular recess and adapted to fit into a correspondingly tapered nose formed on the outer tube. The split coned sleeve is made of a plurality of sprung segments, the springs being biased to allow the tapered end of the cone to expand with respect to its base. Thus, the split coned sleeve can be fitted into the tapered nose and held in position by applied tension.The means for applying tension and the load bearing function of the collet is achieved by the rectangular axial recess on the shaft. When the sleeve is fitted into the nose, the sprung segments close at the recess around the shaft and when tension is applied on the shaft to pull the sleeve into the nose, the radial edges of the axial recess on the shaft abut against the base of the sleeve, thus performing a load bearing function and enabling the entire device to be suspended by the shaft. When the applied tension is released, the radial edges of the axial recess are no longer in abutment with the base of the sleeve and this, combined with the spring action of the segments, enables the sleeve to release the shaft and drop clear of the nose.

The second function of the unit is to be able to load the trigger and unload the trigger when desired. To achieve this function the other components of the unit, namely, the shaft, the transversely oriented pin and the slotted tube are used. In this case at least that part of the elongated inner member which extends from the second valve plate through and beyond the trigger is hollow and tubular. The position of the tubular member beyond the trigger is provided with an integral flange to prevent it from slipping through the boss. The flange is located between the boss and the base of the conical sleeve and is adapted to rest on the boss in the unloaded position of the trigger.

The shaft is slideably mounted within the inner tubular member. The transversely oriented pins on the shaft project through the longitudinal slots on either side of the member. The sliding movement of the shaft within the member is restricted to the length of the shaft by these pins.

When the shaft is forced into the member so that the pin abuts against the valve end of the slot it enables the trigger to be loaded as follows: by applying a force on the shaft the pin abuts against the valve end of the slot thus pushing the tubular member towards the collar end of the outer tube; as a result the flange on the member bears down on the boss of the trigger forcing the trigger down against its natural bias and when the applied force is sufficient to lock the trigger in its loaded position, the force can be withdrawn. In this position, both the valves are open, the pin is bearing against the bottom end of the slot - but only under gravity - and the shaft is again slideable within the inner member. The flange of the latter is also resting on the boss.The entire device can be lowered down into the liquid to be sampled by pushing the conical sleeve into the nose and locking it in position around the rectangular recess on the shaft so that the device can be suspended on the shaft as explained above without unloading the trigger. To maintain the tension on the shaft and to prevent the collet from being released, the outer tube may be of sufficient weight or may carry ballast weights. The means of suspension on the shaft may be a simple eyelet at the top end of the shaft to which a cord or a wire may be fastened.

When the device is slowly lowered down into the liquid to be sampled, it comes to rest on its collar upon contact with the bottom of the tank containing the sample. The first valve plate moves upwards but only as far as the perforated collar.

Further movement of the inner member and hence this valve plate is prevented by gravity, the valves are still open and there is a free flow of liquid in and out of the device across the perforations.

When the device has come to rest at the bottom of the tank, the tension on the shaft may be slackened as a result of which the collet is released and the conical sleeve slips down the shaft on to the flange. The device is allowed to stand in this position for a sufficient period so as to allow the liquid within the tube to attain an equilibrium with respect to the bulk of the sample surrounding the device. The free flow of sample through perforations on the collar and the openings above the second valve seat ensure that this equilibrium is achieved and that any disturbance created at the interface during the lowering of the device is substantially nullified.

When equilibrium is attained, the shaft may be pulled up again. By this operation the transverse pin is pulled along the slot towards the boss.

When the pin abuts against the boss and a further pulling force applied, the effect is to unload the trigger with a rapid upward thrust of the boss which in turn pulls the inner tube. The upward thrust generated by unloading the trigger is sufficient to force both valve plates against the respective valve seats thereby snapping shut both the valves in a fraction of a second, trapping the sample in the chamber formed by the space between the two valves. Thereafter, retrieval of the device does not present any problem because the valve can only be opened by applying substantial force on the trigger in the opposite direction.

The recovered sample may then be decanted, measured and analysed as and when necessary.

The liquid core sampling device of the present invention and its operation is more specifically described below with reference to the accompanying drawings in which: Figure 1 shows a vertical section of the device in its loaded position as it is about to be lowered into a tank containing the liquid to be sampled and in this position both valves are open; Figure 2 shows a vertical section of the device when it has been lowered into the tank containing the liquid and in this position both valves are still open and free flow of liquid in and out of the device is still possible across the perforations; Figure 3 shows a vertical section of the device upon release of the trigger when both valves are shut and the sample is trapped in the space between the valves;; Figure 4 shows a detailed vertical section of the trigger in its loaded position, and Figure 5 shows a planar view of the split coned sleeve in its closed and open positions.

Description of the Device In the drawings, the outer tube 1 has a collar 2 with its perforations 3 at one end, and a hollow, open frame 23 at the other end. The frame 23 is provided with a collet which consists of a split coned sleeve 5 which is adapted to fit into a correspondingly tapered nose 1 8. The split coned sleeve is made of three symmetrically disposed sprung segments 5a, 5b and Sc held together by compressed springs 24 biased to allow the tapered end of the cone to expand with respect to its base. The outer tube 1 has two valve seats 4 and 6. The first valve seat 4 is positioned between the perforated collar 2 and the junction 40 of the frame 23 and the tube 1 at or immediately above the collar 2 whilst the second valve seat 6 is positioned at or just above the junction 40.The frame 23 also houses a trigger (Fig. 4). The trigger has two sets of lever mechanisms symmetrically disposed around a central annular boss 9. One such set is shown in Figure 4. For the sake of convenience and clarity the detailed description of the integers in the lever mechanism and their inter-relationships will be limited to this one set.

The set consists of two slotted cross-heads 31 and 32 each having a slot 26 and 27 respectively.

One end of each of a pair of links 7 and 8 is slideably mounted in the slots 26 and 27 respectively by means of steel pins 28 and 29 respectively. The free ends of the links 7 and 8 are pivoted together to one side of the boss at the same pivot point 30. The ends of a spring 33 are looped under tension around the steel pins 28 and 29. On the valve side of the boss 9 is provided a stop screw 36 mounted on a projection 37 from the frame 23. The stop screw 36 is capable of abutment with the boss 9 and enables the movement of the boss 9 in the downward direction to be controlled and the sensitivity of the trigger response to be adjusted by adjusting the distance between the screw 36 and the lower end of the boss 9. A parallel set of a second lever mechanism (not shown) is similarly disposed symmetrically on the opposite side of the boss 9.

The outer tube 1 has an elongated coaxial inner tube 10 extending from the first valve seat 4 to beyond the boss 9. Centralising lugs 20 are provided on the outer tube to ensure that the inner tube 10 is coaxial with the outer tube. The inner tube 10 is provided at its collar end with a detachable first valve 38 which consists of a valve plate 11 and a stem which is integral and coaxial with the inner tube 10. The valve plate 11 has an outer diameter which is substantially smaller than the inner diameter of the collar 2 and is slideabie within the outer tube 1 as far as the valve seat 4 against which it forms a sealing engagement. This valve plate 11 is provided with O-rings 22 to improve the sealing contact thereof with valve seat 4. The inner tube 10 is provided at its trigger end with a second valve 35 which also has a valve plate 12 and a hollow stem 25 which is an extension of the inner tube 10. the valve 35 is supported by a compression spring 21. The stem 25 extends from the valve 35 to beyond the boss 9 and the end of the stem extending beyond the boss 9 has an annular flange 13 which enables the stem and, therefore the inner tube 10 and the valves 35 and 38 to follow the direction of movement of the boss 9. Stem 25 has a pair of symmetrically orientated longitudinal slots 14 on opposite sides thereof. The slots 14 extend from the second valve plate 12 to beyond the central horizontal plane of the links 7 and 8.A shaft 16, coaxial with and slideably mounted in stem 25 extends trom the second valve 35 through the annular boss 9, the annular flange 13, the split coned sleeve 5 and the tapered nose 1 8 beyond the frame. The shaft 1 6 has a rectangular recess 1 7 on that part of the shaft which is above the flange 1 3 and the recess is fractionally greater in length than the thickness of the split coned sleeve 5. The collet 5 closes around this recess 1 7 and grips the shaft when the split coned sleeve 5 is fitted into the tapered nose 1 8. The rectangular recess 1 7 has radial edges 39 against which the base of sleeve 5 abuts when the collet grips the shaft.The radial edges 39 of the recess are cut deep enough into the shaft to enable these edges, which support the collet and the collet in turn supports the frame 23, to support the entire device and allow the device to be suspended by the shaft in this closed position of the collet. A transversely oriented cross pin 1 5 is provided near the valve end of the shaft 16. The cross pin 15 slots into and projects out of the opposing longitudinal slots 14 on stem 25 and restricts the movement of the shaft within the stem 25 and/or tube 10 to the length of the slots 14.An eyelet 1 9 is provided on the shaft 1 6 at its other end projecting out of the frame 23 through the tapered nose 1 8. The eyelet 1 9 enables the shaft to be suspended by a length of cord or cable (not shown).

The operation and use of this device can be described in four stages.

(a) Preparation and Loading of Trigger A long load carrying cable (not shown) is connected to the eyelet 1 9. The shaft 1 6 is then forced downwards to open both valves 38 and 35 fully and to load the trigger. The loading of the trigger is achieved by abutment of the cross pin 1 5 against the lower end ofthe slots 14 which in turn forces the inner tube 10 down along with its integral flange 13 and consequently the boss 9 on which links 7 and 8 are pivoted. The force applied on the shaft 1 6 is therefore transmitted to the boss 9 forcing the links 7 and 8 below their central horizontal plane. The links are prevented from collapsing completely in the other direction by a prior adjustment of the stop screw 36 against which the lower end of the boss abuts.In this position the trigger is loaded. The shaft 1 6 is then raised until the rectangular recess 1 7 is level with the base of the split sleeve 5.

The sprung segments of the sleeve 5 are then forced together and the sleeve 5, gripping the shaft at its recess 17, fitted into the tapered nose 1 8. Tension is applied to the cable as a result of which the axial edges 39 of the recess 17 are in abutment with the base of the sleeve 5. The device is now ready to be suspended by the cable and to be lowered into a tank containing the liquid to be sampled (Fig. 1).

(b) Lowering of Device and Sampling As the device is lowered into the tank by means of the cable and the bottom of the tank is approached, the first valve 38 is pushed up into the tube but only partially because as soon as the bottom edge 34 of the collar comes into contact with the bottom of the tank, the base of valve plate 11 is also horizontally aligned with the bottom edges of the collar 2 and rests on the bottom of the tank under gravity. In this position both valves 38 and 35 are still open and the perforations 3 on the collar 2 allow free passage of liquid into and out of the tube 1. The device is allowed to stand in this position for a short while to ensure that equilibrium is attained and that any disturbance of the interface during the lowering of the device into the liquid has substantially been nullified.Therefore, the sample within the tube 1 is substantially representative of the bulk of the liquid surrounding the device. As soon as the device has come to rest at the bottom of the tank the tension on the cable may be released by slackening the cable and this in turn will release the grip of the coilet on the shaft 1 6 allowing the split coned sleeve 5 to drop clear of the tapered nose 1 8 and the shaft 1 6 drops to a point at which the cross pin 1 5 comes to rest at the base of slot 14. This stage is shown in Figure 2.

(c) Unloading the Trigger and Valve Closure When equilibrium is reached, the tension in the cable is reapplied, the shaft 1 6 moves upwards taking the cross pin 1 5 with it until the latter abuts against the boss 9. Application of a further pulling force upwards on the shaft 1 6 will cause the boss 9 to move the links 7 and 8 past the central horizontal plane thereof and when this position is reached the tensioned spring 33 takes over and causes the links to collapse rapidly snapping shut both the valves 38 and 35. The sample is now securely locked in the space between the two valves in tube 1. The device containing the sample can now be retrieved from the tank by means of the cable.

(d) Decanting, Measurement and Analysis When the device has been retrieved, its outside surface is cleaned of any adherent liquid from the bulk of the tank. The contents of the device are then transferred carefully into a transparent measuring vessel (not shown) by opening the valves which can be done by simply forcing the shaft 1 6 downwards as explained in stage (a) above. The sample transferred into the measuring vessel is allowed to settle for a few minutes and the depth of water is thereafter noted from the graduations on the measuring vessel. If necessary, a conversion factor may be applied to the reading to account for any difference in the diameter of the measuring vessel and the device. The water may also be further analysed for its composition which may be important in some cases because the water associated, for example, with a particular crude oil is characteristic of the source of the crude oil.

Claims (10)

1. A liquid core sampling device which comprises: A) an outer tube provided with: (a) a first valve seat spaced from one end thereof by means of a hollow perforated collar, (b) means at the opposite end thereof for suspending the tube, (c) a second valve seat located between the first valve seat and the suspending means, (d) an internal over-centred trigger located between the second valve seat and the suspending means, and (e) openings on the walls of the tube between the second valve seat and the trigger to allow egress of fluid from the outer tube; B) an elongated inner member axially oriented with respect to and slideably mounted within the tube and extending from the first valve seat to beyond the trigger, said member being provided with:: (a) a first valve at the collar end thereof capable of sealing engagement with the first valve seat and having an outer diameter substantially less than the inner diameter of the collar, and (b) a second valve capable of sealing engagement with the second valve seat, said member being responsive to the trigger such that loading the trigger opens the valves allowing free ingress of liquid into the tube and unloading the trigger closes the valves trapping the sample in the space between the two valves; and C) means for loading and unloading the trigger.

2. A liquid core sampling device which comprises: A. an outer tube provided with: (a) a first valve seat spaced from one end thereof by means of a hollow perforated collar, (b) a collet at the opposite end thereof, (c) a second valve seat located between the first valve seat and the collet, (d) an internal ovel centred trigger comprising a boss located between the second valve seat and the collet, and (e) openings on the wails of the tube between the second valve seat and the trigger to allow egress of fluid from the tube;; B. an inner member provided with (a) a first valve at the collar end thereof capable of sealing engagement with the first valve seat and having an outer diameter substantially less than the inner diameter of the collar, (b) a second valve capable of sealing engagement with the second valve seat, (c) a flange at the trigger end thereof situated above and adapted to rest on the boss of the over centred trigger, and (d) a longitudinal slot extending from above the second valve to beyond the boss and adapted to receive and allow longitudinal movement of a pin therethrough, said inner member extending from the first valve to beyond the trigger; and C. a suspended shaft capable of longitudinal movement through the collet in its open position, the boss and the inner member, said shaft being provided with (a) a rectangular recess at which the collet closes around the shaft to form an integral unit therewith enabling the device to be suspended by the shaft, and (b) an integral transversely oriented pin which projects through the slot to restrict the movement of the shaft within the inner member to the length of the slot, such that when the pin abuts against the valve end of the slot it enables the trigger to be loaded under applied force thereby opening the valves and allowing ingress of the sample into the outer tube, and when the pin abuts against the boss it enable the trigger to be unloaded, thereby snapping shut the first and second valves against the respective valve seats to form a liquid-tight chamber for retaining the sample.

3. A liquid core sampling device according to claim 1 or2 wherein the over-centred trigger comprises two sets of lever mechanisms pivotally connected to the opposite side of a central annular boss thereby enabling the two lever mechanisms to act in parallel, each lever mechanism consisting of: (a) two opposing slotted cross-heads spaced from each other, (b) two links, and (c) a spring, one end of each link being slideably mounted into the respective slot of each cross-head, said ends also being mutually connected by the spring under tension, and the free ends of the links being pivoted to the same point on one side of the boss such that in the absence of applied force on the boss the tensioned spring urges together the slideably mounted ends of each set of the links, moving the pivoted ends and the central boss away from an imaginary central plane of the opposing set of cross-heads thus causing the links in each set to collapse.

4. A liquid core sampling device according to any one of the preceding claims wherein the extent of vertical movement of the boss in the direction of the perforated collar is controlled by a stopping means.

5. A liquid sampling device according to claim 2 wherein the collet comprises a split-coned sleeve capable of holding the shaft at its rectangular recess and is adapted to fit into a correspondingly tapered nose formed on the outer tube.

6. A liquid sampling device according to claim 5 wherein the split-coned sleeve comprises a plurality of sprung segments, the springs being biased to allow the tapered end of the cone to expand with respect to its base.

7. A liquid sampling device according to any one of the preceding claims wherein the outer diameter of the first valve plate is substantially smaller than the inner diameter of the perforated collar so that when the device rests on its collar, the first valve remains open and is capable of allowing free flow of liquid in and out of the device across the perforations.

8. A liquid sampling device according to any one of the preceding claims wherein the second valve plate is supported by a compression spring so as to enable the second valve to close fractionally before the first valve upon unloading the trigger.

9. A liquid sampling device according to any one of the preceding claims wherein the inner member is retained in a substantially coaxial position with respect to the outer tube by means of centralising radial lugs provided on the latter.

10. A liquid sampling device according to any one of the preceding claims wherein the outer tube is of a corrosion resistant material.