GB2175281A

GB2175281A - Liquid sampling device

Info

Publication number: GB2175281A
Application number: GB08611820A
Authority: GB
Inventors: Marshall Robert Davis; Gordon John Smith
Original assignee: BP PLC
Current assignee: BP PLC
Priority date: 1985-05-18
Filing date: 1986-05-15
Publication date: 1986-11-26
Also published as: GB2175281B; GB8512628D0; GB8611820D0

Abstract

A sampler 1 for sampling liquid composition over a given depth has a variable sample receiving volume which can be filled at a rate relative to the quantity of liquid through which the sampler has passed. The variable volume may be obtained using a piston 5 which is withdrawn as the sampler is lowered through the liquid. Suspension means 11 rotates gears 13, 14 and shaft 12, which via clutch 16 rotates shaft 18 and gears 19, 20, to raise piston 5, the clutch being spring loaded at 22 to be engaged only when float 2 is in a liquid; otherwise the weight of float 2 disengages the clutch. As the sampler 1 is lowered, liquid enters at 3 via non-return valve 4 as piston 5 is raised. <IMAGE>

Description

SPECIFICATION Liquid sampling device The present invention relates to an apparatus for taking liquid samples.

When taking samples of liquids from storage vessels it is often desirable to have a sample which is representative of the liquid contents over a given depth in the vessel, rather than just representing the composition at one given point in the vessel.

Apparatus at present in use for this purpose is not satisfactory. The existing apparatus does not take a sample which is truly representative of the liquid over the full depth of sampling as the quantity of liquid taken at different depths is not constant. The sampling rate at any particular depth depends on hydrostatic head and may be affected by the rate of lowering/raising of the device itself.

According to the present invention a sampler for sampling the composition of a liquid over a given depth comprises, (a) a sample container having an inlet at one end, (b) means for varying the sample receiving volume of the sample container, (c) means for causing liquid to enter the sample container at a rate which is related to the quantity of liquid through which the sampler has moved vertically while collecting the sample, (d) means for lowering the sampling container into the liquid and removing it therefrom, (e) means for retaining liquid in the sample container when the required quantity of sample has been obtained.

In a parallel sided container the quantity of liquid through which the sampler passes will be proportional to the vertical distance through which the sampler moves. In a preferred embodiment the sample is collected in a single pass from the top to the bottom of the liquid to be sampled. Alternatively the sampler can be designed so that sample can be collected by lowering the sampler to the bottom of the liquid to be sampled and collecting sample while raising the device. It is possible to envisage taking a single sample by repeated passes through the depth of liquid to be sampled, although this will increase sampling time.

In a preferred embodiment the sample container has a non-return valve to allow liquid to enter, but not leave the container, through the inlet.

The sample receiving volume may be varied by providing a piston within the sample container movable so as to define a variable sample receiving volume between the inlet and the piston. The means for causing liquid to enter the sample container at a rate which is related to the rate at which the sample container moves vertically through the liquid may be a piston withdrawing means for withdrawing the piston within the sample container as the sample container moves through the liquid.

The piston withdrawing means is preferably actuated by movement of the sample container relative to a support means fixed at one of its ends to a reference datum, e.g. the top of a tank containing the liquid.

The means for lowering the apparatus is conveniently a flexible elongated support means which is connected at one end to the apparatus and which is held at the other end above the surface of the liquid, for example by the person desiring to take a sample. In a preferred embodiment the elongated support means is fixed at one end above the surface of the liquid, passes round a rotatable member, and is held at the other end by the person taking the sample. Lowering the apparatus causes rotation of the rotatable member in one direction. Raising the apparatus causes the rotatable member (eg drum or pulley wheel) to rotate in the other direction. The flexible support means is preferably provided with shaped portions for engaging with corresponding shaped portions on the rotatable member.Thus the flexible connector may consist of links as in a sprocket chain engaging with teeth on the rotatable member. Alternatively the flexible support means may be provided with projections which engage with depressions on the rotatable member e.g. a ball-chain may be used.

The rotation of the rotatable member mentioned above is used to cause liquid to enter the sample container eg by causing withdrawal of the piston when the piston is used to produce a variable sample volume.

Where a piston is used, the means for withdrawing the piston is preferably a rod attached to the piston, which rod is driven by the rotation of a member, e.g. the drum mentioned above, connected to the means for lowering the apparatus.

In the preferred embodiment a locking means prevents the piston withdrawing means from operating except when the apparatus is moving downwardly through the liquid. The locking means may comprise a float connected to the piston withdrawing means to prevent operation of the piston withdrawing means while the float is not in contact with the liquid. The locking means may further comprise a unidirectional clutch, in which the clutch members are resiliently urged into engagement, but are held out of engagement while the apparatus is not in the liquid, by the weight of the float. The clutch may be a ratchet device which operates only when the rotatable member (eg drum or pulley wheel) mentioned above rotates in the direction corresponding to the lowering of the apparatus.The locking means may be arranged so as to release the piston withdrawing means as soon as the sample container enters the liquid.

Preferably, the piston withdrawing means operates to withdraw the piston as the sample container descends through the liquid. It will be frequently necessary to take a sample from a vessel with parallel vertical sides. In order to obtain a sample which is representative of the contents over the full depth of sampling it will be necessary to arrange for the piston to be withdrawn by an amount which is proportional to the distance which the sample container descends through the liquid.

The apparatus of the present invention makes it possible to obtain a representative sample of the liquid in a parallel sided tank. It also enables liquid sample to be obtained without contacting the sample with air so preventing volatile component loss during the acquisition of the sample. It is possible using apparatus made in accordance with the invention to transfer the sample from the sample container directed to analytical apparatus by displacement. This reduces the possibilities of loss of light end (low boiling point) materials from the sample.

A specific embodiment of the invention will now be described with reference to the drawing, which shows a side view of the apparatus, partly in section, with the central portion of the sample container cut away.

The device is used in a vertical position as shown nd references to top and bottom are in relation to the normal orientation of the device in use.

The apparatus comprises a sample container (1).

A float (2) is attached to the lower end of the container so as to move freely up and down relative to the sample container. It will be realised that for a maximum accuracy in sampling the depth of the float should be as small as possible, so that the locking means, described in more detail below, is not disengaged prematurely before the sample inlet has entered the liquid, and to minimise the length of the sample inlet tube. A sample inlet tube (3) projects downwardly through an opening in the float, and is provided with a non-return valve (4) which allows fluid to enter, but not leave, the sam ple container through the inlet. Within the sample container (1 ) is a piston (5) which defines a sample receiving volume between the piston and the inlet.

The piston (5) is attached to a piston rod (6) which extends within the sample container on the side remote from the inlet. The piston rod passes through a closure member (7) which is detachably mounted on the sample container by means of a bayonet fitting. The closure member carries an upwardly extending rod (8) which carries a guide member (9), which supports the piston rod. At the end of rod (8) a drum (10) is rotatably mounted.

This has semi-circular depressions (not visible).

These depressions are adapted to receive the bails attached to a ball-chain (11) which passes round the drum. One end of the ball chain is fixed to a reference on datum eg the top of the tank, the other end is held by the person operating the sampler. The ball chain is used to lower the apparatus into liquid in use. The rotatable drum (10) drives a drive rod (12) through bevelled friction drives (13) and (14).

Drive rod (12) is connected to a first part (15) of a clutch (16). The other part (17) of the clutch is connected to a secondary drive rod (18) which drives piston rod (6), which has a threaded portion, through cogs (19), (20). Clutch part (17) is mounted on a pivoted arm (21) which is biassed so as to move clutch part (17) into engagement with clutch part (16) by spring (22). The tension of spring (22) can be adjusted by nut (23).

A chain (24) connects the float and arm (21), so that when the float hangs freely, clutch part (17) is held out of engagement with clutch member (15).

The clutch (16) is so designed that only rotation in one direction (corresponding to that produced by the lowering of the apparatus) is transmitted from drive rod (12) to secondary drive rod (18).

In use the piston is moved downwardly in relation to the closure member so that it is adjacent to the inlet of the sample container. The ball chain is passed round the drum. The device is then lowered by letting out the chain. While the device is hanging freely in air the float will also hang freely and the clutch will be inoperative. The piston therefore does not move and no fluid (air) enters the sample container. When the float reaches the liquid surface the clutch engages. The device continues to descend through the liquid. The amount by which the piston is withdrawn is directly proportional to the distance covered by the apparatus through the liquid, so that a representative sample is obtained.

When the desired depth has been reached, which is determined by the amount of chain wound over the drum, the apparatus is then raised by means of the chain. However as the rotation of the drum is now in the opposite direction the clutch mechanism ensures that no further movement of the piston takes place. The closure member may then be removed, together with the piston and the container and contents transported to the laboratory for analysis.

Claims

1. The sampler for sampling the composition of the liquid over a given depth which comprises, (a) a sample container having an inlet at one end, (b) means for varying a sample receiving volume of the sample container, (c) means for causing liquid to enter the sample container at a rate which is related to the quantity of liquid through which the sampler has moved vertically while collecting the sample, (d) means for lowering the sampling container into the liquid and removing it therefrom, (e) means for retaining liquid in the sample container when the required quantity of sample has been obtained.

2. The sampler according to claim 1 wherein the means for causing the liquid to enter the sample container acts so as to cause liquid to enter the sample container at a rate which is related to the rate at which the sample container descends through the liquid.

3. The sample according to either one of claims 1 or 2 wherein the means for retaining liquid in the sample container is a non-return valve in the inlet to the sample container.

4. The sampler according to any one of the preceding claims wherein the sample receiving volume is varied by a piston within the sample container.

5. The sampler according to claim 4 wherein the means for causing the liquid to enter the sample container at a rate relative to the rate at which the sample container moves vertically through the liquid is a piston withdrawing means adapted to be actuated by movement of the sample container relative to a support means fixed at one end in relation to the liquid to be sampled.

6. The sampler according to claim 5 wherein the piston withdrawing means is adapted to be actuated by movement relative to a flexible support means with one end fixed to a reference datum and one free end such that the sample container can be lowered and raised by raising or lowering the support means at the free end.

7. The sampler according to claim 6 wherein the piston withdrawing means comprises a rotatable member adapted to be rotated by the movement of the flexible support means.

8. The sampler according to any one of the preceding claims wherein a locking means prevents the piston withdrawing means from operating except when the apparatus is moving vertically through the liquid.

9. The sampler according to claim 7 wherein the locking means comprises a float connected to the piston withdrawing means to prevent operation of the piston withdrawing means while the float is not in contact with the liquid.

10. The process of taking a liquid sample which comprises moving a sample container having a variable sample receiving volume through the liquid vertically over a given sampling path while increasing the sample receiving volume at a rate dependent on the distance the sample container moves vertically through the liquid, and then withdrawing a sample container containing the volume of liquid in the sample receiving volume at the end of the sampling path of the sample container through the liquid.

11. The process according to claim 10 wherein the sample is taken while the sample container while the sampler is descending through the liquid.