GB2173910A - Apparatus for indicating and/or measuring extremely small amounts of flowing media - Google Patents

Abstract

Flow is indicated by movement of a droplet (8) of liquid in a capillary tube 3 which is at an angle of inclination alpha to the horizontal such that the component of the gravitational force acting along the axis of the tube just balances the capillary forces and/or surface tension effects exerted on the droplet. This reduces measurement time and increases accuracy. The tube may be rotated to form the droplet from liquid in the top header and then back to the angle alpha . The apparatus may be manually operable and constructed as a hand gun or it may be an automated measuring instrument associated with a production line of pressure vessels, e.g. a gas flask filling or refilling line where it is used to detect leaks. <IMAGE>

Description

SPECIFICATION Apparatus for indicating and/or measuring extremely small amounts of flowing media The invention concerns apparatus suitable for the rapid indication of flow or leakage of extremely small flow quantities of media such as liquids, gases or vapours, and for the relatively rapid measurement of such quantities of flowing media as well as for the monitoring of the fluid tightness of closures of obturating fittings, e.g. valves on gas bottles.

It is a frequent technological task in relation to very small quantities of fluids passing through predetermined elements of a given apparatus or plant to establish whether in fact a flow of a liquid, a gas or a vapour is present or absent, or to measure the rate of flow or to measure the volume of the flowing medium. The solution of such tasks in practice is derived from the same technical measures.

Thus for instance the presence or absence of flow to monitor fluid-tightness or leakage essentially is effected by measuring the amount of the flowing medium in much the same way as the direct quantitative flow measurement except that perhaps the concept of measurement has to be supplemented or expanded to include the anticipated possibility that the measured magnitude may be zero.

However, the presence of flow may in given cases also be effected by a measurement of pressure or change of pressure, and a change of pressure may also be measured by indicating the presence of material flow by measuring the required make-up or top-up from a reference space. Thus these tasks are based on common fundamental operations.

At the same time, evidently the measurement of flow rate, the measurement of the volume of flow per unit time as well as the measurement of the total quantity discharged are all really the same task, distinguished from each other only by the manner in which account is taken of time. It follows that the determination of a presence or absence of flow for testing for leakage or for fluid-tightness depends on the time of measurement and the time requirement for accurate measurement is highly significant.

When it is desired to sense or measure the flow of relatively small quanta, numerous possibilities are available for performing the task but most usually measuring instruments employing an indicator fluid are employed. Here mostly the measurement takes place by causing a second liquid or gas to occupy the position of a first liquid or gas which is to be measured, the two media being immiscible, and by observing the boundary surface between the two media the possibility of measurement or reading is afforded, and when the measurement liquid is electrically conductive, e.g. mercury, then by employing electrodes that can be bridged over by the liquid an electric indication pulse is obtained, which pulse or signal can then be processed.

In the interests of decreasing the number of variable parameters the pressure of the indicating medium is assured mostly by providing a fixed level, whereby to stabilise the hydrostatic pressure of the medium. Where the medium to be measured is a gas or a vapour, then there is another parameter the variations of which must be eliminated at all-times, namely the change in temperature during the time of measurement. Although the physical laws giving the relationship of the pressure and volume of gases and vapours with changing time are known, nevertheless in the interests of accuracy and simplicity of measurement it is more expedient to eliminate the circumstances rather than having to take them into account in evaluating the measurement.

When the amount of the medium to be sensed or measured is small, the accuracy of the measurement is sought to be increased by narrowing the effective flow cross-section e.g.

by the use of nozzles or venturis as well as by the use of capillary tubes.

One widely used technical solution is the so-called "minimeter" instrument utilising distilled water into pressure which is hydrostati caliy stabilised and the level of which is readily controllable. The flow of the water as the measurement liquid can be triggered by displacing the stabilising vessel via a micrometer screw and this displacement can be read off a scale associated with a micrometric screw.

Another known instrument is the "miniscope" wherein liquid passes from a larger diameter vessel into a capillary disposed adjacent a scale and the position of the liquid in the capillary can be read off at scale.

Another method is the so-called "foam film burette" system wherein the flow is detected by examining the position of a bubble formed from a soap solution.

Another known instrument is the "audiometer" in which mercury at a hydrostatically stabilised pressure is caused to flow through a measurement nozzle between electrodes or terminals of a circuit so that the mercury "makes" the circuits and the time difference between the electric signals obtained in this way is functionally related to the quantity of flowing medium passing through the system.

Hungarian Patent Specification No. 171 149 describes apparatus in which a measurement liquid at a hydrostatically stabilised pressure forms a boundary surface in a capillary tube with the liquid under test and the displacement of the boundary surface is used for detection and sensing.

Hungarian Patent Specification No. 179 263 describes apparatus especially adapted for leakage monitoring with a specially closed pressure space in which the changes in pressure are detected.

Hungarian Patent Specification No. 179 432 describes apparatus based on the measurement of differential pressures in which the effect of changes in temperature under measurement are utilised in a reference space disposed within the measurement (test) space.

All these solutions exploit the advantages of narrowing the flow cross-section in a capillary but they fail completely to take into account phenomena taking place between the capillary tube and the liquids, which phenomena are known well and in detail from scientific knowledge in hydraulics and which phenomena have a disturbing effect on the measurement.

It should be mentioned that the so-called "inclined-tube manometer" in all its variants increases the accuracy of read-off in the capillary tube by conducting the liquid not vertically but rather on an inclined path. In this way the read-off length is increased but of course the above-mentioned disturbing capillary phenomena are not changed.

Thus in all these devices there are forces arising between the wall of the capillary tube and the liquids (in the case of gases or vapours, the indicator liquid), irrespective of whether the indicator liquid wets the wall of the tube, e.g. water or alcohol, or does not wet it, e.g. mercury. These (polar) forces are additional to the surface tension forces of the liquid as well as the so-called capillary forces due to the diameter of the capillary tube; the mathematical sign, plus or minus, of these forces varies according to whether the indicator liquid wets the tube wall or not. These forces can be computed on the basis of already elaborated detailed and known interrelationships.

Since the currently known measurement devices do not take these forces into account, when such forces are neglected then the accuracy of measurement is reduced or the time required for performing the measurement is significantly increased. A similar problem arises in the case of monitoring the various industrial and domestic gas bottles for leakage and tightness.

All the industrial and domestic gases such as propane and butane as well as numerous other gaseous media, such as gases and va pours, are marketed in pressure-resistant ves sels such as bottles, accumulators or batteries mounted on vehicles and purpose-built containers and in many cases there are firms or companies, the so-called charging plants, where these bottles or containers are refilled.

From time to time such vessels may also be tested or examined by authorities during which time not only the condition of the vessels and their fittings but also the tightness of the cou pling between the vessel and its fitting are examined. The safety of marketing gases between two such tests largely depends on whether the shut-off mechanism of the pres sure vessel works satisfactorily, i.e. that the seal performing closure is in a good condition and mainly that immediately after refilling the closure effected is of a sufficiently high tightness. Whether the refilling takes place in a manually or automatically operated filling machine or machine line, the monitoring of the safe closure of refilled flasks before despatch is an indispensable operation.

This control or monitoring is currently mainly performed manually by utilising some medium which forms bubbles or automatically by pressing a sealed bell on the vessel and monitoring the change in pressure in the internal space of the bell.

Monitoring by using bubble-forming media represents significant manual labour and moreover the result greatly depends on the subjective judgment and degree of care and attention of the operator and thus the results are not completely reliable.

On the other hand, the accuracy of the measurement of pressure inside a bell fastened to the vessel is satisfactory only if the measurement takes place over a suitably long time.

This is because a volume of the bell is relatively large: it has to be large to be able to cover e.g. in the case of a gas flask the whole closure fitting together with the handling device. Thus in the case of leakage of small quantities of media the pressure in the bell increases only very slowly.

If in the interests of accurate measurement a significant length of time is assured for the monitoring operation, then the control/check station becomes a choke point in the refill procedure. On the other hand, if the measurement time is short, then leakages are adjudged to be fluid-tight which in fact after storage of one or two weeks can completely empty a pressure vessel and permit the contents to pass into the ambient atmosphere.

With explosive gases this represents a serious risk while in the case of gases or gas mixtures of high purity used for callibration normally used up at a very slow rate, such leakages represent a significant cost or damage factor.

An aim of the present invention is to provide apparatus in which the forces arising in a capillary between the liquids or indicator liquids are compensated during measurement without having to utilise a complicated process or apparatus for computing these forces or for approximating them by some other theoretical manner, wherein this compensation can be achieved very rapidly in every case even when changing the media, wherein the friction arising from the movement of the indi cator liquid is minimised and wherein at the same time the same indicator liquid may be used for a series of measurements.

The invention seeks to achieve a reduction to a fraction of its current value the effect exerted by the displacement of the indicator liquid on the measurement result without forc ing a technical solution to the utilisation of a specific given liquid or liquids; the invention furthermore seeks to increase the measurement accuracy or to maintain the accuracy but significantly reduce the measurement time.

A further aim of the present invention is to provide apparatus with the aid of which the closure fitting employed on the pressure vessel may be checked with appropriate reliability as regards fluid-tightness at a rate which matches the rate of feed or advance of the flasks on a filling line of an automatic filling plant. In this case, naturally the checking itself is also fully automated and a check or test with a negative result produces an error signal which can be used for actuating appropriate intervening devices e.g. for rejecting or marking leaking flasks etcetera while in the case of manual checking the detection of the result of the check requires only a minimal amount of care and attention, the error signal is conspicuous; and in both cases the coupling to the testpiece is fluid-tight, simple and reliable while the handling of the instrument requires no special skill.

One of the discoveries or recognitions forming a basis for the invention is that instead of passing a continuous column of measuring/indicator liquid from the main mass of liquid into the capillary, a well- defined and bounded droplet is to be fed into the capillary as an "indicator droplet" because this indicator droplet or bubble cannot burst in contrast to the soap bubble of the so-called "foam film bu rette", but rather remains at disposal in every case until the measurement is terminated. In addition, because of its finite length, the bubble or droplet reduces the effective length of the section where boundary forces between the tube wall and a liquid may arise, and the forces which do arise at the boundary surfaces at opposite ends of the droplet have the opposite mathematical sign and therefore they cancel each other out.

Another discovery or recognition is that it is advantageous to dispose the measurement capillary at an angle a to the horizontal to slope in the direction of medium flow, and by varying the angle a a position is located in which the component of gravitational acceleration g sin a acting in the direction of flow exactly balances the forces tending to prevent a displacement of the measurement droplet/bubble, thus eliminating the negative influences on the accuracy of measurement.

Of course, both of these recognitions may only lead to an industrially utilisable apparatus if the formation of the measurement bubble, the compensation of the forces, the direction of the location and position of the measurement liquid are all relatively simply achievable in order thus to afford the possibility of performing the measurements rapidly and continuously.

Naturally, apparatus according to the invention should also assure the possibility of utilising an electrically conductive measurement liquid so that by suitably locating electrodes along the flowpath electric signals proportional to the measurement result should be obtainable in the interest of automation of the measurement process, or more accurately in the interest of automatic processing of the measurement data.

On the basis of the foregoing, the task sought to be achieved by the invention has been solved by providing a measurement head coupled to a capillary tube by means of an inlet pipe and forming a measurement droplet/bubble from the measurement liquid in the head, and the forces arising between the wall of the capillary tube are compensated by a component of the gravitational force acting on the droplet which component extends in the direction of the axis of the capillary, which axis is adjustable as regards its angle of inclination or slope in the direction of the discharge end of the capillary.

According to a preferred feature of the invention it is expedient to form a respective measuring head at the ends of the capillary with each head being spherical or cylindrical or part -cylindrical but terminating in a conical part.

Expediently, the inlet pipe is formed with an aperture pointing downwards at 90 while the outlet pipe is formed with an aperture pointing upwardly at 90 .

According to a further preferred feature of the invention, the capillary tube is fixed to a measurement plate which in turn is fixed to a base plate for rotation about a predetermined axis of rotation, and there are two adjustable abutments on the base plate for determining the angle of inclination of the measurement plate, and wherein preferably the axis of rotation is defined by a threaded screw or shaft provided with a longitudinal bore coupled to transverse bores, on the said screw or bolt there being an instrument inlet provided with couplings with internal cavities or spaces and an inlet pipe as well as a closure stopper for closing the longitudinal bore.

In a particular embodiment of the apparatus according to the invention, advantageously there is provided a working cylinder secured to a stable surface for reciprocating the base plate, a further working cylinder mounted on the base plate for rotating the measuring plate upwardly, another working cylinder for angularly displacing the measuring plate in a downward direction, yet another working cylinder mounted on the base plate and provided with a fixing device secured on an arm, a resilient seal bearing against the coupling pipe of the pressure vessel which seal is provided with a bore and is expediently hemispherical, and a per se known sensing device for sensing a change in the position or attitude of the measurement liquid.

In a practical embodiment of the invention it is advantageous to utilise a measurement "gun" for use in checking the fluid tightness of shut-off fittings on pressure vessels, especially gas flasks, which gun has at its end a flexible internally bored seal as well as an internal capillary measuring tube disposed beneath a transparent window and is inclined rearwardly above a measurement scale and is provided at its two ends with a respective measurement head, a measuring liquid in the first measuring head the air space of which is connected by respective coupling tubes with the bore of the seal and an aperture on the "butt" of the gun while its other, rear measuring head is fitted with a coupling tube for connection to an aperture at the rear end of the device.

Preferably, there is provided for the above gun a supporting ring for mechanically supporting the seal of the gun and there is furthermore provided a coupling line for connecting the bore of the seal via a shut-off device to a pipe open to the atmosphere.

Finally, it is advantageous in a preferred embodiment of the "gun" to provide a bubble glass with a stuffing-box.

Preferred embodiments of apparatus according to the invention are diagrammatically illustrated purely by way of example in the accompanying drawings wherein: Figure 1 is a diagrammatic cross-section of the measuring apparatus in its rest position, Figure 2 is a diagrammatic view of the measurement apparatus in its measuring position, Figures 3a and 3b illustrate vectorially the change in the component of the gravitational force along the axis of a capillary tube, forming part of the apparatus according to Figures 1 and 2, at two different angles of inclination of that tube, Figure 4 is a diagrammatic view of a measurement system according to the invention in one preferred embodiment, Figure 5 is an enlarged cross-sectional view of the apparatus shown in Figure 4 to illustrate a possible construction of a rotary shaft and associated parts, Figure 6 is a section taken on the plane indicated by the lines 6-6 in Figure 5, Figure 7 illustrates the different relative positions of parts of the apparatus shown in Figure 4 as the angle of inclination a of the capillary tube changes, and more particularly Figure 7a shows the measurement system in its rest position, Figure 7b shows the measurement system in its measurement position, Figure 7c shows the measurement system in its bubble or droplet formation position, and Figure 7d shows the measuring system in its position in which the measurement liquid is returned to its starting position to ensure continuity of measurements, Figure 8 shows an automated version of apparatus according to the invention, the full apparatus being shown diagrammatically in Figure 8a and certain parts thereof only in various displaced positions in Figures 8b, 8c and 8d, Figure 9 is a diagram of the apparatus in Figure 8 in its position in which the operation required for performing continuous measurements is effected, and finally Figure 10 illustrates a further preferred embodiment of a manually operated apparatus, in diagrammatic form.

In the measuring apparatus illustrated in Figure 1 an inlet pipe 4 leads into a measuring head 1, the inlet pipe having an outlet aperture directed vertically downwardly, as seen.

The measuring head 1 is expediently spherical but it could be cylindrical with a horizontal axis or cylindrical terminating in a conical part.

The measuring head 1 is connected to another, like measuring head 2 by way of a capillary tube 3. An outlet pipe 5 projects into the interior of the measuring head 2 and has an outlet aperture facing vertically upwardly as seen. These constructional elements may be formed by known glass-making technology using seals or welds 6 but may also be formed from transparent plastics substances connected together by adhesives, or by a combination of glass and plastics elements. A measuring liquid 7 is disposed in the measuring head 1 and a measurement bubble or droplet 8 may be formed from the liquid.

In Figure 2 the measuring apparatus of Figure 1 is shown at an inclination of angle a to the horizontal, with the capillary tube 3 sloping downwardly in the direction of the measuring head 2. In this way a component 10 of the acceleration due to gravitation 9 is formed along the direction of the axis of the capillary.

This component 10 tends to drive or force the droplet/bubble 8 into the measuring head 2.

As may be seen in Figures 3a and 3b the axial force component 10 increases with increasing value of the angle a because the force p = g sin a.

The measurement system shown in Figure 4 is carried on a base plate 12. A measurement plate 13 is relatively rotatably fixed on the base plate and carries the measuring apparatus itself. Next to the capillary 3 of the measurement system and parallel therewith a measurement scale 18 is disposed. The inlet pipe 4 of the measurement apparatus is connected to an inlet 15 of the instrument in a gas-tight but bendable manner. The position of the measurement plate 13 on the base plate 12 is limited by abutments 16 and 17 on angular displacement in a clockwise direction. The abutments are formed so that their height is adjustable although this is not shown in the drawing. However, the measuring plate 13 may also be displaced past the abutments by forming them in a depressible manner or by some other known way to enable this to happen.

Figure 5 shows one possible embodiment for forming the axis or shaft of rotation 14.

The base plate 12 and the measurement plate 13 are held together by a screw shaft 14' having a head disposed in a counter- sunk bore in the base plate 12. The inlet 15 to the instrument has a bore capable of accommodating the shaft screw 14', and terminates in a coupling head 19 having a hollow interior 20.

The inlet pipe 4 terminates in a coupling head 22 essentially analogous with the head 19. The two heads are placed on the shaft screw 14' by placing gaskets or seals 21, 23 between the heads and between the head 22 and a screw nut 24. If required, a further seal, not shown, may be placed between the measuring plate 13 and the coupling head 19. The seals and elements are clamped together by means of the screw nut 24 which is then fixed in any desired known manner, e.g. by a second nut or a spring shim etcetera. The screw shaft has an internal blind bore 25 which extends through both the heads 19, 22 and aligned with the respective interiors of the heads, the blind bore 25 has transverse bores 26 in order for the bore 25 to be able to communicate with the interior 20 of the coupling head 19 as well as the interior of the coupling head 22.Thereafter, the bore 25 is blocked off by a stopper member 27.

An amount of measuring liquid 7 is then passed into the measuring head 1, the amount being just sufficient for the level of the liquid not to reach a capillary tube 3 when the measurement plate 13 is turned in a clockwise direction, as illustrated in the drawing, until the abutment 16 is attained, but when the measuring plate 13 is rotated further to the abutment 17, then the liquid can pass into the capillary tube 3.

When using a measuring system formed in this way, it is connected in the flow path of the flowing medium between the inlet 15 of the instrument and the outlet pipe 5 such that the direction of flow is from the left to the right, as seen in Figure 4. Should the instrument be used for testing for leakage it is unnecessary to connect the outlet pipe 5 which can then be connected to the ambient atmosphere.

The measuring plate 13 is then angularly displaced by an angle a2 (Figure 7c) until it is engaged by the abutment 1 7. In this position the measuring liquid 7 forms a measurement bubble 8 in the capillary tube 3. Before performing the first measurement two or three measurement bubbles or droplets are driven through the capillary 3 with the aid of a little gas or air being blown in, whereupon the liquid will be in the measuring head 2. Thereafter the measuring plate 13 is first brought to its horizontal position then angularly displaced by the mentioned angle a2 so that the measurement plate 13 contacts the abutment 16.

Then, by means of an adjusting mechanism for the abutment which is not shown in the drawing but which may be a micrometer abutment screw, the position of the measurement droplet 8 is adjusted such that the component g sin a of the gravitational force is in equilibrium with the other forces acting on the droplet. This equilibrium position will set in when the droplet 8 remains stationary while on gently blowing into the tube the droplet is set into motion at the uniform rate through the capillary 3 as soon as the blowing ceases. In this way the measuring apparatus is brought into a condition ready for performing a measurement.

The above process is then repeated. The measurement droplet 8 is formed by turning the measurement plate 13 to the abutment 17 for a short time then the measurement plate 13 is raised back to the horizontal and then turned to the abutment 16. Then the measurement can commence. Should there be any medium or material flow present, the measurement droplet 8 will pass through the capillary 3 above the measurement scale 18; the magnitude of its displacement can be determined from the scale while the rate of displacement or the velocity can be determined with the aid of the scale and a timer, e.g. a stopwatch. On conclusion of the measurement the droplet 8 passes into the head 2 and remains there.

When a fault is present and the flow is strong, the drop passes almost instantaneously into the measuring head 2 but does not leave the instrument.

The tightness of systems placed under pressure may be examined or checked when the system to be tested is connected to the instrument inlet 15 while the discharge pipe 5 is connected via a by-pass duct to a reference vessel charged to the same pressure. Then, by blocking or interrupting the by-pass duct and setting the measurement droplet 8 to the middle of the capillary tube 3 deductions can be made about the fluid tightness of the system by observing the change of position of the droplet. Errors due to temperature changes may be eliminated by placing the reference vessel in a known manner within the system that is being tested.

The fluid-tightness of shut-off devices of filled or charged and pressurised pressure vessels may be tested by connecting the vessel to the instrument inlet 15 and leaving the discharge pipe 5 free. If the droplet 8 is displaced, then the shut-off device is not fluidtight.

If as a result of measurements the amount of measurement liquid 7 in the measuring head 1 is reduced to such an extent that on angularly displacing the measurement plate 13 as far as the abutment 17 it is no longer possible to form a measurement droplet/bub ble 8, then the series of measurements is interrupted and the measurement plate 13 is brought into the position shown in Figure 7d, that is to say, it is turned counter-clockwise by 90O in an upward direction. Then the measurement liquid 7 which has passed into the measurement head 2 flows back into the measurement head 1. This return flow can be speeded up by pressurising the discharge tube 5, e.g. by blowing into it. When all the measurement liquid 7 has flowed back the measurement may be resumed in the manner described above.

As measurement liquid one may use water, dyed alcohol or any other liquid which does not react with the medium to be measured or tested. If one utilises mercury, then electrodes may be disposed at suitable locations in the apparatus so that the measurement liquid or droplet 8 instantaneously closes or "makes" electric circuits to produce electric pulses which may be suitable for signal processing.

The measurement apparatus according to the invention utilises measurement droplets 8 which are in practice in equilibrium and which are displaceable under the effect of the smallest, almost unmeasurable differential or excess pressure, hence the sensitivity of measurement is so great that the measurement or test time in monitoring media flow such as examination of tightness and leakage is very considerably shortened. Preferred and special embodiments of apparatus according to the invention are shown in Figures 8 to 10.

Describing first the embodiment of Figures 8 and 9 there is shown a pressure vessel 31 provided with a connecting pipe 32. A fixed structural element or stable surface 33 carries a double-acting reciprocating pneumatic or hydraulic piston and cylinder unit 34 the piston of which is secured to a base plate 35 of the instrument. The base plate carries a measurement plate 36, the two plates being relatively rotatable about an axis of rotation 37. A capillary tube is carried on the measurement plate 36 and is provided with a measurement liquid 39, a measurement head 38 and an adjacently disposed measurement scale 49, the tube terminating in another and similar measurement head of part-cylinder part-conical shape designated by the reference number 38a.The first measuring head 38 has an inlet pipe extending into it which pipe is connected via the axis of rotation 37 with a bore in a seal 43. A discharge pipe branches out from the second measuring head 38a and is connected to the atmosphere. The bore of the seal 43 is connected via the coupling passing through the axis of rotation 37 to a branch line 45 and from there via a shut-off valve 46 to a pipe 47, also connected to the atmosphere. A double-acting pneumatic or hydraulic piston-andcylinder unit 40 is fixed to the base plate 35 and its piston is connected via an arm 41 to a securing mechanism 42.

A supporting ring 44 fixes the flexible seal 43 which is provided with a bore and is expediently hemispherical in shape. A double-acting hydraulic or pneumatic piston-and-cylinder unit 48 is mounted on the base plate 35 for rotating the measurement plate 36 in an upward direction about the axis of rotation 37 (as viewed in Figure 8) while a similar piston and cylinder unit 48' is provided to rotate the plate 36 downwardly. The apparatus is furthermore fitted with a per se known mechanism, not shown in the drawing, which lifts the whole apparatus when the pressure vessel 31 is removed or advanced on a production line.

The apparatus may furthermore be provided with a per se known detecting and signalforming device which forms an electrical, pneumatic or hydraulic signal when the measurement liquid 39 passes through the capillary. Such a device may be an optical one such as a light source and a photo-transistor, a pair of contact terminals built into the capillary when the measurement liquid is electrically conductive, or any other suitable device, associated with a per se known automatic sig nal processing unit. These fall within the skill of the average instrument maker and since they do not touch on the essence of the invention, will not be described further.

The embodiment shown in Figure 10 is a manual measuring apparatus in the form of a pistol or gun 52. This gun 52 may be made from any suitable material but is expediently cast from two half-pieces.

The interior of the gun has the seal 43 described in connection with Figures 8 and 9 as well as the capillary tube, the two measuring heads at the ends of the capillary tube and again designated with the numbers 38 and 38a and the measurement scale 49. The capillary tube is disposed obliquely within the barrel of the gun to slope downwardly towards the measuring head 38a at an angle which compensates the capillary forces arising between the wall of the capillary and the measurement liquid 39 on the one hand and the component of the gravitational force along the axis of the capillary. The inlet pipe 50 projecting into the measuring head 38 is connected to the bore of the seal 43 as well as with a duct 53 which communicates with an aperture 51 in the duct 52 of the gun.

A window 54 is disposed above the measurement scale 49 to enable the capillary tube to be observed. A sealed bubble glass 55 is provided on the gun to enable an operator to set the axis of the gun to a horizontal position. The other measuring head 38a is connected to the atmosphere via a duct terminating in an outlet 56.

Reverting to Figures 8 and 9, the automatic apparatus illustrated therein operates as follows. When a pressure vessel 31 transported on a continuous conveyor arrives at the instru ment (testing station) the controlling automatic control unit actuates the piston and cylinder unit 34 as a result of which the base plate 35 is advanced by an amount a and thus the seal 43 is fitted to the coupling pipe 32 of the pressure vessel 31. At the same time the automatic control unit actuates the working cylinder 40 also as a result of which the arm 41 and the fixing device or mechanism 42 are displaced by an amount b and forms a gastight coupling between a pressure vessel 31, or more particularly its pipe 32 and the seal 43.The volume of air arising from the change of shape of the seal 43 is discharged through the open shut-off fitting 46 via the pipes 47 and 45 and thus the apparatus passes through the positions illustrated in Figures 7b and 7c to attain its state of readiness for measurement. Then the automatic control unit actuates the working cylinder 48' and shuts the shutoff fitting 46.

As a consequence, the measuring plate 36 is displaced by an amount c, the measuring liquid 39 flows to the beginning of the capillary tube and the measurement commences.

If there is no leakage, the measurement liquid 39 remains at this position. A timer or clock device contained in the automatic control unit sets a measurement time on the elapse of which the working cylinders 34 and 30 are displaced in the reverse direction to disconnect the apparatus from the pressure vessel 31. The working cylinder 48 is actuated and the measurement plate 36 is brought to its position illustrated in Figure 9 in which the measurement liquid flows back into the measurement head 38. At the same time, the mechanism not shown in the drawings lifts the whole apparatus and the continuous conveyor advances the pressure vessel 31 so that a new pressure vessel may be set in its place.Thereafter, the working cylinder 48 returns the measurement plate 36 to its horizontal position, the non-illustrated raising or lifting device sets the measurement apparatus to its basic position and the cycle repeats.

Should there be a leakage, the leak will cause the measurement liquid 39 to pass through the capillary into the second measurement head 38a during which an error signal is formed by means of the non-illustrated device already mentioned. Thereupon the automatic control unit changes over the controller of the conveyor so that the leaking pressure vessel 31 is ejected from the conveyor and then the apparatus performs the same functions as if it had not detected a leakage, that is to say the working cylinder 48 lifts the measurement plate 36 and the measuring liquid 39 flows back from the second measurement head to the first measurement head.

The operation of the manual apparatus shown in Figure 10 is as follows: The operator picks up the gun 52 in his hand leaving the aperture 51 free and fits the seal 43 against the coupling 32 of the pressure vessel 31. The gun is set into a horizontal position and then the butt is lowered slightly in order to form a measurement droplet or bubble within the capillary, which can be monitored through the window 54. Then a finger is placed on the aperture 51 and the position of the measurement droplet in the capillary is established with the aid of the measurement scale 49. While this is going on the horizontal position of the gun is monitored, if necessary with the aid of the sealed spirit level or bubble glass with stuffing-box 55.

If the drop does not move, then the obturating device of the pressure vessel 31 is faultless. If there is a leakage then the droplet will pass through the capillary at a velocity which is proportional to the leakage and will end up in the rear measurement head 38a.

If the leakage is large, then the droplet will move very fast, whereupon the finger is lifted from the aperture 51 to stop the droplet. On finishing the measurement the gun is held vertically downwardly so that the measurement liquid passes from the rear measurement head 38a to the front measurement head 38. This can be accelerated by gently blowing into the aperture 56.

An indirect leakage measurement may also be performed with the manual apparatus according to Figure 10 by connecting a ducting to the aperture 56 and connecting it with a reference vessel.

The preferred embodiments of the apparatus described above enable refilled or charged pressure vessels to be monitored for pressure-tightness and leakage either on an automated charging machine line or by a manual instrument; the manual instrument may also be used for other leakage tests and the evaluation of the measurement tests eliminates or very greatly reduces subjective errors.

Claims (11)

1. Apparatus for detecting and/or measuring extremely small amounts of lowing media by means of a capillary tube disposed next to a measurement scale, wherein a respective measuring head at each end of the capillary is provided with an inlet and an outlet, the capillary containing a measurement droplet formed from a measurement liquid disposed in the measuring head which is connected with the inlet, and the capillary is inclined at an angle of inclination towards the outlet, the said angle being adjustable to a value at which the forces arising between the measurement droplet and the wall of the capillary balance the component of the gravitational force acting on the measuring droplet in the direction of the axis of the capillary.

2. Apparatus according to claim 1 wherein each said measuring head is spherical, cylindrical or part-cylindrical and part-conical.

3. Apparatus according to claim 1 or claim 2 wherein the inlet is a pipe having an orifice which in normal use is directed at 90" vertically downwardly while the outlet is a pipe with an opening directed at 90" vertically upwardly.

4. Apparatus according to any preceding claim wherein it is fixed on a measurement plate which itself is secured for rotation about a predetermined rotary axis relative to a base plate.

5. Apparatus according to any preceding claim wherein the base plate has two adjustable abutments for setting and determining the angle of inclination of the measurement plate.

6. Apparatus according to any preceding claim wherein the axis of rotation is constituted by a threaded longitudinal shaft screw provided with a longitudinal blind bore and transverse bores, connecting heads on said screw each provided with internal spaces in communication with an instrument inlet and the inlet (pipe), and a closure stopper for closing the longitudinal bore.

7. Apparatus according to any preceding claim wherein there is a first working cylinder for reciprocating a base plate and secured to a stable surface, a second working cylinder mounted on the base plate for turning a measuring plate upwardly, a third working cylinder mounted on the base plate for turning the measuring plate downwardly, a fourth working cylinder mounted on the base plate and provided with a fixing mechanism reinforced by an arm, a resilient seal bearing against the connecting pipe of a pressure-maintaining vessel, which seal is provided with a bore and is e.g. hemispherical in shape, and sensing means for sensing a change in position of the measurement liquid.

8. Apparatus according to any preceding claim in the form of a hand gun for use on pressure vessels, especially for controlling or monitoring the fluid-tightness of closure devices or fittings on gas flasks or compressed gas bottles, comprising a resilient seal provided with a bore at the end of the "barrel" (tip), a capillary measuring tube disposed in the gun under a transparent window and above a measurement scale at an angle inclined rearwardly towards the "butt", a measurement head at each end of the capillary; the first or front measuring head contains a measurement liquid the air space of which is connected with the bore of the seal by way of connecting pipes and with an aperture on the butt of the gun; the rear measuring head is connected by way of a connecting pipe to an aperture on the rear surface of the apparatus.

9. Apparatus according to claim 8 wherein a supporting ring is provided for mechanically supporting the seal, and there is a duct for coupling the bore of the seal via a pipe-shutting fixture with a pipe open to the atmosphere.

10. Apparatus according to claim 8 or 9 whein it has a bubble scale of spirit level provided with a stuffing-box.

11. Apparatus according to any preceding claim substantially as herein described with reference to and as shown in Figures 1 to 7 or Figures 8 and 9 or Figure 10 of the accompanying drawings.