SYSTEMS FOR LEAKAGE

In many distribution systems for fluids, both liquid and gases, there is a great need of being able to detect the occurrence and size of a possible leakage. Also small leakages can be disastrous, for example if the fluid is expensive, (e.g. helium), explosive (e.g. natural gas and liquefied petroleum gas) or poisonous (e.g. carbonyls).

It is of course advantageous if the testing for leak¬ age can be carried out in situ, without necessitating dis¬ mounting of any component of the distribution system, in such manner that the entire system can be tested at once. A method which is close at hand is to provide the system with a pressure guage. The testing for leakage is carried out in that the fluid source as well as all con¬ sumers are closed. If the pressure in the system now drops, this indicates a leakage. However, this procedure is disadvantageous since for all fairly large distribution systems, it is extremely slow, at least for gases, espe¬ cially if very small leakages in relation to the size of the distribution system must be detectable. At low system pressures, it can further be costly. SE 387,740 and US 3,583,435 disclose different appa¬ ratus for detecting the occurrence of leakages in gas dis¬ tribution systems. They are based on the formation of bubbles in a liquid.

All these prior art apparatus suffer from six draw- backs:

1) The leakage indicator has a specific (fixed) inlet and outlet side, which renders installation difficult.

2) Only a leakage downstream of the leakage indica- tor can be indicated, which restricts the use¬ fulness of the leakage indicator and guides the choice of mounting position.

3) The gas leakage cannot be determined as a quanti¬ tative measurement, which makes it more difficult to decide whether the leakage should be accepted or not, and to communicate about the test result. 4) There is no storage function or integrating func¬ tion, which renders it difficult to measure and assess variable or temporary leakages. .5) The liquid receptacle which must be made of plas¬ tic or glass and relatively large, will be a weak point which can easily be damaged, if not care¬ fully protected. Moreover, the manufacture there¬ of will be expensive, if the receptacle is to resist high pressures. 6) Through the shape of the liquid receptacle and the nature of the testing procedure (bubbling), a large surface of the liquid is exposed relative to the volume of the liquid, which increases the possibilities of evaporation of the liquid. The object of the present invention is to provide a method and an apparatus which, while eliminating the above-mentioned drawbacks, allow a reliable, inexpensive and easily installed leakage indicator which is also easy to use.

The object is achieved in that the method and the apparatus have been given the characteristic features stated in the appended claims.

The invention will now be described with reference to an embodiment illustrated in the enclosed drawings in which: Fig. 1 is a schematic view of an apparatus operating according to the technique on which the present invention is based, and

Fig. 2 is a circuit diagramme showing a technical solution for a typical application, a gas distri- bution system including the apparatus shown in Fig. 1.

Fig. 1 shows a transparent U-tube (U) which to a small extent is filled with a liquid (L). A valve (V) which can be manually opened and closed is connected in parallel with U. The apparatus (leakage tester) in Fig. 1 can be con¬ nected as shown in Fig. 2. Owing to its symmetrical shape, the apparatus has no fixed inlet and outlet side. The ap¬ paratus must be mounted substantially vertically (D).

A gas source (G) with a main valve (MV) and a pres- sure regulator (PR) are connected to one side of the leakage tester via the upstream supply mains (UST). The downstream supply mains (DST) is connected to the other side of the leakage tester. Gas consumers (C) can be con¬ nected both to UST and DST. Testing for leakage can be effected both in UST and DST. Such a test can be carried out as follows:

First, DST is tested. MV is left open, and therefore the UST side of the leakage tester is pressurised with the constant pressure that PR provides. All gas consumers con- nected to DST are closed. Any gas escaping from DST can consequently be attributed to leakage.

V is now closed. A leakage., if any, will now cause a flow through U, which moves L in the direction of the DST side. It thus shows on which side of the leakage indicator there is a leakage. The leakage rate can be directly read as L's path of motion from the starting position. Multiplied by the cross-sectional area of U, divided by the time that lapsed from the closing of V until reading is carried out, a measured value of the leakage rate is obtained, e.g. in ml/s.

At a variable leakage rate, this method directly yields a mean value of the leakage rate, owing to the integrating function of the measuring procedure. In case of a temporary leakage, L remains in the position to which it has been moved by the leakage flow and therefore the information on the temporary leakage is stored (storage

f nctio ) .

After it has been established that DST is tight, then UST is tested. MV is now closed. On the DST side there is still the pressure provided by PR. In case of leakage in UST, will, analogously to that said above, move in the direction of the UST side. The leakage rate etc is also determined quite analogously to what has been said above.

When the leakage test is finished, the valve V is opened again. At the same time the leakage indicator is zeroised, in that the liquid column L returns to its state of equilibrium (starting position), when the potential energy of L is discharged.

In an especially preferred embodiment of the appa¬ ratus according to the invention, U is a thin standard type pneumatic tube according to e.g. DIN 73378. Such a tube is most resistant to vibrations, impacts and other forces and resists a pressure of up to 4.5 MPa and tempe¬ ratures between -60°C and +150°C. The tube is inexpensive and can be obtained in suitable dimensions, for example with an inner diameter of 2 mm and an outer diameter of 4 mm. It is also resistant to fuels, such as power gas.

The use of a thin tube also requires but an extremely small amount of liquid L. Moreover, a very small surface of the liquid L is exposed, as compared with the volume thereof, which strongly impedes the evaporation of the liquid L.

Besides, for the above-mentioned tube, low-priced standard tube couplings with an 0-ring are available, which permit quick and simple mounting and dismounting of the tube. The latter property also facilitates filling of the liquid L and exchange of the tube.

As a valve, use is preferably made of commercially available standard valves in the design as required, to which the above-mentioned tube couplings are connected by means of threads.

By means of the method described above, leakage test¬ ers for a variety of different pressures and flows can be manufactured in a simple and inexpensive manner, even in small series. By using e.g. a solenoid valve and a capacitive transducer, a camera etc, remote-controlled testing for leakage can also be effected.

A leakage tester of the type described above can be made very sensitive. In long-term testing, leakages in the order of nl/s can be detected.

The leakage tester also functions at extremely low system pressures, in case a low density liquid L is chosen, for example water or oil, such that the own pres¬ sure of the liquid column is low in relation to the system pressure. The required differential pressure for raising the liquid column L is also essentially independent of the position thereof, since L is short in relation to the length of U.

The leakage tester can readily be provided with a scale (S) which also serves as a protection of U. S is hung on the handle of the valve V, and a suitable gradu¬ ation and directions for use of the leakage tester can be printed on the scale. By means of a suitable design, S can be rotated about the handle of the valve, which makes U easily accessible, e.g. for filling the liquid L.

In case of a heavy leakage, the especially preferred apparatus as described above can cause the liquid L to "run away" and be lost in DST or UST. To prevent this, actions can be taken as described in Fig. 3. One example of an action is to use spheres or other bodies (F), rigid or elastic, which float on both sides of the liquid L inside U and which are sealed against a suit¬ ably designed conduit portion (D) if the liquid "runs away" (Fig. 3). The invention is not restricted to the embodiments described above, but may be modified within the scope of the appended claims.

As shown in Fig. 4, the liquid L may, for example, be replaced by a rigid or elastic solid body, such as a sphere or a cylinder (B), which by means of some suitable lubricant travels at low friction inside the U-tube U (Fig. 4).