TIGHTNESS TESTING OF LARGE VESSELS OR THE LIKE

Abstract: A method and a device for testing the tightness of large vessels (T) in a quick and reliable way. The vessel is filled with liquid under pressure. The liquid pressure unambiguously influences the pressure in a closed gas circuit (R) via a pressure transferring device, e.g. a diaphragm box (M1). To establish a possible leakage in the vessel (T), a pressure reduction in the gas circuit is detected, e.g. by means of a differential pressure sensor (M2).

Description: Tightness testing of large vessels or the like. The invention relates to a method and a device for testing the tightness of large vessels or the like, such as water-heaters, central heating vessels, heat exchangers, compressed air vessels, gas containers, etc. Many different methods for tightness testing of large vessels or containers are known. Thus, in the Swedish patent specifi- cation 205 768 a testing method is described, according to which the vessel is filled with liquid, and the liquid pressure is increased continuously and the relation between the pressure and the volume is registered. As soon as the slope of the pres¬ sure-volume curve changes, the pressure increase is interrupted, and it is established that a leakage exists. This method is of course applicable for large leaks, whereas minor leaks are difficult to detect. Moreover, s.c. pressure increase and pressure reduction methods are generally known involving the use of gas, in particular air, as an operating medium. According to the pressure reduction method, the test object and a reference container are filled with air up to the same pressure. Thereafter, the connection between the reference container and the test object is closed, and a possible difference between the pressures in the separate containers is measured after a predetermined time. This pressure difference constitutes a measure of the degree of leakage. According to the s.c. pressure increase method, the test vessel is filled with pressurized air. Simultaneously, the test vessel is surrounded entirely or partly by a fixture, so that a sealed measuring volume is formed between the fixture and the test vessel. A possible pressure increase in the measuring volume indicates a leak, and even in this case the pressure measurement is performed after a predetermined time period. However, when testing rather large vessels, it has turned o that the measuring time is fairly long, which is obviously a disadvantage in serial production. It is in fact necessar to let the gas pressure become stabilized. Moreover, minor leaks cause only very small changes of the air pressure, an even sensitive measuring equipment does not react until a rather long time. The object of the invention is, therefore, to accomplish a new tightness testing method enabling a quicker and more reliable tightness testing of large vessels or the like, pa ticularly with respect to minor leaks. This object is achieved by the use of a liquid during the tightness test, in particular water, as an operating fluid, i.e. the fluid with which the vessel is filled during the testing process, whereas the measuring is performed bymeans a gas, especially air. During the measuring process, the li and the gas are kept under the same pressure in that they c municate with a pressure transfer device, e.g. a diaphragm box, wherein the chambers on each side of a flexible diaphr contains the liquid and the gas, respectively. The inventive method and device are defined further in the pended claims. The advantages achieved by the invention relate to the feat that the fairly large test vessel is filled with a liquid, an incompressible fluid, whereas the pressure measuring is ried out by means of a gas, i.e. a compressible fluid. Thus, the testing process can be effected quickly, since a minor change of the liquid volume results in a relatively large p sure reduction, whereas the pressure measurement by means o the gas fluid can be carried out reliably and with great accuracy. The invention is described further below with reference to O . W drawing, illustrating schematically a device for carrying out the inventive tightness testing method. On the drawing, a test object T is thus shown schematically. The test object is connected by means of quick connectors SI, S2 at the top and the bottom, and pressurized water is sup¬ plied at the bottom via a first cut-off valve VI (V6 is closed) During the filling process, the water rises in the vessel T and continues up through the upper connection SI to a valve V2. Upon checking, preferably automatically, that the system is vented, the valve V2 is closed and a valve V3 is opened, so that the test object filled with water communicates with one half of the diaphragm box Ml. Thereafter, the water pressure is raised to a predetermined, rather high level by means of a high pressurepumpP, and the valve VI is closed. At the other half of the diaphragm box Ml, air pressure is applied in the following way: A non-illustrated source of pressurized air (or a pressurized air system) is connected via a valve V4, which thereafter is kept closed. A predetermined, rather high air pressure, al¬ though somewhat lower than the liquid pressure generated by the high pressure pump P, now prevails in a reference contai¬ ner R and on both sides of the diaphragm in a differential pressure sensor M2 (a valve V5 is now open) . Upon the above-mentioned increase of the water pressure, the last-mentioned pressure is transferred via the diaphragm box Ml, so that the air circuit as well as both sides of the dif- ferential pressure sensor M2 are exposed to said pressure. If the test object breaks as a result of the pressure increase, the tightness test is of course concluded, and the entire ope¬ ration is repeated for a new or repairedtest object. If, on the other hand, the test object stands the pressure increase, the valve V5 is closed, and immediately thereafter exactly the same pressure (the predetermined pressure level generated by the pump P) .is -exerted on both sides of the diaphragm in th differential pressure sensor M2. When the valve V5 is closed the tightness testing of minor leaks in the test object is started. During a predetermined adjustable time period, a po sible leakage in the test object will cause a reduction of the water volume in the water circuit, thereby causing a fal of the water pressure as well as the air pressure between th diaphragms in M2 and Ml. This pressure reduction can be dete ted by means of the differential pressure sensor M2 operatin with high sensitivity. If no pressure reduction is observed during the predetermine measuring time, the test object T can be considered tight, a the measuring is completed by opening the valves V2, V3 and V whereupon the valve V3 is closed again as soon as the water pressure drops. Thus, the water circuit and the test object are emptied to permit a new test vessel to be connected and tightness tested. On the other hand, it has proven advantage ous to maintain the originally applied air pressure in the air circuit, the diaphragm box Ml preferably being designed such a way that the diaphragm, when deflected towards the wa circuit, will contact a support surface to protect the dia¬ phragm from plastical deformation or breakage. The invention can be applied in many different ways within t scope of the following claims. For example, an entire pipe system can also be tightness tested by the inventive method. CΪ. />. WI

Claims: C L A I S 1. A method for tightness testing of large vessels or the like, c h a r a c t e r i z e d in that the vessel (T) is filled with liquid under pressure, that the pressure of the liquid, by means of a pressure transfer device (Ml), is caused- to unam¬ biguously influence the pressure in a closed gas circuit (R) , and that a pressure reduction in the gas circuit is detected (M2) to establish a possible leakage in the vessel. 2. A method as set forth in claim 1, c h a r a c t e r i z e d in that firstly the pressure in the gas circuit (R) is raised to a first pressure level, whereupon the vessel (T) is filled with a liquid and the liquid pressure is raised to a second pressure level exceeding said first pressure level. 3. A method as set forth in claim 1 or 2, c h a r a c t e ¬ r i z e d in that the detection of said pressure reduction is carried out by differential measurement (M2) , the gas pressure in the closed gas circuit being first equalized in the entire gas circuit, whereupon the gas circuit is divided (V5) into a reference circuit portion (R) and a circuit por¬ tion (between M2 and Ml) connected to said pressure transfer device (Ml) . 4. A device for tightness testing of a large vessel or the like, c h a r a c t e r i z e d by, on the one hand, a liquid cir¬ cuit connectable (S1,S2) to said vessel (T) to be filled with liquid under pressure, and on the other hand a closed gas cir¬ cuit (R) arranged in pressure tansferring contact with the liquid circuit by means of a pressure transfer device (Ml) and having a detecting means (M2) for detecting a pressure reduc¬ tion in the gas circuit caused by a leakage in the vessel. 5. A device as set forth in claim 4, c h a r a c t e r i z in that said pressure transferring device consists of a dia phragm box (Ml) , the diaphragm of which separates the liqui in the liquid circuit from the gas in the gas circuit. 6. A device as set forth in claims 4 or 5, c h a r a c t e r i z e d in that the gas circuit comprises a reference co tainer (R) , which is connected to one side of a differential pressure sensor (M2) , whereas said pressure transferring device (Ml) is connected to the other side of the differenti pressure sensor (M2) . 7. A device as se r forth in claim 6, c h a r a c t e r i z e in that a cut-off valve (V5) is inserted in a shunt conduit connected to both sides of the differential pressure sensor (M2) . OMPI

Inventors: BERGSTRAND G, LOEOEF B
Applicants: BERGSTRAND G, LOEOEF B, NOLEK SYSTEM AB
Application year: 1980
Main classification: G01M3
IPC codes: B65D90, F17D5, G01M3