【正文】 the points to be checked are covered by paint or a strip which chemically reacts with ammonia and changes colour Vacuum pump unit, ammonia sensitive paint or strip Equipment for safe handling and disposal of ammonia Apparatus for post cleaning and inspection Test object material shall be patible with ammonia 107 Pa?m3/s Location Preevacuation may be unnecessary if a loss of sensitivity is tolerated Presence of moisture can significantly reduce the test sensitivity Risk of explosion in mixture with air Ammonia is toxic and requires care in the handling and disposal Vacuum box, using internal pressure of tracer gas Tracer gas (usually helium) The ponent is filled with tracer gas。 the suspect areas are covered by a suitable, gastight enclosure filled with tracer gas As As As Measurement Accuracy dependent on knowing tracer gas concentration in the bag Possibility of missing some leaks Vacuum technique (local) As The object is evacuated and connected to the detector。 3) helium or hydrogen may present problems with some elastomers/polymers since permeation can be significant. NOTE 3: Surface finish can also restrict the applicability of some techniques or influence their results. Examples are evacuation difficulties, inadequate leak tightness for seals in vacuum box applications, false indications (bubble test), etc. Operation and testing conditions Generally a test fluid other than the operating fluid is used in order to increase test sensitivity or to reduce hazard or pollution. The difference between the properties of the fluids shall be taken into account to avoid wrong results due to physical or chemical phenomena (see material patibility) and to evaluate, if necessary, the true leakage under operating conditions. Page 11 EN 1779:1999 Whenever possible the test shall be performed with the leakage flow in the same direction and with the pressure in the same range as under the operating conditions. If it is not possible, deviations from the operating conditions shall be stated in the test report. NOTE 1: Leaks can show a very different behaviour for reverse flow, particularly if elastic or plastic ponents (springs, diaphragms, gaskets) are part of the boundary wall. The leakage rate can also change significantly according to the conditions of gas flow (viscous/molecular). NOTE 2: Generally the pressure difference required to show the presence of a leak is low, not exceeding 0,1 MPa. In some cases, it may be necessary to apply the effective operating pressure in order to reveal the effects of strain in the structure on the leak tightness. For convenience, testing is usually performed at ambient temperature. Thermal expansion due to a temperature difference can however generate strains and geometric deformation. This can affect the dimension of the leak and then the leakage rates but this may only occur during the periods of temperature change. Such changes shall be taken into account when reviewing the results. In pressure change tests, unknown and varying temperature gradients can arise in some circumstances in large test objects or between several parts of a system and may invalidate the test results. Such changes shall be taken into account. A test may be performed on ponents, subassemblies or a pleted object. Testing of sub assemblies may eliminate costly repair in later stages. In this case it is possible to improve the test sensitivity by the use of temporary seals or improve the gasket tightness by means of plugs or welding. When the object under test is part of a pleted plant, it shall be isolated by blanks. NOTE: If this is not possible, leakage rates of points of connection should be measured at the test pressure and these should be subtracted from the total object leakage. Safety and environmental factors Hazard due to a pressure differential Leak testing can be carried out by subjecting the test object to a pressure differential by either evacuation or application of an internal overpressure. In both cases, it is essential that the manufacturer guarantees that the object withstands the pressure differential and does not distort, thereby causing injury to personnel or damage to plant. Many massspectrometer leak detectors contain liquidnitrogencooled traps. Pressures in excess of atmospheric that might cause mechanical failure can be generated when they are allowed to warm up. It is therefore remended to follow accepted venting procedures. Hazardous materials The object to be tested may contain hazardous materials. This shall be recognized and measures to prevent escape shall be taken before testing begins. All gases shall be handled with caution. The properties of the test gas shall be taken into account. NOTE 1: Ammonia, for example, is a toxic, flammable gas which can be corrosive in the presence of moisture. Ammonia needs an absorption treatment and a subsequent neutralization. NOTE 2: Halogencontaining gases cause significant damage to the upper atmosphere. NOTE 3: Most gases, including inert gases, . helium, and nitrogen are asphyxiant. Electrical hazards High voltages are used in many vacuum ponents, including total pressure gauges and mass spectrometers. Electrical safety shall, therefore, always be considered. Adequate protection of all electrical ponents or parts of the system that could produce a discharge is necessary. Page 12 EN 1779:1999 Annex A (normative) Specific features of leak testing methods Table : Specific features of leak testing methods Tracer gas method Gas flows into object Technique Test gas Principle Equipment Restrictions on test object Minimum detectable leakage1) Appli