Abstract: A method is provided for detecting leakage in a heat exchanger by circulating a tracer under pressure from the first side of said heat exchanger to the second side and then from the second side to the first side subsequent to reversing the direction of the pressure. In order to prevent a false test result it has previously been necessary to make sure that all tracers, for example electrolytes, colorants, or fluorofors, were rinsed from the first side prior to circulating the tracers from the second side to the first side. This time consuming and at the same time unreliable rinsing process is avoided by the method of the present invention by adding a second tracer from the second side.

Abstract: A panel for self-supporting roof structures of extruded profile elements having at least one main duct closed at the ends with closing members (10) which are made of plastics material and have the same profile as the profile elements and is closed at one end (17). The closing member (10) is of so reduced dimensions as to fit into any main duct in the profile element while allowing some air exchange without the risk of penetration of dirt.The closing member (10) has preferably resilient sealing flaps (12, 13, 14, 15) on two opposite sides, so that one and the same member (10) can be used for closing profile elements of varying size and shape, e.g. as a result of manufacturing inaccuracies. A V-shaped groove encircles the outer surface of the closing member and permits movement of the two parts of a bipartite flap.