to protect the latter in the event that there is a pressure surge in the opposite direction thus it will be seen that the diaphragm means 12 can be deflected outwardly away from the axis of the tank means 10 only until the diaphragm means 12 engages the inner surface of the wall of the tank means 10 the height of the liquid in the liquid space a is arranged so as to be relatively small as compared with previously known vertical damping tanks for example in this way there is the advantage that the distance from the flow duct to the liquid surface s is minimized the height h of the tank means 10 is in a range which may as a minimum approximately equal the magnitude of the diameter d of the tank means 10 and which as a maximum will be approximately equal to twice the magnitude of the diameter d of the tank means 10 the height h m of the diaphragm means 12 is approximately one half of the tank height h the height h s of the liquid surface s which transmits the pressure between the gas space v and the diaphragm means 12 is preferably only slightly greater than the height h m of the diaphragm means 12 thus the height h s may be on the order of for example 5 20 greater than the height h m of the diaphragm means 12 as contrasted with known damping structures which include elastic diaphragms the structure of the invention achieves a.