European Patent No. 0 337 528 discloses a safety cap for a container containing steam under pressure, comprising a closure member screwed onto the mouth of the container, an external knob which the user can turn to screw the closure member on and off, and an internal diaphragm which is moved by the action of the pressure of the steam. When the pressure of steam in the container is zero or low, the diaphragm is in a rest position, and the closure member and knob are coupled in rotation to allow the cap to be unscrewed. As the pressure of the steam rises, the diaphragm moves into an operating position and uncouples the knob from the closure member to prevent the closure member from being unscrewed.
This safety cap therefore prevents the container from being opened when there is high steam pressure inside it and prevents the pressurized steam from escaping violently and injuring the user.
This safety cap finds advantageous application in, for example, the boilers of steam generators for domestic use, e.g. for supplying steam irons, cleaning equipment, etc. Its virtue is that the domestic user is often technically unskilled and therefore lacks the necessary awareness and understanding to handle a pressure boiler.
It is precisely because of the great danger represented by a container of steam under pressure, and the inexperience of those who usually use it, that it is so important to improve the closure cap of the container in such a way as to lower the risk margin, and hence the likelihood of accidents, towards zero.