Pressure wave sealing

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A pressure wave seal is a door in a fire wall concept that is always open if possible, but can be closed in fractions of a second under certain circumstances.

Examples

Examples of this are the pressure wave bulkheads in bunkers and the pressure wave seals on warships (referred to as such in this case) .

Technical implementation

The functionality largely corresponds to that of a check valve. Technically, this is achieved by making a passage, e.g. B. by a fire wall or a bulkhead , so at right angles to the corridor that hits it, that an approaching pressure wave slams the door. Stored artillery explosives , which when ignited because of the lack of containment, burns very quickly without detonating , pushed a pressure wave in front of the flame front, which had to hit the fire door in such a way that it was thrown by itself. Water tanks were installed in front of and behind this door, in line with the pressure wave propagation, which tore open the pressure wave and fogged its contents. This principle is also used in mining. For this purpose, frames are used in which open tubs with extinguishing water are attached above head height or on the walls of a connecting tunnel. The water not only dampens the pressure surge, but also, finely swirled by the pressure wave, cools the trailing flame.

A prerequisite for such a device to function reliably is that the door has not been laid and that it is light enough, but still sufficiently stable. This can be achieved by dividing the seal on different types of doors. On the one hand, there are doors with a large clear width (with stable locks), which are only opened when necessary in order to e.g. B. to let a train pass in a mine, and which remain consistently closed in the event of an increased risk of explosion, such as when a warship is in readiness for action . On the other hand, there are doors that are much smaller and are used to supply fresh air or to pass objects through and which have such a quick-release system. A major problem arises, especially in shipbuilding: large amounts of ammunition (propellant charges and grenades) have to be transferred from the main ammunition bunker to the guns in battle; a single 38 cm caliber shell (plus propellant charge ) weighs more than 490 kg impossible to feed these to the guns other than via slides, elevators and conveyor belts. However, it is difficult to combine such transport systems with pressure wave seals. Although the problem was known, the dreadnought class preferred to use a stronger outer armor, but dispensed with complicated interior fittings to protect the ammunition stores . In addition, they did not trust the reliability of the transport equipment and stored large quantities of grenades in and under the turrets that had already been detonated - they trusted the superior range of their own artillery, wanted to give them an additional advantage in rapid fire and completely overlooked the consequences that occurred when the ships were exposed to foreign fire in relative close combat.

Further development of pressure wave sealing in shipbuilding

Since the beginning of the Second World War , more doors have been used that can be driven vertically in the way and are moved by an electrically ignited propellant. For this purpose, the conveyor belts of the ammunition system have a gap into which the door moves without an obstacle. A multi-stage system is able - assuming an interrupter system for individual doors - to be able to seal the bulkhead, even if individual doors are blocked by a grenade.

Detailed technical solutions

Another problem with pressure wave seals of any kind is that the door cannot be opened after use. Pressure equalization must be established before opening, but if the door has jammed, only hydraulic winches are suitable to make it work again. It is also problematic if the door is welded by the heat. For this purpose, intermediate media are inserted into such doors that cannot be welded to steel, or that cannot be melted out with a simple burner. The doors of the Cold War nuclear bunker had an aluminum coating, as the force and pressure that acts on the closing door, combined with a relatively low temperature (from 500 ° C), would be enough to "forge" the door and frame. However, since aluminum cannot be forged with steel, tests have shown these doors to be technically mature and are still used in mining today.

The problem with functioning pressure wave containment is that the contained pressure has to escape anyway. This can be done through openings provided in the system or by rapidly cooling the pressure wave, thereby achieving a pressure drop and creating environmental conditions that are compatible with life (so that rescue and rescue teams can advance to the scene of the accident). The problem here is that conventional, line-based extinguishing systems only work if their lines and pressure tanks are still intact. Therefore, water bags are still used today in areas where deflagrations are to be expected .

literature

  • Heinrich Otto Buja: Engineering handbook mining technology, deposits and extraction technology. 1st edition, Beuth Verlag GmbH Berlin-Vienna-Zurich, Berlin 2013, ISBN 978-3-410-22618-5 .