Ruptured Negative Buoyancy Tanks (Q tank)
Let me try and make a fool of myself again...
http://www.uboatarchive.net/DivingRegulations.htm33. The pressure difference meters are to be monitored, particularly during expressing (danger of rupture with closed flood valve) and when the boat rises. More than 2 atmospheres higher than outboard pressure is prohibited and must be equalized.
[size=78%] [/size]Equalization takes place after previous request to the Engineering Officer (for passing on to the conning tower) by complete opening of the "Vent negative buoyancy tank" valve, appropriately up to an internal pressure of 1.5 atmospheres (external pressure at periscope depth).
I can see two ways to rupture the Q tanks and the key element is the flood valve:
1. Fail to close the Flood Valve until at depth
2. Expressing at depth and then close the flood valve
Instance #1 - After expressing at 10 meters and failing to close the flood valve (bottom mushroom valve) will result in the Q tank's air being compressed. This is not a problem for the tank at this point because the internal and external pressure are the same. However, If the crewman closes the flood valve at 100 meters, now we have a problem! As the boat rise with the closed flood valve, the outside pressure will decrease and the high internal pressure will stress the tank structure which was braced for external pressure.
Instance #2 - expressing the Q Tanks at a depth of 100 meters instead of 10 meters. Again this is not a problem (same reason as above). However, if the crewman closes the flood valve after expressing at depth, now we have same scenario with the compressed air in the Q tanks. As the boat rises with the flood valve closed and decreasing external pressure, it is likely that the Q tanks will be ruptured because of the high internal pressure.
I sure hope I got it right this time... If not, then I'll need another post high school lesson from Professor Maciek.
The manual says to monitor the pressure difference meter. I assume that is the meter very close to the Q tank top vent valve (black and red wheel-handle). Does this meter have a input line going to the inside top area of the Q tank, and a second input could be just a hole in the back of the meter to sample the internal hull pressure.
Regards,
Don_