Don.
HP air (205 kg/cm2 as stored in the hp air flasks) is a vital important medium to a submarine, topping up same is noisy and takes time, hence you try to save the HP air as much as possible. Surfacing happens under many different situations and the procedure varies under the various conditions, like the activity on the surface, the submarines depth, weather and the reason for surfacing. The ideal surfacing is as mentioned before, ascending dynamically by speed and hydroplanes, checking the surface by periscope and then blow your tanks at periscope depth using as little HP air as possible, this takes an experienced man as the air in the ballast tanks expands after you have shut the blowingvalve. The idea is to get the submarine in a stable semi surfaced position, then switch over to exhaust blowing, starting with the ballast tanks highest up ( least backpressure) until you are on the required draft. The exhaust blowing is not commonly used on all submarines. In the RN the final blowing is done with an electrically driven LP air blower but the purpose is the same, saving HP air.
The intrusionof seawater into the engines is not a frequent reason during normal surfacing, the most common reason would be during diving via the outboard main exhaustvalve (before the silencer) having a major leak due to carbon formation on the seatings. As you know the valvedisk on this valve was rotated by a pneumatic drive during diving, this grinding was not always successful as the possible grinding intervall was too short (Beckpressure became to big on the valve) causing a massive leakages into the exhaust manifold on the main engines and the via the exhaustvalves into the cylinder and luboil system .
Tore
