Tore,
regarding to the "plan 17b" - I was able to find its origin - it comes from "
U Bootskunde für U Boote Bauart VII C", which translated version is published on uboatarchive.net - which was issued on 15 July 1940.
"
Skizzenbuch fur das Maschinenpersponal" coming from U-570 and published on uboatarchive.net, which contains "plan 17" - was issued March/April 1941.
I think, that this explains differences.
Tore, there is one more thing, that makes me wonder. On the "plan 17" are marked four
Druckunterschiedmessers - pressure differential gauges for the regulating tanks
Regelbunker 1 Bb/Stb and
Regelzelle 2 Bb/Stb. They show pressure differences between the external sea water pressure and inside the tanks - what is useful when fine flooding and blowing regulating tanks. Their are also used for operations described in
Tauchvorschrift (
http://uboatarchive.net/DivingRegulations.htm ) - paragraph 155, 163, 185
These four gauges are gathered on the control panel above the blowing ballast tank distributor (see photo - on both sides, in the middle - pressure gauge of the main blowing valve).
In the control room of U-995 are two more differential pressure gauges - near
Untertriebszelle blowing lines' hull valves. These gauges are not drawn on the "plan 17", but are mentioned in the British report on HMS Graph (table on the page 39 -
http://uboatarchive.net/U-570BritishReport.htm ).
The purpose for these gauges I have found also in
Tauchvorschrift - paragraphs 131 - 133.
Reading these paragraphs I'm wondering about "residual water check" (
Restwasserprufen). It became obvious to me, that main problem while blowing
Untertriebszelle is to stop blowing just before they are emptied - to avoid escaping of compressed air bubbles through the bottom flood valves. For this reason, the residual water check lines were applied. But I can not imagine how they worked. Could you put some light on this topic Tore?
--
Thanks, regards
Maciek