Don.
Before we go into further details may be we should discuss the basic systems of the Schnorchel. I don't`know your knowledge of the systems, so have me excused for going into the some items which might be too obvious to you.
As a consequence of the great losses in 1943 due to allied air superiority, the germans had to do something to protect their Uboats and looked into a dutch system from before WW2 called the "sniffer" translated. The system had to be adapted to the existing Uboats so they had to utilise the existing systems. Thus they had to make some compromises.
In the end of 1943 their system was ready to be installed in the frontline boats. The mast could not be telescopic that would require major changes, so they made a hinged type of schnorchel which could be folded down in the casing ( for VII Cs port side of the forward conningtower). The system utilised the existing exhaust blowingsystem for the ballasttanks using the same pipes up to the distribution chest outside the pressurehull starboard side of the forward conningtower casing. Right before the chest it is a branch off to the schnorchelmast. In order to pass the distribution chest they had to let the pipe to the schnorchelmast go above the casingdeck ending in a schnorchel shut off exhaustvalve before the pipe goes under the deck and connects to the schnorchelmast.
The air intake ( for the first generation of the system) utilise the existing outboard ventilation airduct in the casing outside the pressure hull. The air enters the schnorchel mast via a top floatshutting valve being either ringfloated or hinged floated controlled.
Half way up at the conning tower appr. at the spray deflector the mast air pipe engages a fixed pipe on the conningtower via a rubber flange. This pipe goes to a drainvalve operated from the control room just before it enters the ventilation intakevalve inside the conning tower casing. Then it follows the ventilation duct still outside the pressurehull almost to the pressurehull inlet valve and have a cross over to the dieselair duct. The airinlet follows the dieselair hullvalve into the engine room. The reason for this arrangement was that in case of massive water intrusion, the ventilation fans could be destroyed whereas the large dieselair ducts ended near the bilges. Quite a few VII Cs had this arrangement.
This system was not quite satisfactorily and a modified new system was designed. The new system kept the arrangement for the exhaust, which is quite simple, but the air system was changed. The pipe on the conning tower was removed instead came a hollow schnorchel fulcrumshaft and the air was lead through this shaft and aft under the casing directly to the dieselair duct. One small detail though, it was not sufficient space for the bend leading the pipe aft so they had to make a hole in the casing to let the pipe turn aft outside the casing, hence it was easy to see which U boat had the new design, see my picture.
Puh! some long story, just ask if something is unclear may be I can answer
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Tore
