Dear Jean,
I have some information about the fuel system onbard the Type IX-C U-boats. If that would help, then here goes.

The fuel oil stowage facilities and piping arrangements on the IX-C submarines contain numerious design differences and are in many details simpler than the installations on U.S. submarines.

The tankage layout is different in that four of the fuel tanks lie within the pressure hull and that two of the variable ballast tanks are fitted for carrying fuel. No expansion tanks are provide; however, their function is accomplished by small salt water compartments in the lower sections of the normal fuel tanks. Functions of the collecting tank and clean fuel oil tank are accomplished by the two gravity feed tanks located in the engine room overhead.

Filling of oil tank and transfer of oil from storage tanks to the gravity feed tank is accomplished through a manifold arrangement. Test pressures on inboard piping is limited to 28.4 psi. Pumping arrangements are provided with portable connection to the lub oil tranfer pump.

Fuel ooil purification is dependent upon settling and filtration processes; no purifiers are installed. To detect water in the oil or dirty oil, numerous sight glasses and settling gauges on sampling lines are installed.

The fuel oil service arrangements are essentially similar to those on U.S. submarines. However, no permanently connected standby pump is provided; the functions of the latter are for the most part accomplished by the gravity head on the feed tank. It is also possible to use the lub oil tansfer pump on the service system, if necessary.

This is just brief summary of the system. I can go into greater detail which is about six pages long.

Scott