I have only information on the low pressure exhaust gas blow system that was used on the following boats: Type IXC, IXC40 IXD2, XB AND XXI.

The exhaust gas blow system consists of a pipe extending forward from a point between the inboard and outboard main engine exhaust valves port and starboard, which is joined together and led forward to a manifold in the superstrucure over the control room. There is a stop valve in the pipe to the manifold which serves as a main blow valve.

From the maniflod, individual piping runs extend to MBT 1, FBT4, FBT3, each half of MBT5, TO FBT6, FBT7 and MBT8. The eight associated valves at the manifold are normally open, although they are operable from within the control room.

Normal operation involves starting the main engine as soon as the vessel surfaces, and by throttling the exhaust gas line diverting all or a part of the exhaust gas via the main blow valve and the manifold to the tanks listed above, which are blown simulktaneously when the main blow valve is opened. Pressure gauges in the engine room and at the main blow valve assist in controlling the exhaust gas pressure, which is not supposed to exceed 10 psi.

The exhaust gas blow system has both good and bad points.

Use of exhaust gas for blowing tanks on the surface eliminates the need to install a low pressure blower with its related piping and fittings. The location of the piping and manifold in the superstrucure saves space within the pressure hull, and eliminates the need for high pressure fittings.

At the same time, the system as engineered permits waterand/or air to siphon from one tank to another, as the only valves which separate one tank from another are the ones at the manifold, which are normally left open.

The Germans have been at great pains to specify that blowing with the low pressure system should be done only when htere is no angle on the boat.

With referance to the need to retain an "O" angle mentioned above, this is related to the metod employed for blowing in which all tanks are blown simultaneously. The affect of any pronounced angle is to introduce as appreciable difference in pressure between one tank and another at the point where the blow line enters the tank. The result of blowing with aa pronounced trim angle would be that the exhaust gases, taking the path of least resistance, would blow the highest tank first and in a dynamic state where the trim angle was changing, could permit tanks previously blown to flood again by way of the open blow line.

I hope this helps to understand the low pressure exhaust gas system in the boats.

Scott Sorenson