Finial Comments

The compressed air sotrage capacity is smaller than that on World War II U.S. submarines. The diesel compressor, while it was installed as an auxililary to the electric, in later types of vessel became the principle compressor with the electric compressor as a standby unit. The diesel compressor is a compact, efficient unit which the germans found very reliable, although there has been some informal reports of maintenance difficulty by Amercian crews which may be in large part caused by unfamiliarity and lack of adequate instruction material in english. The extensive use of cast iron on the electric compressor is unfortunate.

The high pressure air system is designed to provide alternate paths for some essential services in case of a need to secure the high pressure manifold. Air for blowing tanks, however, is not available unless the manifold is in operation.

The valves on the manifold are of considerable interest, for they are of the non-packed stem type with a laped fit between the collar on the stem and the related shoulder inside the valve bonnet, and with conical disca and seats. After the war, one of these valves had been cycled 30000 times at the Naval Shipyard, Portsmouth without developing a leak either through the stem or seat. It was easily operable at all times. Informal information from menbers of U.S. Naval crews on german vessels does not bear out the test described, for they report considerable trouble with leakey manifold valves. It is possible that, from the standpoint of the effect of depth chrages, the ease of operation encountered could be a disadvantage if there were any tnedency for the valve to back off the seat under shock conditions.

The arrangement and operation of the high pressure blowing arrangements is not entirely satisfactory. Scrw type valves are used throughout, and a change in set-up cannot be made instantaneously, as it requires operation of two or more valves to effect the change and start blowing.

The vent valve operating arrangements are also relatively inflexible, although the mechanism of the individual vent vlaves ans their operating gear are extremely simple. The extensive use of cocks os also of interest.
The torpedo tube draining and filling system is also simple but effective. Here too, cocks play a major role.
The one way plane clucth operating gear is inderstood to be accounted for by the fact that corrective work is necessary at the location of the plane operating gear in any event, so a return line to reverse the clutching operation is unecessay. This does not appear satisfactory, for the reestablishment of power operation with the existing arrangement reuqires a certain amount of interlocking operation between the torpedo room and the control room. Without such interlock, the planesman may find himself with a dead handwheel.
The exhaust gas blow system has both good and bad points.

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

At the same time, the system as engineered permits water and/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 there is no angle on the boat. In addition to the instructions contained in the insrtuction books on the exhaust gas piping system, part VI of the special war experience book-machinery section - is devoted to discussion of the hazards. Mention is made of running under, cuased by lack of teamwork between the control and engine rooms, diffidukty of maintaining tight vlaves with the small bandwheele provideed, and uncontrollable masses of water in the blow piping caused by lack of vlave tightness and the effect of this water on the trim and weight. Also inadvertent blowing of ballast tanks when snorkeling, caused by lack of tightness in the exaust gas blow system valves, and the resultant difficulty in controoing depth.

With reference to the need to retain an "O" angle mentioned above, this is related to the method employed for blowing in which all tanks are blown simultaneously. The effect of any pronounced angle is to intrduce an appreciable difference in pressrue between one tank and another at the point whrer the bllow line enters the tank. The result of blowing with a 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.