Two nine-cylinder, supercharged four-cycle MANN diesel engines with salt water cooling are installed on the Type IXC submarines. On some vessels of this class the supercharger is driven by an exhaust turbine and on others it is driven mechanically. The diesel engines provide power for proplusion or battery charging both on the surface and submerged (running on snorkel) and provide exhaust gas for blowing main ballast tanks after surfacing, this is lieu of low pressure air.

The snorkel operation was not contemplated in the original engine design as it was an alteration made after the vessel was placed in service. The original diesel design had two sets of cams, one for ahead and one for astern operation. When the snorkel was installed on the submarine the reverse cam on the diesel engine was removed and a snorkel cam was put in its place. This speical cam, by decreasing valve overlap, keeps the exhaust gas temperatures within allowable limits during periods of high back pressure. The exhaust temperatures on the MANN diesel run considerably higher than on the U.S. submairne diesels, maximum temperatures are 1022 degree F and 770 degree F respectively.

A vibration dampener and vibration indicator are on the forward end of the crankshaft. The dampener is a mass inertia flywheel type with eight individuel sets of leaf springs serving as the coulping agent.

Each diesel engine normally has a 200 liter (7.06 cu ft.) starting air flask. The flask when provided are filled from high pressure line through a reducing valve set at 1060 psi. A second reducing valve is inserted in the line to the diesel engine to decrease the pressure to 426 psi.

Two main air induction lines (port and starboard) run from immediately aft of the conning tower, along the out side of the pressure hull, and into the engine room at the forward end of the diesels. The head valve lies just beneath the bridge deck. To give added spray protection an air intake chute leads from this valve up through the conning tower fairwater. The air induction pipe has an inside diameter of 20 in. and wall thickness of .236 in., and is tested to 355 psi so as to be able to take some additional depth charge pressure over and above submergence pressure. Flanged construction is used throughout; all parts are made from medium steel and are galvanized. Inboard of the hull valve the air passes through a flat rectangular duct (55 in. X 8.9 in.) that follows the contour of the hull to a point below the floor plates. This serves to direct all water spray into the bilges.

The head valve and hull valve are very similar in construction. They both close with pressure and have a sloping seat. Dovertail tpye rubber gaskets are used on the dis; a special brass composition ( similar to manganese bronze) is used for the valve seat. Both valves are hand operated and have built-in locking features.The bonnet for the head valve is part of a short bell shaped casting that is secured to the induction piping and contains the valve seat. A drain connection leads inboard from a point directly below the valve.

The valve bonnet for the hull valve is part of a casting to which the inboard duct is secured. The casting serves to bring about a change in direction to the air as it comes inboard and passes into the rectangular duct. Thevalve housing, discs, ect; are made from a good grade of medium steel.

Independent port and starboard exhaust systems are installed. The exhaust from each engine passes through an inboard and outboard exhaust vlave, through the muffer, a damper an exhaust elbow, spark arrestor and the overboard through openings just below the main deck level. All units are waterjacketed.

Part 2 later. The Captain.