On the IX-C submarine the diesel engine and its associated machinery have a forced lubrication system and an oil purifying arrangement while each of the remaining propulsion components requiring lubrication, namely, the main motor bearings and the main thrust bearings, has a self-contained gravity system.  
          The lub oil system used with the diesel engine and its components is for the most part standard.  Piping layouts are similar to those on Electric Boat Company designs, especially with regard to an extensive use of central manifolds.  Filters, strainers, oil purifiers and oil coolers are similar to available U.S. commercial equipment.  Total storage tank capacity is equivalent to U.S. submarine standards; however, individual diesel engine sump tanks are much shorter and of only half the storage capacity.  The major differences from U.S. submarine practice are in the installation on the German vessels of a contaminated oil system, and the use of portable hose and interchangeable pipe connections to permit use of the hand and power driven detached pumps with fuel oil or other systems. In addition, salt water cooling of the main engine lubricating oil is used, compared with the more elaborate fresh water system for that purpose on U.S. submarines.  
June, 1946
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C  O  N  F  I  D  E  N  T  I  A  L
          The forced lubrication system on the IX-C submarine is tied in with an oil purifying arrangement in a manner similar to U.S. submarine practice.  However, within both the lubrication and purifying systems, i.e: in tank design and in piping layouts, several basic and numerous minor differences exist.  
          On each IX-C there are three lub oil storage tanks containing a total of 2620 gals. when 95% full, two diesel engine sump tanks containing a total of 418 gals. when 75% full, and a contaminated oil tank of 296 gals. capacity.  Two of the storage tanks are in the forward end of the pump room and the third is on the after port side of the battery room.  They are of light construction and tested at 11.4 psi.  The port and starboard engine sumps are set low within the pressure hull, extend beyond the centerline of the compartment in a transverse direction and run fore and aft less than one-third the length of the diesel engine (6.5 ft.).  The contaminated oil tank is 9.8 ft. long and is set aft of the sump tanks in the center of the compartment.  On late Electric Boat and Portsmouth designs each main engine sump is built the full length of the engine and contains 382 gals. and 442 gals. respectively - nearly double the IX-C sump capacity, although the diesel engine is smaller and of lower rating then the German diesel.  
          The fuel oil is transferred from the storage tanks to the individual sumps by a lub oil transfer pump or, in emergencies, by a hand lub oil pump.  Three distribution manifolds are located in the engine room adjacent to the pumps - one manifold to select the storage tank to be used, a second one to permit use of the hand or transfer pump for flushing of the main engines and a third master manifold tying in the pumps with the above two manifolds, the lub oil filling line and the individual engine sumps.  On the suction and discharge sides of the transfer pump there are two short sections of lub oil piping that can be removed and replaced by two sections of different shape which tie directly into the fuel oil transfer system, thereby permitting the use of the pump for transferring either lub or fuel oil.  Portable hose connections on the  
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  suction and discharge side of the hand lub oil pump permit the additional use of the pump with the fuel oil and circulating water systems.  
         The forced lubricating system is very similar to the corresponding U.S. system and differs only in minor details.  The system is similar to U.S. practice in that the attached pump take a suction from the sump through a stop-check valve and discharges the oil through an oil cooler and knife-edge filter to the engine.  Also, there is a relief valve (set at 42.6 psi.) on the pressure side of the pump and a bleed off line to the transfer pump and oil purifying system.  However, in addition, the systems on the IX-C are cross-connected (a former U.S. practice when only two diesels were installed) and a second pressure relief valve (set at 56.8 psi.), with a discharge to the sump and located on the discharge side of the lub oil cooler, limits the pressure of the oil entering the engine.  (The circulating water pressure is at all times kept below that of the lub oil.)  No pressure bypass around the coolers is used and the differential pressure gauge normally around both coolers and filter is placed only around the knife-edge filter.  "Cuno" type filters and circular tube, multi-pass oil coolers are used.  The IX-C coolers have much less total cooling surface area then the U.S. submarine coolers, mainly because of the use of fresh water cooling on the latter.  
          The oil purifying system on the IX-C is of much lower capacity and is arranged to function in a somewhat different manner from the system as set up on U.S. submarines.  A single, standard DeLaval purifier, rated at 79.2 gals./hour is installed, while on U.S. vessels two 250-gals./hour purifiers are used.  The piping, pumps and heaters on the IX-C purifier system form an independent system and the units are selected with only that one service in mind, whereas the purifier pump and heater on U.S. vessels are of greater capacity than required for purification alone and are piped so as to be used also for transferring and heating oil from storage of sump tanks.  This dual service requires the installation of a "flow" regulating valve that isn't required with the IX-C arrangement.  A further difference exists in that the German purifier functions on a separator principle requiring a separate salt water feed line and salt water heater that need be kept in constant use and adjustment.  The Sharples purifier on U.S. vessels is presently used only as a clarifier and does not require a separate salt water feed line.  The German purifying arrangement with temperature and flow regulation on both the lub oil and salt water  
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  lines requires more attention during operation then on the U.S. setup with only temperature regulation on the lub oil line.  
          The contaminated oil system installed is tied into the lub oil purifying and transfer systems.  In addition to the tank previously mentioned, a hand pump is also provided.  There are four separate pipes connected to the contaminated oil tank, namely, discharges from the purifier and auxiliary drain pump, a common suction and discharge to the lub oil transfer line, and a vent line.  The hand pump can take suction from the transfer line or directly from either of the engine sump tanks and discharge it to the contaminated oil tank.  The oil can be removed from the tank by the hand pump, purifier pump of the transfer pump.  
          The diesel engine is the only unit having forced lubrication, the remaining units of the propulsion system have independent built-in lubricating oil arrangements and require individual servicing.  
          The main motor bearings have small individual lub oil sumps (not interconnected).  Fixed oil rings rotating with the shaft and bearing against radial white metal surfaces built into the bearing carry the oil to the top of the bearing.  Small knife-like wipers at the top of the bearing remove the oil, whence it flows by gravity to the bearing surfaces.  To provide means for cooling the bearing, circulating water tubes are imbedded into both the longitudinal and radial white metal bearing surfaces of the lower bearing shells.  The thrust of the motor arising from excessive trim angles is taken by the radial bearing surfaces through the medium of the fixed oil rings.  
          The propeller thrust bearing has a much larger lub oil sump than that for each motor bearing.  Two set of copper-nickel cooling cells, one in the sump and the other close to the under part of the bearing, are used for cooling.  The oil is carried to the upper part of the bearing by the thrust collar where it is removed by wiper plates and fed by gravity to the bearing surfaces.  The excess oil flows through a drain pipe to the lower part of the sump, thereby providing a desired amount of circulation.  
          In the German lubricating systems there are numerous places wherein salt water can enter the lub oil from leakage in the cooling water piping.  The German designers were evidently aware of this prevalent source of trouble and have taken certain steps to keep it to a minimum.  Their maintenance instructions call for continual inspections and  
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  oil sampling to detect its presence; also, corrosion of salt water piping is held in check by using anti-corrosion oil in it when machinery os left idle for short periods of time.  The specifications for the type of lub oil to be used call for an oil that will not emulsify with salt or fresh water.  This permits ready separation of the water from the lub oil if detected in a sump or storage tank.  
          a.  Lub oil transfer pump  
Power (KW)
Press. (psi)
Capacity (CFM)
          b.  Attached lub oil pump  
Type - Gear
R.P.M - 705
Capacity - 262 GPM
Operating Pressure - 71 psi
Test pressure - 106 psi
          c.  Lub oil coolers  
Tube diameter (inner) - .394 ins.
Tube wall thickness - .040 ins.
Tube length - 26.8 ins.
Total cooling surface - 345 sq. ft.
Temp. of oil inlet - Not greater than 104°F
Temp. of oil outlet - Not less than 68°F
          d.  Lub oil purifier  
114 lbs.
114 lbs.
110 -
Power Output (HP)
79.2 gals/hour
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          e.  Lub oil purifier pumps  
Driver L.O. purifier motor
No. 2 in same housing
Weight 22 lbs. total
R.P.M. 1270/1600
Suction head 13 ft.
Discharge head 65.6 ft.
          f.  Lub oil specifications  
Viscosity Engler at 50°C
Flash point
Fire point
Should not emulsify when mixed with salt or fresh water
           The lubrication of the propulsion units on the IX-C is accomplished in a very basic manner and with the use od a minimum of weight and space.  Reliance on gravity feed lubrication for all units but the diesel engines decreases the weight requirements for the lubrication of these units to a very minimum; the use of salt water cooling and simple purifying arrangements in the diesel engine lubricating system keeps the weight and space requirements of this system also at a minimum.  Much care, however, is required to prevent salt water leakage into the lub oil.  The simplicity, ruggedness and slow R.P.M. of the propulsion units, in particular the diesel engine, make possible the installation of such a simplified arrangement.  The design and rotating speeds of corresponding U.S. equipment, however, do not permit a similar setup.  
          The use of smaller engine sumps, utilizing the space saved for a contaminated oil tank is recommended for adoption on U.S. submarines.  
          Further exploitation of the lub oil system on this type is not recommended as there are no features warranting it.  
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