CONFIDENTIAL REPORT 2G-21
S45
     
 
FORMER GERMAN SUBMARINE TYPE XXI
 
 
 
 
LUBRICATION
  
     
 
SUMMARY
  
     
          The forced lubrication system for the diesel engine is laid out in most respects like that on the type IX-C and X-B submarines.  An additional attached lub oil pump services the bearings of the exhaust turbine that drives the supercharger when fitted.  
          A forced lubrication system independent of that set up for the diesel engine is used with the remainder of the propulsion arrangement.  This system services the main motor bearings, the reduction gears, the jaw clutches, the Vulcan coupling and the main thrust bearings.  Two attached pumps furnish the lub oil when the machinery is in operation and a separate detached pump furnishes lub oil for flushing or emergency operations.  
          The transfer system used with older type subs has not been adopted for the XXI.  In contrast to the former wide use of manifolds on the type IX and X-B submarines, separate suction and discharge lines run the entire length of the motor and engine rooms; individual suction and discharge cutouts to these lines are located at each tank.  
          The lub oil purifying equipment, although installed as a small compact unit, is of low capacity and does not appear adequate to keep the oil in all the pumps properly purified under all service conditions.  
     
     
     
 
June, 1946
 
 
 
 
PORTSMOUTH NAVAL SHIPYARD, PORTSMOUTH, N. H.
 
     
     
     
 
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  REPORT 2G-21
S45
     
 
LUBRICATION
  
     
  1.  INTRODUCTION  
          Report 2G-9C-S45 gives a description of and comments on the IX-C lubricating system.  Those parts of the forced lubrication system for the diesel engines and of the purifying arrangements that are similar to the ones on the IX-C will not be covered in detail in this section  
     
  2.  GENERAL DESCRIPTION  
          In contrast to the requirements on earlier German types, the lubricating systems on the type XXI submarine had to be laid out to provide forward lubrication for not only the diesel engines but also for practically all of the remaining propulsion equipment.  To do this two independent systems were set up, a relatively high pressure system with the diesel engines and a low pressure system for all of the remaining equipment.  The layout of the former allows IX-C practices while the latter is basically similar to the corresponding part of the lub oil arrangement on U.S. submarines.  
          The diesel engine lubricating system has only two piping changes from the IX-C arrangement.  A priming line to the suction side of the pump permits the diesel transfer pump to automatically prime the pump while flushing the system.  Also, the absorbent type filter on the suction side of the attached pump has been eliminated as it was on the XB.  The pressure bypass relief valve around the attached pump is set at 71.0 psi.  The bypass relief to the sump on the intake side of the engine is set to give a lub oil pressure of 37 psi at 400 - 520 engine RPM at the engine.  The fact that the cooling water pressure is at all times kept below the lub oil pressure reduces the possibility of salt water leakage into the lub oil.  
          A standard forced lubrication arrangement has been installed for the remaining bearings, couplings and gears that require lubrication.  A motor driven pump is set up so as to furnish flushing oil to either or both port and starboard systems from a port or starboard sump.  A pressure relief valve is on the discharge side of the pump.  
     
 
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  REPORT 2G-21
S45
     
  This pump is not connected to the transfer line, however.  The main lub oil service pumps for this system are attached to the main motor reduction gears.  They deliver the oil from the sump through a Cuno type knife-edge filter, through a circular tube oil cooler (salt water cooled) to a branch line running to the units to be lubricated.  Cutout valves are on this branch line to secure the oil to the diesel reduction gears and to the Vulcan coupling when they are not in use.  A second valve is placed in the group leading to the components within the MM reduction gear casing.  The units lubricated include the main diesel jaw clutches, the main thrust bearing, the reduction gears and the reduction gear bearings.  
          The lub oil lines leading to the individual main motor bearings have sight glasses and stop valves to permit proper adjustment of flow to the bearings.  To provide added flexibility, the port and starboard systems are cross connected.  
          Two features of the XXI setup prevent the flooding of the main motors.  The main sumps for this system are built in pressure tight tanks placed below the circular hull, thereby increasing the trim angle that may be taken before a "pressure head" is put on the after main motor bearing; the second and more important feature is in the manner of installation of the main motor bearings.  An appreciable air space has been placed between the bearing and the motor housing, and a good housing seal has been provided so that flooding of the motor itself is practically impossible.  
          The lub oil tanks have all been placed in the after part of the vessel.  One storage tank is in the after room, two storage tanks in the motor room and a fourth under the forward end of the diesels in the engine room.  The engine sumps are placed under the after third of each engine.  The reduction gear sumps overlap slightly into the engine room from the motor room.  All of these lub oil tanks with the exception of the reduction gear sumps are placed within the bilges of the pressure hull.  (It is to be noted that the figure eight hull does not extend aft of the forward engine room bulkhead).  
          The lub oil filling and transfer system is basically similar to the setup on Portsmouth design submarines.  A separate suction line runs from the storage tank in the after room to the transfer and hand pumps in the forward  
     
 
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  REPORT 2G-21
S45
     
  end of the engine room.  Stop-check valves are on the lead-off lines to the engine sumps and stop valves are on the lead-off lines to the remaining tanks.  The discharge line runs only to the contaminated oil tank and the four sumps.  With this arrangement is is not possible to transfer oil from one storage tank directly to another.  The hand lub oil pump and the transfer pump are connected in parallel so that either can be used on the system.  
          The same purifying system with a De Laval oil purifier, attached pumps, and a seawater and lub oil preheaters as used on the IX-C submarines is used on this type.  The suction and discharge piping arrangements to the tanks, however, are different.  The manifold arrangements have been dropped and individual cutouts are provided at each of the four sumps and the contaminated oil tank.  The suction line from the tanks is independent of the transfer piping.  The discharge line to the tanks, however, is a common line.  
          The compactness of the purifying unit is particularly noteworthy.  The driving motor; purifier pumps and purifier are built integral so as to occupy a minimum of space within the vessel.  The pump housing is directly over the motor, and the purifier is placed over the pump housing to form a tight rectangle in cross-section.  
          The contaminated oil system is changed somewhat from that existent on the IX-C.  On the XXI the hand lub oil pump is used for handling contaminated oil.  A portable hose connection is provided at the pump's suction and on the purifier suction piping leading to the sump and contaminated oil tanks.  The discharge can be sent directly to the dirty oil tank through an independent discharge line.  Unless care is observed, contamination of transfer and service lines is possible with this arrangement.  
     
  3.  INDIVIDUAL COMPONENTS  
          a.  Diesel lub oil system  
                  (1)  Attached lub oil pump  
 
Type
-
 Gear pump
RPM
-
 780
Capacity
-
 211 gals./min.
Oper. press
-
 85.2 psi
Oper. press. (piping)
-
 71.0 psi
 
     
 
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  REPORT 2G-21
S45
     
                  (2)  Lub oil cooler  
 
Pipe size
-
 Inner dia.
-
 .394 ins
 
-
 Wall thick.
-
 0.39 ins.
 
-
 Length
-
 26.2 ins.
Cooling surface
-
  
-
 102 sq.ft.
 
                  (3)  Exhaust turbine lub oil pump  
 
Type
-
 Gear pump
RPM
-
 1250
Delivery
-
 3.3 gals./min.
Press
-
 14.2 psi
 
                  (4)  Transfer lub oil pump  
 
 
Pump
Motor
Weight
300
406
Oper. press.
71.0 psi
RPM
2100
2600
2100
2600
Voltage
110
170
KW
8.1
10.3
Capacity (GPM)
132
169
 
     
          b.  Main motor and reduction gear lub oil system  
                  (1)  Attached lub oil pump (to MM reduction gear)  
 
Type
-
 Gear pump
Weight
-
 297 lbs.
Delivery
-
 220 gals./min.
Del. press.
-
 21.3 psi
 
                  (2)  Detached lub oil pump  
 
 
Pump
Motor
Weight
279
285
Oper. press.
21.3 psi
RPM
2100
2600
2100
2600
Voltage
110
170
KW
4.0
5.0
Capacity (GPM)
148
188
 
                  (3)  Lub oil cooler  
 
Weight 837 lbs.
Cooling surface 162 sq.ft.
 
     
 
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  REPORT 2G-21
S45
     
          c.  Lub oil tank capacities (100% full)  
 
No. 1 Storage tank
925 gals.
 
No. 2 Storage tank
528 gals.
 
No. 3 Storage tank
528 gals.
 
No. 4 Storage tank
1080 gals.
 
Gear Sump tank (port)
378 gals.
 
Gear Sump tank (stbd.)
385 gals.
  
Engine sump tank (port)
359 gals.
 
Engine sump tank (stbd.)
359 gals.
 
Contaminated oil tank
299 gals.
  
 
          d. Lub oil purifying system  
                  (1)  Purifier  
 
Weight
-
 220 lbs.
RPM
-
 9250    12000
Capacity
-
 66 gals./hr.
 
                  (2)  Preheaters  
 
 
Seawater
Contaminated Oil
Length
305
381
Breadth
35
35
Width
67
79
Rating
6 KW
12 KW
 
     
  4.  CONCLUSIONS  
          Except for the inadequate capacity of the purifying arrangements, the lub oil systems on the XXI appear well designed and sufficiently balanced to insure proper lubrication of the units serviced under all operating conditions.  However, with salt water cooling of lub oil constant care is necessary to prevent contamination of the oil.  
          A noticeable change from earlier German designs is in the elimination of manifolds from the lub oil systems.  The simplification and weight saved by the use in lieu thereof of individual tank cutout valves more than balances the added time required to line up tanks to be used, especially inasmuch as all the valves concerned are situated within the main motor and main engine compartments.  
          The compactness of the purifying arrangement is of note, and points the way to possible improvement in the purifying arrangements on U.S. submarines.  
     
 
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