CONFIDENTIAL REPORT 2G-9C S48-1
	FORMER GERMAN SUBMARINE TYPE IX-C
	PUMPING AND DRAINAGE SYSTEMS
	SUMMARY
	A trim and drainage system similar in many respects to the system on U.S. submarines has been installed on the IXC submarine.  The main drain, and auxiliary drain and trim pump in the control room correspond to the U.S. trim and U.S. drain pumps, respectively, although their basic functions are reversed.  Some additional flexibility and capacity have been provided on the German arrangement, however, by the installation of separate centrifugal drain pumps, of limited discharge head, in the forward and after torpedo rooms.
	July, 1946
	PORTSMOUTH NAVAL SHIPYARD, PORTSMOUTH, N. H.
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	1.  General Description
	The German trim and drainage arrangements on the IXC submarine are divided into two interconnected systems, a main drainage system and an auxiliary drainage and trimming system.
	The main drainage system is serviced by a relatively high powered four stage centrifugal pump in the control room.  The pump can be operated with the four stages in series to discharge against designed submergence heads or with two pairs of stages in parallel to deliver high capacities against heads up to 50 meters (164 ft.)  This pump has a small built-in centrifugal vacuum pump that can be cut in to remove air from the suction piping and obtain greater suction heads.  Specifications in the pump instruction book state that the pump shall be able to place a vacuum of approximately 12 inches on a 198 gallon container in one minute.  During series operation the water enters the main suction valve, passes through the first two stages (in series), then passes via an external pipe and cut-out valve to the remaining two stages.  During parallel operation a cut-out valve within the pump housing is opened to permit parallel flow to the first and third stages.  A second shut-out valve within the pump housing is opened to connect the discharges from the second and fourth stages.  The pump is directly connected to the driving motor by a flexible coupling.
	The main drain pump can take a suction from the main drain piping that services all compartments, from sea, from the auxiliary ballast tanks or from the auxiliary trim and drainage suction piping.  The main drain line from each compartment leads into a master manifold in the control room.  A line leads from this manifold to the main suction manifold for the drain pump.  The pump can discharge to an auxiliary ballast tank, directly to sea, to No. 5 starboard ballast tank or to the auxiliary drainage and trim discharge piping.  Stop-check valves that may be operated from adjacent compartments are installed on the suction piping of all compartment drain lines.  Stop-check valves are also on the discharge side of the drain pump.  Portable hose connections are of the suction piping in the engine room and galley.
	The auxiliary drain and trimming system is divided into two independent sections, one section that is serviced by the auxiliary drain and trim pump located in the control room and the second that is serviced by the
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	two small auxiliary drain pumps that are located in the forward and after torpedo rooms.
	The auxiliary drain and trim pump is a ruggedly built 2-piston reciprocating pump that corresponds closely in size and service to the Gardner-Denver drain pump used on U.S. Submarines.  The German pump is double acting while the U.S. one is single acting. The capacity of the German pump is materially higher than the U.S. pump while the pressure is somewhat less (150/200 psi.).  The main differences are in the cylinder, and in the power transmission to the piston from the crankshaft.  The IXC design has a crosshead between the piston and crankshaft.  Because of this the cylinder can be sealed by packing around the piston rod.  Also, the double action feature requires an additional suction and discharge valve for each cylinder.  On the U.S. drain pump the piston rod connects directly to the crankshaft, which, in turn, necessitates a seal between the cylinder liner and the piston.  The volume over the piston is the working surface in this case.  The motor for the U.S. and the German pumps are coupled alongside and above the pump, respectively.
	The pump's service is essentially as its name implies.  It is used primarily as a trim pump and acts as an auxiliary pump for use on the main drain system (up to designed submergence).  The pump can take a suction from either trim tank or from the main drain suction.  It can discharge to the opposite tank or from the main drain suction.  It can discharge to the opposite trim tank or to the main drain discharge piping.  Portable hose fittings, for deck washing and for emergency service, are also on the discharge line from this pump.  A flow meter is installed in the trim line.  Also, a reversible exchange valve is in the trim line between the two trim tanks. This valve when set in one position sets up one tank on the suction side of the pump and the other tank on the discharge side of the pump; in the second position the operation is reversed.  Several of the IXC submarines have been rigged for blowing the trim tanks.  In this case a by-pass line and stop valve have been installed around this exchange valve.
	The two small auxiliary drain pumps are single stage centrifugal pumps.  They are meant primarily for use during surface or shallow submergence as their maximum discharge head and test pressure is limited.  The pump is fitted with a similar vacuum pump as built in the main drain pump.  Instruction book specifications call for this pump to develop a vacuum of approximately
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	12" in one minute in a 66 gallon container.
	These drain pumps are used mainly for drainage of the forward WRT tanks, the torpedo rooms and the compartments adjacent to them.  This pump discharges directly to sea through a stop-check and a hull valve.  A cross connection exists between both the forward and the after auxiliary drain pump suction lines and the main drain suction line, giving added flexibility to the entire drainage system.
	Additional drainage in the engine room is provided by a bilge suction connection to the standby circulating water pump.
	2.  Operation
	The reciprocating drain pump acts as a general service pump for handling small quantities of water.  Its ruggedness makes it suitable for this duty.  However, it is a comparatively noisy pump and was not to be used when in contact with the enemy.
	The centrifugal drain pump in the control room was used to handle larger quantities of water.  When in operating areas and subject to sound detection this pump was invariably used in lieu of the noisier reciprocating pump.  To prevent slicks the contaminated water was pumped into No. 5 starboard ballast tank (this tank has been fitted with flood valves).
	The small centrifugal pumps in the forward and after rooms can be used for discharging small quantities of water from the torpedo and adjacent compartments in addition to their use for pumping WRT tanks.  Although they are silent pumps and can take a ready suction from these after compartments they are limited in operation by two features of design.  The pumps discharge directly to sea so cannot be used to pump contaminated bilge water when the vessel is in operating areas.  Furthermore, the pumps cannot discharge against heads in excess of 100 - 150 ft. (dependent on battery voltage) so that they cannot be used to take a ready suction from the forward and after compartments with a large angle on the boat when the control room pumps would lose suction on these compartments.
	The centrifugal pumps can be used with air pressure to pump against heads in excess of those designed submergence (100 meters, 328 ft.).  This was found necessary as the submarines were forced below this depth
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	on numerous occasions.  Bilge water first had to be pumped into the auxiliary ballast tank, and then pumped overboard after placing the necessary "boosting" air pressure on this tank.  The machinery information book (M u E Kunde fur U Boote Bauart IXC) states that the most favourable pressure differential between intake and discharge on the main drain pump when pumping from the regulating tank at greater depths is 114 p.s.i., and that the variable tank pressure must be adjusted accordingly.  The pressure given is the one at which the drain pump motor takes maximum power.
	The use of the drain system is further described in the book on special wartime experience (Besondere Kriegser fahrungen - Abschmitt Maschine), in parts II and XVII, and on page 102.
	In part II, devoted to depth control, mention is made of the necessity to pump while increasing depth to avoid falling beyond the desired point and a figure of 3/4 to 1 (metric) ton for 20 meters is given.  This is 2520 to 3360 pounds per hundred feet, which confirms the findings of the Woods Hole Oceanographic Institution reported in their confidential letter of 14 June 1946 to the Bureau of Ships. In that letter they report that information from the Germans gave 1000 liters pumped to dive 100 meters, whereas the vessels IXC, IXD and XB they had experimented with ran, respectively 1850, 2930 and 2750 pounds for 100 feet.  These figures would give, for U.S. submarines, 3600, 3900 and 3000 lbs. equivalent.
	Further mention is made in the same section to the need for operating the drain pump to the limit of practicable rating "when approaching a heavy depth", and to the difficulty of draining with compressed air alone because of noise and the possibility of straining bulkheads.  Recommendation is made that a pressure of 10 to 12 atmospheres be maintained on the regulating tank to relieve the head on the drain pump.
	Section XVII further amplifies this operation by mention of the fact that where vessels have multiple regulating tanks available, two tanks should be rigged for drain, of which one is under a pressure of 10 to 12 kg/cm2 as a deep drain regulator and the other is carried at about 2.5 kg/cm2 for use at periscope depth.
	Both section II and section XVII mention the need to apply pressure to the regulating bunkers and the negative tanks if pressures higher than 14 atmospheres are placed on the regulating tank, in order to relieve the pressure on the end bulkheads of the regulating tank, which lies between the other two.
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	Section II also mentions that some vessels tend to become heavy aft at greater depths and that water in the after bilges is to be pumped into the regulating tank or bunker which is not under pressure by using hose connections to the main drain or the auxiliary drain and trim pump.
	Page 102 of the war experience book states that the flooding of the main drain line in order to take suction from the forward or after compartments is a necessary evil, and that if proper operation is not followed the vessel can be enhazarded by flooding the battery compartment or maneuvering room.  The time taken to flood the line must be known, and if it is not flooded by the end of that time there must be a leaky valve somewhere.  The instructions also include a direction to watch the battery and maneuvering room bilges all during the time the main fore-and-aft drain line is flooded.
	3.  Individual Components
	(a)  Main drain pump characteristics
	Pump Motor Type - 4 stage centrifugal Weight - 572 lbs.   1150 lbs. Overall Dimensions - 12.8" dia x 40.4" 23.2" dia x 35" Voltage -     110 170 RPM - 2600 3000 2600 3000 Power (Parallel) - 38.5 HP 58.2 HP 44.4 HP 64.1 HP Power (Series) - 29.6 HP   44.4 HP   Disch. Head (Parallel) - 32.8 ft. 32.8 ft.     Capacity (Parallel) - 528 GPM 572 GPM     Disch. Head (Series) - 344 ft.       Capacity (Series) - 176 GPM       Test Pressure - 284 psi
	(b)  Auxiliary drain pump characteristics
	Pump Motor Type - single state centrifugal Weight - 158 lbs.   227 lbs. Overall Dimensions - 10.5" dia x 22.6" 20" dia x 20.1 " Voltage -     110 170 RPM - 2300 2850 2300 2850 Power - 5.7 9.4 6.4 9.9 Disch. Head - 98.5 ft. 154 ft.     Capacity - 66 GPM 75.8 GPM     Test Pressure - 142 psi
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	(c)  Auxiliary drain and trim pump
	Pump Motor Type - 2 cyl. reciprocating Weight - 725 lbs.   563 lbs. Cylinder Dia x Stroke - 4.13" dia x 3.94"   Voltage -     110 170 RPM - 115 138 1600 1920 Power - 11.3 HP 913.8 HP 11 KW 13.6 KW Disch. Head - 344 ft.       Suction Head - 19,6 ft.       Capacity - 79.3 GPM 93 GPM     Test Pressure (Housing and Air Dome - 284 psi
	4.  Conclusions
	The Germans have provided the IXC with relatively greater pumping capacity for both shallow and deep submergence than is provided on late U.S. submarines.  The pumps, however, have somewhat less maximum discharge heads than in U.S. practice.  The centrifugal main drain pump is of similar, but inferior, design to the U.S. Gould pump.  The latter is more compact and simpler of operation.  The reciprocating auxiliary drain and trim pump, however, is considered superior in design to the Gardner-Denver pump selected for use on U.S. submarines.  The German pump has more than double the delivery at 3/4 the discharge pressure although the pump is lighter in weight and approximately equal in size.  Packing and piston troubles are materially less with the use of the shorter piston and of piston rod packing on the German pump in lieu of the long piston and of cylinder packing on the U.S. pump.  However, valve troubles will be enhanced with the use of the additional suction and discharge valves.
	The greater pumping capacity is related to the unfavorable compression ratio and to the division of the drain system into small segregated units not all of which may be available at a given moment.
	The centrifugal pumps in the forward and after compartment provide additional capacity and flexibility to the drainage system for surface and shallow submergence.  However, they do not fulfill a desired function of insuring pumping facilities to these compartments when the vessel takes and appreciable angle and suction is lost by the control room pumps.  Also, they could be made more effective by the provision of a discharge to a "contaminated" water ballast tank.
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