The hydraulic system is used solely to operate the periscope hoists and rotating gear, and the snorkel raising and lowering mechanism.  It is operated at a high pressure, but is not well designed.  The entire system is sound mounted.  
          Exploitation does not appear warranted.  
March, 1946
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C  O  N  F  I  D  E  N  T  I  A  L
          The hydraulic system is used solely for periscope and snorkel hoists, and for rotation of the fixed eye-level periscope.  
          It consists of three accumulator flasks, one main hydraulic oil pump and one standby, and three hydraulic motors, and one hydraulic ram, together with related piping, tanks and controls.  
          The system operates at pressures from 48 to 80 kg/cm2 (682 to 1148 psi).  The pump cuts in at the lower pressure and cuts out at the upper pressure.  
          The volume of each flask is 200 liters, giving a total volume of 600 liters (21.2 cu. ft.).  Inside each flask is a cork float to reduce the area of the air in contact with the oil.  Extending up into the flask are an oil supply line with a deflector, an oil discharge line, and in one of the flasks two test lines (one at the 6 liter oil level and one at the 12 liter oil level).  A high pressure air connection is fitted to the upper end of each flask, with a reducing valve in the air line to reduce the pressure from 3000 psi to 682 psi.  The effective oil capacity of the three flasks is 14300 cu. in. (234 liters).  
          The main pump is a worm pump (IMO type) with one drive shaft and two idlers, operated by a motor with an intermittent rating of 25.4 to 39.4 H.P., dependent on the voltage, which can vary from 110 to 170 volts.  The pump and motor operate at 1470 to 1820 rpm.  
          The standby pump is similar to the main pump, but smaller, and is operated by a motor with an intermittent rating of 14.1 to 17.2 H.P., dependent on voltage.  The pump and motor operate at 1800 to 2300 rpm.  
          The oil supply tank contains 500 liters (17.6 cu. ft.).  
          The system is placed in operation by first raising the pressure in the flasks to 10 kg/cm2 (142.2 psi); then  
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  pumping oil into the flasks until the level reaches the lower (6 liter) test line.  The pump is then shut down and air is bled into the flasks until the internal pressure is 48 kg/cm2 (682 psi).  
          From this point on, normal cycling of the system is controlled by an automatic pressure-operated switch, which starts the pump at 682 psi and stops it at about 84 kg/cm2 (1195 psi).  Only one pump at a time can be used, and changing from one to the other requires manual operation of a selector switch.  
          The pressure switch is not controlled directly by the pressure on the system, but by the static pressure of the oil in the collecting tank.  The basic assumption made in the design is that for a fixed quantity of oil in the system, the amount of oil in the collecting tank will reflect the use being made of the system, and thereby the pressure on the system.  As oil is pumped from the tank into the flasks, the oil level will be lowered and the pressure reduced, and the switch is calibrated to open the pump motor circuit when the level is lowered to a point which would correspond to the maximum level (and maximum pressure) in the flasks.  As oil is used from the flasks, the level of the oil in the collecting tank (and the related static pressure) increases, and when the oil in the flasks has reached the established minimum, the pressure in the collecting tank has reached the point where the switch should be adjusted to start the pump motor.  
          The control system requires very close attention to the oil in the system, as a number of odd conditions can arise if any improper relationship develops between the oil level in the flasks and in the collecting tank.  
          Flasks are of steel.  Piping is of steel, with copper plated interior surfaces.  Pipe connections consist of a collar with a short conical section adjacent to the gasket laying surface, and a loose flange which rotates freely on the collar.  The end of the pipe is expanded into the conical section and is cut off flush with the normal gasket face of the collar, and solder is run in at the other end of the collar into the annular space between the outer surface of the pipe and the inner surface of the collar.  The two halves of the coupling being made up, a gasket is placed between the two halves, and the bolts on the flange are drawn up to complete the joint.  
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          The entire system, including flasks, collecting tank and piping, is sound-mounted on "Schwingmetall" pads.   
          The system is quite large and cumbersome for the character of the work required.  The cork float does not provide adequate oil-air separation and the system is accordingly subject to disabilities resulting from air entrained in the oil.  The indirect control of the system leads to the possibility of a number of different types of malfunctioning of the system.  The soldering of copper-plated pipes does not insure proper condition of the plating.  The spring loaded bypass valve on the pump is probably affected by wire drawing.  
          The pumps themselves are well designed and are thrust compensated.  
          The motors are light by USN standards, as they run approximately 23 lbs. per horsepower as compared with our 34 lbs. per horsepower for the same system service.  In part, this weight saving has been accomplished by using a motor rating based on intermittent service, but the motors, even so, are no lighter than available American commercial types with continuous ratings the same as the intermittent ratings given above.  
          The system operates at higher pressures than those employed in current U.S. submarine practice.  While certain details of design are of interest as paralleling current U.S. Naval practice, the system as a whole is not well conceived as a compact, reliable, light entity.  
          The type of pipe connection has received favorable comment from pipe manufacturers' representatives who have seen it.  Samples have been supplied for test as requested by the Bureau of Ships, but report on the tests is not currently available.  
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