HNSA Crest with photos of visitors at the ships.
12
MAIN HYDRAULIC SYSTEM
 
A. INTRODUCTION
 
12A1. The increasing use of hydraulic power in the modern submarine. In the development of the submarine from pre-war classes, many changes and improvements have occurred. One of the outstanding differences is the large variety of submarine devices that are now operated by hydraulic power. In early classes, there was no hydraulic system, power requirements were met by means of air or electricity. Along with the steady improvement in submarine design has gone a constant extension and diversification of the use of hydraulic power.

12A2. Other sources of power available on submarines. What is the reason for this noticeable trend toward hydraulics? Obviously, hydraulic actuation is not the only means of transmitting power throughout the submarine. The tasks now being done by the hydraulic system were originally performed by hand, electricity, or compressed air.

a. Hand power. Some equipment on a submarine is still operated exclusively by hand, but this practice is rapidly disappearing. This is because the power requirements exceed that which manual effort can provide for long periods of time, and because power operation is faster and can be remotely controlled, greatly reducing the necessary communication between crew members.

b. Electric Power Since the electrical plant is such an important part of the submarine power system and must be used for propulsion in any event, it would be reasonable to expect that electricity would also be used to operate all of the auxiliary equipment as well.

Electricity is ideally adapted for submarine equipment having few or no moving parts; that is, lamps, radios, cooking facilities, and similar devices. But, it is not so ideal when it is necessary to move heavy apparatus such as the rudder and bow and stern planes, because heavy bulky electrical units are required. Also, when instantaneous

  stopping of the driving mechanism is demanded, electric motors have a tendency to overtravel, or drift, making fine control difficult to achieve. A further disadvantage in the operation of electrical units is the noise made in starting and stopping by relays and magnetic brakes, and by shafting and other mechanical power transmission units.

c. Pneumatic power. Since compressed air must also be used aboard a submarine for certain functions, this system, comprising the compressors, high-pressure air flasks, and air lines, offers another source of auxiliary power. However, pneumatic or compressed air power also has definite shortcomings. Pressure drop caused by leakage, and the mere fact that air is a compressible substance, may result in sponginess or lag in operation. The high pressure necessary for compressed air storage increases the hazard of ruptured lines, with consequent danger to personnel and equipment. Another disadvantage of air systems is that the air compressors require greater maintenance than others and are relatively inefficient.

d. Comparative advantages of hydraulic power. Hydraulic systems possess numerous advantages over other systems of power operation. They are light in weight and are simple and extremely reliable, requiring a minimum of attention and maintenance. Hydraulic controls are sensitive and afford precise controllability. Because of the low inertia of moving parts, they start and stop in complete obedience to the desires of the operator, and their operation is positive. Hydraulic systems are self-lubricated; consequently, there is little wear or corrosion. Their operation is not likely to be interrupted by salt spray or water. Finally, hydraulic units are relatively quiet in operation, an important consideration when detection by the enemy must be avoided.

Therefore, in spite of the presence of the two power sources just described, hydraulics makes its appearance on the submarine

 
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because its operational advantages, when weighed against the disadvantages listed for electricity and air, fully justify the addition of this third source of power in the submarine.

12A3. Hydraulic fluids. Almost any free flowing liquid is suitable as a hydraulic fluid, if it does not chemically injure the hydraulic equipment. For example, an acid, though free flowing would obviously be unsuitable because of corrosion to the metallic parts of the system.

Water as a possible hydraulic fluid, except for its universal availability, suffers from a number of serious disadvantages. One is that it freezes at a relatively high temperature, and in freezing expands with tremendous force, destroying pipes and other equipment. Also, it rusts steel parts and is rather heavy, creating a considerable amount of inertia in a system of any size.

The hydraulic fluid used in submarine hydraulic systems is a light, fast-flowing lubricating oil, which does not freeze or lose its fluidity to any marked degree even at low temperatures, and which possesses the additional advantage of lubricating the internal moving parts of the hydraulic units through which it circulates.

12A4. Basic units of a hydraulic system. A simple, hydraulic system will necessarily include the following basic equipment, which, in one form or another, will be found in every hydraulic system.

1.A reservoir or supply tank containing oil which it supplies to the system as needed, and into which the oil from the return line flows.
2.A pump which supplies the necessary working pressure.
3.A hydraulic cylinder or actuating cylinder which translates the hydraulic power developed in the pump into mechanical energy.
4.A Control valve by means of which the pressure in the actuating cylinder may be maintained or released as desired.
 
5.A check valve placed in the line to allow fluid motion in only one direction.
6.Hydraulic lines, that is, piping to connect the units to each other.

While the functions performed by these six units are typical of every hydraulic system, the units are not always identified by similar names, but rather by names descriptive of the specific operation they perform. The submarine hydraulic system is really four distinct systems: the main hydraulic system, the bow plane tilting system, the stern plane tilting system, and the steering system.

The main hydraulic system performs the bulk of the hydraulic tasks aboard a submarine. Lines from the central power source radiate through the ship to convey fluid under pressure for the operation of a large variety of services. The vent valves of the main ballast, fuel oil ballast, bow buoyancy and safety tanks, and the flood valves of the negative and safety tanks are hydraulically opened and shut by power from the main system. It also operates the engine induction and ship's supply outboard valve, the outer doors of the torpedo tubes, the bow plane rigging gear the windlass and forward capstan, the raising and lowering of the echo ranging and detecting apparatus (sound heads), and the main engine exhaust valves on earlier classes of submarines. In the latest installations, the main engine exhaust valves are operated by pneumatic-hydraulic or air-cushion units. In an emergency, the main hydraulic system is also used to supply power for the steering system and for the tilting of the bow and stern diving planes, although these systems normally have their own independent power supply units.

On the latest classes, the periscopes and antenna masts are also hydraulically operated as units of the main hydraulic system. (In earlier classes, they are electrically operated.)

To perform these numerous tasks, a variety of valves, actuating cylinders, tanks, and manifolds are required, as well as the pumps for building up the required power. The units in the main hydraulic system fall conveniently into five groups:

 
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Drawing of IMO Pump
Figure 12-1. IMO pump.
 
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1.Power generating system.
2.Floods and vents.
3.Periscope and radio mast hoists.
4.Forward and after service lines.
 
5.Emergency systems.

FigureA-19 shows a schematic view of the main hydraulic system in the submarine.

 
B. POWER GENERATING SYSTEM
 
12B1. General arrangement. The power generating system comprises a group of units, the coordinated action of which provides the hydraulic power necessary for the operation of the main hydraulic system. It consists of the following principal parts:

a. The IMO pumps, located in the pump room, which supply hydraulic power to the system.

b. The main supply tank, located in the control room, which contains the oil needed to keep the system filled.

c. The accumulator, located in the pump room, which accumulates the oil from the pump and creates pressure oil which is maintained at a static head for instant use anywhere in the system.

d. The main hydraulic manifolds, located in the control room, which act as distribution and receiving points far the oil used throughout the system.

e. The pilot valve, a two-port, fitted lap-fitted trunk, cam-operated slide valve, located in the pump room, which directs the flow of oil that causes the automatic bypass valve to open or shut.

f. The automatic bypass and nonreturn valves which are located in the pump room. The automatic bypass valve directs the flow of pressure oil in obedience to the action of the pilot valve. The nonreturn valve prevents the oil from escaping through the open automatic bypass.

g. Cutout valves, serving various purposes throughout the system and nonreturn valves which allow one-way flow.

h. The back-pressure tank, or volume tank, located in the control room and containing compressed air at a pressure of 10 to 25 psi, provides the air pressure on top of the oil in the main supply tank which keeps the entire system full of oil.

  i. The accumulator air flask, located in the pump room, which serves as a volume tank for the accumulator, allowing the air to pass to and from it when the accumulator is loading or unloading.

12B2. IMO pump. Hydraulic systems need, in practice, some device to deliver, over a period of time, and as long as required, a definite volume of fluid at the required pressure.

The IMO pump (Figure 12-1) is a power-driven rotary pump, consisting essentially of a cylindrical casing, horizontally mounted, and containing three threaded rotors which rotate inside a close-fitting sleeve, drawing oil in at one end of the sleeve and driving it out at the other end.

The rotors of the IMO pump, which resemble worm gears, are shown in Figure 12-1. The inside diameters of the spiral threaded portions of the rotors are known as the troughs of the thread; the outside diameters or crests are known as the lands. The troughs and lands of adjacent rotors are so closely intermeshed that as they rotate, the meshing surfaces push the oil ahead of them through the sleeve, forming, in effect, a continuous seal so that only a negligible fraction of the oil that is trapped between the lands can leak back in the direction opposite to the flow.

The center rotor is power driven; its shaft is directly coupled to a 15-hp electric motor which drives it at 1750 rpm. The other two rotors, known as idlers, are driven by the center rotor which, through the intermeshing of its threads with the idlers, communicates the shaft power to the idlers and forces them to rotate in a direction opposite to the center rotor. The rotation of the center rotor is clockwise as viewed from the motor end of the coupling shaft, while the two idler rotors rotate counterclockwise.

 
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Drawing of hydraulic accumulator.
Figure 12-2 Hydraulic accumulator.
 
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The end of the power rotor nearest the motor rotates in the guide bushing; the rotor shaft extends out through the end plate, where it couples to the shaft of the electric motor which drives it. Leakage around the shaft is prevented by five rings of 3/8-inch square flexible metallic packing which is held in place by a packing gland. Oil which leaks through the packing gland falls into the drip cup.

12B3. The main supply tank. Fluid is supplied to the pumps from the main supply tank. (See FigureA-9). The shape of this tank varies in different installations. Its total capacity is 50 gallons, but the normal supply maintained is only 30 gallons; the 20-gallon difference is an allowance made for discharge from the accumulator and thermal expansion of the oil.

When the system is operating, the fluid circulates through the power system, returning to the supply tank. However, the fluid will not remain in the supply tank for any length of time, but will be strained and again

  pumped under pressure to the accumulator and the manifolds.

Glass tube sight gages mounted on the side of the reservoir, or supply tank, give minimum and maximum readings of the amount of oil in the tank. A drain line and valve near the bottom of the tank provide a means for draining water that may have accumulated there.

The back-pressure tank is connected by a length of pipe to the top of the supply tank (air inlet). It maintains an air pressure of 10 to 25 psi on the oil in the supply tank. This forms an air cushion between the top of the tank and the body of the fluid and maintains the system in a filled condition. An air relief valve set to lift at 40 pounds prevents the building up of excessive air pressures in the supply tank.

12B4. Accumulator. The 1,500-cubic inch air-loaded hydraulic accumulator is located in the pump room. (See FigureA-19.) Figure 12-2 shows a schematic view of the accumulator.

Photo of Main hydraulic control station.
Figure 12-3. Main hydraulic control station.
 
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The accumulator is essentially a hollow plunger free to move vertically within a stationary oil cylinder and over a stationary hollow air piston. The oil cylinder is connected to the pressure side of the manifold and the hollow air piston is connected to an air flask. The air flask is located in the pump room on the port side. The flask is charged through the accumulator air-loading manifold (located in the control room) from the high-pressure air system to a maximum of 1,950 psi to give a maximum oil pressure of 750 psi. The top of the movable plunger is therefore subjecting oil in the cylinder to a pressure caused by the air pressure with in the plunger. An indicator showing the position of the accumulator plunger is installed in the control room adjacent to the main manifold.

The accumulator performs the following functions:

a.It controls oil delivery to the hydraulic system from the hydraulic pump.
b.It maintains a constant pressure on the hydraulic system.
c.It provides a reserve supply of oil under pressure to permit the operation of gear when the pump is shut down and to supplement the supply of oil from the pump when several hydraulic gears are operated simultaneously.
d.It reduces shock to the system when control valves are operated.

12B5. Main hydraulic control station. Normal operation of the various hydraulically operated units of the vessel is controlled from the main hydraulic control station is the forward port corner of the control room. (See Figure 12-3.)

Here, in one group, are located:

1.The main cutout manifold.
2.The vent control manifold.
3.The flood control and engine air induction manifold.
4.The IMO pump stop and start push buttons.
5.The main plant oil pressure gage.
6.The hydraulic accumulator air pressure gage.
 
7.The manual bypass valve.
8.The pressure cutout valve,
9.The hydraulic accumulator charge indicator.
10.The Christmas Tree.

Thus, all units necessary to control the main hydraulic system are grouped in one place for efficiency and facility of operation.

12B6. Main cutout manifold. The main cutout manifold consists of eight valves, four of which are return valves on the upper row of the manifold, and four of which are supply valves on the lower part of the manifold.

The Supply valves from forward to aft, control the following:

a.Hydraulic service forward.
b.Emergency steering.
c.Emergency bow and stern plane tilting and normal bow plane rigging.
d.Hydraulic service aft.

The return valves from forward to aft, control the following:

a.Hydraulic service forward.
b.Emergency steering.
c.Emergency bow and stern plane tilting and normal bow plane rigging.
d.Hydraulic service aft.

12B7. Pilot valve. The pilot valve is used in the main hydraulic system to operate the automatic bypass valve by directing oil under pressure to the automatic bypass valve piston when the accumulator is fully charged, thereby opening the bypass, and then venting off this oil when the accumulator is discharged, allowing the bypass to shut again. It is mounted on or near the accumulator in such a way that the operating arm is actuated by a cam roller which is mounted on the accumulator plunger. Hydraulic fluid from the accumulator under pressure enters the valve at the supply port. As the accumulator is charged, the plunger moves downward, carrying with it the cam roller. As the plunger approaches the bottom of its stroke, the cam bears against the lower end of the pilot valve operating arm, pulling the piston down within the cylinder. In this position, the

 
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Drawing illustrating the charging the hydraulic accumulator.
Figure 12-4, Charging the hydraulic accumulator.
 
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Drawing illustrating the accumulator discharging.
Figure 12-5. Accumulator discharging.
 
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flat-milled surface cut along the side of the piston allows a column of oil to pass from the supply port through the port leading to the automatic bypass valve. (See Figure 12-4.)

This opens the automatic bypass valve, bypassing the pressure oil from the discharge side of the IMO pump back to the supply tank and allowing the nonreturn valve to seat. No more oil is delivered to the accumulator while the pilot valve remains in this position.

12B8. Automatic bypass and nonreturn valves. The automatic bypass and nonreturn valves are installed between the IMO pumps and the accumulator. There is one on each pump pressure line. The automatic bypass valve bypasses hydraulic oil when the accumulator is fully charged. The nonreturn valve prevents backflow of the oil from the accumulator to the pump.

As seen in Figure 12-4, the valve body contains two valve parts. One is the bypass valve which is held on its seat by the valve spring. The nonreturn valve is of the disk type which is also seated by a spring.

During those intervals when the accumulator is being charged, hydraulic oil is delivered by the pump into the automatic bypass and the nonreturn valve housing. The oil pressure unseats the spring-held nonreturn valve disk, and oil, under pressure, goes into the line to the accumulator. When the accumulator is fully loaded, the pilot valve is tripped and oil is directed to the automatic

  bypass piston, thus forcing the automatic bypass valve off its seat, and allowing the oil from the pumps to return to the supply tank. When this happens, there is not enough pressure to keep the nonreturn valve off its seat, so the disk valve spring returns the disk to its seated position, thus blocking the backflow of oil from the accumulator. Oil pressure from the accumulator also assists in the seating of the valve.

When the oil charge in the accumulator is depleted by the use of oil to operate various units in the system, or by leakage, the plunger rises, causing the cam roller to bear against the upper end of the pilot valve operating arm, thus moving the pilot valve piston up until the land between the two flat-milled surfaces on the piston blocks off the supply port from the port leading to the automatic bypass valve. At the same time, the upper flat surface lines up the port with the escape port, venting the oil trapped under pressure in the line leading to the automatic bypass piston out through the port to a vent line, which bleeds into the main supply tank. This removes the pressure from underneath the valve piston of the automatic bypass, allowing the loading spring to reseat the automatic bypass valve and thus shut off the bypass line.

Immediately, oil under pressure from the IMO pump, once more directed against the underside of the nonreturn valve, opens this valve, allowing the oil to flow to the accumulator.

 
C. OPERATIONS
 
12C1. Starting the main plant. Following are the operations for starting operation of the main plant:

    a. Check the supply tank for proper oil level.
    b. Check the back-pressure for proper pressure in the supply tank.
    c. See that the hand levers on the control manifolds are in the NEUTRAL position.
    d. Check the accumulator air flask pressure to see that the AIR TO ACCUMULATOR valve is open on the air-loading manifold.

      e. Check the PRESSURE CUTOUT valve to see that it is open.
    f. The manual bypass valve should be opened before starting the motor; after the motor has come up to speed, shut the manual bypass valve. This procedure is precautionary as the motor is not capable of properly starting and coming up to speed under full load.

12C2. Securing the main plant. Securing the main plant is accomplished as follows:

    a. See that the hand levers are in NEUTRAL position on the control manifolds.

 
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    b. Stop the motor.
    c. Open the manual bypass valve allowing oil to be drained from the accumulator to the supply tank.

12C3. Venting the system. When venting the system, vent all lines, valves, manifolds (except the air-loading manifold), accumulator, gages, control gears, and operating gears. Operating lines are vented by opening the vent valves at the operating gears. Vent valves in the operating lines that require venting are located abaft the diving station on the port side of the control room.

The system should be vented if it has not been in use for several days. The vents should be opened only when there is pressure on the lines.

12C4. Flood and vent control manifold. The main vent control manifold on the submarines built by the Electric Boat Company houses seven control valves instead of six as on the Portsmouth installations.

Reading from right to left, these seven valves operate the following vent valves:

1.Bow buoyancy tank.
2.Safety tank.
3.MBT Nos. 1 and 2.
4.FBT Nos. 3 and 5.
5.FBT No. 4.
6.MBT No. 6.
7.MBT No. 7.

Reading from right to left, the flood and induction valve levers are:

1.Engine induction and ship's supply outboard valve.
2.Negative flood.
3.Safety flood.

Each valve has four positions which are shown on the indicator plates next to the hand levers:

1.SHUT, which closes the vent.
2.OPEN, which opens the vent.
3.HAND, which bypasses the oil allowing hand operation.
4.EMERGENCY, which shuts off the lines to the hydraulic operating cylinder.
  The lines to the hydraulic operating cylinder are shut off so that if there is a break in the local circuit, oil will not leak out of it from the main system, and only the local circuit's oil will be lost.

The frame mounted on the manifold has notches cut into it for each valve position, into which the hand lever is firmly latched by a lateral spring. Once placed in any position, it cannot move unless purposely moved by the operator.

Each of these control valves operates a flood or vent valve, at some point remote from the manifolds, by directing a column of pressure oil to one side or the other of a hydraulic unit cylinder whose piston is connected, through suitable linkage, to the valve operating mechanism. All MBT vent valves and the safety tank and bow buoyancy vent valves are hydraulically operated.

The operating gear consists essentially of a hydraulic unit cylinder and suitable linkage connecting it to a vertical operating shaft which opens and shuts the vent. Fluid under pressure is admitted from the control valve into the hydraulic operating cylinder. As the piston head moves, it actuates the crank shaft. This moves the cam, which, bearing against the groove in the slotted link, causes it to push up or pull down on the flat link, thereby moving the crosshead up or down. Into the top of the crosshead is screwed the lower end of the operating shaft. This shaft goes up through a packing gland in the pressure hull to the superstructure, where the mechanism that opens and shuts the vent is located.

12C5. The hydraulic flood valve operating gear. The flood valves on the safety and negative tanks are hydraulically operated. The crossarm and hand grips are for hand operation in case of failure of the hydraulic power.

It is essential to understand that the main piston rod and the tie rods are all rigidly yoked together through the crosshead. Impelled by the hydraulic pressure against the piston head, all three rods move inward or outward as one solid piece. To open the valve, hydraulic fluid from the control valve is admitted into one end of the cylinder

 
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moving the piston head outward. The motion is communicated through the crosshead. The tie rods, screwed rigidly into this crosshead, are pushed outward; the outboard connecting rods, through the crank, push the operating shaft out, opening the flood valve. Return oil, meanwhile, flows out of the opposite end of the cylinder back to the control valve.

To shut the valve, the flow of hydraulic fluid is reversed, pushing the button inward.

12C6. The periscope. A pair of hydraulic cylinders is bracketed into the periscope fairwater, at the top of the conning tower. The piston heads and piston rods are bolted to a yoke which carries the periscope; in other words, the pistons and periscope are rigidly connected together and travel as a unit. As the pistons are raised by admitting hydraulic pressure to the undersides of the piston heads, the periscope extending through the center of the fairwater slides up from its well and is projected upward.

A distinctive feature of this type of hoist is the fact that the control valve admits

  hydraulic fluid only to the lower ends of the cylinders. No oil is present on top of the piston heads except that which leaks past the piston from the pressure side. Overflow lines and a settling tank located in the conning tower are provided to catch any oil that may leak up past the piston heads.

To lower the periscope, the lines from the ports at the lower ends of the cylinders are simply opened to the return line, and the periscope and pistons are allowed to descend by their own weight, forcing the oil out of the cylinders into the return line.

12C7. The vertical antenna hoist. The vertical antenna hoist need not be discussed in detail, as it is almost identical to the periscope hoist in arrangement, structure, and operating principles.

In addition to the automatic trip arrangement for avoiding the hard stop at the top of its travel, the vertical antenna hoist also has a dash-pot arrangement and a piston head with tapered grooved cut toward its underside, which help to bring it to an easy stop at the bottom.

 
D. FORWARD AND AFTER SERVICE LINES
 
12D1. General arrangement. There are two sets of hydraulic lines extending from the main cutout manifold to both ends of the submarine. These lines, known as the foreward and after service lines, furnish power to a miscellaneous group of hydraulically operated submarine equipment; specifically, these lines service the following apparatus:

a. The after service lines supply power for the operation of:

1.Main engine outboard exhaust valves (hydropneumatic on latest installations).
2.Outer doors of the four after torpedo tubes.
3.Periscopes and vertical antenna hoists (latest installations).

b. The forward service lines supply power for the operation of:

1.Bow plane rigging.
2.Windlass and forward capstan.
 
3.Two echo ranging and sound detection devices (raise or lower).
4.Outer doors of the six forward torpedo tubes.

Hydraulic pressure is distributed to the service lines at the main cutout manifold by two valves. One line is marked Service forward, the other line is marked Service aft. The return lines terminate in two similarly named valves on the main cutout manifold.

12D2. Torpedo tube outer door mechanism. The torpedo tube outer doors are hydraulically operated as separate units from the fore and aft service lines. There are ten torpedo tubes in all, six forward and four aft.

The outer door-operating mechanism consists essentially of the hydraulic cylinder, piston and power shaft, the control valve and operating handle, and a jack screw for hand operation. All parts are mounted on the torpedo tube itself and controlled from its breech.

 
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The hydraulic cylinder contains a piston that is moved by hydraulic power. It is connected rigidly to the power-operating shaft, the motion of which opens or shuts the outer door. The hydraulic power is directed to one side or the other of the hydraulic cylinder by the control valve. This allows flow of hydraulic power from the supply side of the forward or after service lines and feeds it back to the return side. The control valve is operated by the operating handle, a push-pull arrangement which slides in and out lengthwise through the ready-to-fire interlock tube. The operating handle is connected to the control valve by the inner slide which is attached to the control valve linkage by the operating lug.

Safe operation of a torpedo tube is a delicate and complicated process, involving a number of different conditions which cannot be allowed to occur simultaneously. For example, it is obvious that when the outer door is opened to the sea, the inner door must be locked shut and vice versa; the tube must not be made ready-to-fire unless different interlocks are properly engaged. For hand operation of the outer doors, a hand-operating shaft is provided, with a squared end, over which an operating crank fits. This turns the hand shaft driving gear. This gear is meshed with the jack nut, which in turn is threaded into the threaded portion of the power-operating shaft. Therefore, as the jack nut is turned, the power-operating shaft travels through it, opening or shutting the outer door. In order to operate this by hand, the control valve must be in the hand

  position so that the fluid trapped in the hydraulic cylinder will not act as a hydraulic lock against the motion of the piston.

The operating handle therefore has three positions: OPEN (handle pulled all the way out toward the operator), in which the power operating shaft, moved by hydraulic power, will open the outer door; SHUT (handle pushed in all the way away from the operator), in which the power-operating shaft will shut the outer door; and HAND (handle in intermediate position), in which the lines from the hydraulic cylinder are by-passed through the control valve.

12D3. Echo ranging and detecting apparatus. The echo ranging and detecting apparatus is contained in a metal sphere (called the sound head) fixed to a cylindrical tube which is extended downward through an opening in the underside of the vessel in much the same way that the periscope is extended upward through the top. The tube is hydraulically operated by power from the forward service line of the main hydraulic system.

The hydraulic part of the apparatus consists essentially of three hollow tubes, one within the other, so arranged that the two inside tubes act as a stationary piston fixed to the frame of the vessel, while the outermost tube, actuated by hydraulic pressure, acts as a movable cylinder which slides up and dozen over it, raising or lowering the sound head. A control valve directs the oil pressure to one side or the other of the piston head to raise or lower the cylinder.

A hand pump is installed in the lines for hand operation.

 
E. EMERGENCY STEERING AND PLANE TILTING SYSTEMS
 
12E1. General. The steering and plane tilting operations are usually performed by their own individual hydraulic systems. To insure against failure, it is possible to use the pressure in the main hydraulic system to power   the gear that actuates the rudder and the planes. In the main hydraulic system, this is accomplished by connecting supply and return lines from the other systems to the main cutout manifold.
 
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