HNSA Crest with photos of visitors at the ships.

5A1. Introduction. The 10-pound MBT blowing system is used to remove water from the main, ballast tanks when the boat is on the surface. It completes the work started by the 600-pound MBT blowing system, thus saving high-pressure air.

The 10-pound MBT system (see Figure 5-1) consists of a low-pressure blower located in the pump room, a manifold, and blow lines to each of the tanks serviced by the system. The low-pressure blower furnishes compressed air to the manifold in the control room at a pressure of approximately 10 psi. The manifold distributes the air supplied by the blower to the ballast tanks, through nine pipe lines which pass through the hull directly above the manifold and extend outside the

  pressure hull under the superstructure deck.

The air supply to the manifold is controlled by the flapper valve. The manifold and the valves are designed to withstand sea pressure if any of the blow lines fails.

The nine low-pressure lines have lever-operated flapper valves (10-pound blow valves) at the point where they pass through the hull, and swing check valves where they join the main ballast tank (MBT) vent lines.

Gate valves, controlled from the superstructure deck, are installed in the lines leading to main ballast tanks 2A, 2B, 2C, 2D, 6A, 6B, 6C, and 6D.

Detailed operating instructions for blowing the main ballast tanks, using the 10-pound system, are given in Chapter 10.

5B1. Description. The 10-pound blow manifold, located on the starboard side of the control room (Figure 5-1.), serves as a center from which the compressed air supplied by the low-pressure blow is directed to the ballast tanks. The piping outside the pressure hull is hydrostatically tested to a pressure of 300 psi; the system inside the pressure hull is tested by air for strength and tightness to a pressure of 15 psi.

The 10-pound manifold is a boxlike, two-piece casting. (See Figure 5-2.) The top casting, or head, is equipped with nine outlet flanges. It is bolted to the body, or bottom half, of the manifold. The bottom half has an inlet port provided with a flapper valve to admit or shut off the air supply from the blower. The access plate on the bottom forward part of the manifold permits inspection or repair.

The flapper valve is opened by lifting the flapper valve lever which is connected to the

  shaft. Movement of the shaft attached to the lever arm causes the valve to be unseated, and air from the blower enters the manifold to be distributed to the ballast tanks.

The 10-pound manifold is also equipped with two list control dampers, one for each Y-valve, operating on a shaft that runs fore and aft through the head. The dampers are opened and shut by the list control lever located on the after end of the head. (See Section 5E.) The list control dampers are used to correct unequal blowing of the tanks which might cause listing of the boat.

When it is desired to blow the main ballast tanks with the 10-pound MBT blowing system, the 10-pound manifold supply flapper valve is opened by lifting the supply flapper valve lever. With the valve open, the air from the blower passes into the manifold chamber. From there, in accordance with the number of 10-pound blow valves opened in the blow lines above the manifold, the air is


Figure 5-2. The 10-pound main ballast tank blow manifold.
Figure 5-2. The 10-pound main ballast tank blow manifold.

directed to the main ballast tanks. The fuel oil ballast tanks have the same piping and connections as the main ballast tanks and   therefore can be blown by the 10-pound blowing system when they are used as main ballast tanks.
5C1. Description. The low-pressure blower supplies compressed air for blowing the main ballast tanks after the boat has surfaced. As the submarine surfaces, the outside air is admitted to its interior. This provides a continuous supply of air to the low-pressure blower, and conserves the supply of compressed air in the ship's air banks. The blower is mounted on the starboard side of the pump room with the electrical controls in the control room.

The low-pressure blower is of the rotary, positive displacement, Roots type. It is powered by a 90-hp motor, connected by means of a flexible coupling to the blower driving shaft.

The mechanical construction of the blower is shown in Figure 5-3.

Two lobe-shaped impellers divide the case into two chambers, the upper and lower. The impellers are connected to steel shafts, and rotate with just enough clearance to avoid contact with the casing and with each other. Gears keyed to the shafts maintain the proper relation between the two impellers. A double row of contact bearings at the ends

  of the shafts farthest from the gears, together with a bearing carrier, positively secure the shaft and the impellers axially, thus preventing possible friction between the ends of the impellers and the head plates.

As the impellers rotate, more space is made available in the lower chamber, causing suction, and less space becomes available in the upper chamber, causing compression. The suction of the blower draws air from the boat's atmosphere, through the screened silencer attached to the air intake, and into the lower impeller chamber. The air thus admitted is forced by impeller action to pass into the upper chamber, where it is compressed, and finally expelled through the discharge connection which is connected by piping, extending through the platform deck to the 10-pound blow manifold in the control room.

Should the volume of compressed air be excessive, or should the discharge valve be closed while the blower is in operation, a spring-loaded relief valve at the entrance to the discharge connection operates automatically to relieve the pressure.

5D1. Description. The 10-pound blow valves direct the flow of air from the 10-pound manifold to the main ballast tanks, and to the fuel ballast tanks when desired. There are nine such manually operated valves, one on each of the blow lines extending from the 10-pound MBT blow manifold, at the point where the lines pass through the inner hull on the starboard side of the control room.

The mechanical construction of a 10-pound blow valve is shown in Figure 5-4. Each 10-pound blow valve has a lever grip and spring latch connected to a shaft which is supported by the valve body near the valve seat. A lever arm mounted on the other end of the shaft is connected to the valve disk by a pivot bolt and socket which enable the

  disk to adjust itself to the valve seat, thus assuring an airtight fit. When the lever is pulled down, the valve disk is raised and the valve is shut. When the grip is released and the lever is pushed up, the valve is opened and air flows from the manifold to the tank vent risers. A heavy rubber gasket ring on the disk forms an airtight contact surface. A notched quadrant holds the latch, the lever, and the valve disk in a set position. On the quadrant, a name plate marked OPEN and SHUT indicates the position of the valve.

The discharge end of the valve body extends through the inner hull, to which it is bolted at the intermediate flange, to form a watertight joint. The flanged end of the valve outside the hull is connected by piping to


Figure 5-3. Low-pressure blower.
Figure 5-3. Low-pressure blower.

Figure 5-4. The 10-pound blow (flapper) valve.
Figure 5-4. The 10-pound blow (flapper) valve.

the tank vent riser. The flanged end inside the hull is connected to the 10-pound blow manifold.

5D2. Location of 10-pound blow valve. The following table lists, from forward aft, the nine 10-pound blow valves in the order in which they are installed on the overhead. Figure 5-2 shows the connection to the manifold.

  1. Main ballast tank No. 1
2. Main ballast tanks No. 2B and 2D
3. Main-ballast tanks No. 2A and 2C
4. Fuel ballast tanks No. 3A and 3B
5. Fuel ballast tanks No. 4A and 4B
6. Fuel ballast tanks No. 5A and 5B
7. Main ballast tanks No. 6B and 6D
8. Main ballast tanks No. 6A and 6C
9. Main ballast tank No. 7
5E1. Description. The list control dampers are used to correct a list during the blowing of the main ballast tanks. The list control dampers adjust the amount of air admitted into the port or starboard ballast tanks of the No. 2 and No. 6 MBT group, increasing or decreasing the rate at which the tank is blown. The dampers are located at the Y-valve outlet connections on the 10-pound blow manifold (See Section 5B).

Figure 5-5 shows the construction of the damper. Both list dampers are attached to a shaft that runs through the manifold chamber. The shaft is operated by a hand lever at the after end of the manifold. The handle assembly consists of a push rod at the top of the handle, a handle, a spring, a latch, a name plate, and a bracket. A connecting rod attached to the handle is equipped with a

  turnbuckle secured with a bolt and nut. Pressing down the pushrod releases the spring, lifting the latch, and leaving the lever free to move inboard or outboard. As the shaft turns, the list dampers are swung to shut one port, or open both ports of the Y.

The movement of the lever and the attached connecting rod turns the shaft by means of an offset arm. Outboard movement of the lever causes the damper to restrict the flow of air to the starboard side. Inboard movement of the lever causes the damper to restrict the flow of air to the port side. Normal position of the damper is neutral, allowing equal flow to both sides.

List control dampers control the flow of air to main ballast tanks 2B and 2D, 6B and 6D on the port side, and to main ballast tanks 2A and 2C, 6A and 6C on the starboard side.

5F1. Description. A swing check valve is located in the piping at the entrance to each main and fuel ballast tank, outside the pressure hull and under the superstructure deck. It prevents air from backing up from the tank into the lines of the 10-pound blowing system.

Figure 5-6 is an illustration of a typical swing check valve. The valve has a swinging disk mounted on a hinge attached within the valve body. The valve opens when the flow of air to the tank forces the disk away from

  the seat, and shuts when the flow of air in the opposite direction forces the disk against the seat. This prevents a backflow of air into the lines. A hinge pin supports both the hinge and the disk, permitting the swinging motion. A lock nut and pin fasten the hinge and disk together. The disk and seat ring are removable for regrinding. A removable cap on top of the valve allows servicing of the working parts. A gasket between the cap and the valve body prevents leakage.

Figure 5-5. List control damper.
Figure 5-5. List control damper.

Figure 5-6. The 10-pound blowing system swing check valve.
Figure 5-6. The 10-pound blowing system swing check valve.

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