GENERAL DESCRIPTION
 

Actually, however, the operation is not quite so simple as that. There are other factors which must be taken into consideration. The spindles which set the gyro, speed, and depth mechanisms must be removed from engagement with the torpedo and retracted from the tube, and the stop bolt which holds the torpedo in position in the tube must be retracted.

Hence, the firing mechanism is so planned and arranged that it can not be set in operation until, first, the interlocking mechanism described in the preceding chapter has been properly set; and second, until the depth and speed setting mechanism spindles have been retracted from the torpedo and are clear of the tube. The gyro setting mechanism spindle is retracted by the stop rod at the same time the torpedo stop bolt is raised, the stop rod being attached to the piston of the torpedo stop cylinder.

The air going into the stop cylinder through the stop cylinder valve moves the stop piston which raises the torpedo stop bolt and retracts the gyro setting spindle. The stop piston extension then moves through its matching hole in the firing interlock shutter bar (J and K in Figure 96), contacts the pilot valve stem and opens the pilot valve, releasing the air pressure above the firing valve, thereby releasing the charge of air into the torpedo tube and launching the torpedo.

The complete firing system includes, in addition to the firing mechanism, an impulse tank which is arranged for charging from the submarine's high pressure air system through a reducing valve and manifold; piping to connect the impulse tank to the firing valve; and electrical firing and indicating circuits.

The impulse tanks are mounted inside the pressure hull in some submarines, and outside the pressure hull in some others, while in other submarines the forward tanks are mounted outside and the aft tanks inside the pressure hull. Each impulse tank carries seven cubic feet of compressed air, and each tank serves one torpedo tube.

The firing mechanism, in its relation to the torpedo tube and the other operating mechanisms, is shown in Figure 86, this being a view from the outboard side of the tube, and in Figure 87, which

There are eight entirely distinct but related units which comprise the complete firing mechanism, each unit having its own particular function. Taking these units in their sequence of operation, though it must be understood that the operation is simultaneous, they are as follows:

Figure 87 Top of tube, showing position of firing mechanism in relation to other operating mechanisms. (A) Firing valve filling funnel; (B) Firing and check valve bonnet; (C) Connection to stop valve, or to impulse air line; (D) Interlock shutter bar; (E) Stop cylinder and pilot valve body; (F) Electric solenoid.

Figure 88 Inboard side of tube, showing position of firing mechanism in relation to other operating mechanisms. (A) Firing valve filling funnel; (B) Firing valve body; (C) Electric solenoid; (D) Stop cylinder and pilot valve body; (E) Hand key for operating firing lever; (F) Stop rod spring.

Should the electric circuit get out of order so the solenoid can not be operated, a hand key is attached to the firing lever so the stop cylinder valve can be

Figure 92 Firing by hand (guard over hand firing lever not installed).

Figure 93 Guard over hand firing lever to prevent accidental operation of the firing mechanism.

As explained in the preceding chapter, in the section dealing with the firing interlock mechanism,

As the stop cylinder piston moves to the rear, through the opening in the interlock shutter bar, it comes in contact with and pushes the pilot valve stem, thereby tripping the pilot valve and allowing the firing valve to be opened (see Figure 96).

The stop cylinder body and the pilot valve are in one housing, as shown in Figure 96, the stop

The muzzleward end of the stop cylinder and

The breech end of the torpedo stop piston rod projects through the stop cylinder into a recess

The muzzle end of the stop piston rod is fitted with an extension which is secured to the gyro setting spindle retraction slide, and this slide is, in turn, secured to the torpedo stop operating rod, so that the stop piston rod, the gyro retraction slide, and the torpedo stop operating rod act essentially as one part.

Figure 100 Stop valve, firing, and check valve bodies, showing position on outboard side of tube. (A) Stop valve body, (B) Pipe leading from impulse tank; (C) Stop valve elbow; (D) Firing and check valve body; (E) Check valve cover.

The stop valve, bolted to a pipe from the impulse tank and to the firing valve, consists of a stop valve body (Figure 100) with a seat for the valve and a connection to the firing valve. To the valve body

The valve stem (see Figure 102), which is threaded to the bonnet, projects through the bonnet and its packing nut. To the outer end of the stem are fastened a hand wheel and a collar which engages the interlock bolt. Rotatably mounted on the inner end of the valve stem is a valve disc, which is prevented from turning by engaging two keys formed in the valve body (Figure 101). A rubber gasket makes a pressure-tight seal.

The firing and check valve body is connected at one end to a pad on the barrel. The other end is connected by a flange to the stop valve body, where the stop valve is installed; where the stop valve is not installed, this end is connected to the impulse air line.

The firing valve, which occupies the upper part of the housing, as shown in Figure 104, is of the differential piston type, held in position by the firing valve head and the firing valve spring. The firing valve cup, and a skirt on the firing valve head, each have a groove in which is inserted a piston ring. A firing valve orifice disc is secured to the firing valve cup by a dowel pin and bolt with a locking screw.

When clean, fresh water is poured in the filling funnel on the head, and the filling and overflow valves are opened, the water level is built up around the firing valve cup and head to the level of the overflow valve. The firing valve orifice disc in conjunction with the skirt of the firing valve head forms a throttling orifice to control the rate of opening of the firing valve and, therefore, the air pressure in the tube when the chamber above the valve is vented. The size of this orifice determines the rate of opening of the firing valve, and therefore the maximum tube pressure and the ejection velocity. One manufacturer of this type of valve has stated that a diametral increase of .001 inch in the size of this orifice above the nominal figure will result in an increase of maximum tube pressure of ten pounds per square inch.

The operation of the firing valve is as follows Starting with no air pressure tending to open the firing valve, which will then be held seated by spring pressure and gravity, clean, fresh water is put

in through the filling funnel (see Figure 107) with both the filling valve and the overflow valve open, until the water comes out of the overflow valve, showing that the water level in the firing valve is correct. The water must flow, not merely drip, out of the overflow valve. After the water stops flowing, both the filling valve and the overflow valve should be closed.

The water goes down into the space inside the firing valve cup, around the spring, through the two lower five-sixteenth inch diameter equalizing holes in the cylindrical projection of the firing valve head and outside skirt of the firing valve head, to the overflow level determined by the overflow globe valve.

Figure 107 Filling the firing valve through the filling funnel. Only clean, fresh water should be used, and it requires about one and one half pints to fill the valve.

The forces which now tend to keep the valve closed are (1) the impulse tank pressure built up above the cup; (2) spring pressure; and (3) the weight of the cup. The spring pressure and the weight of the cup are relatively negligible as compared with the impulse tank pressure built up about the cup.

The only force tending to open the firing valve cup is the impulse tank pressure against the 45 degree beveled edge of the cup next to the seat. When the air pressure which holds the firing valve cup seated is vented through the exhaust pipe (as explained in the description of the pilot valve on page 52 of this chapter), the impulse tank pressure against the beveled edge of the cup lifts the cup, allowing air to go to the tube.

As an alternative to opening the stop valve (if one. is installed) at the point indicated in the foregoing, it may be left closed up to the time when preparing to fire. However, if this is done, the stop valve should not be opened to the full extent rapidly. It should first be "cracked" to allow pressure to build up above the cup by leakage past the cup ring to equalize that pressure on the 45 degree beveled edge of the cup which tends to lift the cup.

Opening either the filling valve or the drain or overflow valve of the firing valve after impulse air pressure is on the firing valve may fire the tube. To prevent this being done, accidentally or unintentionally, the replacement of the hand wheels originally fitted on these two valves, using small square knobs in their place, has been authorized. This has been done for the purpose of making it necessary to use a wrench or pliers to open these two valves.

Also, there is no way of knowing exactly how many shots one priming of the firing valve is good for. Very little, if any, of the priming water should be lost, either by firing or by evaporation. However, the possible excessive tube pressures due to firing

The firing valve may be exercised by hand, as it should be frequently to test its operation, by removing the filling funnel and inserting the firing valve lifter, which is a rod threaded at the end to fit into the tapped hole in the head of the bolt which secures the orifice disc to the firing valve cup. Figure 106 shows the firing valve lifter being used to remove the valve from the firing valve body.

As this pamphlet goes to press, a modification is being effected in firing valves with the object of making their operation less critical, more uniform, and less subject to variation under actual operating conditions. The modification is not supposed to change the operating principle of the valve in any particular. The basic features of the modification are:

The throttling diameter is reduced from 2".50 to ".75, which increases the width of the throttling

The inner bearing for the firing valve cup has been divorced from the skirt of the firing valve housing cover, so that even if this cover is bolted down more tightly on one side than on the other, the firing valve cup will not thereby be jammed as may be the case in the original design.

The differences between the original valves and the modification will be apparent from the line sketch which is reproduced below.

Figure 108 The check valve seat, showing check valve in place. (A) Firing valve body; (B) Connection for stop valve; (C) Check valve disc; (D) Retaining ring for, check valve seat; (E) Flange for connecting to barrel.

Figure 109 The check valve as it appears looking into the tube through the breech door. Its purpose is to keep sea water out of the firing system when the torpedo tube is flooded, closing by spring pressure after firing.

The check valve is located, as already described, in the lower part of the same housing with the firing valve (see Figures 103 and 104), at the point where the firing valve body opens into the torpedo tube, as shown in Figure 108. The valve disc as seen from the inside of the barrel is shown in Figure 109. Disassembled views showing the parts of the check valve are given in Figures 110, 111, and 112.

Normally, the check valve is held by a spring against a rubber seat (see Figure 104). It opens under a slight air pressure, the spring washer taking up against a rubber buffer.

The rubber buffer must be very carefully inspected when the tube is being overhauled. This is important. Wear and aging reduce the length of the rubber buffer, which will cause the check valve

An automatic drain valve is provided, as shown in Figure 104, this being located just behind the check valve. This drain valve remains open by spring pressure (see Figure 113), thereby allowing any water which leaks into this section of the firing valve body to drain out. The drain valve closes when air pressure enters the firing system.

It is essential that this automatic drain valve be kept tight, in order to prevent loss of impulse air with resulting lower tube pressure.

With these interlocks set, and the spindles retracted, the muzzle door operating shaft is released so the muzzle door can be opened. After the muzzle door is opened, the firing interlock lever can be

At the same time, moving the firing interlock lever to "Tube Ready to Fire" position moves the firing interlock shutter bar to lock the impulse stop valve open, and also brings the opening in the shutter bar into line with the piston extension of the torpedo stop cylinder so that, when the firing key is pressed, that extension may pass through the opening in the shutter bar to trip the pilot valve piston, thereby setting the firing valve in action.