MPA Logo, San Francisco Maritime National Park Association, USS Pampanito, Historic Ships at Hyde Street Pier, Education Programs Maritime Park Association Home Page Maritime Park Association Home Page Events Maritime Park Association Home Page Maritime Park Association Home Page Maritime Park Association Home Page Volunteer Membership Donate Maritime Park Association Home Page USS Pampanito Submarine Historic Ships at Hyde Street Pier Education Programs About Maritime Park Association Home Page Directions to Maritime Jobs at Maritime Facility Rental at Maritime Trustees of the Association Calendar Press Room Store Maritime Map
CHAPTER 5, THE FIRING MECHANISM

The Firing Mechanism--General Description48
The Solenoid50
The Stop Cylinder Valve51
The Torpedo Stop Cylinder52
The Pilot Valve52
The Stop Valve55
The Firing Valve56
The Check Valve58
The Interlocking Mechanism60
 
47

 
THE FIRING MECHANISM

GENERAL DESCRIPTION
 

In its most simple form, the operation of firing a torpedo tube may be said to consist of releasing a charge of compressed air into the torpedo tube behind the torpedo. This charge of air starts the torpedo on its way out of the tube, after which it travels through the water under its own power.

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.

  Were these spindles not entirely retracted from the tube, they would interfere with the ejection of the torpedo and cause it to jam in the tube.

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in the preceding chapter has been properly set; and second, until the depth and speed setting mechanism spindles have been retracted from the torpedo and are clear of the tube.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.

Figure 86 Outboard side of tube
Figure 86 Outboard side of tube, showing position of firing mechanism in relation to other operating mechanisms on the tube. (A) Firing and check valve housing; (B) Firing valve filling funnel; (C) Connection for stop valve, or to impulse air line; (D) Electric solenoid.
 
48

Briefly, the sequence of operation of the firing mechanism may be described as follows: When the various interlocks have been properly set so that the tube is ready for firing and the command to fire is given, a key in the electric circuit is pressed down, sending the electric current to the solenoid, which is an electrical magnet. The solenoid raises the firing lever, opening the stop cylinder valve (F in Figure 96) so as to allow air from the ship's service line (200 pound) to flow to the stop cylinder. A hand key also is attached to the firing lever for use in the event the electric circuit should be out of commission or for testing the firing mechanism.

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

  is a view taken from above, looking down on the tube. Figure 88 is a view of the inboard side of the tube showing the position of the hand firing key, the solenoid, and the firing valve filling funnel, though the other parts of the firing mechanism are obscured in this view.

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
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
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.

 
49

 
THE SOLENOID
 
The solenoid, Figures 89, 90, and 91 (also see Plate One and Figures 86, 87 and 88), is an electrical plunger magnet. It is mounted on a bracket secured to the stop cylinder casting, and is wired in series with the firing circuit. In the lower part of the solenoid (see Figure 89) is a movable iron core   is drawn upward. As the armature is drawn upward the hook raises the firing lever, thereby tripping the stop cylinder valve.

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 89
Figure 89 (at left) Electric solenoid, interior, showing (A) Housing; (B) Magnet wire; (C) Armature; (D) Firing lever hook; (E) Wiring to electric circuit; (F) Gland nut; (G) Cap; (H) Armature stop; (I) Armature key. Figure 90 shows the solenoid, exterior view, with the firing lever hook down, and Figure 91 shows the firing lever hook up.
or armature, to which is attached a firing lever hook. Under the influence of the magnetic field caused by the electric current passing through the solenoid winding, this movable iron core or armature   tripped by hand (see Figure 92). In order to prevent this lever from being struck accidentally, a guard is fitted around it (see Figure 93) in an effort to avoid unintentional firing.
 
50

Figure 92 Firing by hand (guard over hand firing
lever not installed).
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.
Figure 93 Guard over hand firing lever to prevent accidental operation of the firing mechanism.

 
THE STOP CYLINDER VALVE
 
The stop cylinder valve-piston, when lifted by the firing lever through the operation of the solenoid (see Figure 94 and 95), or when the hand firing   key is pressed, permits the passage of air from the submarine's 200-pound air service line to pass into the torpedo stop cylinder.
Figure 94 Complete assembly of solenoid
Figure 94 Complete assembly of solenoid, firing lever, and stop cylinder, showing (A) Solenoid; (B) top cylinder valve body; (C) Connection for air pressure supply; (D) Stop cylinder valve stem (valve closed); (E) Firing lever; (F) Hand firing key; (G) Stop rod spring and connection with stop rod. At right, Figure 95, firing handle is depressed, stop cylinder valve stem lifted to open valve.
 
51

 
THE TORPEDO STOP CYLINDER
 
The muzzleward end of the stop piston rod is joined to the gyro setting spindle retraction slide, which in turn is coupled to the torpedo stop connecting rod which operates the stop bolt. As the pressure of air enters the torpedo stop cylinder through the stop cylinder valve, it forces the piston rod toward the breech, and through the opening in the interlock shutter bar, retracting the gyro setting spindle and raising the torpedo stop bolt.

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

  the interlocking shutter bar must be in the correct position to permit the piston rod to pass through the opening in the shutter bar, as it will when the firing interlocking mechanism has been properly set, otherwise the firing mechanism can not be put into operation.

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 PILOT VALVE
 
When tripped by the stop cylinder valve piston rod, the pilot valve opens and releases the banked up air pressure from above the firing valve, thereby allowing the firing valve to be forced open by the pressure of air from the impulse tank.

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

  cylinder valve body being bolted to the upper part of it (see Figures 97 and 98), the whole being mounted on the torpedo tube as shown in Figures 87 and 88 on page 49. A view of the interior of the body is shown in Figure 96 and the parts disassembled are shown in Figure 99.

The muzzleward end of the stop cylinder and

Figure 99 first half
Figure 99 second half
Figure 99 Parts of the stop cylinder valve, stop cylinder, and pilot valve disassembled.
A Adjusting nut for stop cylinder piston rod
B Sleeve for stop rod
C Stop rod spring
D Spring seat
E Stop cylinder head
F Stop cylinder piston rod
G Firing lever
H Taper pin for firing lever
I Stop valve body
J Plug for stop cylinder valve
K Washer for stop cylinder valve guide
L Stop cylinder valve spring
M Stop cylinder valve
 
N Interlock shutter bar
O Stop cylinder and pilot valve body
P Pilot valve piston
Q Pilot valve spring
R Gasket for pilot valve plug
S Pilot valve plug
T Opening in housing for interlock shutter bar
U Gasket
V Bolts for attaching stop cylinder valve body to stop cylinder body
W Locating pins for attaching body to tube
X Bolts for solenoid clamp
Y Bolts for attaching vent line
Z Bolts for attaching body to tube
 
52

Figure 96 Interior view of torpedo stop cylinder, pilot valve, and stop cylinder valve.
Figure 96 Interior view of torpedo stop cylinder, pilot valve, and stop cylinder valve. (A) Connection with stop rod; (B) Stop rod spring; (C) Solenoid; (D) Stop cylinder valve; (E) Air, pressure supply to stop cylinder valve; (F) Stop cylinder valve; (G) Firing lever; (H) Firing lever handle; (I) Torpedo stop cylinder; (J) Interlock shutter bar, removed; (K) Interlock shutter bar in place; (L) Air exhaust; (M) Opening for releasing banked up air from firing valve head; (N) Pilot valve; (O) Pilot valve plug.
 
Figure 97 Torpedo stop cylinder and pilot valve, side
view.
Figure 97 Torpedo stop cylinder and pilot valve, side view.
  Figure 98 Torpedo stop cylinder and pilot valve, top
view.
Figure 98 Torpedo stop cylinder and pilot valve, top view.
 
53

pilot valve body is bored for the piston, and threaded to take the cylinder head, which is bored for the torpedo stop piston rod. A spring holds the piston in its extreme position toward the muzzle until it is acted upon by the air pressure. A passage leads to the stop cylinder valve chamber, into which the 200-pound air service line is connected. The upper part of this chamber is threaded for the valve guide, which houses the spring, while the lower part is drilled to permit the valve stem to project below, in position to be lifted by the firing lever when the tube is fired either electrically or by hand. The valve spring normally keeps the stop cylinder valve closed.

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

  which is open to atmospheric pressure. This recess has a slot, through which the shutter bar of the interlocking system slides. When all the related mechanisms of the interlocking system have been properly set and the tube is ready for firing, the hole in the shutter bar is lined up with the torpedo stop piston rod, thereby allowing the torpedo stop piston rod to pass through the hole and strike the pilot valve stem, as shown in Figure 96.

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
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.

  Figure 101 Stop valve body
Figure 101 Stop valve body, showing (A) Key, one of two which engage valve disc; (B) Valve seat.
Figure 102 Stop valve disassembled.
Figure 102 Stop valve disassembled.
A Valve disc
B Slots which engage keys in valve body
C Annular ring for rubber gasket
D Connection to valve disc
E Valve bonnet
 
F Bracket for interlock shutter bar
G Valve stem collar which engages interlock bolt
H Valve stem
I Hand wheel
 
54

Figure 103
Figure 103
  Figure 104
Figure 104
The firing and check valve body, as it appears on the tube at left, and interior view at right. (A) Filling funnel; (B) Filling valve; (C) Firing valve cover; (D) Opening for connection to pilot valve; (E) Overflow valve; (F) Firing valve body; (G) Check valve opening and flange for attaching to barrel; (H) Automatic drain valve; (I) firing valve head; (J) Firing valve spring; (K) Orifice disc; (L) Skirt on firing valve head; (M) Piston rings; (N) Firing valve cup; (O) Check valve disc; (P) Check valve spring; (Q) Rubber buffer.
 
THE STOP VALVE
 
The purpose of the stop valve as originally included in the firing mechanism was to provide a closure between the firing valve and the impulse tank so (1) to prevent accidental firing; (2) to the lifting of the firing valve during the operation of charging the impulse tank; (3) to prevent the loss of air due to a leaky firing valve; and (4) to permit access to the firing valve without "blowing, down" the impulse tank.

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

  (Figure 101) is bolted a bonnet (Figure 102), bored and threaded for the valve stem and stuffing box. To the bonnet is bolted a bracket for the shutter bar and the stop valve interlock bolt.

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.

 
55

 
THE FIRING VALVE
 
The firing valve is housed in the same body with the check valve as shown in Figure 103 (also see Figure 100). A break-away view, showing the interior of the firing and check valves, is shown in Figure 104. Figure 105 shows the firing valve disassembled.

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

  Figure 105 Firing valve disassembled, showing parts.
Figure 105 Firing valve disassembled, showing parts.

A Firing valve head ring
B Nuts for attaching cover to body
C Firing valve cup ring
D Filling funnel
E Filling valve
F Firing valve head
G Piston ring
H Firing valve spring
I Bolt for attaching firing valve cup and orifice disc
J Orifice disc
K Firing valve cup
 
56

Figure 106
Figure 106 Removing valve from firing valve body with lifter provided in the tool kit. This lifter may also be used for exercising the valve or testing its operation, as explained in the accompanying text.

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.
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.

  Assuming that the tube is ready for firing, the stop valve, if installed, is opened, and pressure in the impulse tank is built up. Air leaks by the cup ring and builds up pressure within the cup and head through the two equalizing holes at the water level and the seven five-sixteenth inch diameter equalizing holes in the upper portion of the head.

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

 
57

with too little water in the throttling chamber are considered sufficient to warrant the extra trouble of filling the throttling chamber frequently, especially when firing is anticipated.

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

  orifice in inverse proportion, thus making it unnecessary to adjust the "firing valve clearance" with any thing like the degree of accuracy hitherto necessary in order to insure proper performance.

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.

Sketch of firing valve with and without mod.

 
THE CHECK VALVE
 
The purpose of the check valve is to keep the sea water out of the firing system when the torpedo tube is flooded. If the space between the check valve disc and the firing valve cup should fill with water

Figure 108 The check valve seat, showing check valve in place.
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.

  there would be no air cushion, and the full impulse tank pressure would be transmitted to the torpedo's afterbody when the firing valve first opened. Also, after firing, water would tend to pass the firing valve

Figure 109
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.

 
58

Figure 110 The check valve seat, showing parts disassembled.
Figure 110 The check valve seat, showing parts disassembled.
A Check valve cover flange
B Check valve seat
C Flange for connecting to barrel
D Cotter pin for (E)
E Nut for valve disc stem
 
F Spring washer
G Rubber buffer
H Check valve spring
R Spring seat
I Check valve disc

Figure 111 Check valve parts, housing end.
Figure 111 Check valve parts, housing end. (A) Check valve cover; (B) Nuts for attaching cover to body; (C) Gasket; (D) Cotter pin for (E) Nut for valve disc stem; (F) Washer for valve spring; (G) Valve spring; (H) Rubber buffer; (I) Spring seat.
 

Figure 112 Check valve parts, barrel end.
Figure 112 Check valve parts, barrel end. (A) Gasket for attaching to barrel; (B) Rubber check valve seat; (C) Retaining ring for rubber check valve seat; (D) Machine screws for attaching retaining ring; (E) Check valve disc.
 
59

and back up in the impulse air line.

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

  to open more than it should so that the disc may strike the outboard rudder bearing on the tail vanes of a torpedo. On the other hand, should the rubber buffer be too long it would prevent the check valve from opening completely, and throttling of the impulse pressure might then occur at the check valve rather than at the firing valve cup.

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.

Figure 113 Automatic drain valve parts.
Figure 113 Automatic drain valve parts. (A) Valve body; (B) Valve spring; (C) Valve disc and stem; (D) Valve connection.
 
THE INTERLOCKING MECHANISM
 
As described in Chapter 4, the firing mechanism can not be set in operation until the firing interlock lever is set at "Tube Ready to Fire" as shown in Figure 83 on page 45. Before this interlock lever can be, moved to that position, however, the breech and muzzle door interlock lever must be set at "Muzzle Door Unlocked" position, and the drain valve and muzzle door interlock lever must be set at "Drain Valve Locked" position, as shown in Figure 79 on page 43. The depth and speed setting spindles also must be retracted.

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

  moved to "Tube Ready to Fire." This rotates the interlock sleeve to lock the other mechanisms, and also brings the firing interlock bolt down, as shown at C in Figure 83 on page 45, thereby preventing movement of the muzzle door operating shaft and locking the muzzle door open.

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.

 
60

Previous chapter
Previous Chapter
Sub Tubes Home Page
Sub Tubes Home Page
Next chapter
Next chapter


Copyright © 2013, Maritime Park Association
All Rights Reserved
Legal Notices and Privacy Policy
Version 1.10, 22 Oct 04