As shown in the foregoing chapter on the firing
system, the torpedo is ejected from the barrel by
means of a charge of compressed air. As much of
that air as possible must be removed from the barrel
immediately after firing, before it has "a chance to
escape through the muzzle door and out into the
water. Otherwise, it would cause bubbles to rise and
one-fifth second after firing), and allowing the air
charge to vent within the hull, then closing the vent
before an unduly large amount of water has been
Closing the vent, which is a manual operation,
requires accurate timing. Experience in actual operation has demonstrated that, at periscope depth, and
Figure 114 The poppet valve, detached from tube, showing (A) Flange for connecting to barrel; (B) Access
opening, with cover plate attached; (C) Access opening, with cover plate attached; (D) Flange for connecting to
drain pipe; (E) Gag nut, for "gagging" valve; (F) Connection for rod link to poppet valve indicator.
create an excessive disturbance on the surface of the
sea and disclose the location of the submarine.
The poppet valve (see Figures 114 and 115) is
designed to perform that function of removing the
impulse air before it escapes into the sea. This is
accomplished by automatically opening an inboard
vent from the tube immediately after the torpedo
has received a sufficient launching impulse (about
with an impulse tank pressure of 300 pounds per
square inch, the poppet valve must be closed three
to five seconds after the tube fires in order to secure
satisfactory operation. From this it can readily be
seen that the operation of the poppet valve system is
very closely related to the operation of the firing
mechanism, in fact, the operation of the two is
There are two types of poppet valve systems, one
known as the basic, the other as the variant. The
basic system is sometimes referred to as the Portsmouth
system, and the variant is sometimes called
the Mare Island system.
In the basic system, the instant at which the inboard
vent opens is determined by the travel of the
torpedo in the tube. The poppet valve operating
unit, when set to operate, is put under air pressure
and will open the poppet valve when triggered by
the torpedo in the tube. In vessels already in
commission, however, this location was at such a place
in the ship's structure that it was impracticable to
install roller trip units there. Hence these units were
installed as far toward the muzzle as practicable
(about seven feet from the breech), and a throttling
valve was fitted in the actuating air line to introduce
a time delay. In connection with this variant of the
basic system, if ejection of the torpedo tended to be
sluggish due to improper operation of the firing
Figure 115 Poppet valve in position on tube. (A) Poppet valve housing; (B) Lead to drain; (C) Airline to poppet
valve; (D) Poppet valve operating unit; (E) Connection from air supply line; (F) Casing through which pull rod
from operating unit connects with roller crank.
the roller trip unit. This latter unit, however, is kept
from moving so as to let the operating unit open the
poppet valve by the presence of a torpedo in the
tube. SS 198 and up, and in some earlier vessels in
which poppet valves were also installed before their
launching, the roller trip units, are located about
11 1/2 feet from the breech, so that the poppet valve
will be opened at the proper point of the travel of
valve, this tendency would be aggravated by the
opening of the poppet valve after a constant time
delay instead of at a constant point in the travel of
the torpedo in the tube.
In either the basic or the variant system, the poppet valve, or inboard vent, must be closed by manual
operation, as will be described in later pages of
THE POPPET VALVE
The poppet valve, assembled but removed from
the barrel, is shown in Figure 114, while in Figure
115 it is shown in place on the barrel with the
operating unit assembled. Figure 116 shows the
parts of the valve disassembled, while Figure 117
shows the poppet valve housing with the access
plates, or the access opening covers, and gaskets
disassembled, also the parts of the valve which
are put in place through the access opening. In
Figures 118 and 119, looking into the interior of
the housing through the connection to the drain,
the valve is shown both open and closed. An interior view of the poppet valve, with the outer casing
broken away, is shown in Figure 120.
Figure 116 Parts of poppet valve disassembled
Valve stem, with cotter pins
Poppet valve spring
Gag collar, with pin and chain
Valve stem stud
Gag collar, with taper pin
Shoulder stud for link to poppet valve indicator
Figure 117 The poppet valve, showing access opening cover
plates removed and also attached, also the parts of the valve
assembled through the large access opening.
Nuts for attaching large cover
Large access opening cover plate
Nuts for attaching small cover
Gasket for large cover
Small access opening cover plate
Gasket for small cover
Large access opening, cover plate attached
Small access opening
Connection for air from operating unit
flange for connection to drain pipe
Flange for connection to barrel
Gasket for connection to drain
Gasket for connection to barrel
Screws for attaching retaining ring to valve disc
Vent valve disc
Figure 118 (above left) Interior of poppet
valve, looking through lead to
drain, valve open.
Figure 119 (above right) Interior of poppet
valve, looking through lead to
drain, valve closed.
Figure 120 Interior view of poppet valve, showing,
(A) Shoulder stud for link to poppet valve indicator;
(B) Gag collar; (C) Gag nut; (D) Valve stem
spring; (E) Valve stem; (F) Piston; (G) Rubber
cushion; (H) Vent valve disc.
THE OPERATING UNIT
The poppet valve proper is actuated by the operating unit, which is shown removed from the tube
in Figure 121. Figure 122, the reverse side, shows the
interior of the operating unit, also the action of the
pull rod which connects with the roller crank and
releases the valve as the torpedo moves forward in
the tube. Figure 123 shows the position of the pull
rod after the torpedo has left the tube and the valve
is opened. The parts of the unit disassembled are
shown in Figure 124.
Figure 121 Poppet valve operating unit as it appears mounted
on the tube
Figure 122 Showing interior mechanism of poppet
valve operating unit, from
reverse side, position of pull
rod being for torpedo in
tube, vent valve closed.
(A) Lead from vent closing
valve; (B) Valve spring;
(C) Air line to poppet
valve; (D) Piston; (E) Piston fork; (F) Lead from
air supply line; (G) Pull
rod fork; (H) Pull rod.
Figure 124 Parts of poppet halve operating unit disassembled.
(A) Cap; (B) Washer; (C) Collar; (D) Piston;
(E) Packing; (F) Piston ring; (G) Piston; (H) Collar
and pin; (I) Housing; (J) Housing cap, with pin;
(K) Pull rod guard and set screw; (L) Valve; (M)
Valve spring; (N) Washer; (O) Cap; (P) Plug;
(Q) Gland nut, washer, and packing ring; (R) Piston
fork; (S) Pull rod fork; (T) Pull rod head; (U) Pull rod
pin; (V) Cap; (W) Washer; (X) Shaft; (Y) Bolts
and locating pins; (Z) Gasket.
THE ROLLER CRANK
Figure 126 shows the roller trip unit, "A" being
the rod which connects the roller crank and the
poppet valve operating unit. Figure 127 shows the
roller trip unit disassembled. This figure shows two
rollers, one for torpedoes and one for mines. In later
ships, minor changes have been made so that one
roller can be used for both. The relative positions of
the two units are shown in Figure 125, the connecting rod, or pull rod, passing through the casing
seen on the side of the tube.
Figure 123 Reverse side of operating unit, showing position for vent
Figure 125 Showing position of and connection between poppet
valve operating unit and the roller trip unit. (A) Operating unit; (B) Casing through which the pull rod passes; (C) Roller trip housing
Figure 126 Interior view of the roller trip,
unit. (A) Pull rod; (B) Roller crank; (C) Roller.
Figure 127 Parts of the roller trip unit, disassembled. (A) Pull rod; (B) Pull rod head; (C) Pull rod
pin; (D) Cotter pin; (E) Roller crank; (F) Roller used
with mines; (G) Roller used for firing torpedoes; (H)
Roller pin and cotter pin; (I) Roller crank bracket;
(J) Roller crank bracket pin; (K) Taper pin; (L)
Bracket tap bolts; (M) Gasket; (N) Roller crank housing;
(O) Location pins for attaching housing; (P) Tap bolts.
OPERATION OF THE POPPET VALVE
Tracing the operation of the poppet valve in so
far as that operation relates to these three units, we
find the following: Air is admitted to the piston
cylinder and to the valve chamber of the operating
unit by placing the setting lever of the vent closing
valve (which is described on page 71) in the "On"
position, and tends to force the piston toward the
breech. The piston is restrained, however, by the
piston fork, which is linked to the roller crank in
the roller trip unit. As the fired torpedo moves toward the muzzle, the trip roller rides down the slope
of the torpedo's afterbody, releasing the restraint on
the piston of the operating cylinder, and allowing
it to move toward the breech end of the tube.
As the piston moves, its stem contacts the stem
end of a valve in the breechward end of the cylinder
housing, driving the valve open and allowing the air
pressure to pass through to the piston chamber or
cylinder of the poppet or vent valve, opening that
valve against the pressure of air from the tube. This
causes the impulse air in the tube to vent through
the poppet valve.
THE POPPET VALVE DRAIN
All of the air charge can not be vented without
some water also passing. The arrangements for disposing of the water which enters through the poppet
valve vary somewhat in different submarines.
In earlier vessels, various forms of ducts and
hoods were installed to conduct the water into the
bilges with the least practicable spray or splashing.
In later vessels, there is a drain line leading from
each poppet valve to an open tank beneath the
working platform in the torpedo room. In some
other vessels, all poppet valves on each side of each
torpedo room open into a common drain, in which
swig checks (non-return valves having a swinging flap with a hinge on one edge, which closes
against an inclined seat) are installed.
One form of lead to the drain is shown in Figure
115 on page 63. Another more recent form is shown
in Figure 128. In the lower part of the lead to
the drain is the poppet system discharge angle valve,
or the emergency stop valve (C in Figure 128).
As originally installed in earlier vessels, this was an
automatic stop valve, "backing up" the main vent
valve. The automatic stop valve closed by means of
a spring, its own weight and, when the main vent
valve was open, by whatever air or water pressure
existed in the tube. It opened by admitting air
pressure from the ship's 200 pound air service line
to the inlet side of the valve-operating piston by
placing the hand setting lever of the vent-closing
valve in its "on" position. It closed by the return of
the hand setting lever to its "off" position, which
closed off the 200 pound air supply and vented the
space behind the piston.
A drain valve was connected by piping to the
bottom of the valve-operating piston cylinder, and
could be used in an emergency to close the automatic stop valve in case the 200 pound air supply
was not shut off and vented with sufficient rapidity
by the operation of the vent-closing valve hand
In poppet valve systems of later design, the automatic stop valves are replaced by manually operated
stop valves, as shown in Figure 128, and the installation of this form of stop valve has been largely
completed in those vessels which had the earlier
Figure 128 Lead from puppet valve to drain, with emergency stop valve and linkage to hand wheel. A Flange for connection to drain; B Lead to drain; C Emergency stop valve; D Poppet valve housing; E Emergency stop valve operating handle
The operating parts of the emergency stop valve,
disassembled, are shown in Figures 129 and 130,
Figure 129 showing the valve housing, the casting
being the form shown in Figure 115 on page 63,
and Figure 130 showing the valve bonnet and the
other operating parts.
When preparing the tube for firing, the manually
operated stop valve must be opened so the drain
line is clear. If the poppet valve discharges into a
Figure 129 One form of emergency stop valve
housing (fits type shown in Figure 115, page 63).
Figure 130 parts of emergency stop valve disassembled. (A) Pin for (B) Valve stem collar; (C) Valve
bonnet; (D) Valve disc nut; (E) Pin for (F) Valve
stem; (G) Cotter pin for (H) Valve disc; (I) Pin for valve stem; (J) Valve stem head; (K) Grease fitting;
(L) Nuts for fastening (M) Gland; (N) Packing.
bilge or open tank which already contains water,
some of the water will be blown up into the torpedo
room when the impulse air is vented from the tube,
giving the impression that water is entering through
the poppet valve before such is actually the case.
An interval of at least five seconds is to be expected
between firing and the entrance of any large quantity
of water through the poppet valve, when firing
at periscope depth. At greater depths the increased
sea pressure causes the tube to flood in less time.
An interval of about three seconds has been observed between firing and the entrance of solid
water through the poppet valve drain at a depth of
THE POPPET VALVE CONTROLS
The controls of the poppet valve system are located in the torpedo room, above the breech end of
the tubes, as shown in Figure 131. These controls
consist of a vent-closing valve, a quick-opening vent
valve in the blow and vent manifold, and an emergency
vent-closing valve. These are shown, assembled, in Figures 132 and 133.
The poppet valve must be set for each shot. This
is done by setting the lever of the vent-closing valve
in the "on" position, as shown in Figure 134.
Blow and vent manifold,
with quick-opening vent
in open position.
Quick-opening vent in
A Quick-opening vent in open position.
B Link connecting quick-opening vent and vent-closing valve.
C Latch release button.
D Vent-closing valve, cover plate removed to show interior.
E Setting lever.
F Emergency vent closing valve (quick as-a-wink valve).
G Quick-opening vent, in shut position.
Figure 135 shows the lever in the "off" position,
the cover plate of the housing being removed to
show the interior. Figure 136 shows the lever in
the "off" position, with the cover plate in place on
the housing. The parts of the vent-closing valve,
dissembled, including the setting lever and the
valve parts, are shown in Figure 137. Figure 138
shows the vent-closing valve with thumb on the
latch release button.
About 3 to 5 seconds after the tube has fired, the
poppet valve must be closed, in one of the following
(1) By placing the lever of the tube vent valve
(A in Figure 132) in the open position.
(2) By placing the setting lever of the vent-closing
valve (Figures 134, 135, or 136) in the off position,
after pressing its release button (see Figure 138).
(3) By moving the handle of the emergency
vent-closing valve (see Figures 139 and 140) to the
Figure 134 Vent-closing valve, with
setting lever in on position, cover
plate moved to show interior.
Figure 135 Vent-closing valve, with
setting lever in off position.
Figure 136 Vent-closing valve, setting lever in off position, cover plate attached.
Figure 137 (A) Cover plate for top of housing, with screws; (B) Washer;
(C) Latch pivot stud and pin; (D) hand lever latch; (E) Cover
plate for side of housing; (F) Latch spring; (G) Guide pin; (H)
Washer; (I) Setting lever; (J) Pivot stud; (K) Plunger; (L) Lever
pivot stud and pin; (M) Gland, with bolts and packing; (N) Housing for setting lever and valve; (O) Vent valve; (P) Supply valve;
(Q) Vent valve spring; (R) Supply valve spring; (S) Washers;
(T) Valve adapters.
Considering that adequate safety is afforded by
other means, the Bureau of Ships has authorized the
omission of the emergency vent closing valves in
The poppet valve should be gagged closed by
means of the gag nut (E in Figure 114), except
when it is intended to function in connection with
the firing of a torpedo or dummy.
The operation described under paragraph (1)
above moves the lever of the vent closing valve to
the "off" position by means of the link (B in Figure
132). This causes the vent (Poppet) valve to close
while the tube vent valve remains open to allow the
escape of any air which might still be in the tube.
The tube vent valve is closed directly by the operator when venting is observed to be completed. The
closing of this valve has no effect upon the Poppet
The vent closing valve body contains two small
valves of poppet type, both of which are operated
Vent-closing valve with
thumb on latch release
by setting lever. One of these valves is a shut-off
and supply valve for the ships' service air to the
Poppet Valve system. The other valve serves to vent
the air line to the Poppet Valve when the setting
lever moved to the "off" position thus relieving
the pressure in the air cylinder of the vent valve and
allowing the vent valve to close instantly.
The hand lever latch (D in Figure 137), when
engaged insures that the two valves in the vent
closing valve will remain in position to allow operation
of the Poppet System until released intentionally
and the lever returned to the "off" position by the
The latch release button is furnished solely for
releasing the latch. Continued thumb pressure on
this button will move the setting lever some distance,
but to insure that both valves in the vent closing
valve are fully in the "off" position the setting
lever should be pushed to the limit of its motion.
(A) Emergency vent-closing valve (quick-as-a-wink valve) in place
on vent-closing valve; (B) Normal position; (C) Open position.
Quick-as-wink valve, detached, in normal position at left, in open position in center, parts disassembled at right. A Valve body; B Stem; C Valve; D Sleeve; E Pipe adapter; F Handle; G Fork; H, I Nut, with cotter pin
Figure 144 Poppet valve indicator (A) in shut position;
(B) and (C) Linkage to (D) Stud on poppet valve.
A "gagging" device (E in Figure 114) is provided for the purpose of gagging the poppet valve
when its use is not desired. Also, after firing a
torpedo, and when the firing operation has ended,
the main vent valve, located in the poppet valve
body, should be locked closed by means of this
Figure 145 Poppet valve indicator (A) in open position; note changed position of stud (B) on poppet valve.
gagging device. An indicator is also installed to
show whether the poppet valve is open or closed.
This indicator is shown, in "shut" position, in Figure 144, and in "open" position in Figure 145. Figure
146 shows the linkage from the poppet valve to the
Figure 146 Linkage from poppet valve to indicator. (A) Connection with shoulder stud on poppet valve; (B) Poppet valve indicator; (C) Linkage connected with shoulder stud on poppet valve.