Chapter XVII: Section XVII: Gun Group

72. GENERAL

The gun group consists of the fuel-hose assembly and the gun. The gun includes the fuel valve, which controls the ejection of fuel, and the ignition head, which ignites the fuel.

73. FUEL-HOSE ASSEMBLY.

_a. Description and functioning._ (Fig 47) Hose, fuel, flame thrower, M1, assembly, provides a flexible connection between the fuel tanks and the gun.

(1) _Hose._ Made of synthetic rubber and reinforced with a cover of
metal wire and cotton braid, the hose resists the action of gasoline
and oil, and withstands a pressure of approximately 1,000 pounds per
square inch. Its inside diameter is 7/8 inch; its outside diameter is
approximately 1-1/4 inches.

(2) _Nipples._ The hose nipple, tank end, connects the hose to
the tank coupling on the tank group. The hose nipple, gun end, is
a threaded connector between the other end of the hose and the
fuel-valve body.

_b. Removal of fuel-hose assembly._ Remove the hose from the gun only when necessary for maintenance. The threads in the fuel-valve body will be damaged by frequent screwing and unscrewing of the hose because the body is a lightweight aluminum casting. Fuel hose is replaced as a unit and is not disassembled in the second echelon. To disconnect from tank group, see Paragraph 70 _b_.

_c. Installation of fuel-hose assembly._

(1) To install in tank group, see Paragraph 70 _c_.

(2) To install in gun, apply anti-seize compound (from service kit)
lightly to threads and screw hose in fuel-valve body by hand. Use
wrench only enough to make a secure connection.

_d. Maintenance of fuel-hose assembly._ If the hose nipple, tank end, is badly nicked and does not provide a tight connection with a new coupling washer (Par 70):

(1) File the end surface, being careful to keep the surface at a
right angle to the sides of the nipple.

(2) Couple hose nipple, tank end, to tank coupling. If coupling
closes very easily, indicating washer is not being compressed,
replace the washer and recouple. If coupling still closes too freely,
the nipple has been filed too short, and the fuel-hose assembly
should be replaced as a unit.

74. VALVE GRIP.

_a. Description and functioning._ (Fig 47) The valve grip is part of the fuel valve. It includes the controls and is held by the firer in his right hand to support the gun group. Parts of the valve grip are:

(1) _Left and right valve grips._ A pistol-type grip is formed by two
aluminum housings designated as the left valve grip and the right
valve grip. The two parts are held together by four screws and four
lock washers.

(2) _Grip support._ This aluminum housing is mounted above the left
and right valve grips and connected to them by two screws and lock
washers.

(3) _Valve lever._ This control is made to fit the fingers and is
mounted in front of and between the two parts of the valve grip. A
pin at the top of the lever fits into holes in left and right valve
grips and serves as a pivot, governing the movement of the lever.
When the lever and the grip safety are compressed simultaneously by
the operator, the valve is thereby opened and fuel is ejected from
the gun.

(4) _Grip safety._ This control is grasped by the hand simultaneously
with the valve lever. It is mounted back of and between left and
right valve grips. A pin at the base of the safety fits into holes
in the left and right valve grips and serves as a pivot in a manner
similar to the pin on the valve lever. The fuel cannot be discharged
unless both the valve lever and the grip safety are compressed
simultaneously.

(5) _Rocker arm._ The rocker arm, a boat-shaped metal part, is
mounted near its center on a pin. It is held in contact with the
valve lever by means of a valve-grip spring and spring pin. At its
top end, the rocker arm touches the yoke shaft of the valve-diaphragm
assembly. When the valve lever and the grip safety are compressed,
the rocker arm pushes the valve diaphragm assembly forward.

(6) _Valve-grip spring._ When the firer’s hand releases the valve
grip, the valve-grip spring forces the valve lever, the grip safety,
and the rocker arm back to their normal, nonoperating positions.

_b. Removal of valve grip._

(1) Unscrew the four screws and lock washers that hold the grip
support to the valve body. Remove the valve grip as a unit.

(2) To disassemble valve grip, remove screws and lock washers from
the grip. Lift off the left valve grip, exposing contents of grip.
Lift out the following parts: valve-grip spring, rocker arm, grip
safety, and valve lever.

_c. Installing valve grip._

(1) Place grip safety, valve lever, and rocker arm in position in
right valve grip. (Fig 48) Be sure the shorter end of rocker arm is
at the top. Place grip spring over spring pin. Slip short end of grip
spring in groove of rocker arm. Place long end of grip spring on
outside of grip safety.

(2) Put left valve grip in place and insert the two lower lock
washers and screws. Tighten the two screws enough to hold parts in
place and still leave space for moving long end of spring into the
groove in grip safety. Push spring into groove with a screw driver.
(Fig 49)

(3) With spring in place, fully tighten the two screws with screw
driver.

(4) Place grip support in position, and insert the two upper lock
washers and screws. Tighten screws, using screw driver.

(5) Attach valve grip to valve body, using the four lock washers and
inserting the four screws through the grip support. Make sure that
the yoke shaft of the valve-diaphragm assembly is in front of rocker
arm.

_d. Maintenance of valve grip._ No maintenance is required for the valve grip other than replacement of worn or damaged parts, tightening of screws, cleaning, and lubrication. (Par 49)

75. BARREL AND VALVE-BODY ASSEMBLY.

_a. Description and functioning._ (Fig 47) This assembly is part of the fuel valve. It includes the barrel, valve body, and operating parts contained in the barrel and valve body. The assembly consists of:

(1) _Valve body_, an aluminum housing, located at the rear of the
gun and mounted on the grip support by means of four screws and lock
washers. The valve body has four large threaded openings. The lower
opening leads into the valve grip. The side opening, which forms a
Y with the main portion of the body, is connected to the fuel-hose
assembly. The front opening is screwed on the barrel. The rear
opening is closed by the spring retainer and plug.

(2) _Valve-diaphragm assembly_, which transmits and reverses the
movement imparted to it by the rocker arm of the valve grip. (Par 74
_a_) It also serves as a seal, keeping fuel from entering the valve
grip. The valve-diaphragm assembly includes:

(_a_) _Yoke shaft_, on which the rocker arm bears at the lower end
of the shaft.

(_b_) _Yoke_, a Y-shaped metal part which fits on the upper end of
the yoke shaft and is held to it by a steel pin. The yoke transmits
motion from the shaft to the yoke block, and is located within the
valve body when the valve is assembled.

(_c_) _Diaphragm_, a synthetic-rubber diaphragm held in a steel
sleeve, which fits snugly in the lower opening of the valve body.
The yoke shaft passes through the diaphragm.

(3) _Diaphragm support, washer, and cap_, which hold the
valve-diaphragm assembly in place in the valve body.

(4) _Spring retainer_, a brass, hollow bushing which screws into the
rear opening of the valve body, and which is threaded internally
to receive the plug. The retainer has a hexagonal head to take a
1-3/8-inch wrench. As its name implies, the retainer holds the valve
spring in position.

(5) _Plug_, a brass part, resembling a cap screw, which fits into
the spring retainer, closing off the rear end of the gun. It permits
adjustment of the needle (see _d_ below) without removing the valve
spring and spring retainer.

(6) _Valve spring_, a coil spring located in the valve body between
the spring retainer and the yoke block. The spring keeps the needle
seated in the nozzle until compression of the grip safety and valve
lever forces back the yoke block, spring, and needle.

(7) _Yoke block_, a steel piece, 1 inch long, which fits into the
arms of the yoke Y. It is secured by an internal thread to the valve
needle. Movement of the yoke in turn moves the yoke block and the
valve needle.

(8) _Lock nut_, on the valve-needle thread at the rear of the yoke
block, which locks the block on the needle.

(9) _Valve-needle_, a pointed rod, which extends through the inside
of the barrel from the yoke block to the nozzle. The valve needle is
seated in the nozzle except when firing. It controls the ejection
of fuel from the nozzle. Two sets of three fins each, known as
needle guides, are mounted on the front and rear of the needle,
respectively. These guides keep the needle centered in the barrel.
The rear end of the valve needle is threaded to hold the yoke block
and permit adjustment of the needle by means of the lock nut which
screws on the threads. (See _d_ below.)

(10) _Barrel_ (Figs 47 and 54), which carries the fuel to the
ignition head. It also supports or contains other components of the
gun. The barrel assembly is replaced as a unit with the needle. It
consists of a tube, made of thin metal, with a threaded fitting at
the back end, and a nozzle brazed into the front end of the tube. The
nozzle ejects the fuel from the barrel through the ignition head. The
fuel emerges from two holes in the nozzle:

(_a_) _Atomizer hole_, a small opening which sprays a fine, readily
ignited mist of fuel. This helps ignite the main stream of fuel.

(_b_) _Main hole_, which is tapered inside, and which conveys the
main stream of fuel from the barrel. When the gun is not being
fired, the valve needle is seated in the main hole of the nozzle.
When the gun is being fired, the needle is withdrawn from the
nozzle seat, permitting the fuel to be forced from the gun.

_b. Removal of barrel and valve-body assembly._ If gun group and tank group are connected, release any pressure in the fuel tanks by compressing the valve lever and the grip safety. Then disassemble as follows:

(1) Unscrew the fuel-hose assembly from the fuel-valve body only if
this is necessary for maintenance.

(2) Remove spring retainer and plug from end of fuel-valve body and
remove valve spring.

(3) Unscrew diaphragm cap and pull out washer, support, and
valve-diaphragm assembly. To prevent loss of valve-needle adjustment
(Fig 54), do not disturb position of yoke block by turning the needle.

(4) Slide the valve needle out of barrel; the yoke block and the lock
nut may then be unscrewed from the valve needle, but adjustment (see
_d_ below) will be necessary when reinstalling.

_c. Installation of barrel and valve-body assembly._

(1) To install valve needle, screw the yoke block and lock nut on the
needle (Fig 50). Insert needle in valve body and barrel.

(2) Insert valve-diaphragm assembly into valve body (Fig 51), making
sure that the yoke slips into the flat notches of yoke block.

(3) Slip the diaphragm support, washer, and cap over the yoke shaft.
(Fig 52) Screw on the diaphragm cap by hand. Do not use a wrench.
Install valve grip. (Par 74 _c_)

(4) Place valve spring over end of needle and install spring
retainer. (Fig 53) Apply wrench very lightly to tighten spring
retainer.

(5) Adjust needle (see _d_ below), and screw plug into the spring
retainer.

(6) If hose has been removed, apply anti-seize compound lightly
to the threads. Screw hose into fuel-valve body. Wrench should be
applied very lightly to tighten.

_d. Adjustment of valve needle._ Needle is adjusted after installation of parts in barrel and valve assembly. Use care when resetting needle, as smooth operation of the weapon depends on accurate adjustment.

(1) Remove ignition shield (Par 18) and plug from gun.

(2) Use the valve-adjusting wrench (Fig 8) to hold the lock nut and
apply a cabinet (narrow-bladed) screw driver (Fig 8) in the end of
the needle. Turn needle until it makes a snug fit in the nozzle
opening.

(3) Compress the valve lever and grip safety. The needle should draw
back into the nozzle with the tip of the needle at the smallest
diameter opening in the nozzle. (Fig 54)

(4) When the needle has been correctly adjusted, as in (3) above,
tighten the lock nut with the valve-adjusting wrench, keeping the
needle from turning with the screw driver. This will lock the
adjustment. Screw plug into the spring retainer.

(5) Replace ignition shield. (Par 18)

_e. Maintenance of barrel and valve body._

(1) _Damaged parts._ Replace worn or damaged parts. If the diaphragm
shows evidence of tears or separation, or if leaks occur at the
diaphragm, replace the valve-diaphragm assembly.

(2) _Valve spring._ If valve spring has lost resiliency, grasp it by
the ends and stretch slightly, or replace.

(3) _Nozzle leaks._ If valve leaks at nozzle, and cleaning (Par 55
_d_) does not remedy the leak, adjust needle (see _d_ above). If
leak persists, either replace barrel and needle, or lap seat. To
lap, place lapping compound on seat (in nozzle) and on needle point.
Turn needle in seat until parts make a tight connection when seated.
Remove lapping compound, reassemble, adjust needle, and test fire.

(4) _Atomizer hole._ If atomizer hole is clogged, clean with fine
wire. (Par 52 _i_)

76. IGNITION HEAD.

_a. Description and functioning._ (Fig 55) The ignition head ignites the fuel when the flame thrower is fired. It is mounted on the fore part of the barrel. It consists of:

(1) _Ignition-head body_, which includes half of the front grip.
Three set screws serve to tighten the ignition-head body to the
barrel. The ignition-head body is made of aluminum.

(2) _Trigger and trigger bearing_, held between the ignition-head
body and the coverplate by the trigger screw.

(3) _Trigger rod_, one end of which is held in the trigger bearing,
the other extending through the ignition-head body. Pulling the
trigger shoves the trigger rod forward, causing it to push a match in
the ignition cylinder. The match ignites an incendiary charge in the
ignition cylinder.

(4) _Trigger spring_, which hooks over a projection of the trigger
and is held at its lower end by a screw, which is held in the
ignition-head body. This spring pulls the trigger rod back from the
firing position after the firer releases the trigger.

(5) _Latch_, located in the ignition-head body, in front of and above
the trigger guard. The latch, set on a pin, engages the notch of the
ignition shield, locking it in place. A latch spring holds latch in
position.

(6) _Coverplate_, an aluminum casting which constitutes the left
section of the front grip and covers the working parts seated in the
ignition head body. The coverplate and body are held together by four
screws and four lock washers.

(7) _Spring case_, which turns the ignition cylinder when the trigger
is pulled.

(_a_) Four projections on the inner spring case are bent over the
outer spring case to hold the two parts together.

(_b_) The inner-case pin (Fig 56) engages a stop on the inside of
the ignition cylinder. The five projecting metal matches on the
inside of the ignition cylinder are each in turn stopped by the lug
on the forward-facing surface of the ignition-head body.

When the trigger is pulled, the trigger rod pushes a match forward,
causing an incendiary charge in the ignition cylinder to ignite.
The spring in the case rotates the ignition cylinder until another
match is stopped by the lug.

(_c_) The outer-case pin (on the outside surface of the outer
spring case) fits into the notch in the ignition shield and holds
the spring case as the shield is screwed into position. This action
winds the spring in the case.

(_d_) A snap ring holds the spring case on the ignition-head body.

(8) _Ignition shield_, a cylindrical, thin-metal tube with a conical
front end. The shield guides the flame and protects the firer. Eight
holes around the base of the cone provide an air intake for burning
the fuel. The base of the shield is threaded, and it screws onto
the ignition-head body. A notch (Fig 56) in the base of the shield
receives the latch and the outer-case pin of the spring case.

_b. Removal of ignition head._ To remove the ignition head, proceed as follows:

(1) Remove shield by lifting latch and unscrewing shield
counterclockwise. (Fig 14) Keep hands and face away from front of
barrel.

(2) If ignition cylinder has not been removed, remove it or allow it
to fall off barrel.

(3) Pry off snap ring which holds spring case in position, using
screw driver. (Fig 57) Be careful not to damage or break the
ignition-head body by applying too much leverage.

(4) Remove the four screws and lock washers which hold ignition-head
body and coverplate together. Lift off coverplate.

(5) Trigger, trigger spring, trigger rod, latch, and latch spring may
be removed.

(6) Using a hex wrench, loosen set screws (Fig 58) and withdraw
barrel from ignition head.

_c. Installation of ignition head._ To install ignition head, proceed as follows:

(1) Insert barrel in ignition-head body, pushing it as far forward as
the shoulder on the barrel permits.

(2) Aline front grip and valve grip.

(3) Using hex wrench, tighten set screws on barrel enough to hold but
not so tight that barrel is dented.

(4) Place latch, latch spring, trigger and bearing, trigger rod, and
trigger spring in position.

(5) Put coverplate on ignition-head body and replace the four lock
washers and screws.

(6) Slip spring case over barrel, and lock by forcing snap ring into
the groove.

(7) When weapon is to be used on a mission, fit ignition cylinder
and ignition shield in place on nozzle end of barrel as described in
Paragraph 18.

_d. Maintenance of ignition head._

(1) _Servicing._ The ignition head should be cleaned and lubricated
each time it is disassembled. (Par 49)

(2) _Spring-case assembly._ If outer case rotates and inner case does
not, and no spring action occurs, spring is broken and spring case
should be replaced as a unit. Do not disassemble or repair this part.

(3) _Trigger rod and lug._ When trigger is pulled all the way, end
of trigger rod should extend 1/16 inch beyond lug on forward-facing
surface of ignition-head body. If end of trigger rod is worn, replace
rod. Lug on the ignition-head body should be approximately 7/32 inch
high. If lug is worn or broken, replace ignition head body.