4A1. Introduction. The 225-pound compressed
air system, known as the ship's service
air system, performs or controls many operations
other than those discussed in the chapters
dealing with the 3000-pound, the torpedo
impulse, and the 600-pound air systems. The
225-pound air system provides the air for
approximately 100 operations which are discussed
in later sections of this chapter and in
Chapter 9. The system extends from the forward
torpedo room to the after torpedo room,
with service connections in every compartment
of the vessel, and supplies air at pressures
ranging from 225 to 8 psi. The center
of direction of the system, the 225-pound service
air manifold (see Section 4B) is located in
the control room. The 225-pound system is
hydrostatically tested to 350 psi or 155 percent
of its maximum working pressure of 225 psi.
shows the nomenclature, location,
and relationship of the parts of the system.
Detailed descriptions of the main components
of the system are given in later sections
of this chapter.
Discussion of the ship's service air system
will start with the control room, describing
each component part of the system located
there, and explaining its function in the operation
of the submarine A similar procedure
will be followed for each of the compartments
of the vessel, proceeding first forward and
then aft of the control room.
4A2. Control room. The 225-pound service
air manifold is located in the control room on
the starboard side, aft of the high-pressure
manifold. This manifold receives its air supply
through two Grove pressure-reducing
valves, which reduce the high-pressure air
from 3000 psi to 225 psi. Stop valves are
provided on the low-pressure side of the 225-pound
Grove reducers, cutting them off the
225-pound system. This permits removal of
Grove reducer without impairing the operation
of the 225-pound system. The 225-pound
service air manifold can also be supplied from
the 225-pound bypass which is controlled by
a manually operated 225-pound bypass valve
located at the high-pressure distributing
manifold. When the 225-pound bypass is used,
the high-pressure air bypasses the reducing
valves and is admitted directly into the 225-pound
system. The bypass valve is opened
only partly, so that the pressure can be built
up gradually. The 225-pound manifold pressure
gage must be watched constantly and
the pressure must never be allowed to go
beyond 225 psi.
The 225-pound air system is protected by
one sentinel valve and two relief valves
located in the line between the Grove reducers
and the 225-pound manifold.
If the air within the 225-pound system
reaches a pressure of approximately 250 psi,
the sentinel valve opens, allowing the excess
air to escape into the compartment. The
sentinel valve has a comparatively small capacity,
and serves primarily to warn that the
normal working pressure is exceeded.
If the rise in pressure is rapid and above
the capacity of the sentinel valve, the two
relief valves, set to operate at 275 psi, open
and allow the excess air to escape into the
The relief valves and the sentinel valve
shut automatically when the normal working
pressure is restored.
The supply line from the Grove reducing
valves has two branches. One branch supplies
225-pound air to the hydraulic oil supply
volume tank, the signal ejector, the drain
pump air domes, the negative tank blow valve,
and the sea pressure and depth gage blows.
The other branch supplies air to the 225-pound
service air manifold. This air is directed
by means of valves to the forward and
after service air mains, the auxiliary tank
blow and vent line, and the forward and after
trim tank blow and vent lines. A hose connection
to the manifold provides for air supply
from the dock or tender.
Figure 4-2. Pneumatic tool connection.
A line from the forward service air main
is provided with a reducing valve which furnishes
air at a pressure of 100 psi to a connection
for pneumatic tools. (See Figure 4-2.)
A bypass is provided for emergency operation,
with a relief valve set to open at a pressure
of 110 psi as protection against excessive
The after service air main carries a connection
supplying air to the whistle and siren.
The after service air main has branch
connections to the sea pressure gage and to
the compartment salvage air. It supplies air
through a reducing valve, at a pressure of 12
psi, to fresh water tanks Nos. 3 and 4. A bypass
is provided for emergency operation,
with a relief valve set to open at a pressure
of 15 psi.
4A3. Forward battery compartment. In the
officers' quarters, the forward service air
main supplies the compartment air salvage
valve, mounted on the after bulkhead. This
valve can be operated from either side of the
bulkhead. A branch of the service air line,
passing through an 8-pound reducing valve,
supplies air at a pressure of 8 psi to the four
battery fresh water tanks, Nos. 1, 2, 3, and 4,
in the forward battery compartment. A bypass
line is provided for emergency operation,
with a relief valve set to open at a pressure
of 10 psi.
4A4. Forward torpedo room. In the forward
torpedo room, the forward service air main
extends to the torpedo tube blow and vent
Figure 4-1.). The service air main
is also provided with branch lines to the torpedo
stop cylinders, the escape trunk blow,
the volume tank, the sanitary tank, the QC
and JK sea chests, the Pitometer log, the
compartment air salvage valve, and the fuel
oil blow and vent manifold. Two other branch
lines, equipped with reducing valves and bypass lines,
furnish air at 100 psi to the
pneumatic tool connection, and at 12 psi to the
No. 1 and No. 2 fresh water tanks. The line
to the escape trunk supplies air for the ship's
diver's air connection, and a blow and vent
line supplies the escape chamber. The forward
trim tank blow and vent line from the
225-pound manifold in the control room terminates
at the forward trim tank and connects
with the forward trim tank blow and vent
line from the forward torpedo tube blow and
4A5. After battery compartment. The galley
and mess room compartment has one
connection from the after service air main,
which supplies air to the blow and vent manifold
for fuel ballast tanks 3A, 3B, 4A, and 4B.
A second connection through an 8-pound reducing
valve supplies air at 8 psi to the four
battery fresh water tanks, Nos. 5, 6, 7, and
8, located in the after battery compartment.
A bypass is provided for emergency use with
a relief valve set to open at 10 psi. The lines
for blowing and venting the auxiliary ballast
tanks connect from the 225-pound manifold
to the auxiliary ballast tank angle stop valves,
located at the tank top in this compartment.
4A6. Crew's quarters. In the crew's quarters,
the after service air main supplies air
to the crew's forward water closet and the
No. 2 sanitary tank blow line. The sanitary
tank is equipped with a relief valve set to
open at 105 psi.
4A7. Forward engine room. The forward
engine room has direct connecting lines from
the after service air main to the compartment
air salvage valve, the No. 5A and No. 5B fuel
ballast tank manifold, the exhaust valve operating
gear, and the lubricating oil tanks'
blow and vent manifold. The supply to the
fuel oil manifold is protected by a relief
valve set to open when the pressure exceeds
15 psi. The air for the lubricating oil manifold
is reduced to 13 psi by a reducing valve.
A bypass is provided for emergency operation,
with a relief valve set to open at 15 psi.
In addition, the forward engine room is provided
with a pneumatic tool connection
equipped with a 100-pound reducing valve
and a bypass for emergency. A relief valve
set to open at 110 pounds safeguards the line
against excessive pressure.
4A8. After engine room. In the after engine
room, the after service air main has direct
connections to the compartment air salvage
valve, the auxiliary engine shutdown, and
the air manifold which controls the blowing
and venting of the Nos. 6 and 7 normal fuel
oil tanks, the expansion and the collecting
tanks. A relief valve, set to open at 15 psi,
protects the Nos. 6 and 7 normal fuel oil tanks
and the expansion and collecting tanks against
excessive internal pressure. A pneumatic tool
connection is also provided; it is equipped
with a 100-pound reducing valve, a 110-pound
relief valve, and a bypass line to supply air
at 100 psi.
4A9. Maneuvering room. The maneuvering
room contains lines extending from the after
service air main to the after water closet, the
compartment air salvage valve, and the main
engine shutdown connection.
4A10. After torpedo room. In the after torpedo
room, the service air main has branches
leading to the 225-pound compartment air
supply valve for the escape hatch, the torpedo
tube stop cylinder, the volume tank, and the
pneumatic tool connection. The pneumatic
tool connection is provided with a 100-pound
reducing valve and a bypass protected by a
110-pound relief valve. The service air lines
terminate at the after torpedo tube blow and
The after trim tank blow and vent line,
which extends from the 225-pound manifold
in the control room, connects with the after
trim tank by a branch line extending to the
after torpedo tube blow and vent manifold,
similar to that of the forward torpedo room.
The compartment air salvage valves are
mounted on the transverse bulkheads of each
compartment so that they may be operated
from either side, releasing air into the compartment
from which they are worked or into
the adjoining compartment. The compartment
air pressure gages are also mounted on
either side of the bulkheads to permit a reading
of air pressure in the adjoining compartment.
All manifolds and lines equipped with reducing
valves and blow valves are provided
Figure 4-3. The 225-pound service air manifold.
with pressure gages. All fuel oil, lubricating
oil, collecting, expansion, sanitary, and
variable tanks are provided with pressure gages
located in the various rooms and compartments
as shown in Figure 4-1.
The main parts and controls of the 225-pound
system are described in detail in the
following sections of this chapter.
Step-by-step instructions in the use of
this system will be found in Chapter 9.
B. THE 225-POUND SERVICE AIR MANIFOLD
4B1. Description. The 225-pound service air
manifold which was introduced in the preceding
section controls the blowing and venting
of the forward and after trim tanks, the
No. 1 and No. 2 auxiliary ballast tanks, and
the air supply to the forward and after service
Figure 4-3 shows the mechanical construction
of the manifold as well as the
proper nomenclature of its parts. The manifold
is located on the starboard side of the
control room, just aft of the 3000-pound air
manifold. Gages indicating the air pressure
in the manifold, in the forward and after trim
tanks, in the No. 1 and No. 2 auxiliary ballast
tanks, and a gage registering sea pressure are
mounted on the gage board directly above the
The body of the manifold is a one-piece
bronze casting, divided into eight compartments.
There is one large rear compartment
provided with a flanged inlet for connection to
the 225-pound air supply. Each of the seven
smaller front compartments is provided with
a flanged port for connection to one of the
lines of the 225-pound system. There are
four vent ports in the bottom of the manifold,
one from each of the four lower compartments.
A drain pan is mounted directly below
the manifold to catch any drain water.
4B2. Valves. Eleven valves are provided on
the front (or inboard) side of the manifold,
each with a bolted bonnet on which a name
plate designates the function of that particular
valve. The ends of the rising valve stems
are shaped to fit the special wrench provided
for their operation.
The valves are arranged in three horizontal rows.
Reading from left to right, the
first valve on the top row directs the air
supply to the forward service air line, the
middle valve is a spare, and the end valve
directs airflow to the after service air line.
These valves lead to the forward and after
service air mains and are normally locked
open to insure an uninterrupted air supply.
The locking caps and padlocks are used to
lock the valves in the open position.
The middle row contains the valves controlling
the blowing of the forward trim tank,
the auxiliary tank No. 2 blow, the auxiliary
tank No. 1 blow, and the after trim tank blow.
The bottom row of valves controls the venting
of the forward trim tank, the auxiliary
tank No. 2, the auxiliary tank No. 1, and the
after trim tank.
4B3. Operation. In operation, the air supply
from the two 225-pound reducers enters the
rear compartment of the manifold. When any
one of the blow valves (the middle row) is
opened, the air in the rear compartment
passes to the front part of the manifold leading
to the line in which the valve is open.
In venting, the opening of any vent valve
(the bottom row) allows the air in the corresponding
line to flow into the front passage
and out the vent port, which discharges into
the drain pan.
Step-by-step instructions for the use of
the 225-pound service air manifold will be
found in Chapter 9.
C. GROVE REDUCER
4C1. Description. The 225-pound service air
system is supplied with air by the 3000-pound
air system. In turn, the 225-pound system
supplies air at 100, 12, 13, 10, and 8 psi to the
various service lines, such as the pneumatic
tool connections and the fresh water tanks.
This reduction or lowering of air pressure
is accomplished by a device known as the
Grove reducing valve, (See Figure 4-4.)
Figure 4-4. Grove reducing valve.
Both the high-pressure and the 225-pound
service air systems are provided with pressure
reducing valves. There are two 3000-to-600-pound
reducing valves for charging the
torpedo tube impulse flask, and two 3000-to-500-pound
reducing valves for the main engine starting air.
Two 3000-to-225-pound reducers are used on the
supply line to the 225-pound service air manifold.
The other reducing valves (a total of 12
on the 225-pound air system) are distributed
throughout the submarine as follows: five
supplying the pneumatic tool connections
with 100-pound air; two supplying the battery
fresh water tanks with 8-pound air; one supplying
the lubricating oil manifold with 13-pound air;
one delivering 10-pound air for
the distillate tank; one delivering 40-pound
air to the brine tank; and two supplying 12-pound
air to the fresh water tanks.
Figure 4-4, which illustrates a typical
reducing valve, shows that it consists principally
of an air dome, a diaphragm, a regulating valve,
and a body provided with both a
high-pressure inlet and a low-pressure outlet.
4C2. Operating principle. The reducing
valve acts on the balanced pressure principle.
As the air is used, and the pressure on the
discharge side decreases, the diaphragm is
forced down and the valve admits high-pressure
air until the correct pressure is restored.
The dome chamber is charged by a loading channel,
controlled by two needle valves
as shown in Figure 4-4. The dome is loaded
Place the loading wrenches in the
dome and body needle valves.
Back off the dome valve, to vent the
pressure in the dome.
Shut both needle valves.
Shut the inlet line stop valve.
Shut the outlet line stop valve.
Open the body needle valve one half
Watching the outlet pressure gage,
carefully open the dome needle valve. When
the desired delivery pressure is shown on the
outlet gage, shut the dome needle valve.
Shut the body needle valve.
The reducer is now ready for service.
The reducing valve provides a close, accurate
control of air pressure. If the delivered
pressure rises or falls, it is necessary to correct
it, by reloading the dome, as described
D. AUXILIARY BALLAST TANK BLOW AND VENT STOP VALVE
4D1. Description. The connection from each
blow and vent line of the 225-pound system
to the auxiliary ballast tanks serviced by it
is made through a blow and vent stop valve,
a typical example of which is shown in Figure
4-5. The flange on the discharge end of the
valve body is bolted to the tank opening, and
the pipe flange is bolted to the flange on the
inlet side of the valve. Thus the flow of air
between the pipe and the tank can be stopped
by operating the valve.
The valve is of the disk and seat type
with a rising stem. The valve body is a one-piece
bronze casting with the bonnet bolted
on it to give access for inspection or repair.
The seal between bonnet and body is made by
an asbestos gasket. An adjustable packing
gland and braided flax packing prevent
The blow and vent stop valves are opened
and shut by a manually operated handwheel.
Counterclockwise rotation of the handwheel
raises the valve disk from the seat
and allows the passage of air for blowing or
venting. Figure 4-5 shows the flow of air
through the valve when blowing. In venting,
the flow of air is reversed.
Figure 4-5. Auxiliary ballast tank blow and vent stop valve.
Figure 4-6. WRT BLOW AND WRT OVERFLOW INTERLOCKING SYSTEM.
E. WRT BLOW AND WRT OVERFLOW INTERLOCKING SYSTEM
4E1. Description. The purpose of the WRT
overflow interlocking system (see Figure
4-6) is to prevent blowing from the WRT tank
to the trim tank by way of the overflow piping
and overflow valve. This precaution is
necessary in order to assure that needless and
useless air pressure will not be put on these
two tanks without actually transferring the
water ballast from the WRT tank to the trim
To prevent this condition, the quick-acting blow
valve for the WRT tank, located
in the WRT blow and vent line, is mechanically
interconnected with the overflow valve
in such a way that the opening of the overflow
valve automatically shuts the blow valve,
and vice versa.
The interconnection consists of a single
lever which operates both valves, with connecting
links to cams actuating the valves.
The linkage is shown in Figure 4-6.
The operating lever for the forward system
is located adjacent to the torpedo tubes
in the forward torpedo room. The lever for
the after system is located forward of the
tubes on the port side of the after torpedo
The upper diagram of Figure 4-6 shows
water being blown from the torpedo tubes and
entering the WRT tank through the open
torpedo tube drain stop valve to the WRT
tank. Assuming that the WRT tank is already
filled, it therefore cannot hold the entering
water which forces the excess water into the
overflow pipe, past the open overflow valve,
and into the trim tank.
The flow arrows in the lower diagram of
Figure 4-6 trace the path of flow and the valve
line-up required to get air to the WRT tank
and transfer water from the WRT tank to the
torpedo tubes or the trim system by way of
the torpedo tube drain stop valve to the WRT
The lower diagram also shows the conditions
existing when blowing the WRT tank
to the torpedo tubes or the trim system. The
quick-acting blow valve is open, allowing air
to enter the WRT tank and to force the water
in it to the torpedo tubes, via the open torpedo
tube drain stop valve to the WRT tank.
If the system were not protected with
an interlock during this operation, the overflow
valve could be opened, allowing the water
to be blown from the WRT tank to the level
of the overflow pipe, and then the air would
rush into the trim tank, through the overflow
pipe, and exhaust itself through the trim tank
F. TORPEDO TUBE BLOW AND VENT MANIFOLD
4F1. Description. When a torpedo is fired,
sea water rushes in and fills the empty tube.
Before the breech door can be opened for reloading,
this water must be removed by blowing or draining
Similarly, after loading and before firing,
the excess air in the tube must be vented and
the tube flooded with water.
The basic function of the torpedo tube
blow and vent manifolds is to direct the 225-pound
air used to blow the tubes during draining,
and to vent the tubes during flooding. It
also provides for blowing and venting the
WRT tank and the trim tank when the water
from the tubes is transferred to or from either
of these tanks.
Each manifold consists of a bronze
casting, fitted with blow valves with bolted bonnets,
and provided with flanged connections.
The cutaway illustration, Figure 4-7, shows
the mechanical construction typical of all
three manifolds. All blow valves are provided
with extended stems and manually operated
handwheels. The vent valves are lever-operated.
The access plates on the bottom
permit inspection and repair of the vent
Figure 4-7 illustrates the port side manifold
in the forward torpedo room. Two hundred
and twenty-five pound air is supplied
through the upper flanged connection on the
side, filling the upper longitudinal compartment.
When any of the blow valves is opened,
air is permitted to enter the corresponding
Figure 4-7. Torpedo tube blow and vent manifold (port side).
rear compartment, or passage, to the desired
torpedo tube blow and vent line. Shutting
the blow valve will stop the flow of air.
The lower flanged outlet on the side connects
the lower longitudinal compartment of
the manifold to the torpedo tube vent line.
Opening any one of the vent valves allows
air from the desired tube or tank to flow into
the vent line.
4F2. Location. There are three torpedo tube
blow and vent manifolds in the submarine.
(See Figure 4-1.) Two are mounted aft of the
torpedo tubes in the forward torpedo room;
the manifold on the port side servicing torpedo
tubes Nos. 2, 4, and 6, and the forward
WRT tank. The starboard manifold services
torpedo tubes Nos. 1, 3, and 5, and the forward
trim tank. The third manifold is mounted in
the after torpedo room just forward of the
torpedo tubes and services tubes Nos. 7, 8, 9,
and 10, and the after trim and WRT tanks.
G. PNEUMATIC TOOL CONNECTIONS
4G1. Description. Among the functions of
the 225-pound service air system is that of
supplying air under pressure to the pneumatic
tool connections (Figure 4-2) which provide
air pressure to operate the grease guns
and other air-driven tools necessary to service
There are five such connections, located
one each in the forward torpedo room, the
control room, the forward engine room, the
after engine room, and the after torpedo room.
Each connection is supplied with 100-pound
air through a Grove reducer which receives
225-pound air from the forward or after service
air main. In addition, each pneumatic
tool connection is provided with a bypass
which permits the use of the connection
even if the reducing valve is not functioning.
The connection is opened or shut by a manually
Figure 4-8. Sentinel valve.
Figure 4-9. Relief valve.
H. SENTINEL VALVES
4H1. Description. If the working pressure
of the 225-pound service air system rises to
a pressure of approximately 250 psi, the sentinel
valve (Figure 4-8) opens automatically,
allowing the excess pressure to escape. It will
close when sufficient air has been exhausted
to lower the pressure below 250 pounds.
The discharge capacity of the sentinel
valve is limited and hence it serves principally
as a warning that excess pressure is
being built up in the system. If the pressure
in the system becomes so great that the sentinel
valve is unable to discharge fast enough
to lower it, the two relief valves automatically
open and reduce the system pressure. The
relief valves are discussed in detail in Section 4I.
Figure 4-8 is an illustration of the sentinel valve.
Its internal construction is similar to that of the
relief valve shown in Figure
4-9. The sentinel valve is set into the line by
the threaded male inlet. Air from the 225-pound
line fills the lower chamber and exerts
pressure against the valve disk which is held
shut by the spring. The spring is preset to
allow the disk to open when the pressure in
the lower chamber approximates 250 psi. The
rising of the valve disk allows excess air to
escape through the side outlet. When the line
pressure drops below 250 pounds, the spring
closes the valve. The hand lever permits
manual operation of the valve when necessary.
I. RELIEF VALVES
4I1. Purpose. Relief valves are used to protect
the lines of the 225-pound service air
system from excessive pressure. Placed directly
in the lines, they are set to open at a
predetermined pressure, thus allowing air to
escape from the lines into the boat, and so
relieve internal pressure. When normal pressure
in the lines is restored, the valve shuts
4I2. Description. The construction of a
typical relief valve is shown in Figure 4-9.
The arrows indicate the flow of air when the
valve is blowing, or relieving pressure.
The bottom outlet is fitted to the line or
manifold to be protected, thus allowing the
air to enter the lower chamber and push
against the bottom of the valve disk. The
valve disk is held against the valve seat by
the tension of the spring, which is adjusted
to exert a downward force equal to the maximum
allowable pressure in the air line. When
the pressure in the air line exceeds this limit,
it forces the valve disk up and allows air
to escape into the boat through the side outlet.
As soon as enough air has escaped to
lower the pressure, the spring forces the disk
downward and shuts off the flow through the
escape outlet. The regulating ring controls
the rate of escape by opening or closing the
blowdown vents. The hand lever allows the
valve to be operated manually. Lifting the
lever will raise the valve disk and allow the
escape of air.
The cap, body, and bonnet of the valve
are made of bronze with a steel spring and
4I3. Location. Relief valves are located
throughout the 225-pound service air system
as outlined, in the table on page 28, which
also shows the service performed and the pressure
at which the valve is set to blow.
Forward torpedo room
Sanitary tank Fuel oil manifold Fresh water tanks Pneumatic tool connection
105 15 15 110
Forward battery compartment
Battery fresh water tanks
Pneumatic tool connection 225-pound manifold Fresh water tanks
110 275 15
Galley and mess room
Battery fresh, water tanks Fuel oil manifold
Forward engine room
Pneumatic tool connection Fuel oil manifold Lube oil manifold Brine tank Distilling tank