Ohio Class, Ballistic Missile Nuclear Powered Submarine, USS Kentucky SSBN737

Pressurized air system, monitoring, regulating, tank &  manual valves:

The air pressure is regulated (limited) and monitored at all times using an electronic manometer, and if it drops below a critical limit, then diving is disabled. The sub is now ready to return to port for service. Diving is re-enabled once the situation has been corrected.

It will almost not be necessary to build any electronics for this, as units are available that fully suit our needs. First we need a unit that will reduce the system air pressure to somewhere between ½ to 2 bar, as the full air pressure from the air tank are much too high for both smooth operation and the system in general. We also need is a switch that has an adjustable activation pressure point around 1 to 3 bars. The units can be bought from RS Components, Herga or Clippard. 

Pressure calculation, necessary air system pressure:

When I designed my regulated air system, I decided that I would be diving no deeper than 9.8 ft. (3 m.) Then I went ahead and calculated the required air pressure to re-surface from a depth of 9.8 ft. (3 m.): 

Finding the relative pressure at 9.8 ft.:   9.8 x  0.4335147 = 4.25 psi / 0.293 bar / 0.289 atm
(Knowing that the pressure increases with 0.4335147 psi. pr. ft.)

I then added a safety margin of an additional 6 ft. worth of air pressure, just to play it safe. Then I went ahead and calculated the
required air pressure to re-surface from a depth of 9.8 + 6 = 15.8 ft. (4.8 m.): 

Finding the relative pressure at 15.8 ft.:   15.8 x 
0.4335147 = 6.85 psi / 0.472 bar / 0.466 atm
(Knowing that the pressure increases with 0.4335147 psi. pr. ft.)

I then knew the minimum pressure to adjust my regulator to, and what pressure my valves, hoses and MBT would need to be able to operate at. My regulated air system will be pressurized to about 1.6 atm, just to play it safe, to have yet another safety margin, and a good system response with fast surfacing capability. Pressure test your construction along the way doing production, and plan ahead. My WTC2, valves and associated air / water hoses tested tight up to about 2.5 bar, at which pressure I dared not go further. (Was afraid the hoses might burst...)

Adjust your regulator / limiter unit to a pressure that allows the sub to operate in a nice and smooth manner (App. 1.6 atm.), and adjust your switch to activate at the lowest allowable pressure at which you still have air enough to blow even full MBT and surface from the max. diving depth. This will call for a few tests, as it depends on the size of your main air tank. The switch is located before the regulator, as it gives you more safety margin getting an alarm when the main air tank pressure is at fx. 2 atm. with plenty to go for one more trip up, than it would getting the alarm when the regulated air pressure drops below normal operating pressure. 

Here’s the RS Components pressure activated switch, RS 398-7045, monitoring the air pressure:


Operating pressure: 1 -> 10 bar
Contacts: 1 x
Switch temperature tolerance: +/- 0.5 bar at room temp.
Dimensions: 55 mm tall, OD = 29 mm
Connections: 1/4" BST

It is not waterproof, and needs a housing!

Complete datasheet available here.

Here's the RS Components pressure regulator, RS 398-5544, regulating system pressure:


Operating pressure: 1 -> 16 bar
Regulation range: 1 -> 8 bar

Dimensions: 68 mm tall, OD = 19 mm
Connections: 1/4" BST + 8 mm conex.

Complete datasheet available here.

In addition you'll need two manual valves, one to open and close the connection used when adding new air to the tank (using a compressor), and another to open and close for the air supply to the system. Here I'd like to suggest a "ball valve" (RS Components stock number RS 243-3339) with a nice and easy to operate-handle. You will also need a little "plumbing", and some OD 8 mm cupper pipe etc.

Air tank:

The air tank is an old fire extinguisher, collected at the local recycling station. It's made of metal, and stamped with a test pressure of 30 bars. The volume is app. 2 liters of air. The original top piece was reworked, thus removing the valve, and the handle. A hole was drilled for the quick-coupling for the 8mm copper pipe. Please see the chapter about the finished system for further details.

The air tank seen in the picture, lying within the sub, is the first (too small) tank. It has now been scrapped.

Click to enlarge..

Please observe: I was a bit worried, that the tank might not be able to handle the pressure, so I filled it almost completely up with water, leaving only a little bit of air in there. I then pressurized the tank to app. 7 bar (100 psi).
This approach is VERY important, because IF the tank ruptures, then it'll only leak and quickly be at normal pressure. If the tank had been filled with air only, and then ruptured, then the forces released would have been far greater, and potentially dangerous! A tank holding only air, almost explodes very violently, if it breaks. The reason for this, is that water can not be compressed, and because of this we only have a small media that can expand, if we follow the first procedure.

System schematics:


The making:

This is my home made pressurized air system. The sub's main dive system is static (dynamic also possible), and it has one Main Ballast Tank. The propellant needed for such a system can be either atmospheric air, or CO2. I choose to go with the air, pressurized to about 8 bar (14 bar possible) in the supply tank, and regulated down to 1 -> 3 bar for the diving system, using a pressure regulator. The tank pressure is monitored using a pressure switch.

The add air valve is a valve from a car tire, with a secondary manual valve in series for safety. The manual valve fitted where all of the gadgets go, turns on and off the air supply for the entire secondary system. (Regulator, pressure switch) 


The old and new tank.

Learning to solder copper pipe.

Well.. I'm happy..

Quick-connect fitted.

Crowded shipyard.

The mounting bracket.

Tubing comming under way.

Testing first time.

Top view of the completed sys.

"Large Reward!" JUUUST in case..

Clear view of press. switch.

What does what, and where..

Closing in the wireing.

Twist-on cap works fine!!

Air tank fitted.
The hoses in the picture to the left is
from the drain ports right behind the
air tank. (Center of gravity)

Click images to enlarge.

Mechanical Data:
Propellant: Max. tank pressure: Dive system pressure:
Atmospheric air 10 bar (145 psi) 1 -> 3 bar (14 -> 45 PSI)

Air system connections:

The first tank proved to hold only enough air for four times to the surface, not quite enough, I thought. Therefore, I got a bigger one, got it from the recycle station. After having removed all of the (MESSY) powder, I poured sand in it. After shaking the thing quite a while, the sand had cleaned the last powder out, and I could prime it inside with an anti-rust agent.

I then made the mounting bracket, and fitted it on to the tank using thickened epoxy. The white writing on the tank came off real easy using acetone. The rest was pretty straight forward. Bending pipe, soldering it, and fitting it. The front support bracket for the tank has an outer diameter equal to the inner diameter of the sub, thus ensuring a safe fix. The gray paint on the ends are the "stand alone" anti-rust agent. After building this system, I submerged it in water while pressurized. It had only a tiny leak, which is now fixed.

The buoyancy of the entire system is positive (It floats), so the hull will "hang" in it, while submerged. The mass of the system is
2000 grams (4,4 lb), and displaces a little more than 2 liters of water. In round numbers, that's about 500 grams (1.2 lb) of positive buoyancy.

The mounting bracket with all of the valves and regulator etc. will fit inside the missile deck, when it's all in the sub. This will put the center of gravity above the center of buoyancy when looking isolated at the air system. Therefore, I will have to compensate for that, so that the stability of the sub will not be compromised by this.

The air system is quite simple, and pretty safe as well. The manual valve in the add-air-side should be closed when ever possible, just to make absolutely sure that the air can not escape the way it came in.
The pressure switch in the secondary side, has been set to switch when there's just enough pressure left for one complete surfacing blow of the MBT. This ensures that the sub will end up at the surface, when air runs out.


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