OK, I’m not sure what Darrin is still after, so here goes nothing as they say…
First there are 5 main air systems on the Balao-class submarine
1. 3000# High Pressure and Torpedo Impulse air
2. 600# MBT blow system
3. 225# service air system
4. 10# MBT blow system
5. Salvage Air system
So if Darrin is talking about low air pressure system, he may just be referencing the 10# MBT blow system because the 225# air maybe low but it is dangerous. Also. because is has so many reductions to other pressures, it is widely used for justd about anything. Common reductions include 100#, 13#, 12#, 10# and 8#.
The 10# MBT blow system has a LP blower, driven by a 90 HP motor, located in the pump room, a manifold located in the control room, and 9 blow lines extending out of the manifold through the pressure hull that run outside in the superstructure to all ballast tanks. (1 – 7). Each tank is control by a flapper valve and swing-check valves. There is also a gate check valves that are operated from the deck.
The 10# MBT blow system is used on the surface to complete the job of blowing the MBT’s that is done by the 600# MBT blow system.
In addition, the 10# MBT blow system is used for list control during and after blowing the main ballast tanks. This is done using the list control dampers to adjust the amount of air admitted into the port and starboard MBT (#2 and #6 groups – remember each group has four main ballast tanks - A, B, C, D). The dampers are located at the Y connections of the 10# Blow Manifold, and are hand operated at the aft end of the manifold.
Important – the 10# manifold and its valves are designed to withstand sea pressure if any blow line fails.
So the 10# MBT has two main functions – 1) complete the blowing of the main ballast tanks (and fuel ballast tanks if needed), and 2) list control using the #2 and #6 MBT groups.