The remainder of the compressed air system is the piping and valves that distribute the compressed air to the points of use.

HIGH-PRESSURE AIR

Refer to figure 14-22. View A shows the first part of a high-pressure air sys-tem aboard a surface ship. The 3,000/150-psi reducing station is used for emergencies or abnormal situations to provide air to the low-pressure air system.

LOW-PRESSURE AIR

Low-pressure air (sometimes referred to as LP ships service air) is the most widely used air system aboard the ship. View B of figure 14-22 shows the first part of a low-pressure air system. Many of the low-pressure air systems are divided into subsystems, referred to as VITAL and NON-VITAL air.

Vital air is used primarily for engineering purposes, such as automatic boiler controls, water level controls, and air pilot-operated control valves. Vital air is also supplied to electronics systems. Vital air systems are split between all main machinery groups with cross-connect capability.

Nonvital air has many different purposes, such as laundry equipment, tank-level indicating systems, and air hose connections. Air for a nonvital air system is supplied through a PRIORITY VALVE. This valve will shut automatically to secure air to nonvital components when the pressure in the air system drops to a specified set point. It will reopen to restore non-vital air when pressure in the system returns to normal This system gives the vital air first priority on all the air in the low-pressure system.