Various types of valves are installed in gaseous oxygen systems. Among the most commonly used are check valves, pressure-reducing valves, and filler valves.

CHECK VALVES.- Check valves are in-stalled at various points in the oxygen system. Their purpose is to permit the flow of oxygen in one direction only. Check valves are located in the system to prevent the loss of the entire oxygen supply in the event a cylinder or line is ruptured.

Various styles of single, dual, and triple check valves are available, as shown in figure 4-3. The arrow (or arrows) embossed on the valve casting indicates the direction of flow through the valve.

PRESSURE-REDUCING VALVES.- Pres-sure-reducing valves (or pressure reducers) are used in certain oxygen systems for the purpose of reducing high cylinder pressure to a working low pressure. In most installations the pressure reducers are designed to reduce the pressure from 1,800 psi to a working pressure of 60 to 70 psi. They are always located in the oxygen distribution lines between the cylinders and the flight station outlets. Figure 4- 4 illustrates a typical pressure-reducing valve.

FILLER VALVES.- A11 oxygen systems are designed so the entire system can be serviced (refilled) through a common filler valve. The filler valve is generally located so it may be reached by a man standing on the ground or wing. The filler valve contains a check valve, which opens during the filling operation and closes when filling is completed. A dust cap keeps out dust, dirt, grease, and moisture.

Gauges

Gauges are used in gaseous oxygen systems to indicate the oxygen pressure in pounds per square inch (psi). All systems are equipped with at least one gauge that indicates the amount of oxygen in the cylinder( s). The gauge also indicates indirectly how much longer the oxygen will last.

Figure 4-3.- Oxygen system check valves.

Figure 4-4.- Pressure-reducing valve.

The volume of any gas compressed in a cylinder is directly proportional to the pressure. If the pressure is half, the volume is half, etc. Therefore, if 900 psi of oxygen remains in an 1,800 psi system, half the oxygen is left. A pressure gauge is always mounted at each flight station, usually on the regulator. These gauges are calibrated to indicate from 0 to 2,000 psi on high-pressure systems and 0 to 500 psi on reduced high-pressure systems.