As a gas separation equipment in the air separation system, valves are the most frequently switched components. Good quality valves can ensure high switching speed and tightness, which have a positive effect on the performance of the device, allowing the equipment to operate efficiently and long-term. However, if the valve is of poor quality, it will cause medium and low pressure air blow-by, increase in air flow or decrease in air pressure, etc.

The location of the valve is generally where the air flow disturbance and impact are the most severe in the system. In long-term production practice, people have found that as long as the valve material is selected correctly, it can safely and stably cope with different working pressures and achieve long-term and efficient production purposes. Specifically:

1. When the working pressure of the oxygen production system is <0.6p/MPa, the valve body and valve cover should be made of malleable cast iron, ductile iron or cast steel, the valve stem should be made of carbon steel or stainless steel, and the valve disc should be made of stainless steel.

2. When the working pressure of the oxygen generation system is ≥0.6 p/MPa, but not more than 10 p/MPa, all stainless steel, copper-based alloy or a combination of the above two materials can be used

3. When the working pressure of the oxygen production system is ≥10 p/MPa, copper-based alloy, nickel and nickel-based alloy are used.

In addition, it is recommended to use graphite-treated asbestos or polytetrafluoroethylene materials, or expanded graphite for the sealing packing of the valve. These can well ensure the sealing of the valve.

Table 1  Selection requirements for oxygen valve materials