What position must the valve on oxygen cylinders be in when in use?

The valve on oxygen cylinders must be fully open for proper use. This is because a fully open valve ensures that there is an unobstructed flow of oxygen, which is essential for a safe and effective operation, especially in applications such as welding or medical use where a constant supply of oxygen is required.

A back seated valve design allows the valve stem to be securely seated against the back of the valve, preventing any leakage while still allowing full flow when needed. This means that once the valve is fully opened, it can provide high flow rates necessary for efficient operation.

Partially open or quarter open positions may create an inconsistent flow of oxygen, which can lead to inadequate performance or increased risk of complications, such as back pressure or possible flashback in welding scenarios. Similarly, a fully closed valve does not allow any oxygen flow at all, which would be inappropriate during use.

Therefore, the safest and most effective practice for oxygen cylinder operation is to keep the valve in the fully open position.