What will result if the vapor return line on a metering station is not open?

What will result if the vapor return line on a metering station is not open?

• A. The system will operate at higher pressure
• B. Meter will read inaccurately
• C. There will be no effect
• D. Propane will not flow through the meter

Answer: (D)

The key idea is that the vapor return line provides a path for the gas to vent and complete the flow loop through the metering station. If that line isn’t open, the flow loop is blocked and propane can’t move through the meter. Without a vent path, the pressure can’t be relieved and the meter cannot pass gas, so propane will not flow through the meter. The other possibilities don’t fit the situation because they don’t describe the immediate effect of an blocked return path—the meter simply won’t see flow when the return line is closed.

The key idea is that the vapor return line provides a path for the gas to vent and complete the flow loop through the metering station. If that line isn’t open, the flow loop is blocked and propane can’t move through the meter. Without a vent path, the pressure can’t be relieved and the meter cannot pass gas, so propane will not flow through the meter. The other possibilities don’t fit the situation because they don’t describe the immediate effect of an blocked return path—the meter simply won’t see flow when the return line is closed.