Why reduce pressure in the fuel line keep the engine running while the propane cylinder valve is turned off?

Reducing pressure in the fuel line allows for a controlled flow of propane, ensuring that the engine can continue to run even when the cylinder valve is turned off. This is because the residual pressure in the fuel line can still supply enough propane to maintain combustion for a short period. By managing the pressure, the engine can operate smoothly without sudden interruptions, providing a buffer until the propane is fully depleted. However, this is typically a temporary solution, and the engine will eventually stop once the fuel in the line is consumed.