What device indicates an obstruction in the suction line?

The vacuum gauge is the correct device that indicates an obstruction in the suction line because it measures the pressure in the suction line of the oil burner system. When there is an obstruction, the vacuum created by the pump is disrupted, leading to a change in the pressure reading on the vacuum gauge. A decrease in vacuum pressure can indicate a blockage or restriction, allowing the operator to diagnose potential issues with fuel flow before the burner malfunctions or shuts down due to inadequate fuel supply.

In contrast, while oil pressure gauges monitor the pressure of the oil after it has been pumped, they do not specifically indicate issues in the suction line. Flow switches are designed to detect whether there is adequate flow of oil but do not provide specific information on suction line obstructions. Temperature sensors measure the temperature of the fluid and do not give insights into the flow or vacuum within the suction line. Understanding the function of each device emphasizes the vacuum gauge's role in ensuring a properly functioning oil burner system.