A relief valve must be installed on the _________ of fuel-oil-heating appliances?

A relief valve must be installed on the discharge line of fuel-oil heating appliances to ensure the safe and effective operation of the system. This type of valve is designed to release excess pressure from the system to prevent overpressure conditions, which can lead to potential hazards such as equipment damage or catastrophic failures.

Positioning the relief valve on the discharge line allows it to monitor the pressure of the media (in this case, fuel oil) effectively. When the pressure exceeds the predetermined safe limit, the relief valve opens, allowing excess fuel to escape safely back to the storage tank or to a designated safe area, thereby protecting the entire heating system.

In contrast, installing the relief valve in the inlet line, return line, or vent line would not provide the same safety measures. The inlet line carries fuel oil to the appliance, and placing a relief valve there could interfere with the flow necessary for proper operation. Similarly, the return line is responsible for recycling heated fuel back to the tank, and a relief valve in this line might not effectively alleviate pressure buildup in the system. The vent line is designed to release gases and should not be used for liquid fuel such as oil; thus, using a relief valve there wouldn't address pressures within the fuel system itself.

Therefore