What type of valve must be installed on fuel-oil piping at each appliance connection if multiple appliances are present?

A shutoff valve is essential for fuel-oil piping at each appliance connection when multiple appliances are present. This valve allows for the quick isolation of any individual appliance from the fuel supply. In case of maintenance, emergencies, or appliance malfunction, the shutoff valve can be turned off to stop the flow of fuel, ensuring safety and preventing potential hazards such as leaks or fire.

The use of shutoff valves is a standard safety practice in fuel systems. It allows operators to carry out repairs or inspections without having to shut down the entire system, maintaining the operation of other appliances connected to the same fuel supply.

In contrast, other types of valves serve different functions. A pressure relief valve is designed to relieve excess pressure in a system, while a flow control valve regulates the flow rate of the fluid. A check valve prevents backflow, ensuring that the fluid flows in only one direction. None of these functions directly relate to isolating appliances for maintenance or safety in the way that a shutoff valve does, highlighting why the shutoff valve is the correct choice for this application.