If a shutoff valve is installed in the line to a pressure gauge, what type of valve must it be?

The proper type of shutoff valve to use in the line to a pressure gauge is a directional valve. Directional valves are designed to control the flow of fluid in a specific direction and can also facilitate the isolation of the pressure gauge from the system. This ensures that maintenance or calibration of the gauge can be done safely without affecting the functionality of the rest of the system.

Using a directional valve allows for easy opening and closing to isolate the gauge, providing a means to safely monitor and maintain the pressure in the system. The design and function of a directional valve make it suitable for this application as it can be configured to meet the specific requirements of flow direction and control.

In contrast, a check valve is used to prevent backflow, which is not necessary for a gauge application. A butterfly valve is typically used for regulating flow and may not provide the necessary tight seal needed for gauge isolation. A ball valve, while it can be used for shutoff purposes, is particularly known for its quick operation and tight closure, making it another viable option, but it does not specialize in directing flow like a directional valve. Hence, the requirement for a directional valve is the optimal choice for ensuring proper installation and functionality in relation to a pressure gauge.