What is the primary function of control valves in a piping system?

The primary function of control valves in a piping system is indeed to provide variable resistance. Control valves adjust the flow of fluid through a piping system by changing their position in response to control signals. This capability allows them to finely regulate the flow rate, pressure, and temperature of the fluid, facilitating various operational requirements in the system.

By altering the degree to which the valve opens or closes, control valves can ensure that the desired flow rate is maintained despite fluctuations in system conditions. This modulation can help optimize efficiency and maintain safety standards within a facility.

While tight flow shut-off and the ability to modulate flow are essential characteristics of control valves, they specifically exist to vary the flow resistance in a system, making option B the most accurate choice regarding their primary function.