What does a check valve do?

A check valve is designed specifically to permit fluid flow in only one direction. This function is crucial in various applications, as it prevents backflow, which can lead to system inefficiencies, damage, or contamination. By allowing flow in one direction only, check valves help maintain proper pressure and protect equipment from reverse flow conditions.

While some of the other choices refer to features or requirements associated with valves, they do not accurately describe the primary function of a check valve. For instance, the use of a heavy spring to set a valve typically refers to pressure regulating valves rather than check valves. Additionally, a check valve does not inherently require an inspector's seal for installation, as this is a regulatory aspect that varies depending on the installation context, rather than a defining characteristic of the valve itself. Finally, the reference to a locking spindle pertains to valves designed specifically for safety applications and flow control, rather than the straightforward operation of a check valve. Thus, the primary feature of a check valve is its ability to permit flow in one direction only.