Since both devices allow fluid flow in one direction only, I see no functional difference. Different applications may have labeled them as you stated, but that doesn’t affect their basic purpose or operation.
Check valves are used in a wide variety of equipment, cars, planes, pneumatic and fluid systems, while backflow preventers are typically used in plumbing systems for structures.
A check valve has a variety of roles but is mostly used to regulate and control the flow of fluids, especially into pumps. A check valve is a single way valve which only allows water to flow in a certain direction. Once the water has gone through the valve, it cannot go back the way it came. During installation, you are required to check the valve arrow and confirm the expected direction of the flow.
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