Distinguish between a check valve and a relief valve; what does each protect against?

• A. Check valve prevents backflow; Relief valve protects against overpressure by venting fluid to atmosphere.
• B. Check valve lubricates moving parts; Relief valve filters impurities.
• C. Check valve measures temperature; Relief valve regulates speed.
• D. Check valve prevents backflow; Relief valve protects against overpressure by venting fluid to prevent damage.

Answer: (D)