What are the two basic types of relief valves used on refrigeration systems?

• A. An automatic relief valve and a one-time relief valve
• B. A manual relief valve and a spring-loaded relief valve
• C. A pressure relief valve and a vacuum relief valve
• D. A shutoff valve and a check valve

Answer: (A)

Relief devices in refrigeration are there to protect equipment from overpressure, and they fall into two fundamental forms: automatic relief devices that vent automatically and reseat, and one-time relief devices that vent once and then must be replaced. Automatic relief valves respond to a set pressure, opening when that limit is exceeded and closing again as pressure falls, which allows repeated protection without manual action. One-time relief devices, such as rupture discs or fusible plugs, provide a single venting event and are not resettable, so they’re used where a one-off failure mode must be prevented and then the device is replaced. This pairing covers the typical safety needs: ongoing automatic protection, plus a single-use sacrificial vent for extreme overpressure. The other options don’t fit because manual relief would require operator action and isn’t automatic protection; a spring-loaded valve is a kind of automatic relief but doesn’t represent the two-category distinction; vacuum relief deals with unintended low-pressure situations rather than overpressure protection; and shutoff or check valves are not relief devices at all.