What is the purpose of a relief valve in the pump output circuit?

• A. To increase discharge pressure to a higher level.
• B. To vent air from the system as needed.
• C. To backflow prevent water from returning to the pump.
• D. To limit discharge pressure to a safe level and protect lines and appliances from over-pressurization.

Answer: (D)

The main idea is protecting the system from overpressure. A relief valve on the pump’s output is set to open at a safe pressure limit. If the discharge pressure tries to rise above that limit, the valve opens and allows water to bypass the tight pressure boundary (usually back toward the suction side or to a drain). This keeps downstream piping, fittings, hoses, and appliances from being stressed or damaged and helps prevent water-hammer effects when demand changes.

It isn’t meant to raise pressure higher, which is the job of controlling elements or pumps, nor to vent air (that’s an air-release function), nor to prevent backflow with a check valve. The relief valve explicitly limits pressure to a safe level to protect the system.