The pressure at which a relief valve actually begins to open is called what?

The pressure at which a relief valve actually begins to open is called what?

• A. Full flow pressure
• B. Cracking pressure
• C. Operating pressure
• D. Downstream pressure

Answer: (B)

The main idea is the cracking pressure—the pressure at which a relief valve starts to crack open and begin to relieve flow. Below this pressure, the spring and mechanism hold the valve shut with little or no flow. When system pressure reaches the cracking pressure, that force overcomes the spring, a small opening forms, and leakage or relief begins. As pressure climbs further, the valve opens more to pass the relieving flow, until it reaches its full opening and carries the expected flow rate. Downstream pressure is the pressure on the outlet side after the valve, and is influenced by how much the valve is opening, not the threshold at which it first starts to open. Operating pressure is the normal system pressure the system aims to maintain, not the point where the valve begins to open.

The main idea is the cracking pressure—the pressure at which a relief valve starts to crack open and begin to relieve flow. Below this pressure, the spring and mechanism hold the valve shut with little or no flow. When system pressure reaches the cracking pressure, that force overcomes the spring, a small opening forms, and leakage or relief begins. As pressure climbs further, the valve opens more to pass the relieving flow, until it reaches its full opening and carries the expected flow rate. Downstream pressure is the pressure on the outlet side after the valve, and is influenced by how much the valve is opening, not the threshold at which it first starts to open. Operating pressure is the normal system pressure the system aims to maintain, not the point where the valve begins to open.