Cracking pressure is defined as the pressure at which a pressure-operated valve begins to pass fluid.

• A. The pressure at which a pressure-operated valve begins to pass fluid.
• B. The pressure at which a relief valve vents to atmosphere.
• C. The pressure at which a pump starts.
• D. The pressure at which a gauge stops registering.

Answer: (A)

Cracking pressure is the threshold that starts the flow through a pressure-operated valve. It’s the pressure needed to overcome the spring (and any other sealing forces) so the valve first cracks open and fluid begins to pass. Once you exceed this pressure, the valve moves toward full opening and more flow as the pressure rises.

That makes the statement describing cracking pressure as the pressure at which a pressure-operated valve begins to pass fluid the best fit. The other ideas aren’t what cracking pressure is about: venting to atmosphere relates to where the fluid goes once the valve opens, not the initial opening threshold; the pump start pressure is about starting the pump, not the valve’s opening; and a gauge stopping registering isn’t a descriptor of valve opening at all.