When does a crankcase psi regulator open?

• A. As the outlet pressure decreases
• B. As the inlet pressure increases
• C. When the crankcase temperature rises
• D. When the platform load changes

Answer: (A)

The regulator’s job is to keep the crankcase pressure at a set level by sensing the pressure on the outlet side and adjusting flow accordingly. It uses a diaphragm and spring to balance forces. When the outlet pressure falls below the setpoint, the diaphragm allows the valve to open, letting more gas flow in and raise the outlet pressure back toward the desired value. If the outlet pressure rises above the setpoint, the spring pushes the valve closed and flow decreases.

So, it opens as the outlet (downstream) pressure decreases. Inlet pressure increasing, crankcase temperature changes, or platform load changes don’t directly trigger the opening in the same feedback-controlled way.