🔍 Key Concepts
• Study how a pneumatic control signal (0–50 psi) is used to position each actuator in the system during start‑up.
• Identify which labeled items (B, C, D, E) are valves or ports that can be either open or closed and which are merely gauges or fixed components.
• Think about the purpose of start‑up / unload mode on an air compressor: preventing full loading until system oil and air pressures stabilize.
💭 Think About
• From the illustration, decide which of B, C, D, or E is actually a control valve or port that changes position with air pressure, rather than just an indicator or connection.
• Ask yourself: during start‑up, do we want air to flow into the system freely, or do we want to bypass / unload / vent the compressor until normal operating pressure is reached? Which labeled item is arranged to do that?
• Trace the small control line coming from the control box: which labeled component does that line ultimately actuate when the signal is between 0–50 psi?
✅ Before You Answer
• Verify which of B, C, D, or E is directly connected to a pneumatic actuator or diaphragm housing—that’s the one whose position is controlled by the 0–50 psi signal.
• Confirm on the drawing which labels are simply pressure gauges; those cannot be “open” or “closed” and can therefore be ruled out.
• Check the flow path of air leaving the compressor during start‑up: does it go toward the receiver sump or to a vent / bleed location? Match that path to the correct labeled component.