Question 52 3AE02 - Third Assistant Engineer (Alt)

The Correct Answer is D **Explanation for Option D (Cylinder Unloader):** A cylinder unloader (or capacity control system) is a mechanism specifically designed to reduce the compression load on a refrigeration compressor, particularly during starting or when managing capacity demands. It achieves this by physically preventing the suction valve of one or more cylinders from closing. When the suction valve is held open, the refrigerant vapor drawn into the cylinder is immediately pushed back into the suction manifold during the compression stroke instead of being pressurized and discharged. By effectively taking cylinders offline, the device significantly lowers the required starting torque and the overall load on the motor, matching the exact function described in the question. **Explanation for Incorrect Options:** * **A) Relief valve:** A relief valve is a safety device designed to open and vent high-pressure fluid (gas or liquid) if the system pressure exceeds a predetermined safety limit. It is not used to manage starting loads or hold open suction valves. * **B) Discharge line bypass:** A discharge line bypass typically routes high-pressure vapor back to the suction side (or sometimes an intermediate point) to control capacity or prevent extremely low suction pressure, but it does not directly manipulate the cylinder valves to reduce the starting compression load. * **C) Suction line bypass:** A suction line bypass (often associated with hot gas bypass systems) generally deals with capacity control by introducing discharge gas into the suction line, but it does not involve the mechanical unloading of cylinders during startup.