During operating periods of a multi-box...

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Question 1 of 205eccef9dbacbc34ba4d4604a

During operating periods of a multi-box refrigeration system using a capacity controlled compressor, when only one of the evporators of a four box plant are actively being fed with liquid refrigerant, the control oil pressure acting on the hydraulic relay piston will be at what value? See illustration GS-RA-13.

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🔍 Key Concepts

• Capacity control on reciprocating refrigeration compressors and how cylinder unloading is achieved using oil pressure. • Relationship between suction (crankcase) pressure, the capacity control valve, and the control oil pressure acting on the hydraulic relay piston. • What happens to the number of loaded cylinders when the plant is at minimum refrigeration load (only one evaporator calling).

💭 Think About

• When only one out of four boxes is calling for cooling, is the compressor operating at maximum or minimum capacity? How many cylinders should be loaded in that condition? • Look at the illustration: as the system unloads more cylinders, does the control oil pressure going to the hydraulic relay piston increase or decrease? • How does the capacity control valve respond when suction (crankcase) pressure drops below the setpoint—does it send more, less, or no control oil pressure to the hydraulic relay?

✅ Before You Answer

• Trace the dark control-oil line from the capacity control valve to the hydraulic relay piston and note under what load condition that line is at its maximum or minimum pressure. • Confirm whether low box demand (only one evaporator fed) corresponds to unloaded or fully loaded compressor operation. • Make sure you distinguish between oil pump pressure (to all bearings) and control oil pressure (used only for the unloader mechanism); the question is asking specifically about the control oil pressure acting on the hydraulic relay piston.

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