In a water-cooled ship's stores refrigeration plant using a high pressure refigerant as defined under the EPA Clean Air Act rules, which of the following applications would be appropriate for a permanently intalled compound pressure gauge?
• Compound pressure gauge meaning (ability to read both vacuum and positive pressure) • Typical pressure conditions at compressor suction vs. discharge in a high‑pressure refrigerant system • Which parts of the system can ever experience sub‑atmospheric (vacuum) conditions in normal operation
• Think about which side of the refrigeration compressor can sometimes fall below atmospheric pressure during operation or when the plant is secured • Ask yourself: where in the system would it be useful to see both vacuum and positive pressure on the same dial? • Consider whether lube oil and cooling water systems in this plant ever legitimately operate under vacuum or only above atmospheric pressure
• Verify the function of a compound gauge: does it read vacuum plus pressure, or only pressure? • Identify which line(s) in a high‑pressure refrigeration system can be below atmospheric pressure during running or shutdown • Confirm whether water and lube oil systems in a ship’s plant normally need vacuum indication on their pressure gauges
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