Suppose the illustrated pneumatically...

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Question 1 of 2066636eee28f7522a1c51f42f

Suppose the illustrated pneumatically operated diaphragm actuated control valve is used to control the fuel oil outlet temperature of a steam-heated heavy fuel oil heater by controlling the steam flow. What would be the result if there was a complete loss of pilot air being delivered to the valve actuator? Illustration GS-0051

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Question 1 of 20

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🔍 Key Concepts

• Look at the spring and diaphragm arrangement in the actuator to decide whether this is an air-to-open or air-to-close valve. • Think about what happens to the stem position when pilot air pressure is removed and only the spring force and process forces remain. • Relate the valve fail position (open or closed to steam flow) to the expected change in fuel oil outlet temperature and which alarm (high or low) that would trigger.

💭 Think About

• In the illustration, does air pressure on the diaphragm tend to compress the spring and push the stem down, or does it tend to lift against the spring and pull the stem up? What stem direction corresponds to the valve plug moving toward the seat? • If the valve fails to the position given by the spring alone, will steam flow to the heater increase, decrease, or stop? How would that affect the fuel oil temperature over a few minutes? • Which option best matches a predictable fail-safe design normally chosen for a fuel oil heater steam control valve on a ship?

✅ Before You Answer

• Identify clearly which way the spring force drives the plug relative to the seat (toward closed or toward open). • Confirm which direction of stem travel (up or down) equals increasing steam flow in this specific valve construction. • Match that fail position to the corresponding alarm condition: more steam → higher fuel temperature; less/no steam → lower fuel temperature.

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