Suppose the illustrated pneumatically...

Question 1 / 2066636eee28f7522a1c51f436

Question 1 of 2066636eee28f7522a1c51f436

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 the stem packing was over-tightened and the stem was unable to vertically move in either direction? Illustration GS-0051

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🔍 Key Concepts

• Operation of a pneumatically operated diaphragm actuator and how air pressure and spring force move the stem • Difference between an air failure (fail-safe position) and a mechanical jammed stem • How a fixed steam valve opening affects fuel oil outlet temperature as fuel demand changes

💭 Think About

• If the stem packing is so tight that the stem cannot move up or down, what happens when the temperature controller tries to increase or decrease the air signal to the actuator? • With the steam valve stuck at one fixed opening, what will fuel oil outlet temperature do when fuel flow to the heater increases or decreases? • Does a mechanically stuck stem automatically drive the valve to fully open or fully closed, or does it simply prevent it from changing position?

✅ Before You Answer

• Be clear on the valve fail-safe action with air loss versus what happens when the stem is physically locked • Decide whether a stuck stem means the valve will be forced to an end position or held at whatever position it was in when it jammed • Relate a fixed steam flow through the heater to the likelihood of high temp alarm, low temp alarm, or fluctuating temperature with load changes

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Question 1 of 20

The valve would fail in the fully closed position, most likely resulting in a low fuel oil temperature alarm condition.

The valve will lose control of the fuel oil temperature with the result that the fuel temperature will fluctuate with changes in fuel demand.

The valve would fail in the fully open position, most likely resulting in a high fuel oil temperature alarm condition.

Question 1 / 2066636eee28f7522a1c51f436

Question 1 of 2066636eee28f7522a1c51f436

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Question 1 of 20

66636eee28f7522a1c51f436

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🔍 Key Concepts

💭 Think About

✅ Before You Answer

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