How would the illustrated valve respond to a complete loss of charge from the remote bulb-to-control diaphragm power element if the valve is used as a temperature control valve for a steam-heated heavy fuel oil service heater? Illustration GS-0045
• Fail-safe position of control valves in steam heating service • How a temperature-sensing bulb and power element (diaphragm) move the valve stem in this design • Relationship between spring force vs. bulb pressure when the bulb charge is lost
• Trace the force path from the remote bulb, through the diaphragm/power element, to the valve plug. If bulb pressure goes to zero, which force is left to move the stem? • For a steam-heated heavy fuel oil heater, which failure position (steam on or steam off) would be chosen to best protect the fuel system and burner operation? • Look at the orientation of the plug in the body: does pushing the stem down open or close the steam port?
• Identify which component in the illustration provides force when the bulb is charged and which component provides force when the bulb loses charge (springs). • Verify whether upward or downward motion of the stem opens the steam passage from inlet to outlet. • Consider the system consequence: with steam flow stopped, what happens to fuel temperature and which alarm (high or low temperature) would occur first?
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