Suppose the pilot controller for the...

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Question 1 of 2066636eee28f7522a1c51f43f

Suppose the pilot controller for the illustrated pneumatically operated diaphragm actuated control valve is supplied with 20 psig control air and is designed to operate the valve with a pilot pressure ranging from 3 to 15 psig. What would be the indication of a properly adjusted spring (6) by means of the adjusting nut (12)? Illustration GS-0051

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Question 1 of 20

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🔍 Key Concepts

• Study the illustration to see whether increasing air pressure on the diaphragm moves the valve plug toward opening or toward closing. • Remember that the pilot output range is 3–15 psig, not the 0–20 psig supply range; the spring adjustment sets the valve travel over that 3–15 psig band. • Think about the valve’s fail position (what position it goes to at 0 psig) based on the direction the spring (6) is pushing the stem and plug.

💭 Think About

• From the drawing, when the diaphragm chamber is pressurized, does the stem move with or against the spring force, and does that motion uncover or cover the port between inlet and outlet? • If at 0 psig the spring alone determines position, is the port between inlet and outlet mostly open or tightly seated, and how does that relate to the choices that mention 0 psig? • Given that 3 psig is the low end and 15 psig is the high end of the control range, which end of that range should correspond to the same position as the 0-psig fail position you identified?

✅ Before You Answer

• Confirm from the figure which way the spring (6) is trying to push the valve plug (toward open or toward closed). • Verify whether the increasing diaphragm pressure will compress the spring and move the plug off the seat or onto the seat. • Make sure the choice you pick uses the 3–15 psig pilot range (not the 0–20 psig supply) and matches the valve’s fail-closed or fail-open behavior you deduced.

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