🔍 Key Concepts
• This is a pneumatic force-balance system: all diaphragms have 1 in² area, so pressure = force directly (in pounds).
• The lever with arms L1 = 3.1 in and L2 = 2.9 in must be in moment balance: (force × distance) must be equal on both sides of the pivot.
• The spring on diaphragm 4 has a rating of 50 lb/in², and the supply pressure to diaphragm 1 is 50 psi, so think about what happens to valve 1 (wide open, throttling, or closed) when P4 = 48 psi.
💭 Think About
• Write the forces from each diaphragm acting on the lever. Since area is 1 in², replace each pressure with an equal force in pounds and set up a moment balance about the pivot.
• Compare the force from the spring and P4 at diaphragm 4 to the force coming from the side connected to diaphragms 2 and 3. In which direction will the lever move as P4 approaches 50 psi?
• Once you know the lever position, decide whether valve 1 is passing full 50 psi, some reduced pressure, or essentially no pressure to P1, and then match that condition to the closest answer choice.
✅ Before You Answer
• Confirm that you are using pressure × 1 in² = force (so 48 psi = 48 lb, 50 psi = 50 lb).
• Be sure your moment balance uses the correct lever arms: 3.1 in on one side and 2.9 in on the other.
• Before choosing an answer, ask: is P1 likely to be equal to supply, equal to P4, some fixed fraction of supply, or near zero based on the lever and spring balance?