If 40 psi of pressure is applied to a brake chamber diaphragm of 30 square inches, the maximum force exerted would be
- 7,200 pounds.
- 70 pounds.
- 3,500 pounds.
- 1,200 pounds. ✓
Answer: D. 1,200 pounds.
The maximum force exerted would be 1,200 pounds.
Why this is the answer
The handbook says pushrod force depends on air pressure and the diaphragm's effective surface area. A Type 30 chamber has 30 square inches of diaphragm area. Applying 40 psi to that area gives 40 times 30, which equals 1,200 pounds of force. The handbook's example points the same way: 100 psi on a Type 30 chamber produces 3,000 pounds, so a lower application pressure produces proportionally less force.
Why the other answers are wrong
- A. 7,200 pounds. — This does not match pressure times the 30-square-inch diaphragm area; it would require a much larger effective area than the Type 30 chamber described.
- B. 70 pounds. — This looks like adding or loosely combining the pressure and area values rather than multiplying pressure by the diaphragm area.
- C. 3,500 pounds. — This is near the handbook's 3,000-pound example for 100 psi on a Type 30 chamber, not the result for 40 psi.
Remember it
Picture the air pushing on every square inch of the diaphragm; the total push is pressure times that area.