What does a rapid pressure decay in a cylinder leakage test indicate?

• A. Pressurize the cylinder and measure pressure decay over time
• B. Slow pressure decay indicates valve leakage, ring wear, or head gasket faults
• C. Rapid loss indicates valve leakage, ring wear, or head gasket faults
• D. No decay indicates cylinder is sealing perfectly

Answer: (C)

In a cylinder leakage test, you pressurize the cylinder with air and watch how quickly the pressure falls. The speed of that pressure drop shows how well the cylinder is sealing. A rapid loss means air is escaping through a leakage path, most commonly through worn piston rings, leaking or imperfectly sealing valves, or a faulty head gasket. Those paths allow air to escape quickly, so the pressure decays fast.

If the pressure decays slowly or stays fairly steady, the seal is effectively intact, which is the opposite of what rapid decay indicates. No decay at all would mean the cylinder is sealing perfectly, with no detectable leakage.

So, rapid pressure decay points to substantial leakage through valve seats, piston rings, or the head gasket.