🔍 Key Concepts

• Function and purpose of starting air check valves in diesel engines • How spring force and air pressure are commonly used to keep valves seated • The role of a differential piston in controlling valve opening and closing

💭 Think About

• Think about what must happen to the valve when starting air is NOT being used – what force or pressure should naturally keep it closed? • Which of these forces (mechanical spring vs. air pressure on top or bottom of a piston) would safely prevent backflow of cylinder pressure into the starting air system? • How does the direction of pressure acting on a differential piston affect whether it helps close or open the valve?

✅ Before You Answer

• Identify which method gives a fail-safe closed position if air supply is lost • Consider how back pressure from the cylinder would act on the valve and piston surfaces • Decide which side of a differential piston (top or bottom) would logically be pressurized to keep the valve seated under normal, non-starting conditions