The pressure spring K 43571 is an important mechanical component of the automatic starting-air stop valve used in the starting-air system of the Adriadiesel/Jugoturbina/Zgoda/Sulzer ZV40/48 engine. Its primary function is to provide a controlled spring force within the valve assembly, supporting the correct positioning, movement, and return of the associated operating components during the automatic opening and closing sequence. Working in coordination with the valve piston, sealing elements, and pneumatic control system, the pressure spring helps maintain the required mechanical balance between spring force and compressed-air pressure, contributing to predictable valve response and dependable starting-air control. The spring's wire diameter, coil geometry, free length, stiffness, material properties, and resistance to fatigue are particularly important because deviations from the specified characteristics can affect valve movement, closing force, response time, and operational reliability. During engine operation, the K 43571 pressure spring may be subjected to repeated compression cycles, vibration, temperature variations, and extended periods under mechanical preload, requiring good elasticity, dimensional stability, and resistance to corrosion and fatigue. During maintenance or overhaul, the spring should be inspected for cracks, corrosion, permanent deformation, loss of free length, damaged coils, and signs of fatigue, while its dimensions and mechanical characteristics should be checked against the manufacturer's specifications. By providing consistent mechanical force and supporting reliable valve actuation, the K 43571 pressure spring contributes to accurate automatic starting-air control, dependable valve closure, reduced risk of malfunction, and long-term operational readiness of the ZV40/48 engine.