The O-ring K 43596 is an essential elastomeric sealing component designed for the connecting plug K 43557 within the automatic starting-air stop valve assembly of the Adriadiesel/Jugoturbina/Zgoda/Sulzer ZV40/48 engine. Its primary function is to provide a reliable pressure-tight seal between the connecting plug and its corresponding mating surface, preventing unwanted compressed-air leakage and helping maintain the pressure integrity required for accurate operation of the starting-air control system. Working together with the K 43557 connecting plug, the O-ring supports effective sealing of the associated connection and contributes to stable pneumatic pressure conditions within the automatic starting-air stop valve. The sealing performance of the K 43596 O-ring depends on correct cross-sectional dimensions, suitable elastomer hardness, elasticity, chemical compatibility, surface condition, and proper compression within the designated sealing groove. During operation, the O-ring may be subjected to repeated pressure fluctuations, vibration, temperature changes, and prolonged periods of standby readiness, which can gradually cause hardening, compression set, cracking, swelling, or loss of sealing capability. During maintenance or overhaul, the K 43596 O-ring should be inspected for cuts, deformation, flattening, surface deterioration, and loss of elasticity, while the sealing groove, connecting plug K 43557, and corresponding contact surfaces should also be examined for scratches, contamination, or damage. Replacement and installation should follow the manufacturer's specifications, with particular attention to correct positioning, cleanliness, and avoiding damage during assembly. By providing dependable sealing around the connecting plug K 43557, the K 43596 O-ring contributes to reduced compressed-air leakage, consistent valve response, reliable starting-air control, and long-term operational readiness of the ZV40/48 engine.