The piston K 43555 is an important moving and pressure-responsive 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 convert the applied pneumatic pressure into controlled mechanical movement within the valve assembly, supporting the automatic opening or closing of the starting-air passage according to the operating conditions and control sequence of the engine starting system. Working in coordination with the associated valve seat, sealing elements, and guiding surfaces, the piston helps ensure accurate valve response and reliable regulation of compressed-air flow during starting operations. Correct piston diameter, surface finish, dimensional tolerances, and compatibility with the corresponding cylinder bore and sealing elements are essential because excessive clearance, friction, contamination, or seal deterioration can cause internal leakage, sticking, delayed response, or incomplete valve movement. During operation, the K 43555 piston is subjected to repeated pressure cycles, axial movement, mechanical loading, vibration, and extended periods of standby readiness, requiring resistance to wear, corrosion, deformation, and surface damage. During maintenance or overhaul, the piston and its associated guiding and sealing surfaces should be inspected for scoring, uneven wear, corrosion, deposits, dimensional deviations, and restricted movement, with particular attention to the condition of the related seals and mating components. By ensuring accurate pressure-actuated movement and dependable operation of the automatic starting-air stop valve, the K 43555 piston contributes to reliable starting-air control, efficient compressed-air utilization, reduced mechanical wear, and long-term operational reliability of the ZV40/48 engine.