A Study on Reliability Assessment Criteria of Diaphragm-type Accumulator for Intake and Exhaust Valve of Large Ship

Abstract

A diaphragm type accumulator ("accumulator") is used in a wide range of hydraulic systems, especially the intake valve for fuel injection and the exhaust valve activated after a stroke in the electronic control unit of a ship to reduce shock waves and pulsation pressure and compensate for pressure. In this application, the diaphragm operates in the same manner as in the engine operation mode (240 rev/min : 4 Hz) and is exposed to harsh conditions including abrupt surge pressure (ΔP). Given these such conditions, the diaphragm is physically and structurally vulnerable to recurring faults. While existing local and international assessment standards largely attribute faults in accumulators to damaged diaphragms, screws in the caps and body assemblies break due to structural problems. This leads to loss of functionality and safety issues instead of decreasing performance. This study assumes that the main cause of faults in diaphragm type accumulators are damaged screws and explores the method of assessing reliability using pressure rating testing on a pressurized vessel of NFPA T/2.6.1 dimension. It also looks into a monitoring system to identify any N2 gas leakage during testing.