Abstract: The EH oil pressure of a new domestic 330MW unit became lower. Some possible reasons, such as the insufficient output of the oil feed pump, the leakage of the energy accumulator, the leakage of the overflow valve in outlet of the oil pump, the internal leakage of the regeneration device, the internal leakage of the main stop valve and the regulating valve and the incomplete close of the AST electromagnetic valve, were excluded one by one. At last, it was found that in the inlet thin tube of the OPC electromagnetic valve, one designed orifice was not installed, and this is the real reason of the lower oil pressure.

Key words: thermal power unit, subcritical, high pressure fire-resistant oil, electro-hydraulic control system, overspeed protection control (OPC), electromagnetic valve