Development of a Hydraulic Filter for Nozzle Actuation System of a Gas Turbine Engine

The Integrated Nozzle Actuating System (INAS) of a gas turbine engine is used to vary the exhaust nozzle area to achieve an optimum performance. The nozzle actuating system is operated by four actuators driven by an Integrated Hydraulic Power Pack (IHPP) connected to the Engine Gear Box (EGB). The quality of the oil operating the precision hydraulic actuators of the INAS should be maintained contamination free to achieve an optimum efficiency of the actuators. Hence a fine hydraulic filter is used in the IHPP circuit to maintain the cleanliness level of the hydraulic oil operating the actuators. The design and development of a hydraulic filter for an aircraft engine is a challenging task involving material selection, manufacturing process quality control and stringent performance qualification test schedule to follow the International standards. The present work describes the development of a 10 micron hydraulic filter operating at 30 bar pressure with a flow of 20 lpm designed according to the specifications of a typical aircraft gas turbine engine IHPP system. The filter has been qualified through all the tests prescribed by the International MIL-F-8815E standards. The tests like Multi-pass test, cold start test, Flow fatigue test, extreme temperature test, vibration test and bubble point test are described and the results are discussed.