Establishing Hydraulic System Operational Contamination Limits 650333
This paper presents the method used for determining the YJ93-GE-3 turbojet (XB70 Engine) hydraulic system contamination limit. The most contaminate sensitive hydromechanical component (the control) is subjected to bench tests determining the level of system contamination which impairs proper operation of the components' servo valves. This empirical particle count data, per ARP 598, establishes the failure or improper operating level for the system from which safe operating limits are set.
Included is the following supporting information:
Diametrical clearance, hardness, flow rates and spool forces are identified for the component servo valves.
Block diagram of system showing all components including filters and their respective types and micron rating.
Curve showing the contamination generating characteristics of the system piston type pump versus operating time.
The paper concludes that this engine hydraulic system maintains an operational contamination level equivalent to or possibly one class level cleaner than aircraft hydraulic systems and that the proper contamination limit for this engine is Class 8 as defined by NAS 1638.