Abstract : The adoption of an automatic hydraulic leveling system is an important measure to improve the mobility of a large radar. Oil leakage from the pressure relay affects the reliability of the leveling system and the overall safety of the radar. This paper starts with the mechanical structure of the pressure relay, the characteristics of the nitrile rubber seals and No. 10 aviation hydraulic oil, and conducts quality analysis and demonstration. It shows that the direct cause of the oil leakage is not severe corrosion of the nitrile rubber seals, but rather improper installation of the seals. It points out that the lack of a limit mechanism in the seals of a certain type of pressure relay is a fatal flaw in this structure. Keywords : Pressure relay; Nitrile rubber seals; No. 10 aviation hydraulic oil; Limit mechanism 1 Introduction To adapt to the needs of modern warfare and improve the mobility of radar, most modern radars have automatic leveling, automatic north-finding, and automatic positioning technologies. A certain large radar adopts automatic hydraulic leveling technology. During routine testing of a complete unit, continuous oil leakage from the pressure relays was found. Investigation revealed that seven or eight of these pressure relays had already been replaced during production, some of which leaked immediately after replacement and could not function properly. Upon consulting the supplier and requesting a re-inspection of the pressure relay, the response was that the seals (made of nitrile rubber) of this type of pressure relay cannot be used with No. 10 aviation hydraulic oil, and the failure was caused by the improper selection of the pressure relay seals; nitrile rubber seals would be severely corroded in No. 10 aviation hydraulic oil, and the quality of the components could not be guaranteed. Since this failure involves the reliability of the leveling system and the safety of the entire machine, quality analysis and verification work was carried out from the following aspects. [b]2. Inspect the direct cause of pressure relay oil leakage 2.1 Test the usage of pressure relays[/b] (1) Disassemble two leaking pressure relays and reassemble them to confirm that the assembly is correct and find the cause of the oil leakage; (2) Connect them to a test bench using standard No. 46 hydraulic oil for testing. Input oil pressure of 18MP, pressurize and release, and the guide column reciprocates twenty times. No oil leakage was found; (3) Connect these two pressure relays to a test bench using No. 10 aviation hydraulic oil. Input oil pressure of 18MP, pressurize and release repeatedly forty times. Then directly install these two pressure relays into the machine system and run them twenty times. No oil leakage was found. [b][align=center]For details, please click: Analysis of the causes of oil leakage faults in pressure relays of automatic hydraulic leveling systems[/align][/b]