Aimed at the problem that the existing models of hydraulic damper with pressure relief valve consider different factors and have different forms,a unified dynamic model was presented for hydraulic damper with pressure relief valve internal and external by analyzing the effects of oil mixed with gas and oil compressibility,valve port dynamic flow force,valve port discharge coefficient and equivalent area,and string pipeline resistance on equivalent damping and damping force peak.The theoretical results of equivalent damping and damping force peak were compared with the test data while some hydraulic damper with 1, 9 and 26 mm excitation amplitude.The results showed that the errors of equivalent damping are -9.994 5 %,0.672 4 % and -2.757 2 %, respectively. and the errors of damping force peak respectively are -0.457 4 %,1.973 3 % and -4.074 9 %.The model accuracy has been validated by the results of errors.Furthermore,the analysis results of influence factors showed that oil elastic modulus is sensitive to air percentage in low pressure,it descends rapidly with air percentage increasing,and oil elastic modulus has great influence on equivalent damping and damping force peak,especially with small excitation amplitude. Valve port dynamic flow force has large effect on damping force peak while pressure relief valve opening,but has little effect on equivalent damping. The simplification of valve port discharge coefficient and equivalent area almost have no influence on equivalent damping and damping force peak and the pipeline resistance and oil compressibility of pipeline have slight influence on equivalent damping and damping force peak.
