Valve assembly is the critical component of mud pump fluid end, with high operation frequency and great impact subjected. The quality of valve assembly will have a direct effect on the service life of the hydraulic cylinder. Valve assembly is the major easily damaged parts of mud pump. Valve assembly consists of valve body assembly and valve seat. According to the type of the inner hole of the valve seat, valve assembly can be classified as full open valve, three-way valve and four-way valve. Generally, valve assembly refers to full open valve.