In the hydraulic system of agricultural machinery, the pressure valve is a kind of component used more, the sudden failure of the pressure valve will directly affect the normal operation of the mechanical equipment, this paper points out the failure reason of the pressure valve.

(1) The hydraulic spool and the valve body in use continuously produces the wear, causes the part size, the shape and the surface quality to change.

(2) Hydraulic valve balance spring, spool and seat, in the long-term variable load work, resulting in fatigue and crack, resulting in spring, broken or seat seal surface peeling, damage.

(3) The residual stress in the process of hydraulic valve parts processing and the external load stress in the course of use, exceeding the yield strength of the parts material and deforming the parts.

(4) Hydraulic oil mixed with water or acidic substances too much, the use of a longer period of time, corrosion of hydraulic valve parts, so that it loses due precision.

(5) Valve core and valve suite fluid radial force imbalance, the final valve core pressure to the valve sleeve inside the wall appears clamping phenomenon. (6) When the hydraulic valve is manufactured or repaired, the technical requirements are not met, or the parts are not kept properly, rust occurs, and dirt is mixed.