Image Number 2 for United States Patent #6352085.
A pressure relief valve for an oil pump of an automotive internal combustion engine. The pressure relief valve comprises a wall defining thereinside a valve accommodating bore. The wall is formed with a plurality of pressure relief holes including first and second pressure relief holes through which oil in the valve accommodating bore is releasable to an outside of the valve accommodating bore. A valve body is provided to be slidably movable in the valve accommodating bore and along the wall under balance between oil pressure acting on the valve body in a first direction and biasing force of a spring acting on the valve body in a second direction opposite to the first direction. In this arrangement, the second pressure relief hole is opened after the first pressure relief hole is opened to have a maximum cross-sectional opening area in a process of movement of the valve body in the first direction along the axis of the valve accommodating bore.