The invention discloses a
backflow preventer of a hand-operated
oil pump. The
backflow preventer is arranged at an oil inlet of the pump, and comprises a built-in
valve seat, a valve plug and a spring. An inner hole of the oil inlet of the pump is fitted with the
valve seat, the bottom surface of the inner hole is provided with an annular step, and the axial section of the step is in the shape of isosceles triangle. Radial ribs are uniformly distributed at a big-end orifice of the
valve seat, and a cross
pitch point of the ribs is provided with an axial through hole; and a umbelliform valve-plug shaft section after being sleeved with the spring is in clearance fit with the axial through hole, the valve plug is axially limited by a clamp spring, and a rubber flat mat is embedded into a downward external umbrella frame. Through fitting with the annular step to form a normally
closed state, the seal surface is in a line
contact mode, which is helpful for separating the valve plug from the annular step under the condition of negative pressure, so that
oil can be inhaled successfully. The
backflow preventer is good in tightness and flexible in startup, does not affect the oil pumping efficiency, and can prevent the occurrence backflow, therefore, even if the pump stops operating, the pump still stores oil for a long time, so when being used again, the pump can output oil quickly just by shaking the pump for multiple circles by hand.