Air suction valve

The utility model discloses an air suction valve, which comprises a valve body, wherein a protective cover is arranged below the valve body, an unloader piston is arranged above the valve body, a spring is arranged inside the unloader piston, a first control piston is arranged on the unloader piston, a second control piston is arranged on the outer side of the unloader piston, a clearance is left between the second control piston and the unloader piston, and a valve cap is arranged on the first control valve and the second control valve. Washers are arranged between the valve body and the protective cover. A first O-shaped ring is arranged on the lower edge of the valve cap. The upper end of the first control piston is sheathed with a second O-shaped ring. The position at which the first control piston and the unloader piston are connected with each other is sheathed with a ring. The air suction valve can prevent the difference between internal pressure and external pressure from influencing a pipeline, so as to effectively prevent the flattening or damage of the pipeline, thus being convenient to use.