A check valve for a pump delivery port includes a body having inlet and outlet portions joined by a duct and an opening; a curve having an inlet end to be connected to the delivery port and an outlet end to be connected to the body; and a valve member having a disk-shaped locking portion sealingly interacting with an edge of the curve and a locking portion secured in a seat by a lid of the opening. The valve member moves between open and closed positions and has a metal core made while the locking portion is metal-free. The lid cooperates with the locking portion through a protrusion or a cavity and pushes the valve member toward the curve to the closed position and allows the valve member to deflect to the open position under pressure of a working fluid in equilibrium with the weight of the blocking portion.