Drain valve for tanks of pneumatic systems, comprising: - a valve body, defining a cavity, and comprising: - an inlet, whereupon compressed air contained in the tank is intended to act; - an outlet, adapted to be in communication with the outside of the tank; - a chamber intended to be filled with air coming from the inlet, and wherein such air is intended to exit the chamber through said outlet; - a shutter device comprising: - a first piston adapted to slide in said cavity and adapted to selectively close said outlet; wherein the first piston is subject to the pressure of the air coming from the inlet; - a second piston adapted to slide in said cavity and subject to the pressure of the air coming from the inlet; wherein the first and second pistons (8, 9) are configured to take: - a closed configuration, in which such pistons (8, 9) prevent air from flowing to and from the chamber; - an intake configuration, in which air can flow into the chamber from the inlet, and air is prevented from flowing from the chamber through the outlet; - an ejection configuration, in which air is prevented from flowing into the chamber from the inlet, and air can flow from the chamber through the outlet; characterized in that the pistons (8, 9) are adapted to take a closed position, in which they (8, 9) are in abutment with each other and prevent air from flowing between the inlet and the chamber, and an open position, in which they (8, 9) are spaced apart and permit such air flow. - a valve body, defining a cavity, and comprising: - an inlet, whereupon compressed air contained in the tank is intended to act; - an outlet, adapted to be in communication with the outside of the tank; - a chamber intended to be filled with air coming from the inlet, and wherein such air is intended to exit the chamber through said outlet; - an inlet, whereupon compressed air contained in the tank is intended to act; - an outlet, adapted to be in communication with the outside of the tank; - a chamber intended to be filled with air coming from the inlet, and wherein such air is intended to exit the chamber through said outlet; - a shutter device comprising: - a first piston adapted to slide in said cavity and adapted to selectively close said outlet; wherein the first piston is subject to the pressure of the air coming from the inlet; - a second piston adapted to slide in said cavity and subject to the pressure of the air coming from the inlet; - a first piston adapted to slide in said cavity and adapted to selectively close said outlet; wherein the first piston is subject to the pressure of the air coming from the inlet; - a second piston adapted to slide in said cavity and subject to the pressure of the air coming from the inlet; wherein the first and second pistons (8, 9) are configured to take: - a closed configuration, in which such pistons (8, 9) prevent air from flowing to and from the chamber; - an intake configuration, in which air can flow into the chamber from the inlet, and air is prevented from flowing from the chamber through the outlet; - an ejection configuration, in which air is prevented from flowing into the chamber from the inlet, and air can flow from the chamber through the outlet; - a closed configuration, in which such pistons (8, 9) prevent air from flowing to and from the chamber; - an intake configuration, in which air can flow into the chamber from the inlet, and air is prevented from flowing from the chamber through the outlet; - an ejection configuration, in which air is prevented from flowing into the chamber from the inlet, and air can flow from the chamber through the outlet; characterized in that the pistons (8, 9) are adapted to take a closed position, in which they (8, 9) are in abutment with each other and prevent air from flowing between the inlet and the chamber, and an open position, in which they (8, 9) are spaced apart and permit such air flow.