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 are configured to take: - a closed configuration, in which such pistons 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 are adapted to take a closed position, in which they are in abutment with each other and prevent air from flowing between the inlet and the chamber , and an open position, in which they 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 are configured to take: - a closed configuration, in which such pistons 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 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 are adapted to take a closed position, in which they are in abutment with each other and prevent air from flowing between the inlet and the chamber , and an open position, in which they are spaced apart and permit such air flow. <EOS>