Drip-proof devices prevent liquid leaching from the nozzles after the nozzle has been cut off. Their operation is usually carried out by a simple mechanical device, but there are also less common types in which the anti-drip works by aspiration and is therefore of a pneumatic type; the speed of intervention of these systems is however reduced compared to the simplest mechanical devices.
The mechanical anti-drips, undoubtedly the most common, are essentially made up of a calibrated spring capable of closing the duct that transports the liquid to the nozzle when the operating pressure drops below certain values (normally 0.4 – 0.5 bar). They can be divided according to the system of closing the adductor tube in valve, ball or membrane. In the membrane system the spring never comes into contact with the mixture to be stribuire ensuring a longer life of the device.