The non-return valve is an attachment that connects to a road tow compressor between the machine and the hose. This device circulates the air in such a way that the air is only diverted to the hose instead of going back through the machine creating back pressure. The back pressure can have a harmful effect on the machine and the non-return valve must be used with the road tow compressor on certain jobs such as when the compressor is filling a tank that stores compressed air.