Marvac's No Drain "Coolant Barrier" can perform two distinct functions. First, the tool allows the technician to change a cooling system component without draining the cooling system. Openings as large as 21mm in diameter will result in little to no leakage. The tool can also pressure test the system for leaks. The tool does this by clearing a "pathway of air" from where the component can be removed to where the tool can be attached to the cooling system. The compressed air enters the open port continuously, preventing coolant from draining.