Often found in plumbing and HVAC systems, vent valves are generally utilized to vent hot water and control temperature and pressure. Their operating principle is relatively straightforward: vent valves allow the pressure in a tank or boiler to balance while preventing fluid spillage through the vent lines. The valves permit the free flow of fluid or air in or out of a chamber or tank until closed. Air admittance valves and vents—as well as steam vent valves—are all part of the valve vent family. To install your vent valve, you might also require pipes, fittings or plumbing tools like cutters, wrenches or benders to complete the job.