TN 10318 - Air admittance valve

Where branch pipes are long or steep, negative pressures can develop in the system which can cause loss of seal in water seal traps by self siphonage. EN 12056-2, Table 6 and Approved Document H1, Diagram 3 give guidance on when provision of branch pipe ventilation is required. This is traditionally by provision of a water seal trap incorporating an AAV. Where HepVO ® is used in place of a water seal trap there is no further need for a branch air admittance valve for venting protection at that appliance. The HepVO ® will only allow air to enter the systems and will prevent backflow of air from the stack.