In the engineering design, all kinds of exhaust valves should be selected according to the specific site conditions, and the composite exhaust valve should be installed at the local highest point; For long-distance horizontal pipe section and long-distance down pipe section without break point, composite exhaust valve or micro exhaust valve should be installed; The micro exhaust valve should be selected when the descending slope becomes larger and the ascending slope becomes smaller; When vacuum protection is needed, composite exhaust valve should be selected; For long-distance upward pipe without break point, composite exhaust valve can be selected.

The diameter of exhaust valve is micro exhaust valve, which can be directly selected due to its small scope of application. The general pipe diameter is DN20 and DN25; Because the composite exhaust valve is a combination of micro exhaust valve and high-speed exhaust / suction valve, the diameter selection standard of composite exhaust valve and high-speed exhaust / suction valve is the same.

According to the performance curve, since the high-speed exhaust / suction valve is used to discharge air during water filling and to inhale air during venting, the amount of air to be discharged during water filling and the amount of air to be inhaled during pipe drainage venting or pipe burst protection should be comprehensively considered. The diameter of the exhaust port during water filling and the diameter of the suction port during venting should be calculated, Select the larger diameter as the exhaust / suction valve diameter.