空气阀数学模型及排气性能研究

空气阀是输水管道进排气的重要设备，具有充水排气、放空吸气，正常输水排气等功能，而且越来越多地用来作为水锤防护措施，因此空气阀的合理选型至关重要。从热力学基本原理出发，推导了理想气体和不可压缩气体两种假设空气阀数学模型，并对美国给水工程协会M51指南所提供的空气阀排气性能参数进行了误差分析。分析结果表明：理想气体假设模型具有较高的精度，不可压缩气体假设模型在压差较小的情况下具有较高的精度，在初次充水、放空等小压差工况下可采用该模型。同时，还以CJ/T217-2013中FGP型复合式空气阀排气性能参数为例进行了流量系数分析。结果表明：流量系数并非常数，而是一个随压差、口径变化的变量，因而在水力过渡过程计算中，流量系数应通过实测得到。研究结果可为空气阀的合理选型提供理论依据，同时也可为工程安全运行提供技术保障。

Study on mathematical model and exhaust performance of air valve

The air valve is an important device for the air intake and ventilation of water pipelines and more and more used as water hammer protection measures, it is of vital importance to the selection of the air valve. This paper deduces two mathematical models of hypothetical air valves for ideal gas and incompressible gas respectively based on the basic principle of thermodynamics and analyzes the error of the air valve exhaust performance parameters according to the AWWA M51 guideline. The results show that the ideal gas hypothesis model has higher accuracy while the incompressible gas model has higher accuracy in the case of small pressure difference. This model can be used under the condition of small pressure difference such as initial filling and venting. This paper also uses the CJ/T217-2013 FGP composite air valve exhaust performance parameters for flow coefficient analysis. The results show that the flow coefficient is not constant but varies with pressure difference and pipe diameter. The flow coefficient should be measured by experiment in the calculation of the hydraulic transition process. The result can provide a theoretical basis for the type selection of air valves and project′s safe operation.