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Abstract
The mathematical model of vacuum breaker valve is significant to the protection scheme. The more accurate the vacuum breaker valve model, the more reliable the calculation results. In this study, the application conditions of the air valve model are analyzed according to the assumptions used in the derivation, and the contradictions between these assumptions are proposed. Then, according to the different working characteristics between the vacuum breaker valve on the siphon outlet pipe and the air valve, the vacuum breaker valve model is deduced based on the modified assumptions. In the derivation process, the thermodynamic change of the gas in the vacuum breaker valve is assumed to follow the isentropic process rather than an isothermal process, and the water level in the vacuum breaker valve is considered to be changeable. An engineering case is introduced, and the results calculated according to the vacuum breaker valve model are compared with those resulting from the air valve model. The results indicate that the vacuum breaker valve model is suitable for large air mass conditions and can provide a theoretical basis for the numerical simulation and settings of vacuum breaker valves.
Highlights
The head loss of the siphon pipe is small, the flow control in the siphon pipe is convenient when the pumps are powered off, and the water level at the end of the siphon pipe can be lowered [1,2,3].many large pump systems with low heads and large flow usually have siphon outlet pipes behind the pumps
The vacuum breaker valve is numerically simulated according to the air valve model as well as the vacuum breaker valve model
The proposed vacuum breaker valve model (28) shows that the air valve model can be regarded as a special case under the condition that the vacuum breaker valve model has less
Summary
The head loss of the siphon pipe is small, the flow control in the siphon pipe is convenient when the pumps are powered off, and the water level at the end of the siphon pipe can be lowered [1,2,3].many large pump systems with low heads and large flow usually have siphon outlet pipes behind the pumps. To prevent serious negative pressure damage when the pumping station is powered off, a vacuum breaker valve is usually installed at the top of the siphon pipe for security protection. As a kind of safety device, the vacuum breaker valve can be both electronically and automatically controlled. If it is in electronic control mode, it will open immediately as soon as the power failure happens, while if it is in automatic control mode, it will work as long as the piezometric head in the pipe at the location of the vacuum breaker valve decreases sharply and becomes smaller than the set intake pressure [4]. The air sucked into the vacuum breaker valve releases the vacuum, preventing the pipe from liquid column separation and rejoining
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