| There are some factors, such as frequently changing water demands, scheduling pumps to change working condition, opening and closing the valve and stopping of pumps in emergency, etc., in actual operations of the sencondary pressure system in the city’s water distribution network, which create transient flow in the pipe network and an increasing hydraulic loading as well. The pressure fluctuation value results from the transient flow may times of the stable value or more, leading a great harm to the pressurization water supply system and the safety operation of water distribution system. Thus it’s necessary to analyse the transient operating condition of the sencondary pressure system in water supply network by numerical simulation.In this paper we choose the FLOWMASTER which is a one-dimension analysis sofeware to perform the dynamic simulation of the transient operating condition of the pressure-superpositional system in water supply network, using the original database component of sofeware to get a simplified model of the pipe network system, then make a comprehensive analysis according to the simulated result, which offers theory and technology supports for the pressure-superpositional water supply system and the entrance criterion of network superposition water supply equipment. Conclusions of the numerical simulation on a practical engineering as follows:(1) Using a pressure pump to pump directly from the pipe network is good for a stable running of the municipal pipe, for the pressure fluctuation resulted from close-valve-startup of the pressure pump by is obviously small; A reasonable optimization of the valve action and using air vessel can reduce the impact of water hammer; As to the regions with a large hourly variation coefficient, a combination of general pressure pump and overhead water tank can improve the balance of water supply, thus let down the scale and invest of municipal water supply facility to some extent, besides, it’s beneficial for the safety and energy saving of the whole water supply system.(2) Comparing pressure tank water supply system, direct pumping pressurized water supply system is more technical and economic advantages, but the critical level of tank is reasonable assurance that pressure tank system can effectively reduce energy waste.(3) The entrance criterion of network pressure-superpositional water supply equipment must accord with some qualifications. First, it’s underdraft pumping. Second it can prevent the negative pressure effectively. Moreover the equipment meet the need of hygienic security; As to the practical engineering simulation, we can get a max water intake of a certain pipe section by a quantitative analysis and determine the setting elevation of the equipment by calculation. It’s of significance for the safety of water supplying.(4) Results of the simulation on transient phenomenon caused by network pressuresupostional water supply equipment as follows:Slow startup of pressurization pump can mitigate the after-pump pressure effecting on the network, and before-pump pressure effecting on the municipal pipe network; Several small pressurization pumps starting at the same time is less effecting on the pressure fluctuation of municipal pipe network and the after-pump pipe network, instead of each large pump starting by turns; As to the same pipe section connecting with two or more network superposition water supply equipments, it’s advantage for the stable running of municipal water supplying by start the equipments by turns, which can reduce the potential harm of the transient flow to the pipe network; According to the operating condition, we need to take a hydraulic simulation on the whole switch process before the switch of network superposition water supply equipments, thus, control the impact of the water hammer wave pressure on the whole system effectively. |
