Scope and Applicability of the Item This Item is intended to provide simple approximate methods that may be used to estimate the magnitude of surge pressures following complete power failure to a booster pump or booster pump station. The effect on these surge pressures of a pump bypass@ fitted with a one-way valve to allow forward flow only@ may also be investigated. A simple idealised model of a typical system with a booster pump station@ shown in Sketch 2.1@ is considered in this Item. It is assumed that the pipe diameter (and friction factor@ where applicable) in both the suction and discharge lengths of pipe (relative to the pump) are constant. Component losses are assumed to be small compared with the pipe friction and are neglected. The pump is protected by a one-way valve (commonly referred to as a reflux valve or check valve) that prevents reverse flow through the pump by closing completely when the discharge falls to zero. The system may also be further protected by a bypass circuit that allows the full flow of liquid to bypass the pump when the pressure on the discharge side falls to the pressure of the suction side following pump trip. This bypass includes a one-way valve that closes completely when the flow through the bypass falls to zero at a later stage in the transient cycle@ thus preventing all reverse flow round the pump. The bypass is normally isolated from the flow during normal steady-state flow conditions. Following bypass operation@ some liquid will@ in most cases@ continue to be drawn through the pump but this is usually small relative to the flow through the bypass and is neglected. The model will allow systems with pressurised tanks to be considered@ provided suitable adjustments are made to the tank head values. The effect of bypass circuits on the suppression of pressure surges following pump trip is explained in Section 3.1 using a series of sketches illustrating a typical sequence of events. The use of bypass circuits is explained in more detail in Section 3.2. Data are presented in Section 4 that allow estimates to be made of the head and flow conditions at the suction and discharge sides of a booster pump with or without a bypass circuit. The effect of pipe friction on the pressure changes is also considered in that section. A worked example that illustrates the use of these data is given in Section 5. The computer program@ ESDUpac A8727@ introduced in Item No. 87027 allows the pressure changes to be estimated after pump trip without the simplifying assumptions required here for a graphical presentation.
ESDU 85044-1985 history
1985ESDU 85044-1985 FLUID TRANSIENTS IN PIPES Pressure surge following booster pump trip. Suppression using pump bypass