Differential Surge Tank.ĭifferential surge tanks have a vertical riser about the same diameter as the pipe. If the tank is closed at the top, the air cushion absorbs a portion of the water hammer and the tank need not be so high as a simple surge tank. The simple surge tank is often adequate for low heads, but under high heads some modifications to improve the damping action and minimize cost are desirable.Ī restricted entry increases the damping action and reduces the initial surge. Read Also: A Detailed Guide on Reciprocating, Rotary, Air Lift, & Jet Pump. However, the results provide a conservative estimate for preliminary design of simple surge tanks. Since the derivation neglected tank friction and velocity head and entrance losses and assumed instantaneous valve closure with all water-hammer effects dissipated in the tank and not the pipe, the estimate of y max will be too large. Which expresses the relation between velocity in the pipe and water-surface level in the tank over the interval from valve closure to the top of the first surge.Įquation (3) may be used to estimate the maximum height of surge y max by finding the constant of integration C for steady-state conditions at the instant of closure (y = y1) and then solving for y max when V = 0. V 2 = 2gAD 2 / LA sf 2 ( 1 – fA s / AD * y) – Ce -(fA s / AD)y…….equation (3) …and A s is the cross-sectional area of the surge tank.Ĭombining these two equations, integrating, and solving for V yields. Where y is the water level in the surge tank measured from the static level (positive upward), L, f, and D are characteristics of the pipe between the tank and the reservoir, Y + f * L / D * V 2 / 2g + L / g * dV / dy * dy / dt = 0…….equation (1) The energy equation for unsteady flow, neglecting fluid friction and velocity head in the surge tank and loss at pipe and surge-tank entrances, can be written as The water surface in the tank then fluctuates up and down until damped out by fluid friction. When the valve is suddenly closed, water rises in the surge tank. With steady flow in the pipe, the water level ‘Y1’, as shown in the below figure, in the surge tank is below the static level (y = 0). The valve might represent turbine gates which may open or close rapidly with changes in load on the generators. Surge tanks are installed on large pipelines to relieve excess pressure caused by water hammer and to provide a supply of water to reduce negative pressure if a valve is suddenly opened.Ī simple surge tank is a vertical standpipe connected to a pipeline.
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