Characteristics Curves of Centrifugal Pumps

Characteristics Curves of Centrifugal Pumps > > Characteristics curves of centrifugal pumps are defined as those curves which are plotted from the results of a tests on the centrifugal pumps and these curves are necessary to predict the behavior and performance of the pump when the pump is working under different flow rate, head and speed. > > Main Characteristics Curves > > (a) This curves consist of variation of head (manometric head, Hm), power and discharge with respect to speed. > > (b) For plotting curves of Hm v/s N, Q is kept constant. We know that $√{h_m}$/DN is a constant or Hm α N2, this means the head developed by a pump is proportional to N2, hence the curve of Hm v/s N is a parabolic curve as shown in figure below. > > (c) For plotting curves of Q v/s N, Hm is kept constant. We know that, Q/D3N is constant, hence Q α N, this means that the curve Q v/s N is a straight line. > >
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(d) For plotting curves of P v/s N. Hm and Q are kept constant. We know that P/D5N3 is a constant, hence P α N3. This means that curves P v/s N is a cubic curve as shown in Figure above. > > Operating Characteristics Curves
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<div> > 1. If the speed is kept constant, the variation of manometric head, power and efficiency with respect to discharge gives the operating characteristics of the pump. above figure shows operating characteristic curves of a pump. > > 2. This input power curve for pumps shall not pass through the origin. It will be slightly away from the origin on the y-axis, as even at zero discharge some power is needed to overcome mechanical losses. > > 3. The head curve will have minimum value of head when discharge is zero. > > 4. The output power curve will start from origin as at Q = 0, output power (ρQgH) will be zero. > > 5. The efficiency curve will start from origin as at Q = 0, η = 0. > $(∵ \η = {\Output}/{\Input})$ </div>