FK 40 - Tri-Canada

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Centrifugal pumps Pumps connected in series Cavitation A multistage centrifugal pump performs as single stage pumps connected in series. Note: A st at ionary pump in a syst em creat es a considerable pressure drop. Theref ore it is recommendable to install a by pass around pumps which are connected in series. The overall performance curve of centrifugal pumps connected in series can be calculated by adding the differential head of each pump at the relevant flow rate . Cavitation can be recognised by a strongly increased noise level of the pump with a simultaneous reduced flow rate. What causes cavitation in centrifugal pumps ? The lowest pressure point in a pump occurs at the inlet of the pump impeller. Due to local pressure reduction part of the fluid may evaporate generating small vapour bubbles. These bubbles are carried along by the fluid and implode instantly when they get into areas of higher pressure. These implosions can create local pressure peaks up to 100.000 bar. If a pump is cavitating over longer periods, the impeller, the pump housing and cover will wear out. The surface is typically perforated and pitted.
How to avoid cavitation? We should ensure that at all points of the pump, the fluid pressure is higher than the vapour pressure at t he corresponding t emperat ure. Take t he pressure st at ed in t he vapourpressure- table of the product to be transfered. The NPSH value of the plant must be at least 0.5 m higher than the NPSH value of the pump. For a safe and cavitation free operation the following formular is valid: NPSH plant > NPSH Pump + 0.5 m The vapour pressure of the product is dependent on the temperature and will rise with increasing t emperat ure. If the product is pumped at different temperatures the maximum vapour pressure should be used to determine the NPSH value of the plant. Centrifugal pumps Vapour pressure
Page 2 and 3: Content Pump technology terms . . .
Page 4 and 5: Pump technology terms Flow rat e [m
Page 6 and 7: Pump technology terms Flow behaviou
Page 8 and 9: Pump technology terms Types of flow
Page 10 and 11: Pump technology terms NPSH value [m
Page 12 and 13: Loss of head calculation Loss of he
Page 14 and 15: Loss of head calculation Example: F
Page 16 and 17: Centrifugal pumps Feat ures of t he
Page 18 and 19: Centrifugal pumps Correction of the
Page 22 and 23: Centrifugal pumps Centrifugal pump
Page 24 and 25: Centrifugal pumps Centrifugal pump
Page 26 and 27: Centrifugal pumps Power consumption
Page 28 and 29: Centrifugal pumps Self- priming cen
Page 30 and 31: Centrifugal pumps Multistage centri
Page 32 and 33: Positive displacement pumps Perform
Page 34 and 35: Positive displacement pumps Selecti
Page 36 and 37: Positive displacement pumps Case 1:
Page 46 and 47: Positive displacement pumps Rotary
Page 58 and 59: Mechanical seal selection Double me
Page 60 and 61: Mechanical seal selection “Face t
Page 62 and 63: Mechanical seal selection Elastomer
Page 64 and 65: Pump cleaning SIP After CIP cleanin
Page 66 and 67: Index Cavitation . . . . . . . . .

FK 40 - Tri-Canada

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