Surges in Pumping Systems

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           Pressure surging in pumping systems can be fatal and potentially destructive to pumps. Surging is “A sudden increase in the pressure of the liquid in a pipeline brought about by an abrupt change in flow velocity”1. The change in pressure can be a drastic increase or a decrease. A surge is also defined as “An unstable operating condition when the flow through a compressor is decreased to the point that momentary flow reversals can occur.”2 The reason why pressure surging is an issue is because it “can lead to major damage of the compressor”3 or pump. Though surging is not frequent, it can still occur unexpectedly. There are, however, means of preventing and otherwise reducing the frequency of pressure surges in pumping systems.

           Surging can be sudden, unexpected and random, or surging can eventually become constant. “Random surging is caused by an air pocket getting loose in the suction piping”4 While there are many potential causes of air pockets to develop in suction piping, the most typical reasons are usually due to improper installation or dissolved gases in the piping system. “Constant surging is usually a result of a low NPSHA”5. NPSHA is “Net positive suction head available to a centrifugal pump.”6 NPSHA is determined by combining “the effect of atmospheric pressure, water temperature, supply elevation and the dynamics of the suction piping”7. When surging is constant, the issue is typically due to recirculation, such as “Internal recirculation is heating the liquid to its vapor point”8 or “A stuffing box suction recirculation line is being used with fluid at or near its vapor point.”9

            One of the simplest ways to prevent pressure surges in pumps is to ensure, via protective measures, that a pressure surge will not occur. “If a preliminary calculation shows a need for additional protective devices, an attempt is always made first to reduce the primary pressure change.”10 To reduce the pressure, it is necessary to allow for a change of speed. Changing the speed can be accomplished by employing a flywheel, which prolongs rundown time for a pump. Another method of preventing surges quite effectively is by installing a surge tank. A surge tank “takes over full pipeline flow surge with virtually no time lag. With a suitable surge tank, the minimum admissible pressure is maintained in most systems”11 One other method of reducing surges in pumping systems is to reduce the active length of the system. Although there is no definite “best way” to prevent pressure surges due to the varying factors of pumping systems (such as flow rate, fluid temperature & viscosity, length of pumping systems, etc.), it is recommended to design pumping systems in a protective way so as to prevent (or greatly reduce) the occurrences of pressure surges, and/or install a surge tank in a pumping system.

  1. https://www.wartsila.com/encyclopedia/term/pressure-surge
  2. Oxford Dictionary of Chemical Engineering by Carl Schaschke, p. 368
  3. Same as 2
  4. https://mcnallyinstitute.com/17-html/17-12_surging_pump.htm
  5. Same as 4
  6. https://www.pumpsandsystems.com/net-positive-suction-head-npshr-and-npsha
  7. Same as 6
  8. Same as 4
  9. Same as 4
  10. Sulzer Pumps – Centrifugal Pump Handbook, Third Edition (2010, Butterworth-Heinemann), p. 116-117
  11. Same as 10

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