Old K says every week – talking about things in the petrochemical design industry. Post 19: Understanding pump NPSH in a few words

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This post was last edited by henglinkou on 2020-10-25 08:58. Old K’s weekly series – Talks about matters in the petrochemical design industry, Post 19: Understanding pump net positive suction head in a few words. From forum discussions, it’s clear that many members have some confusion regarding pump net positive suction head; indeed, some materials provide insufficiently clear or overly complicated explanations on this topic. Here are a few sentences to explain what cavitation head is in a pump: 1. When the liquid boils inside the pump chamber, it causes cavitation in the pump ； 2. The boiling point of a liquid is related to pressure; the higher the pressure, the higher the boiling point. The pressure corresponding to the boiling of a liquid at a certain temperature is the saturated vapor pressure of that liquid at that temperature. 3. To prevent the liquid from boiling inside the pump chamber, the inlet pressure of the pump must be greater than the saturated vapor pressure of the liquid at the operating temperature. 4. Required NPSHr (also known as allowable NPSHr): It is the safety margin provided by the pump manufacturer to prevent cavitation in the pump; in other words, it is the minimum required value for the inlet pressure of the pump to be higher than the saturated vapor pressure of the liquid (expressed in terms of liquid column height). 5. Effective NPSHa (also known as the plant NPSHa): The inlet pressure of the pump is calculated based on the layout of the plant and relevant parameters; the effective NPSHa is obtained by subtracting the saturated vapor pressure from this inlet pressure (expressed in terms of liquid column height). Generally, it is required that NPSHa ≥ NPSHr + 1.5 (depending on the requirements of different types of pumps). 6. Pump inlet pressure = Pressure of the gas phase in the container at the suction side + Pressure generated by the head difference (liquid level height – height at the pump inlet) – Frictional loss in the inlet pipeline. 7. When the calculated effective net positive suction head is not sufficient, one or a combination of measures such as increasing the installation height of the suction-side equipment, reducing the pump’s installation height, and enlarging the inlet pipe diameter must be taken. The above is my explanation of net positive suction head; I hope it will help everyone understand. For specific calculations regarding pumps, please refer to the post I shared: https://bbs.hcbbs.com/thread-1764877-1-1.html. Lao K says every week – talking about things in the petrochemical design industry. For previous posts, please see the links below: Post 1: The development history of China’s survey and design industry https://bbs.hcbbs.com/thread-3031149-1-1.html Post 2: **Management of the survey and design industry** https://bbs.hcbbs.com/thread-3036417-1-1.html Post 3: The development of drawing techniques in design institutes https://bbs.hcbbs.com/thread-3039960-1-1.html Post 4: The evolution of professional division of labor in petrochemical design institutes https://bbs.hcbbs.com/thread-3045261-1-1.html Post 5: The organizational structure of petrochemical engineering companies https://bbs.hcbbs.com/thread-3050591-1-1.html Post 6: Contract management in design management https://bbs.hcbbs.com/thread-3054762-1-1.html Post 7: Management of basic design data in design management https://bbs.hcbbs.com/thread-3058184-1-1.html Post 8: Quality management in design management https://bbs.hcbbs.com/thread-3061718-1-1.html Post 9: Schedule management in design management https://bbs.hcbbs.com/thread-3062161-1-1.html Post 10: Document management in design management https://bbs.hcbbs.com/thread-3069580-1-1.html Post 11: Meeting management in design management https://bbs.hcbbs.com/thread-3073327-1-1.html Post 12: Management of bonus distribution in design management https://bbs.hcbbs.com/thread-3077492-1-1.html Post 13: The construction process for petrochemical projects https://bbs.hcbbs.com/thread-3082708-1-1.html Post 14: Illustrations of the content and procedures involved in process design https://bbs.hcbbs.com/thread-3086849-1-1.html Post 15: Explanations regarding PID versions and PID modification management https://bbs.hcbbs.com/thread-3091076-1-1.html Post 16: Common energy-inefficient designs in the petrochemical industry https://bbs.hcbbs.com/thread-3095859-1-1.html Post 17: Project work breakdown https://bbs.hcbbs.com/thread-3100837-1-1.html Post 18: Issues related to the training of design professionals https://bbs.hcbbs.com/thread-3105529-1-1.html