There are parallel pipelines at the pump outlet; how should the pump head be calculated?

Thank you. One more question: specifically, is the head 50–62 m or 62–75 m? Is there a calculation formula?

Thank you; I didn’t make myself clear. What I meant was that the resistance in branch one is 50 m and the resistance in branch two is also 50 m, without taking into account any margin for the pump’s head pressure. So why is the pump’s head pressure in the range of 50–75 m? Is there a formula or any basis for this value?

Thank you. Sir, could you please explain why it’s 50m?

Chapter 1 of Principles of Chemical Engineering: Parallel Pipelines

This post was last edited by weilongwu on 2023-10-21 at 14:47. If the margin for pump head is not taken into account, A=50m can be chosen (this factor must actually be considered, as the equivalent length values for fittings and valves, etc., can vary significantly when calculating pipe resistance); this value can be determined directly from the calculation of the pipe resistance in the branch lines. For more details, refer to “HGT 20570.7-95 Pipe Pressure Drop Calculation”. However, since the problem states that the pipes for Q and H are identical, the parameters QX2 and H remaining constant can be used for selecting the pump. If a margin for the pump’s head is taken into account, then C=50-75 m should be chosen; the theoretical value for pipeline resistance is 50 m, but when designing the pump, a certain margin is reserved. According to the standard “HGT 20570.5-95 – Calculation of system characteristics of pumps and determination of relative installation heights of equipment”, this margin is set at 30 KPa ； The book \"System Design for Chemical Plants\" recommends a total dynamic pressure drop of 10%-20%, or 30-50 KPa, depending on the conditions of the system ； When selecting pumps as recommended in the \"Petrochemical Design Manual (2015 Revised Edition), Volume 3, Upper: Chemical Unit Processes,\" 1.1 times the calculated head value is used. Based on the actual situation, the most appropriate answer is C.

Looking at the big shot’s reply, learning*learning*

I won’t do the specific calculations; the calculation of pipe resistance is similar to the calculation of resistance in electrical circuits

This post was last edited by *nht1 on 2023-10-28 at 14:45. It’s not enough to consider only the resistance; there is also the potential difference. If the resistance includes the potential difference, then that would be sufficient. I would appreciate some guidance from an expert. When calculating the head of a pump, the pipe resistances in series are added together, while the flow rates are also added together. For parallel pipelines, the highest pipe resistance is taken into account. In actual design, a margin of 1.1 is applied; thus, it is 50×1.1, so option C is chosen