Knowing the flow rate, how do I choose a pump? The pump’s power and head

The head is determined based on your entire chilled brine piping system. Simply put, the head must be greater than the total resistance loss of the piping system + the maximum height difference in the system + the back pressure at the destination.

Thank you. Could you be more specific?

With the flow rate known, the head required for the process can be determined through calculation. Then, an appropriate pump is selected based on the flow rate and the head required by the process, and the choice is finalized after calculating the efficiency.

The basis for pump selection should be determined by considering five aspects in light of the process flow and water supply/distribution requirements: namely, the liquid flow rate, the head provided by the pump, the properties of the liquid, the piping layout, and the operating conditions. 1. Flow rate is one of the important performance parameters for selecting a pump; it is directly related to the production capacity and conveying capacity of the entire system. If the process design in the design institute can calculate the normal, minimum, and maximum flow rates of the pump. When selecting a pump, the maximum flow rate should be taken as the basis, with consideration also given to the normal flow rate. In cases where a maximum flow rate is not available, 1.1 times the normal flow rate can generally be used as the maximum flow rate. 2. The head required by the installation system is another important performance parameter for selecting a pump; generally, the head value should be increased by 5%–10% as a safety margin when making the selection. 3. Properties of the liquid, including the name of the liquid medium, its physical properties, chemical properties, and other characteristics. Physical properties include temperature, density, viscosity, the diameter of solid particles present in the medium, and the gas content; these factors are relevant to calculating the system’s head, the effective net positive suction head, and determining the appropriate type of pump. Chemical properties refer mainly to the chemical corrosiveness and toxicity of the liquid medium, and they serve as important criteria for selecting the material for the pump as well as the type of shaft seal to use. 4. The pipeline layout conditions of the plant system refer to data such as the liquid delivery height, distance, and direction; the lowest liquid level on the suction side and the highest liquid level on the discharge side; as well as details regarding pipe specifications, their lengths, materials, fitting specifications, and quantities. These are necessary for calculating the system head and verifying the net positive suction head. 5. There are many aspects related to operating conditions, such as the operating temperature of the liquid, the saturated vapor pressure P, the suction side pressure PS (absolute), the pressure in the discharge side container PZ, altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the pump’s location is fixed or movable.

X, thank you all! I don’t have much wealth – I can only manage a profit of three points per day. I’ll ask my colleague to rate you for me

The head must be greater than the total resistance loss of the piping system + the maximum height difference in the system + the back pressure at the destination. If I know the maximum height difference in the piping system, how can I calculate the total pressure drop across the entire system? What is the backpressure at the destination – is it a required value or a calculated value? Thank you all; please let my colleague handle this for you

1. The pressure drop across the entire piping system can be determined by consulting relevant data; straight sections, elbows, valves, etc., all have corresponding resistance coefficients. By knowing the length of the straight sections, the number of elbows and valves, etc., it is possible to calculate the pressure drop. (Many experienced people can estimate this directly.) 2. Backup pressure: This generally refers to the pressure required at the destination; for example, if the destination requires a pressure of 1 kilogram, then the pressure of the fluid reaching that location must be greater than 1 kilogram in order for it to enter the device (of course, there is some margin allowed, and this depends on the actual conditions). After calculating the head pressure, don’t forget to include a margin as well – usually, the calculated value is multiplied by 1.05 to 1.1.

For specific details, refer to pages p3–p39 of the second volume of the Chemical Process Piping Manual, or HG/T 20570-95, which provide comprehensive information on this topic. It’s a pity that the level isn’t high enough to upload the materials. There’s no need to rush, you’ll definitely learn it after reading it.

The total system pressure drop can be estimated using the pressure drop per 100 meters of pipe specified in the manual, along with an approximate count of the fittings. The backpressure is the operating pressure at the destination site; adding a certain margin will suffice

Head is calculated based on pipeline losses: Bernoulli’s equation! Power and pump efficiency, medium density, head, as well as the safety factor determined by the size of the pump!

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The selection of the pump can be calculated using Bernoulli’s equation