How To Choose The Type And Model Of Pump

Feb 23, 2025

The selection criteria for pumps should be based on the process flow, water supply and drainage requirements, and considered from five aspects: liquid delivery capacity, device head, liquid properties, pipeline layout, and operating conditions.

1. Flow rate is one of the important performance data for pump selection, which directly affects the production and transportation capacity of the entire device. If the design institute can calculate the normal, minimum, and maximum flow rates of the pump in the process design. When selecting a pump, the maximum flow rate should be taken as the basis, taking into account the normal flow rate. When there is no maximum flow rate, 1.1 times the normal flow rate is usually taken as the maximum flow rate.

2. The head required for the installation system is another important performance data for selecting pumps, and generally the head should be selected by amplifying the margin by 5% to 10%.

3. The properties of liquids include the name of the liquid medium, physical properties, chemical properties, and other properties. Physical properties include temperature, density, viscosity, solid particle diameter, and gas content in the medium, which involve the system's head, effective cavitation allowance calculation, and suitable pump type. Chemical properties mainly refer to the chemical corrosiveness and toxicity of the liquid medium, and are important criteria for selecting pump materials and choosing the appropriate shaft seal type.

4. The pipeline layout conditions of the device system refer to the height, distance, and direction of the liquid delivery, as well as data such as the lowest liquid level on the suction side and the highest liquid level on the discharge side, as well as pipeline specifications and their lengths, materials, pipe specifications, quantities, etc., in order to calculate the comb head and verify the cavitation allowance.

5. There are many operating conditions, such as the operation of liquid T, saturation vapor force P, suction side pressure PS (absolute), discharge side container pressure PZ, altitude, environmental temperature, whether the operation is intermittent or continuous, and whether the pump position is fixed or movable.

3, The specific operation of pump selection is based on the principles and basic conditions of pump selection. The specific operation is as follows:

1. Based on the layout of the device, terrain conditions, water level conditions, and operating conditions, determine the selection of horizontal, vertical, and other types of pumps (pipeline, submersible, submerged, unobstructed, self-priming, gear, etc.).

2. Based on the properties of the liquid medium, determine whether to use a clean water pump, hot water pump, oil pump, chemical pump, corrosion-resistant pump, impurity pump, or an unobstructed pump. Pumps installed in explosive areas should use corresponding explosion-proof motors according to the level of the explosive area.

3. Determine whether to use a single suction pump or a double suction pump based on the flow rate; According to the head, whether it is a single-stage pump or a multi-stage pump, whether it is a high-speed pump or a low-speed pump (air conditioning pump), multi-stage pumps have lower efficiency than single-stage pumps. If both single-stage and multi-stage pumps can be used, single-stage pumps are the first choice.

4. After determining the specific model of the pump and choosing which series of pumps to use, the specific model can be determined based on the maximum flow rate (usually 1.1 times the normal flow rate can be taken as the maximum flow rate when there is no maximum flow rate), and the head after amplification by 5% to 10% can be taken as the main performance parameters. The specific model can be determined on the model spectrum or series characteristic curve.

The operation is as follows: Using the pump characteristic curve, find the required flow rate value on the horizontal axis and the required head value on the vertical axis. Draw vertical or horizontal lines from the two values upwards and to the right respectively. If the intersection of the two lines happens to fall on the characteristic curve, then the pump is the one to be selected. However, this ideal situation is generally rare, and the following two situations are usually encountered:

The first type: If the intersection point is above the characteristic curve, it indicates that the flow rate meets the requirements, but the head is not enough. At this time, if the head difference is not much, or about 5%, it can still be selected. If the head difference is significant, the pump with a larger head can be selected. Or try to reduce pipeline resistance losses.

The second method: If the intersection point is below the characteristic curve and within the fan-shaped trapezoidal range of the pump characteristic curve, this model is preliminarily determined. Then, based on the difference in head, it is decided whether to cut the impeller diameter. If the head difference is very small, it is not cut. If the head difference is very large, it is cut according to the required Q H,, According to its ns and cutting formula, when cutting the impeller diameter, if the intersection point does not fall within the range of the fan-shaped trapezoid, a pump with a smaller head should be selected. When selecting a pump, sometimes it is necessary to consider the production process requirements and choose different shapes of Q-H characteristic curves.

5. After determining the pump model, for pumps or pumps with physical and chemical media similar to water, it is necessary to go to the relevant product catalog or sample and make corrections based on the performance table or performance curve of the model to see if the normal working point falls within the priority working area of the pump? Is the effective NPSH greater than (NPSH). Can NPSH be used to correct the geometric installation height in reverse?

6. For liquid pumps with a conveying viscosity greater than 20mm²/s (or a density greater than 1000kg/m³), it is necessary to convert the water experimental pump characteristic curve into a performance curve for that viscosity (or density), especially by carefully calculating or comparing the suction performance and input power.

7. Determine the number and standby rate of pumps:

a, For normally operating pumps, only one is usually used because a large pump is equivalent to two small pumps working in parallel (referring to the same head and flow rate), and the efficiency of the large pump is higher than that of the small pump. Therefore, from an energy-saving perspective, it is better to choose a large pump instead of two small pumps. However, in the following situations, parallel cooperation of two pumps can be considered: the flow rate is large, and one pump cannot reach this flow rate.

b, For large pumps that require a 50% backup rate, two smaller pumps can be switched to work, with two as backup (a total of three pumps)

c, For some large pumps, pumps with a flow rate requirement of 70% can be operated in parallel without the need for a backup pump. When one pump is under maintenance, the other pump still undertakes 70% of the production transportation.

d, For pumps that require 24-hour continuous operation, three pumps should be standby, one in operation, one as backup, and one for maintenance.

8. In general, customers can submit their "basic conditions for pump selection" and our company will provide selection or recommend better pump products.