In industrial production, water supply and drainage systems, and many other fields, pumps play an indispensable role. They convert the mechanical energy of a prime mover into fluid energy to achieve liquid transportation. However, faced with numerous pump types and complex selection requirements, how to correctly choose a suitable pump to ensure efficient and reliable operation becomes a key issue. This article provides a detailed introduction to basic pump parameters, selection criteria, and selection principles and steps, helping you better understand and apply pump-related knowledge.
Before selecting a pump, it is very important to understand its basic parameters. These parameters help us accurately evaluate pump performance and thus select the most suitable pump.
Flow rate refers to the amount of liquid passing through a cross-section per unit time, usually expressed in volume or mass. Units include cubic meters per hour (m³/h), cubic meters per second (m³/s), and liters per minute (l/min). Flow rate is directly related to the production capacity and conveying capacity of the entire device. For example, in process design by engineering institutes, normal, minimum, and maximum flow rates are calculated. When selecting a pump, the maximum flow rate is usually used as the basis while also considering normal flow. If maximum flow data is not available, 1.1 times the normal flow may be taken as a reference.
Head refers to the energy gained per unit mass of liquid from the pump inlet to the pump outlet. Units include megapascals (MPa) and meters (m). The head required by the system is one of the most important performance data for pump selection. In practice, the calculated head is usually increased by 5–10% as a margin to ensure that the pump can meet system requirements.
Rotational speed refers to the number of revolutions of the shaft per unit time, measured in revolutions per minute (r/min). Different pump types and application scenarios require different rotational speeds. For example, centrifugal pumps typically operate at high speeds, enabling them to achieve higher flow rates and head.
Rated Power (N): The rated power of the prime mover, in kilowatts (kW). It determines the maximum power the pump can deliver.
Shaft Power (P): The power transmitted from the prime mover to the pump shaft, also in kilowatts (kW). This represents the actual power consumed during pump operation.
Effective Power (Pa): Also known as output power, referring to the effective energy gained by the liquid transported by the pump per unit time, measured in kilowatts (kW). It reflects the actual working efficiency of the pump.
Efficiency (η): The ratio of effective power to shaft power. A higher efficiency means better energy conversion and lower power consumption.
NPSH (available): The surplus energy of liquid per unit mass at the pump suction above its vaporization pressure, expressed in meters of liquid column. This parameter reflects the vaporization tendency of the liquid during pump operation.
NPSHr (required): The NPSH determined by pump manufacturers through testing, also in meters of liquid column, representing the pump's cavitation resistance. To improve cavitation performance, the NPSH should be minimized.
Suction vacuum height refers to the vacuum at the pump suction calculated from the reference plane, expressed in meters of liquid column. This index was once used to indicate pump cavitation performance but has gradually been phased out. However, it has a conversion relationship with NPSHr: NPSHr ≈ 10 – Hs.
Viscosity is the internal friction resistance of a lubricating liquid. Liquid viscosity affects pump efficiency and energy consumption. For example, when viscosity is high, special pump types such as rotary pumps or reciprocating pumps may be required.
Pump selection is a process that requires comprehensive consideration of many factors. The following are five main aspects to consider during selection.
Flow rate is one of the most important selection criteria. As mentioned earlier, the normal, minimum, and maximum flow rates required by the process must be determined and used as the basis for pump selection.
Head required by the system is also a key selection factor. After calculating the required head, a certain margin must be added to ensure the pump meets system demands.
These include physical, chemical, and other characteristics.
Physical properties include temperature, density, viscosity, solid particle diameter, and gas content. These affect system head, NPSH calculation, and suitable pump types.
Chemical properties include corrosiveness and toxicity of the liquid, key considerations for pump materials and shaft sealing methods.
System piping conditions include delivery height, distance, direction, suction-side liquid level, discharge-side liquid level, pipe specifications, length, materials, fittings, and quantities. These details are critical for calculating system head and verifying NPSH.
Operating conditions include liquid temperature, vapor pressure, suction pressure, discharge container pressure, altitude, ambient temperature, operation mode (intermittent or continuous), pump installation location (fixed or mobile), etc. These factors influence pump selection and performance.
Pump selection must follow certain principles and steps to ensure that the selected pump meets process requirements while providing high reliability and economic performance.
Meet process requirements: Pump performance must satisfy process design requirements. This is the basic rule for pump selection.
Prefer pumps with simple structures: These pumps offer higher reliability, easier maintenance, and lower lifecycle costs. For example, single-stage pumps are simpler than multistage pumps; vane pumps are simpler than reciprocating pumps.
Select pump types based on application: Centrifugal pumps are common because of their high speed, small size, light weight, simple structure, non-pulsating flow, stable performance, and easy maintenance. They are preferred in most cases.
However, in special scenarios such as metering, small flow with high head, high gas content, or high viscosity, other pumps, metering pumps, vortex pumps, reciprocating pumps, rotary pumps, must be used.
Consider environmental and operating conditions: Pumps in hazardous or explosive areas must use explosion-proof motors or other safety measures. Environmental factors (temperature, humidity, atmospheric pressure, corrosive air, safety classification) and operational factors (suction pressure, discharge pressure, duty mode, installation convenience) must also be checked.
Choose materials and structures based on the medium: Pump wetted parts must meet corrosion-resistance requirements without exceeding needs to avoid unnecessary cost increases. Solid particle hardness, content, medium temperature, and pressure must also be considered. The pump structure should allow easy cleaning.
Determine process requirements: Identify flow rate, head, and other performance parameters.
Choose pump type: Select a suitable pump based on process conditions. Centrifugal pumps are first choice unless special conditions require other types.
Determine pump specifications: Choose a model based on required flow rate and head, considering speed, power, and other parameters.
Consider backup pumps:
For large flow systems: multiple pumps may be needed in parallel
For 50% standby rate: two operating + one standby
For 24-hour continuous operation: one running, one standby, one under maintenance
Work with pump suppliers: When encountering complex situations, cooperation with pump manufacturers helps ensure correct pump selection.
To better understand pump selection, here is an overview of common pump types and their features:
Centrifugal Pumps: These pumps use centrifugal force to transport liquid. They feature high speed, small size, lightweight, simple structure, non-pulsating flow, stable performance, and easy operation and maintenance. Suitable for most applications but not ideal for small flow & high head, high gas content, or high viscosity.
Metering Pumps: These pumps precisely control flow and are suitable for precise dosing applications, such as adding reagents in chemical processes.
Vortex Pumps: These pumps utilize vortices formed inside the pump for liquid delivery. They are simple, compact, lightweight, with small flow and high head. Suitable for small-flow high-head applications, but flow and pressure pulsate.
Reciprocating Pumps: These pumps use piston or diaphragm reciprocation. They offer small flow, high head, and no pulsation. Suitable for applications requiring small flow, high head, and zero pulsation.
Rotary Pumps: These pumps use rotor rotation to transport liquid and are suitable for high-viscosity media such as oils or pastes.
Axial-Flow and Mixed-Flow Pumps: Suitable for large flow and low head conditions.
Self-Priming Pumps: Self-priming pumps are ideal for applications with frequent startup or where priming is inconvenient, such as self-priming centrifugal pumps, vortex pumps, and diaphragm pumps.
Special Pumps: Such as jet pumps, hose pumps, etc., used in special conditions.
To better understand the pump selection process, consider the following example:
A chemical plant needs to pump a corrosive liquid with:
Flow rate: 50 m³/h
Head: 30 m
Temperature: ambient
Density: 1.2 g/cm³
Viscosity: 10 mm²/s
Solid particles < 0.1 mm
No gas content
Determine process requirements: Flow rate 50 m³/h and head 30 m represent a medium-flow medium-head application.
Choose pump type: A corrosion-resistant pump is needed. A centrifugal pump is suitable based on flow and head, but the material must resist corrosion; stainless steel is an option.
Determine pump specifications: Select a centrifugal pump that meets the flow and head requirements, considering speed and power (e.g., 2900 r/min, 5.5 kW).
Consider backup pump: A chemical plant requires high reliability, so a standby pump is recommended.
Work with the supplier: Process details should be provided to the pump supplier to recommend the most suitable model.
Pump selection is a complex process requiring comprehensive consideration of many factors. By understanding basic pump parameters, selection criteria, and selection principles and steps, we can choose pumps more effectively. In practice, selecting the right pump type and model based on process requirements and fluid properties is critical. Cooperation with pump suppliers is also essential, as they can provide professional advice and technical support. Only by correctly selecting pump type and model can pumps operate efficiently and reliably, meet system design requirements, reduce maintenance costs and energy consumption, and improve production efficiency and economic benefits.
