How much do you know about the selection errors of Dalian Chemical Pump?

The selection of pumps for Dalian Chemical is a crucial step in ensuring the stable operation of the process flow, but in practical operation, misunderstandings often arise due to insufficient understanding of operating conditions, parameters, or equipment characteristics. The following are common misconceptions and explanations to help avoid selection errors:

1、 Neglecting the complexity of medium characteristics

Misconceptions manifested as:

Only focus on flow rate and head, ignoring medium corrosiveness, viscosity, solid content, etc

For example, when transporting strong acids (such as sulfuric acid) or highly corrosive media (such as chloride ion solutions), using ordinary cast iron or stainless steel pumps can cause rapid corrosion and perforation of the impeller and pump casing.

Insufficient understanding of material adaptability to high and low temperature media

For example, when transporting molten salt (high temperature) or liquid oxygen (low temperature), failure to use high-temperature resistant alloys (such as Hastelloy) or low-temperature resistant stainless steel (such as 304L) can cause material thermal expansion and contraction deformation or brittle fracture.

Improper selection of medium containing solid particles

Using a regular centrifugal pump to transport slurry, mud, etc. may cause blockage or increased wear due to small impeller clearance and poor wear resistance (a positive displacement pump made of wear-resistant materials or a centrifugal pump designed specifically for impurities should be selected).

Solution principle:

Priority should be given to clarifying the full characteristics of the medium, including corrosiveness, viscosity, density, temperature, solid content, volatility, etc., and matching the material (such as fluoroplastic, duplex steel) and structure (such as open impeller, unsealed magnetic pump) of the pump.

Special media follow industry standards: explosion-proof motors are required for transporting organic solvents, and leak free shielded pumps or magnetic pumps are required for transporting highly toxic media.

2、 Misconception of "excessive safety factor" in flow and head parameters

Misconceptions manifested as:

Blindly amplifying parameters leads to 'big horse pulling small car'

For example, the actual demand is a flow rate of 50m ³/h and a head of 30m, but choosing a pump with a flow rate of 100m ³/h and a head of 50m results in:

The pump operates in the low efficiency zone (deviating from the high efficiency point), resulting in an increase of over 30% in energy consumption;

High flow design may increase the required NPSHr and pose a risk of cavitation;

Excessive motor power increases procurement and operating costs.

Ignoring the dynamic requirements of process fluctuations on parameters

For example, when discharging from an intermittent reactor, the flow rate may change with the decrease of liquid level, and no adjustable margin (such as variable frequency control) is reserved, resulting in frequent replacement of pumps or pipeline modifications in the later stage.

Solution principle:

Accurate parameter calculation: Determine parameters based on the maximum/minimum operating conditions of the process flow, combined with pipeline resistance (detailed calculation of losses along the way and local losses is required). The safety factor is usually taken as 1.1-1.2 to avoid excessive amplification.

Adopting adjustable speed schemes, such as variable frequency motors or variable speed drives, to adapt to flow fluctuations while reducing energy consumption.

3、 Calculation and verification of NPSH is missing

Misconceptions manifested as:

Relying solely on NPSHr data from pump samples, ignoring on-site suction conditions

For example, the pump is installed at a height of 10 meters from the storage tank, without calculating the pressure loss of the suction pipeline, resulting in insufficient effective cavitation head (NPSHa) and frequent cavitation during operation, manifested as head fluctuations and abnormal noise.

Insufficient understanding of cavitation risks in high viscosity or easily vaporized media

For example, when transporting high-temperature hot water (close to boiling point), the influence of temperature on saturated vapor pressure was not considered, resulting in NPSHa approaching the critical value of NPSHr and the pump being unable to operate stably.

Solution principle:

Strictly perform NPSHa calculation: combine installation height, pipeline resistance, medium temperature and other parameters to ensure that NPSHa ≥ NPSHr+safety margin (usually 0.51m).

Advanced simulation of special working conditions: For easily vaporized media (such as liquefied gas), manufacturers may be required to conduct cavitation tests or use reverse flow installation (with the liquid level higher than the pump inlet) to increase NPSHa.

4、 Ignore installation environment and system compatibility

Misconceptions manifested as:

Not considering on-site space limitations and maintenance convenience

For example, using a large multi-stage centrifugal pump in a narrow workshop makes it impossible to disassemble the impeller during maintenance; Or the lack of reserved space for motor heat dissipation may cause the motor to overheat and burn out.

The pipeline design does not match the pump interface

The diameter of the suction pipe is smaller than the inlet size of the pump, resulting in a significant increase in local resistance and a decrease in NPSHa; Or the discharge pipe may be too thin, causing pressure buildup and resulting in pump overload.

Unassessed vibration and noise requirements

In laboratories or noise sensitive environments, using high-speed centrifugal pumps (such as 2900r/min) instead of low-speed volumetric pumps can result in environmental non-compliance.

Solution principle:

On site inspection of installation conditions: confirm space dimensions, pipeline routing, power specifications (such as explosion-proof level), and select suitable pump structures (such as horizontal, vertical, and pipeline).

Follow the pipeline design specifications: the suction pipe should be short and thick (1-2 sizes larger than the pump inlet), and avoid sudden diameter changes; The discharge pipe needs to be equipped with a check valve and pressure gauge for monitoring the working conditions.

5、 Blindly pursuing low prices or brands leads to performance compromise

Misconceptions manifested as:

Low price selection ignores long-term costs

Choosing low-priced cast iron pumps to transport corrosive media has a low initial cost, but due to corrosion and scrapping within six months, the replacement cost is much higher than the initial cost savings.

Superstition in imported brands, neglecting localization adaptation

The performance parameters of foreign brand pumps may be based on standard operating conditions (such as room temperature clean water), but domestic chemical media are complex, and manufacturers are not required to adjust them specifically (such as impeller material and sealing form), resulting in a "mismatch between water and soil".

Solution principle:

Comprehensive life cycle cost: Calculate procurement cost+energy consumption cost+maintenance cost+replacement cost, and prioritize cost-effective solutions (such as corrosion-resistant engineering plastic pumps or alloy pumps).

Deep technical communication with manufacturers: provide detailed operating data, request selection calculation sheets, and confirm the compatibility of key components such as materials, seals, and bearings.

6、 Other common misconceptions

Improper selection of sealing form

Misconception: Ordinary mechanical seals are used for high viscosity or granular media, which can cause wear and leakage of the sealing surface (bellows seals or labyrinth seals should be selected).

Correct: Select the sealing type based on the characteristics of the medium, such as single end mechanical seal for cleaning liquids and double end seal+flushing system for hazardous media.

Neglecting the explosion-proof and energy efficiency rating of the motor

Using non explosion proof motors in flammable and explosive environments can cause safety accidents; Or choose low energy efficiency motors (such as IE1 level), which do not comply with energy-saving policies and result in high long-term electricity costs.

Not considering the backup pump setting

The key process is not equipped with a backup pump. If the main pump fails and the entire line is shut down, a 100% or 50% backup capacity should be set according to the importance of the process.

Selection core logic

The selection of chemical pumps should follow the principles of "working condition priority, accurate data, margin, and cost consideration" to avoid single dimensional decision-making. Suggested step-by-step execution:

Clarify the characteristics of the medium and process parameters (flow rate, head, temperature, corrosiveness, etc.);

Calculate key parameters (NPSHa, pipeline resistance, power, etc.);

Match pump type and material (centrifugal pump, positive displacement pump, corrosion-resistant material, etc.);

Technical confirmation with the manufacturer (obtaining selection reports, material certificates, and testing data);

Consider installation and maintenance convenience (space, spare parts supply, operational difficulty).

Through systematic analysis, selection errors can be avoided to the greatest extent possible, ensuring the safe and efficient operation of pumps in chemical systems.