The centrifugal pump is a core equipment widely used in the three major industries of water treatment, petrochemical industry and agricultural irrigation. Its high efficiency, energy saving and reliability make it widely used in many industries. As key equipment, centrifugal pumps are used to varying degrees in various industries, and their design and maintenance need to take actual working conditions into consideration. Therefore, in actual use, reasonable operating procedures are crucial. It can not only help users better understand and manage the operation of the equipment, but also effectively improve the service life and economic benefits of the equipment.

 

I: 7 major operating steps of centrifugal pump:

Step 1: "5 inspections" before starting the centrifugal pump

1. Check the status of the centrifugal pump and motor to ensure that there is no obvious abnormality and meet the working conditions

 

2. Check whether the connection of each part is good, whether the anchor bolts are firm, and whether the lubricating oil is sufficient (the oil level needs to be kept between 1/2-2/3) ‌

 

3. Fill the pump, check the water level, and the pipe and pump body must be filled with water (water can be seen from the exhaust hole with the naked eye)

 

4. Check the valve: the inlet valve is fully open, and the outlet valve is closed to 1/4 first (to prevent overload at startup)

 

5. Check the instrument: Is the pressure gauge zeroed? Is the voltage normal? Is the ground wire securely connected?

 

Step 2: Test the feel of the gear by turning the coupling manually for 2 to 3 turns. If it is normal, it will be smooth and without jamming. If jamming and friction sound occur, stop the machine immediately for inspection.

 

Step 3: Press the centrifugal pump switch, press the start button and release it immediately (no more than 2 seconds). Correct steering: The centrifugal pump body vibrates little and the sound is stable (refer to the direction of the arrow on the pump body). If reversal occurs, cut off the power immediately and replace the motor wiring.

 

Step 4: Formal start of the centrifugal pump, slowly open the outlet valve, and control the process within 30 seconds. At the same time, observe the pressure gauge: stable in the green area (such as 0.4-0.6MPa). If the pressure fluctuates, it may be air intake. If the current exceeds the red line, you need to close the valve immediately.

 

Step 5: During the operation of the centrifugal pump, you must "look at three things and listen at one time". Look at the pressure: fluctuation ≤10%, look at the temperature: bearing temperature ≤75℃, look at the leakage: leakage at the machine seal is ≤3 drops per minute, and listen to the abnormal sound: humming sound is normal, metal friction sound is dangerous!

 

Step 6: The shutdown sequence must be correct. First close the outlet valve (to prevent water hammer impact), then press the stop button, close the pressure gauge hand valve, wait until the pump temperature drops below 80 degrees before stopping the cooling water, and finally close the inlet valve as needed (if it is out of service for a long time), and drain the inside of the pump body.

 

Step 7: Winter special operation, when the ambient temperature is less than 5℃: the water in the centrifugal pump should be drained in time to prevent freezing and cracking, and then low-temperature grease should be added to the bearings

 

II: 5 taboos during the operation of centrifugal pumps

1: No idling must not exceed 30 seconds, and the centrifugal pump body should be affixed with a "No idling" label and a dry-running protector

 

2: Do not use the valve to "hold pressure" to adjust the flow, which will seriously cause the motor to overload and burn out. If there is a need for adjustment, the centrifugal pump variable frequency motor or cutting impeller should be replaced

 

3: Pumping liquid containing particles without a filter can easily break the impeller and incur high replacement costs

 

4: The centrifugal pump directly pumps high-temperature liquid. During the use of the centrifugal pump, the temperature difference of ＞50℃ will explode the seal, and it is generally preheated in advance (temperature rise ≤3℃ per minute)

 

5: Maintenance under pressure, this illegal operation is expressly prohibited, and the correct operation should be shutdown → pressure relief → hang up → double confirmation

 

III. FAQ

Question 1: No water after starting?

- Check 1: Is the centrifugal pump filled with water? (Re-exhaust)

- Check 2: Is the inlet valve blocked? (Disassemble and check)

- Check 3: Is the motor reversed? (Change the line sequence)

 

Question 2: Sudden large vibration during operation?

Possible causes:

1. Impeller blocked (stop and clean)

2. Loose anchor bolts (tighten diagonally)

3.Bearing wear (locate the abnormal sound point with a stethoscope)

 

Question 3: Severe water leakage at the seal?

- Temporary treatment: tap the sealing gland lightly (adjust the gap)

- Fundamental solution: replace the mechanical seal

As the "liquid porter" in the industrial field, centrifugal pumps are responsible for more than 70% of the world's fluid transportation tasks. From waterworks to petroleum refining, this rotating machinery's impellers spin thousands of times per minute, creating astonishing industrial efficiencies. This article will disassemble the advantages and disadvantages of centrifugal pumps in plain language, and attach a practical selection parameter table and a guide to avoid pitfalls.

 

1. Advantages of centrifugal pumps

1. Simple structure:

The centrifugal pump has only 6 main components: impeller, pump body, shaft, bearing, seal, coupling, simple structure, few failures, durable, and low manufacturing and later maintenance costs.

 

2. Uniform flow

The flow and pressure of the centrifugal pump are stable, and the operation is smooth, which is very important for use scenarios that require stable flow output.

 

3. High efficiency

The efficiency curve is parabolic: the best efficiency point (BEP) can reach 92%. The efficiency of the centrifugal pump is much higher than other types of pumps, which can reach more than 50%, which can save a lot of energy.

 

4. Wide range of applications

According to the structure: single-stage/multi-stage, single-suction/double-suction

According to the medium: corrosion-resistant pump, impurity pump, high-temperature pump

According to the installation: vertical, horizontal, pipeline

Centrifugal pumps can transport a variety of liquids such as clean water, sewage, seawater, oil and chemicals, and are widely used in municipal engineering, agricultural irrigation, industrial production, ships and other fields.

 

5. Stable flow and easy adjustment

Centrifugal pumps can work stably in a wide flow range, and the flow can be easily adjusted by adjusting the speed, impeller diameter or changing the opening of the pump outlet valve.

 

2. Disadvantages of centrifugal pumps

1. Before running the centrifugal pump, the pump must be filled with liquid, because if the centrifugal pump runs dry for 5 minutes, the life of the bearing will be reduced by 80%, greatly increasing the failure rate of the centrifugal pump.

 

2. Centrifugal pumps are sensitive to cavitation, which causes damage to the impeller. Cavitation must be prevented during use. The required NPSHr is 3-5 times higher than that of the positive displacement pump!

Anti-cavitation formula:

Actual NPSHHa = atmospheric pressure (10.33m) - vaporization pressure - suction line loss - installation height

Safety criteria: NPSHa ≥ NPSHr + 0.5m

 

3. Centrifugal pumps are sensitive to high-viscosity liquids. The higher the viscosity, the lower the efficiency and performance. They are not suitable for high-viscosity fluids and need to choose other types of pumps (such as screw pumps, gear pumps, etc.).

4. The head of a centrifugal pump is greatly affected by the flow rate. When the flow rate deviates from the design, the head will drop significantly.

 

III. Comparison table of centrifugal pump selection parameters

Centrifugal pumps are like "panacea" in the industrial field. Their universal advantages coexist with the defects of working condition sensitivity. Therefore, detailed working condition simulation must be carried out when purchasing. For special medium transportation, the "centrifugal pump +" combination solution can be considered. It is recommended to ask the manufacturer to recommend a suitable centrifugal pump combination solution.