The standard centrifugal pump operation procedure is often not shared by many people, but by the technicians themselves who learn and practice through basic instructions from the manufacturer. Since then, the technician has drawn for himself the experience of operating a centrifugal pump in the actual process…
Why is it important to operate the centrifugal pump properly?
Nowadays, centrifugal pumps have been improved in design, materials and applied advanced technology to monitor performance effectively. However, despite all the care in operation and maintenance, engineers are often faced with the statement “The pump has failed and cannot function anymore”.
One of the most common causes of pump downtime is the inability to deliver the desired flow and head. But that’s only one part, there are many other conditions in a pump, not flow or head problems, but are also considered broken and must be stopped as soon as possible. These include issues related to:
- Seals (leakage, loss of exhaust system, cooler, …)
- Pump and motor bearings (out of lubricating oil, coolant, oil contamination, unusual noise,…), leaks from the pump housing, noise, and vibration levels.
- Control panel (engine or turbine).
Often the root cause of problems is the same, but the symptoms are always different. A little care when the first signs of trouble appear can save your pump from failure.
There are two types of problems most commonly encountered with centrifugal pumps: poor design, poor performance, and poor maintenance practices.
This article, presented by Thai Khuong in 4 parts, covers all aspects of centrifugal pump operation, maintenance, and troubleshooting, making it easy for you to increase the service life and reduce operating costs for your pump. your centrifugal pump.
Notes before operating centrifugal pump
Before starting the centrifugal pump operation procedure, it is necessary to prepare and follow these notes for the smoothest start-up.
- Since centrifugal pumps are not self-priming, it is necessary to fill the pump with fluid or vacuum the piping before operating the unit.
- Do not operate the pump below the minimum rated flow or close the suction and discharge valves. Because these things can cause the centrifugal pump to fail easily.
- Always disconnect and power off the driver before performing any installation or maintenance tasks.
- Check the direction of rotation of the pump in the direction of the arrow shown on the pump body (clockwise rotation). Starting the centrifugal pump in the opposite direction can lead to metal parts friction, heat generation, and water line breakage.
- Connect to a stable voltage source: 3 phase (380V, 50Hz) or 1 phase (220V, 50Hz) depending on different centrifugal pump models.
- The system should be flushed and cleaned thoroughly to remove all dirt or debris in the piping. This is to avoid damage when starting the pump.
- If the temperature of the pumped liquid exceeds 93°C, the pump should be warmed up before starting.
- Pass a small amount of liquid through the pump until the housing temperature is within 38°C of the liquid temperature before starting the centrifugal pump. This helps the pump avoid thermal shock to the bearing (liner), impeller (impeller) and avoid damaging the mechanical seal (mechanical seal).
- Open all backend systems and let them run for at least 10 minutes. Wait until the entire backend system is stable and then take the next step. These auxiliary systems include a lubricating oil system, closed exhaust system, cooling, and insulation system.
After the centrifugal pump test is completed, proceed to start the unit according to the procedure below.
Centrifugal pump operation process
Before starting the pump, do the following:
- Step 1: Open the suction valve
- Step 2: Open any coolant lines present in the pump system
- Step 3: Depending on system conditions, you can fully or partially open the exhaust valve
- Step 4: Start the driver
- Step 5: Open the relief valve slowly until the pump reaches the desired flow
- Step 6: Check the pressure gauge to make sure the pump reaches the correct discharge pressure
- Step 7: If, after the above check, the pump has not reached the required discharge pressure, perform the following steps:
- Stop the driver
- Restart the pump
- Restart the driver
- Step 8: Monitor the operation of the pump
- Perform a pump test for bearing temperature, vibration, and noise during operation
- If the pump is operating beyond normal levels, the pump should be turned off immediately and the problem corrected
- Step 9: Repeat steps 7 and 6 until the centrifugal pump ensures normal operation.
Some important notes in centrifugal pump operation
- The maximum frequency of starting the pump is not more than 12 times/hour.
- The pressure difference should not be lower than the design point, nor should it cause fluctuations in the operating parameters of the system. The pump output manometer value is equal to the differential pressure plus the input manometer value.
- Make sure that the current does not exceed the value displayed on the motor meter.
- During test operation, the power of the motor should be considered. If the actual density of the medium is less than the specific gravity of the test medium, it is necessary to strictly control the valve opening during the test run to avoid overloading or burning the engine.
After completing the centrifugal pump operation procedure according to the above steps, it is necessary to pay attention to the shutdown operation to ensure that the centrifugal pump can work normally and prolong the life of the equipment.
Steps to stop centrifugal pump operation
Steps you need to follow to stay safe:
- Step 1: Slowly close the drain valve until the flow reaches the minimum flow
- Step 2: When the circulation line has a minimum flow, proceed to close the relief valve when the circulation valve is fully open, then disconnect the power to stop the pump. If the pump has a high temperature, the water circulation should be stopped when the temperature is below 80°C, and the sealing system (including discharge liquid, sealing gas) should be stopped after 20 minutes of stopping the centrifugal pump.
- Step 3: Backup pump: The suction valve is fully open and the discharge valve is completely closed (when there is a minimum flow), leaving the pump in a state of sufficient suction pressure. It is advisable to continue using the backup pump coolant to keep the lubricating oil level below the specified level. In particular, in winter, care should be taken to keep the hot and cooling water pipes unclogged.
- Step 4: After stopping the pump, first need to close the dry nitrogen inlet valve of the sealing system, reducing the pressure in the sealing chamber. Then completely drain the liquid in the pump and the coolant in the cooling system so that the pump body has a pressure drop to zero. At the same time, the remaining substances in the pump are purged, all valves is closed and all power sources are disconnected.
Important Notes When Stopping Centrifugal Pump Operation
- All of the above processes need to ensure health, safety and environmental requirements.
- The backup pump must be controlled according to regulations.
- If the pump stops the motor first and then closes the outlet valve, the high-pressure liquid in the extrusion line may back into the pump. This causes the impeller to rotate at high speed and lead to pump failure.
- If the pump is not used for a long time or the ambient temperature is lower than 0°C, the water in the pump should be drained.
Centrifugal pump inspection and maintenance
Centrifugal pumps need to be monitored regularly and precisely according to a specific plan implemented by highly trained personnel.
Periodic maintenance of centrifugal pumps is an extremely important step that should not be ignored, if you want to increase the service life and reduce the operating costs of centrifugal pumps.
6 parameters to regularly monitor on a centrifugal pump
- Suction pressure (Ps)
- Discharge pressure (Pd)
- Flow (Q)
- Pump speed (N)
- Pump efficiency (η)
During periodic pump inspection, only easy-to-follow factors such as pressure, temperature, vibration, etc. can be checked, etc. But during quarterly inspection, alignment should also be checked. shaft and oil level.
Below is the work to be done for centrifugal pump maintenance that you can refer to!
Issues that need to be checked on a daily basis
- Check the level and condition of the oil through the glass of the pump holder
- Check for abnormal noise, vibration and bearing temperature
- Check pump and pipes for leaks
- Vibration Analysis
- Check discharge pressure
- Check temperature
- Check the sealing chamber and stuffing box for leaks
- Make sure that there are no leaks from the mechanical seal
- Adjust or replace the sealing ring (paking) in the sealing housing if excessive leakage is found
Issues that need to be checked every 3 months
- Check if the base and bolts of the centrifugal pump are loose
- Check the mechanical seals, if they don’t work properly, they need to be replaced as required
- Change oil at least every three months (2000 operating hours)
- Change the oil regularly if they work in adverse environmental conditions or other conditions that could contaminate or damage the oil
- Check that the shaft is aligned and readjust if necessary
Problems that need annual inspection on centrifugal pumps
Perform the following checks once a year:
- Check pump capacity
- Check pump pressure
- Check the power of the pump
If the pump performance does not meet the process requirements, do the following:
- Remove the pump separate parts
- Check out the details inside
- Replace worn parts according to centrifugal pump operation
Maintenance of all pump components is also important. It is best to service the centrifugal pump every 6 months, or more often depending on the frequency of use. Inspection and cleaning should be done at regular intervals. This is to prevent debris from accumulating and blocking the flow through the filter.
The best solution to avoid unexpected repair costs or unforeseen damage to production quality, is to ensure that your centrifugal pump is being monitored and take appropriate preventive maintenance measures. fit.