When Starting, Stopping, And Switching Centrifugal Pumps, These Must Be Noted!

Jul 09, 2025

The three processes of starting, running, and stopping a centrifugal pump are crucial for the normal operation of the equipment itself and the entire workflow. Next, let's summarize the common pump start stop operation steps and the precautions to be taken during operation.

Preparation work before starting the pump

1. Pump filling (except for the submersible pump, all other pumps must be filled with the pump chamber before starting (the first time the self-priming pump is started))

2. Backflow device pump: Open the shut-off valve of the inlet pipeline, open all exhaust pipelines, discharge gas, slowly rotate the rotor, and close the exhaust valve when there are no bubbles in the pumped medium.

3. Pump suction device: Open the shut-off valve of the inlet pipeline, open all exhaust pipelines, discharge gas, inject into the pump (the suction pipeline must be equipped with a bottom valve), slowly rotate the rotor, and when there are no bubbles in the pumped medium, close the exhaust valve.

4. Open all auxiliary systems and require them to work for at least 10 minutes until the entire auxiliary system is stable before proceeding to the next step. The auxiliary systems include the lubricating oil system, sealing and flushing system, cooling and insulation system, etc;

5. Perform a turning inspection on the equipment to ensure that it rotates smoothly; Tap the motor and check again if the pump rotation direction is correct; After confirmation, fix the coupling guard securely.

6. The dry gas seal system is put into use for the pump equipped with a dry gas seal system. Open the nitrogen inlet valve and pressurize the sealing chamber. The gas source pressure of the dry gas seal must be between 0.5 and 1.0 Mpa. Each pump adjusts the sealing chamber pressure and flow rate according to specific requirements.

Pump start-up

1. Confirm that the suction valve is fully open and the discharge valve is closed or slightly open; When there is a minimum flow pipeline, the discharge valve is fully closed and the minimum flow valve is fully opened.

2. Close the shut-off valve of the outlet pipeline (minimum flow must be ensured);

3. Start the motor to bring the pump rotor to operating speed;

4. Slowly open the outlet valve to ensure that the outlet pressure and flow rate of the pump reach the specified values. At the same time as opening the outlet valve, the motor current change should be checked to avoid motor overload. When the flow rate increases, attention should also be paid to whether there are any abnormal leaks in the pump seal, whether the pump vibration is normal, whether there are any abnormal sounds in the pump body and motor, changes in outlet pressure, etc. If the pump has abnormal leaks, abnormal vibrations, abnormal noise, or outlet pressure lower than the design value, the cause should be identified and dealt with.

5. After the pump is running normally, check the outlet pressure, outlet flow rate, motor current, temperature of bearings and seals, oil level of lubricating oil, pump vibration, noise, and leakage of seals; Close the valve of the minimum flow bypass according to the process requirements. Keep records of the operation of relevant equipment.

be careful:

(1) The maximum starting frequency of the pump cannot exceed 12 times per hour;

(2) The pressure difference cannot be lower than the design point, nor can it cause fluctuations in performance parameters in the system. The outlet pressure gauge value of the pump is equal to the pressure difference plus the inlet pressure gauge value;

(3) The reading on the ammeter at full load should ensure that the current does not exceed the value on the motor nameplate;

(4) The motor equipped with the pump may be selected based on the actual medium density according to the buyer's requirements. When conducting trial operation, the power of the motor should be considered. If the actual specific gravity of the medium is smaller than that of the trial operation medium, please strictly control the valve opening during the trial operation to avoid motor overload or even burnout. If necessary, contact must be made with the pump manufacturer.

Pump shutdown

1. Slowly close the discharge valve until the flow reaches the minimum flow rate.

2. Cut off the power, stop the pump, and close the outlet valve.

3. When there is a minimum flow bypass pipeline, close the discharge valve with the bypass valve fully open, and then cut off the power to stop the pump. The high-temperature pump can only stop circulating water when the temperature drops below 80 ℃; The sealing system (flushing liquid, sealing gas) should be stopped after 20 minutes of pump shutdown depending on the situation.

4. Backup pump: The suction valve is fully open and the discharge valve is fully closed (when there is a minimum flow bypass pipeline, the bypass valve is fully open and the discharge valve is fully closed), so that the pump is in a full suction pressure state. The cooling water of the standby pump should continue to be used, and the lubricating oil level should be kept not lower than the specified level. Special attention should be paid to checking in winter, keeping the heating wire and cooling water unobstructed, and avoiding freezing.

5. The standby pump should be turned according to regulations.

6. After parking, for pumps that require maintenance, first close the nitrogen inlet valve of the dry gas sealing system to relieve pressure in the sealing chamber. Then completely discharge the liquid inside the pump and the cooling water in the cooling system, so that the pressure inside the pump drops to zero. The remaining material in the pump is blown clean, all valves are closed, and power is cut off by contacting the substation.