Thread Content
1. Startup procedures for centrifugal pumps 1) Preparations before starting the centrifugal pump ① Inspect the pump and the motor, confirm that the centrifugal pump has been properly installed, that the motor has passed individual testing, that all process conditions are met, that the centrifugal pump is in a ready state for testing, and that the relevant personnel are present at the site. ②Check whether the anchor bolts of the pump and motor are secure. Remove the coupling cover, rotate the pump three times in the direction of rotation, and check whether the couplings are aligned, free from jamming, or any abnormal noises. ③Check whether the lubricating oil in the pump is at 1/2 to 2/3 of the oil level mark; if emulsification occurs, the lubricating oil should be replaced. ④There is a valve for opening the mechanical seal flushing fluid, as well as a valve for turning on the cooling water; these valves ensure smooth operation without any leaks. ⑤ Close the drain pipes at the inlet and outlet as well as those on the pump body, and check whether the inlet and outlet valves are airtight and operate smoothly, as well as whether the pressure gauge functions properly. ⑥ Once all the above checks show normal results, conduct a short trial run of the pump on-site to verify that its rotation direction is correct, then reinstall the coupling cover. 2) Starting the centrifugal pump: ① Open the exhaust valve of the pump, open the inlet valve of the pump; the outlet valve remains closed. Once water starts flowing out of the exhaust valve, close it and simultaneously open the pressure gauge valve. ②Contact the control room to prepare for starting the pump; press the start button to initiate operation, while paying attention to any abnormal noises. ③Once the rated speed is reached and the outlet pressure stabilizes, slowly open the pump outlet valve and adjust the opening degree of the outlet flow control valve to keep the pressure and current values within the specified operational ranges. Note: a. While gradually opening the pump outlet valve, pay close attention to changes in the motor current, pump outlet pressure, and flow rate. If a sudden drop in the pressure reading is observed, close the outlet valve first; wait until the pressure returns to normal before gradually reopening it. b. If a control valve is used at the pump outlet to regulate the flow rate, the outlet stop valve must be fully open. c. The pump should be avoided from operating for long periods with the shut-off valve closed (the time should not exceed 3 minutes). d. When starting a new pump for the first time, the load must be increased gradually until the rated current is reached ； e. While the pump is in operation, the inlet valve must be fully open; it is absolutely not allowed to use the suction valve to regulate the pump’s flow rate in order to avoid cavitation. f. The preparations before starting a routine centrifugal pump, as well as the starting process itself, should also be carried out in accordance with the above procedures. 3) Operation monitoring of centrifugal pumps ① Check whether the pump and motor are operating smoothly without any abnormal noises; regularly feel, listen, observe, and inspect them. ②Check whether the cooling water circulation is normal; an appropriate flow rate is required, with no leaks. ③Check whether the mechanical seal flushing fluid is functioning properly, ensuring an appropriate flow rate is maintained. ④Note that the oil cup should be kept in such a way that the oil level remains visible to prevent false readings; the oil level should be maintained at 1/3 to 2/3 of the level indicator. Lubrication system: no leaks required ； Check the quality of the lubricating oil; if it is emulsified and degraded, it should be replaced immediately. ⑤Is there any unusual odor in or around the pump room or pump? ⑥Check whether the readings on various instruments (vacuum gauge, pressure gauge, ammeter) are normal and stable. Pay special attention to whether the motor current exceeds the rated value; if the current is too high or too low, the machine should be stopped immediately for inspection. Common causes of excessive current include damaged bearings, the impeller getting stuck due to dirt, friction between the impeller cover and the pump casing or pump cover, and failure of the pump’s axial force balance mechanism. Causes of excessively low current include: the outlet valve not being fully open, cavitation or air intake in the pump, blockage in the pump’s flow path, etc. A low pressure gauge reading may indicate a leak inside the pump, such as severe wear of the sealing rings. ⑦Records of the pump’s operation should be kept as required. 2. Shutdown procedures for centrifugal pumps 1) Shutting down the centrifugal pump ① Contact the control room to prepare for the shutdown. ②Close the pump’s outlet valve, turn the motor switch button to the “O” position, and observe that the pump decelerates uniformly before coming to a stop. After the pump is shut down, the following three operations can be carried out as needed to put the pump in standby, long-term shutdown, or maintenance mode: a. If it is to be used as a standby pump after shutdown, the inlet valve should be fully open, the cooling water should continue to circulate, and the sealant valve should be closed. b. If the pump is not to be used for an extended period of time, close the pump’s inlet valve and pressure gauge valve; once the bearing temperature has dropped to normal levels, cut off the cooling water and sealant. c. If the pump body needs maintenance, the inlet valve should be closed, and the pump body drain valve as well as its self-sealing drain valve should be opened to drain all liquid. Then, the cooling water should be turned off, and the electrical department should be notified to cut off the power supply. Finally, the pump body should be cleaned and purged. 2) Switching operation of the centrifugal pump ① Follow the startup procedure to conduct a thorough inspection of the standby pump and prepare it for operation. ②Start the standby pump; once it reaches its rated speed and the pressure stabilizes (within 3 minutes), slowly open the outlet valve of the standby pump. Adjust the flow rate using the control valve. Once the values on the pump’s pressure gauge and ammeter are within the specified range and stable, gradually close the outlet valve of the pump that is currently in operation, striving to maintain a stable flow rate in the main outlet pipe. It is strictly prohibited to allow the system to become empty or to have an uneven flow rate. ③Once the standby pump is operating properly, close the outlet valve of the original pump in operation, and shut down the pump following the standard shutdown procedure. ④Once the standby pump is operating normally, inspections shall be carried out in accordance with the operation monitoring requirements for centrifugal pumps. 3) Maintenance of centrifugal pumps ① Regularly check the quality of the lubricating oil; if emulsification or deterioration is detected, it should be replaced immediately ； During the initial phase of operation of a new pump, the lubricating oil tends to become dirty; it is generally replaced after three months of operation, or in accordance with the manufacturer’s maintenance manual. ②In winter, the pump cooling water should be kept flowing continuously or drained to prevent the pump from freezing. ③The standby pump should be turned over regularly. The cold pump should be turned manually once a day, with each rotation covering an angle of 180° ； Within 1 hour after shutdown, the heat pump should have its shaft rotated every 30 minutes; thereafter, it should be rotated 180° every 8 hours. ④The standby pump should be operated for short periods of time on a regular basis, or used in a switching operation. ⑤The pump should not be operated continuously at conditions where the flow rate is less than 30% of its rated flow. If operation under such conditions is unavoidable, a bypass line must be connected to the pump outlet to meet the requirements of the operating conditions.