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This post was last edited by sdwfsgyykai on 2018-6-2 at 14:23. A centrifugal pump is a type of vane pump; it relies on the rotating impeller, and through the interaction between the vanes and the liquid as the impeller rotates, the vanes transfer mechanical energy to the liquid, thereby increasing its pressure energy and enabling the transport of the liquid. Before starting a centrifugal pump, the operator responsible for it should carry out the following inspections on different models of centrifugal pumps to ensure that they can operate safely. So, what are the main precautions for starting and stopping centrifugal pumps? The technical staff from Hunan Zhongyi Water Pumps will explain them to you below. Steps for starting a centrifugal pump: 1. Before starting, manually turn the coupling or shaft of the horizontal centrifugal pump slowly to check whether the pump rotates smoothly, without any signs of jamming or difficulty in turning it. Check whether there are any foreign objects inside the pump body, and whether the impeller is rubbing against the pump body. Also, examine whether the bearings make abnormal noises or are not properly tightened. For pumps with packing seals, check whether the packing is too tight or too loose; if it’s too tight and the pump won’t turn, loosen it slightly. If it’s too loose, water leakage will occur, so tighten the packing gland gradually as the pump operates. 2. Check and retighten all the unit bolts. Check whether the lubricating oil and grease in the centrifugal pump bearing housing are clean; otherwise, they should be replaced. The amount of grease should be 2/3 of the bearing housing volume, and the lubricating oil level should be within the range indicated by the sight glass. 3. Before starting the centrifugal pump, the outlet gate valve should be closed first; this is done to prevent the motor from being damaged due to excessive flow at the moment of startup. After the pump starts, the outlet gate valve should be gradually opened, with this process completing within 3 minutes at most. The valve should not remain closed for more than 5 minutes, as this could cause the liquid being pumped to circulate inside the pump for an extended period, leading to overheating of the pump and damage to its components. 4. The gate valve on the outlet pipe must be closed; this prevents any flow of water from the pump, thereby reducing the starting current of the motor and facilitating its smooth start-up. Once the pump has started properly, the gate valve should be gradually opened. A centrifugal pump creates a vacuum by means of the centrifugal force generated by the impeller, which in turn draws water upward. Therefore, when starting a centrifugal pump, it is necessary to first close the outlet valve and fill it with water. The water level must be above the impeller area in order to expel the air from the centrifugal pump and enable it to start. Once it starts, a vacuum is created around the impeller, which draws water upward; the valve then opens automatically to lift the water. Therefore, the outlet valve must be closed first. 5. When starting a centrifugal pump, the outlet valve must be closed first. An important characteristic of centrifugal pumps is that their flow rate is high when the pressure (head) is low, as can be seen from the pump’s performance curve. The power of the pump is proportional to its flow rate. When the pump starts, there is no pressure in the pipeline, which results in a high flow rate and thus high pump power. Additionally, the rotating parts of the motor and pump need to accelerate from a stationary state to high speed, which inevitably leads to a high starting current. Therefore, the outlet valve is closed to prevent water from being discharged by the pump during startup, thereby minimizing the pump’s power. Once the pump reaches its rated speed, the outlet valve is gradually opened to increase the water flow rate, allowing the motor current to rise steadily to the rated value. Switching and shutting down of centrifugal pumps: 1. A thorough inspection and all necessary preparations must be carried out before starting the standby pump. 2. Open the pump inlet valve to fill the pump chamber with the medium, and use the vent valve to remove all air. 3. Start the motor, then check the vibration levels in various parts as well as the temperature of the bearings. Ensure that everything is normal, that the current is stable, and that the pressure inside the pump is higher than the normal operating pressure. Gradually open the outlet valve, while simultaneously closing the outlet valve of the pump that is currently in operation until it is fully closed, after which stop the pump. When shutting down a centrifugal pump, the following points should be noted: 1. First close the pump’s outlet valve before stopping the pump, to prevent it from reversing. 2. When stopping the pump, pay attention to the speed reduction of the shaft; if this process takes too little time, check whether there is any grinding or jamming inside the pump. 3. If it is a hot oil pump, stop the flushing oil or seal oil first, and open the balance or connection valve of the inlet pipeline to prevent the inlet and outlet pipelines from freezing and cracking. 4. If the pump needs repair and the inlet valve is also closed, it should be determined whether to purge and depressurize based on the nature of the repair work; if there is pressure inside the pump, it may be due to the inlet and outlet valves not being sealed properly. Centrifugal Pump Start-Stop Operation Procedure Table: Procedures and Steps. Pre-operational checks: ① Check that all connection bolts are tight and that all instruments are in good condition. ②Check whether there is sufficient lubricating oil (grease) in all lubrication points. ③Check whether the electrical components in all areas are in good condition. ④The electrician wears insulating rubber shoes and gloves to check whether the motor’s insulation resistance meets the requirements. ⑤It is a high-voltage motor; contact the substation to determine the pump startup time and the power supply circuit to be used. ⑥For those equipped with an auxiliary lubrication system or an auxiliary cooling system, it is necessary to check whether these auxiliary systems are functioning properly. ⑦Pumps that have been out of service for an extended period should be rotated 3 to 5 times; the rotation should be smooth with no signs of jamming. ⑧Reverse the pipeline flow and close the outlet valve and the return valve. ⑨Empty or fill the pump. Operation steps ① If there is an auxiliary lubrication system or an auxiliary cooling system, start the auxiliary system first to ensure it is functioning properly. ②Arrive at the designated location at the time agreed with the substation, and get ready to start up (it is a centrifugal pump driven by a high-voltage motor; the electrical part should be operated by an electrician). ③Press the start button and observe the current changes; if it exceeds the limit, stop the pump immediately, and restart it after fixing the fault. Once the outlet pressure stabilizes, slowly open the outlet valve, and adjust the pump’s outlet valve or return valve as well as the motor frequency until the production requirements are met and the pump operates under the most optimal parameters. After operation, once the pump has started running, it is necessary to check the conditions of the liquid in the pump, the lubrication, the cooling water, the temperature of the packing, any leaks in the packing, and the temperature of each bearing, by using the methods of listening, observing, touching, and smelling. ①The temperature of the rolling bearings in pumps and motors must not exceed 80°C (the temperature of sliding bearings must not exceed 70°C). ②Check the liquid level in the supply system to prevent pump drying out; there should be no abnormal noises, burning smells, or smoke inside the pump. ③The motor operates within the range of -5% to +10% of the rated voltage, and the stator temperature does not exceed the values specified on the nameplate. Risk identification 1: Pressure injury to people caused by not turning sideways when operating switches and valves ； 2. Explosion-proof tools were not used during operation ； 3. Failing to stand on insulating rubber when starting or stopping the equipment. Precaution 1: When turning on or off valves, turn sideways to avoid being injured by pressure ； 2. When performing relevant operations, explosion-proof tools should be used ； 3. When starting or stopping the equipment, one must stand on insulating rubber to avoid electric shock accidents. Emergency response: 1. In the event of a mechanical injury, take immediate action to remove the injured person from the dangerous area, provide first aid and bandaging, and then transport them to the hospital for further treatment. 2. Once a person gets an electric shock, immediately cut off the relevant power supply or remove the victim from the power source, then provide first aid to the victim; in severe cases, take them to the hospital.