Operation of centrifugal pumps
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Operation of centrifugal pumps: The correct way to operate a centrifugal pump is to first open all the inlet valves and close the outlet valve. Then start the motor; once the rotational speed is normal, the outlet valve can be gradually opened to adjust the pump to the desired operating conditions. The correct way to operate a centrifugal pump: The operation of a centrifugal pump can be divided into three steps, namely startup, operation, and shutdown. Start-up: The following preparations should be made before starting: (1) Check the condition of the water pump equipment. (2) The bearings are properly filled with oil, the oil level is normal, and the oil quality is satisfactory. (3) Open all the inlet valves of the centrifugal pump. (4) Fill the pump with water or use a vacuum pump to draw in water (excluding backflow), then open the vent valve to release air. (5) Check for leaks at the shaft seal; a slight drip from the packing seal is acceptable. (6) The motor rotates in the correct direction. Once the above preparatory work is completed, the motor can be started. Once its speed is normal, check the pressure and current, and pay attention to any vibrations or noises. Once everything is normal, gradually open the outlet valve and adjust it to the desired operating condition; be careful that the valve should not remain in idle operation for more than 3 minutes. During operation, routine inspections are carried out, and there are four aspects to be checked: 1. Inspection of bearings (1) The bearing temperature should not exceed 75°C. (2) The bearing chamber must not be flooded with water or contaminants, and the oil must not become emulsified or turn black. (3) When a rolling bearing is lubricated with thin oil, the oil level should not be below the center line of the oil gauge. (4) Are there any abnormal noises? Abnormal sounds usually occur when rolling bearings are damaged. 2. Are the readings of the vacuum gauge, pressure gauge, and ammeter normal? (1) The pointer of the vacuum gauge should not swing excessively; excessive movement may cause vaporization at the pump inlet. Additionally, the reading on the vacuum gauge should not be too high, as this could indicate that the inlet valve is blocked or stuck, or that the water level in the suction tank has dropped. (2) If the reading on the outlet pressure gauge is too low, it may be due to severe wear of the sealing ring and guide vane sleeve. The gap between the stator and rotor is too large, or the outlet valve is opened too wide, resulting in high flow rate and low head pressure. (3) If the ammeter reading is too high, it may be due to a high flow rate or friction between the stator and rotor. 3. Does the pump unit generate excessive vibration? The reasons for this vibration include: (1) Misalignment of the shaft axes of the water pump and the motor. (2) The foot bolts of the pump or motor are loose, or the foundation is not solid. (3) Unbalanced rotor mass. (4) When the pump operates at low flow rates, radial forces, backflow, and cavitation occur. 4. Is the sealing functioning properly? (1) A K-type dynamic seal should not leak when it is operating normally. (2) In cases with a cooling water system, check whether the water flow is normal. Shutting down the pump: (1) When shutting down a centrifugal pump, the outlet valve should be closed first, to prevent backflow of pressurized water from the outlet pipe into the pump in case the check valve fails, which could cause the impeller to rotate in the reverse direction and lead to damage to the pump. (2) If the inertia is low when stopping the pump, that is, the pump stops quickly after power is cut off, it indicates that there is wear or eccentricity inside the pump. Conclusion: The three steps of starting, operating, and stopping a centrifugal pump are all important, but the most crucial one is the adjustment of the outlet valve. If it is in the suction state, the opening degree of the outlet valve can be relatively larger; if it is in the backflow state, the opening degree of the outlet valve can be relatively smaller. The operating point of the outlet valve should be as close as possible to the pump’s design point; this enables the actual flow conditions to be more in line with the theoretical design, resulting in higher pumping efficiency and resource savings. Since the efficient operating points of the pump are all at or near the design point, it is of course necessary to ensure that the current does not exceed its limit.
It’s quite detailed and is very helpful for beginners and field operators.
What are the steps to start a centrifugal pump? What issues should be noted? ⑴Preparations before startup. ①Carefully check whether the pump’s inlet pipelines, valves, flanges, and pressure gauge connections are all properly installed and meet the requirements; ensure that the cooling water flow is unobstructed, and verify that the anchor bolts and other connection parts are not loose. ②Add lubricating oil (or grease) to the bearing housing, with the oil level at 2/3 of the level indicator in the housing. ③Rotate the shaft to check whether the rotor is loose and flexible, and listen for any metallic knocking or grinding sounds inside the pump. ④Install the protective cover for the backrest wheel; it is strictly prohibited for the cover to come into contact with the backrest wheel. ⑤Clean the pump housing base and maintain good hygiene. ⑥Open the inlet valve to fill the pump with liquid, then open the vent valve to expel all air and close it afterward. In the case of a hot oil pump, it is not allowed to use the vent valve to remove air, in order to prevent hot oil from escaping and catching fire. (If there are dedicated vent lines and oil tanks, air and cold oil can be sent through the vent lines.) ⑦Before starting a hot oil pump, it should be preheated gradually; especially in winter, both the pump body and the pipes should be preheated so that the temperature difference between the pump body and the medium being transported remains below 52°C. ⑧The sealing oil must be thoroughly dehydrated before being introduced into the oil pump. ⑵Starting of the centrifugal pump. ① The pump inlet valve is fully open, the outlet valve is fully closed, and the motor is started to thoroughly check the operation of the pump. ② When the pump outlet pressure is higher than the operating pressure, gradually open the outlet valve to control the pump’s flow rate and pressure. ③ Check whether the motor current is within the rated value. If the pump is operating at its rated flow rate but the motor is overloaded, the pump should be stopped for inspection. ④When the hot oil pump is operating normally, seal oil should be injected. ⑶Another point to note is also. ①Under no circumstances should a centrifugal pump be operated without liquid to avoid damaging its components. ②Hot oil centrifugal pumps must be preheated to avoid accidents caused by excessive temperature differences between hot and cold substances. ③After the centrifugal pump is started, it is not allowed to operate for an extended period of time (less than 1–2 minutes) with the outlet valve closed. ④Under normal conditions, centrifugal pumps should not be used with inlet valves to regulate flow in order to avoid cavitation; instead, outlet valves should be used for this purpose
Could we discuss in more detail the operation of low-temperature centrifugal pumps? In particular, I’m interested in the operation of the auxiliary sealing systems of such pumps as well as the pre-cooling process. The key is to have more quantitative standards for these operational procedures; I look forward to learning and discussing this with everyone. :handshake
I learned from it; last time, the centrifugal pump in my home burned out due to excessive current