Weekly Topic 3.14 Issue **: Precautions for Operating Centrifugal Pumps

Before starting a centrifugal pump, it is necessary to vent air in order to prevent air locking of the pump

Reply to 1# wawjia: Let me say a few words; please correct me if I’m wrong: 1) Regularly turn the shaft by hand. There were a few times when I forgot to do this, and as a result it became impossible to turn it – it took a lot of effort to get it moving again； 2) Use cooling water to ensure the bearing temperature remains within the acceptable range ； 3) Strict process conditions (which must match the operating requirements of the pump); otherwise, high temperatures in the bearings, high current levels, and high water temperature may occur. 4) Proper matching between the pump and the motor is essential to avoid overloading the pump or underutilizing it. 5) Process adjustments should be made gradually, without sudden changes, as this could lead to pressure buildup, excessive flow, or shutdown of the pump

Perform regular shaft turning; in some cases, cooling water is used to ensure that the bearing temperature remains within acceptable limits； Strict control is required over process parameters such as oil temperature and pressure, as well as the compatibility between the pump and the motor. It is necessary to prevent excessive loads, and process adjustments should be made gradually without sharp changes, otherwise it may lead to pressure buildup or overflow. During operation, pay attention to fluid feeding, air release, and the appropriate operating pressure. If the liquid temperature is too high, cavitation may occur; failure to release air can lead to similar issues, and the pump will not be able to generate pressure

This post was last edited by wawjia on 2011-3-14 21:29. Be careful of the inlet pressure and temperature of the pump when operating! The feed pump in the methanol distillation unit is prone to cavitation and gas entrapment, which results in no flow

–(1) When the turning gear is newly installed, after maintenance, or after being out of use for an extended period, the coupling should be turned by hand 1–2 times before starting to check for any signs of jamming, tightness issues, or looseness that could allow lubricant to enter various lubrication points. Any abnormalities found must be resolved before starting the equipment. – (2) Lubrication: It is necessary to check the lubrication condition both before starting and during operation. For initial use, bearings should be filled with an appropriate amount of clean lubricating oil or grease. In the case of bearings lubricated using oil rings, these rings should be submerged by about 15 mm. For bearings lubricated with grease, the amount of grease used should account for 1/2 to 1/3 of the bearing chamber’s volume. Lubricant should be free from water and impurities. During operation, the temperature rise of the bearings should not exceed 35°C, while their surface temperature should not exceed 75°C. (3) Cooling: For centrifugal pumps equipped with a stuffing box water seal tube, water-cooled bearings, water-cooled mechanical shaft seals, or those having balance pipes and balance discs, check whether the corresponding water pipelines are unobstructed; also inspect the amount of cooling water and its temperature. (4) When the discharge valve is closed, the pump operates at its lowest power level; however, the pump should not remain in this closed state for too long, as this can cause the liquid to heat up. (5) It should be checked that the steering pump can generate normal discharge pressure when operating in reverse direction; therefore, when starting a new pump or one that has been repaired for the first time, it is necessary to verify its steering function. (6) To avoid dry running, open the inlet valve to release the gas inside the pump, fill the pump with the liquid to be transported, and then close the outlet valve. The clearance between rotating and fixed components is usually very small, or there is direct contact (such as in shaft seals); dry operation can lead to severe wear, heating, and even shaft seizure. In the case of self-priming centrifugal pumps, it is necessary to fill them with liquid during the first start-up. Some centrifugal pumps equipped with their own vacuum pumps may operate in a dry state during startup, so their self-priming time should be limited, and mechanical shaft seals should not be used. (7) To prevent freezing and rusting, when the ambient temperature is below 0°C, any remaining liquid should be drained. Pumps that will not be used for an extended period should have anti-rust oil applied to their exposed metal surfaces. (8) Check the valves, flange bolts, couplings, thermometers, pressure gauges, and other components on the pump’s inlet and outlet pipelines. Check safety equipment such as wheel guards and grounding wires. Establish good contact with all relevant positions and units. Get ready to start.

To prevent excessive load, process adjustments should be made gradually, without sharp changes; otherwise, pressure buildup or overflow may occur. During operation, pay attention to liquid filling, exhaust, and maintaining an appropriate operating pressure

When controlling, pay attention to the inlet pressure and temperature of the pump; strive to increase the saturated vapor pressure of the fluid to avoid cavitation

Before starting, be sure to turn the machine manually, check the exhaust, pay attention to the sound of the motor, the oil level, the outlet pressure, and the temperature of the incoming fluid, in order to prevent overheating

1. First, you need to understand what type of centrifugal pump you are using. 2. All pumps must be rotated manually before operation. 3. Lubricate the moving parts with lubricant. 4. Fill the pump so that there is liquid inside it. 5. Ensure proper sealing depending on the type of seal used. 6. In the case of horizontal centrifugal pumps, the couplings must be aligned correctly. 7. It is advisable to install a pipe filter at the pump inlet

Everything mentioned above is quite detailed. A small addition: 1. When the process conditions and weather conditions vary, make sure to turn on the cooling valve or the heating valve accordingly. 2. After repairing or reinstalling the electrical equipment, it is necessary to conduct a test drive to determine the steering direction. 3. During daily inspections, it is necessary to monitor temperature and vibration, as well as pressure fluctuations. Pressure and vibration levels are most evident when mild cavitation or gas entrapment occurs. 4. The motor also requires maintenance, with grease applied regularly. In winter, after starting up, the temperature of the motor grease is low, the motor makes a lot of noise, but it improves once it starts rotating. 5. Ensure an adequate supply of mechanical seals to achieve a cooling effect. This causes a loud noise when the mechanical seal is dry-ground. During winter, the mechanical seal of the standby pump will leak; this is due to low temperatures that cause an increase in the gap between the components of the seal, and it stops leaking once the temperature rises.