With advantages such as good performance, high efficiency, long service life, and large flow rate, large-flow pumps are widely used in industries including electronics, electric power, chemical industry, metallurgy, medicine, food, electroplating, environmental protection, fire protection, municipal administration, water purification, textile printing and dyeing, mining and mineral processing, and civil construction. In actual operation, the flow rate of large-flow pumps can be steplessly adjusted through various methods. Generally, it is reasonable for the pump to work under the rated operating condition. However, sometimes due to certain reasons, long-term operation below the rated flow rate will cause some negative impacts. The editor from Zoomlian Pump Industry will take you to understand the effects of long-term operation of water pumps below the rated flow rate and the main aspects they are reflected in.
Increase in pump body temperature: Since the actual flow rate of the pump is extremely small, that is, the useful work done by the pump is very small, most of the shaft power is converted into heat energy, which is transferred to the liquid in the pump, causing the entire shell to heat up. The radial thrust increases. Under extremely small flow rates, unreasonable continuous operation will lead to excessive shaft bending deflection, rapid wear of bearing rings, and even shaft breakage due to excessive shaft fatigue. During long-term operation at small flow rates, there will be a regular periodic change in flow rate and pump outlet pressure, which is called surge. When surge occurs, there will be vibration and noise, which have adverse effects on the pump.
Significant increase in internal reflux of the pump: The internal heat accumulation increases, causing the temperature of the liquid in the pump to rise, leading to heating of the pump body, affecting the mechanical properties of pump components, and at the same time deteriorating the cavitation performance of the pump, further affecting the suction conditions of the pump.
Increased radial force of the pump, deteriorating the force condition of the pump rotor: When the pump works in the small flow area, it deviates from the design operating point. The flow velocity of the liquid in the volute decreases, but according to the analysis of the velocity triangle, the outflow velocity of the liquid in the impeller increases instead. As a result, the liquids cannot converge, forming an impact, and the pressure continues to increase, generating radial force.
Reduced efficiency and increased power consumption: Pumps are generally designed so that the highest efficiency point is near the rated operating condition. If a large-flow pump operates at a small flow operating point, its operating efficiency will drop rapidly. Generally, for the same pump, the smaller the flow rate, the lower the efficiency. Therefore, operating under small flow conditions is very uneconomical. In general, it is necessary to re-equip a suitable small pump at this time.
Increased vibration and noise, causing environmental pollution, damaging pump components, and affecting the service life of the pump: At the design operating point, due to the consistent direction of the liquid flow and the blade direction, the flow separation loss, impact loss, and vortex loss are relatively small, close to zero. However, when the pump works in the small flow area, due to deviation from the design point, the flow separation loss, impact loss, and vortex loss of the pump's flow-passing components are further increased. These losses are accompanied by a large amount of hydraulic noise and mechanical vibration when they occur.
To ensure the stability of use, we need to inspect the large-flow pump before each use, especially:
Check whether the rotating parts of the pump are stuck or collided, and whether the nuts at the pump base and each connection are loose.
Check the coaxiality and parallelism between the pump shaft and the motor main shaft, and whether the pipeline is leaking. If there is a leak, it must be eliminated.
Check whether the liquid storage in the pump shell is higher than the upper edge of the impeller. If it is insufficient, the liquid can be directly injected into the pump body from the liquid filling port on the pump shell. It should not be started and run when the liquid storage is insufficient, otherwise it cannot work normally.
According to the working operation conditions, use calcium-based butter and No. 10 engine oil for lubrication respectively. For pumps lubricated with butter, butter should be regularly added to the bearing box; for pumps lubricated with engine oil, if the oil level is insufficient, it should be filled up.