Analysis of reasons why chemical pumps fail to discharge liquid and solutions

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Analysis of reasons why chemical pumps fail to discharge liquid and solutions. A chemical pump is a machine that converts mechanical energy into energy of the liquid, used to increase pressure and transport liquids. Chemical pumps are the most widely used and common type of general-purpose machinery in chemical and pharmaceutical industries. In addition to being extensively utilized in fields such as water management, power generation, agriculture, and mining, they are used in the largest quantities in petrochemical production. Moreover, since many of the raw materials, semi-finished products, and final products in chemical manufacturing are liquids with different physical properties, such as corrosiveness, solid-liquid two-phase flow, high or low temperatures, there is a need for a large number of chemical pumps with specific characteristics to meet the requirements of these processes. I. Analysis of the reasons why a chemical pump does not discharge liquid 1. Air in the inlet pipe and inside the pump ①. Before starting the chemical pump, insufficient water is not filled in; sometimes it may seem that the water has overflowed from the vent hole, but the pump shaft is not rotated to completely expel the air, resulting in some air remaining in the inlet pipe or inside the pump. ②The horizontal section of the inlet pipe in contact with the chemical pump should have a slope of more than 0.5% in the direction opposite to the flow of water; the end connected to the inlet of the chemical pump should be at the highest point, and it should not be completely horizontal. If it tilts upward, air will remain in the water inlet pipe, reducing the vacuum level in the pipe and the chemical pump, which affects water absorption. ③In chemical pumps, the packing has worn out due to long-term use or is tightened too loosely, resulting in a large amount of water spraying out from the gaps between the packing and the pump shaft sleeve. As a consequence, external air enters the interior of the chemical pump through these gaps, affecting its ability to lift water. ④Due to being submerged underwater for an extended period, the walls of the water inlet pipe corroded and developed holes; as the chemical pump operated, the water level continued to drop. Once these holes came above the water surface, air entered the pipe through them. ⑤Cracks at the bend of the water inlet pipe, as well as a slight gap at the connection between the water inlet pipe and the chemical pump, can both allow air to enter the water inlet pipe. 2. Low water pump speed ①. Human factors. Some users, due to the damage of the original motor, arbitrarily installed another electric motor to drive the system, which resulted in low flow rates, low head pressure, or even no water delivery. ②Mechanical failures of the chemical pump itself. Loose fastening nuts on the impeller and pump shaft, or deformation and bending of the pump shaft, can cause the impeller to shift significantly and come into direct contact with the pump casing; in addition, damaged bearings can also lead to a reduction in the speed of chemical pumps. ③, The power machine cannot be repaired. The motor loses its magnetism due to burned-out windings, and changes in the number of windings turns, wire diameter, or wiring method during maintenance, or factors such as incomplete elimination of faults during repair can also cause a change in the speed of the chemical pump. 3. The suction lift of the chemical pump is too high. In some cases, the water source is deep, or the area surrounding the water source is relatively flat; the allowable suction lift of the chemical pump is not taken into account, which results in little water being drawn up or no water being drawn up at all. It should be understood that the degree of vacuum that can be achieved at the suction inlet of a self-priming centrifugal pump is limited; the suction height achievable in an absolute vacuum is approximately 10 meters of water column, and chemical process pumps are not capable of creating an absolute vacuum. Moreover, an excessive vacuum level can easily cause the water inside the pump to vaporize, which is detrimental to the operation of the chemical pump. Therefore, each centrifugal pump has its maximum allowable suction head, which is generally between 3 and 8.5 meters. When installing chemical pumps, one must not prioritize convenience and simplicity. 4. Excessive frictional losses in the inlet and outlet pipes for water flow. Some users, after conducting measurements, find that although the vertical distance from the reservoir or water tower to the water surface is still slightly less than the head capacity of the chemical pump, the amount of water pumped is low or no water can be pumped at all. The reason is often that the pipeline is too long and has many bends, resulting in excessive flow resistance loss within the pipeline. Under normal circumstances, a 90-degree elbow creates more resistance than a 120-degree elbow; each 90-degree elbow results in a head loss of about 0.5 to 1 kilometer, while the resistance over every 20 meters of pipe causes a head loss of approximately 1 meter. Furthermore, some users arbitrarily choose the diameters of the water inlet and outlet pipes, which also has a certain impact on the head pressure. 5. Unbalanced electric rotor: Severe vibration in chemical pumps can lead to an unbalanced electric rotor, or poor coupling alignment, as well as worn or bent bearings ； It’s also possible that some rotating parts have become loose or cracked ； Perhaps it's due to unstable pipeline supports or something similar. Adjustment, repair, reinforcement, replacement, and other methods can be employed separately to address it. Leakage of fluid or air in the pipeline may be due to loose nuts during installation. If the leakage is not severe, cement can be applied to the area where air or water is leaking, or a cement slurry mixed with asphalt oil can be used. For temporary repairs, some wet mud or soft soap can be applied. If water leaks at the joint, the nut can be tightened by hand. Those with severe leaks must be disassembled and reassembled. Overheating of the packing is often caused by the packing being pressed too tightly, preventing cooling water from reaching it, or by damage to the shaft surface. Appropriate measures such as loosening the filler and clearing blockages in the sealing tube can be taken. The filler that is worn out must be replaced with a new one. Soak it in engine oil before installation, insert it ring by ring with the cuts offset from each other, which helps to reduce leaks. After the filler for the last loop is installed, tighten the gland, and adjust its tightness during operation. The reasons why chemical pumps fail to draw in or discharge water are often a stuck foot valve, blockage in the strainer section, excessive suction height, or air leakage during suction. It may also be due to incorrect rotation direction or blockage in the impeller passages. After checking each item one by one, measures such as repairing the bottom valve, removing blockages, correcting the steering, and cleaning the impeller can be taken to address the issue. 6. Severe vibration or noise from the pump: This can be caused by the pump not being installed properly, being installed at too high a height, damaged ball bearings in the motor, a bent main shaft of the pump, or misalignment or non-parallelism between the pump’s main shaft and the motor’s main shaft. The chemical pump should be installed firmly, or its installation height should be reduced; the motor’s ball bearings should be replaced, any bent shafts in the chemical pump should be corrected, or the relative position between the chemical pump and the motor should be adjusted. Due to the influence of other factors, the bottom valve cannot be opened. It is usually because the chemical pump has been left unused for too long, causing the gasket of the bottom valve to stick; a bottom valve without a gasket may also rust. 7. Influence of other factors: ① The bottom valve cannot be opened. It is usually because the chemical pump has been left unused for too long, causing the gasket of the bottom valve to stick; a bottom valve without a gasket may also rust. ②The bottom valve filter screen is clogged ； Or the bottom valve can cause clogging of the filter screen in the underlying layer of sludge in the water. ③The impeller is severely worn. The impeller blades wear out over time, affecting the performance of the chemical pump. ④If the check valve or throttle valve is faulty or clogged, it can result in a reduced flow rate or even an inability to draw water in. ⑤Leaks in the outlet pipeline can also affect the water extraction volume. II. Troubleshooting the problem of no liquid output from chemical pumps 1. No water output after startup: There is air inside the pump or air accumulation in the inlet pipe, the bottom valve is not sealed properly resulting in insufficient filling with water, the packing of the vacuum pump leaks severely, or the gate valve or check valve is not closed properly. Solution: Remove debris, replace the damaged rubber gasket, and change the direction of the valve disc ； Compress or replace the packing, close the gate valve or flap valve ； Increase the irrigation volume until no bubbles appear at the vent plug ； Replace cracked pipes ； Reduce the head by submerging the outlet of the chemical pump 0.5 meters underwater. 2. The pump does not rotate at startup: the packing is too tight, debris is stuck between the impeller and the pump body causing a blockage, or there is a problem with the pump shaft or bearings. The leakage reduction ring is rusted, or the pump shaft is severely bent. Solution: Loosen the filler and clear the water guide channel ； Disassemble the pump body to remove debris and rust ； Remove the pump shaft to correct it or replace it with a new one. 3. Overheating of bearings in chemical pumps: Damaged rolling bearings or excessive tightness of the bearing housing cover ； The pump shaft is bent or the two shafts are not aligned ； The tape is too tight ； Lack of oil or poor oil quality ； The balance holes on the impeller are blocked, causing the impeller to lose its balance and increasing the thrust in one direction. Solution: Replace the bearing ； Remove the rear cover and install shims between the bracket and the bearing housing ； Adjust the pump shaft or adjust the concentricity of the two shafts ； Adjust the tape tension appropriately ； Add clean butter; the butter should fill 60% of the voids inside the bearing ； Remove the blockages from the balance hole. 4. Insufficient flow after startup: Incompatible rotation speed or belt slippage results in a low rotation speed ； The installation angle of the axial flow pump blades is too small ； Insufficient head ； Excessively high suction lift ； Local blockage of the bottom valve, pipelines, and impeller, or damage to the impeller ； The water outlet pipe is leaking severely. Solution: Restore the rated speed, remove oil buildup from the belt, and adjust the belt tension properly ； Adjust the blade angle and lower the installation height of the water pump ； Seal the leak in the chemical pump by compressing the packing ； Remove the blockage and replace the impeller ； Replace the leak-reducing ring to seal the leak.