Common Faults and Solutions for Chemical Dosing Metering Pumps | Shanghai Shenyin Pump Manufacturing Co., Ltd.
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Common faults in chemical dosing metering pumps include low rotational speed, excessive suction lift, and high resistance losses in the inlet and outlet piping. Given how frequently these issues occur, it is important to understand the repair methods. Let’s discuss these common faults and how to fix them. I. Low Rotational Speed (1) Human factors. Some users replace a damaged original motor with an arbitrary substitute, resulting in low flow rates, insufficient head, or a failure to pump water at all. (2) Mechanical faults within the pump itself. Issues such as a loose impeller-to-shaft nut, a bent pump shaft causing the impeller to shift and rub against the pump body, or damaged bearings can all reduce the pump's rotational speed. (3) Improper motor repair. Factors such as winding burnout leading to demagnetization, changes in winding turns, wire gauge, or wiring configuration during repair, or a failure to completely resolve the original fault can alter the pump's speed. II. Excessive Suction Lift. When the water source is deep or located far away on flat terrain, the pump's permissible suction lift limit is often overlooked, resulting in reduced water intake or a total failure to draw water. It is important to note that there is a limit to the vacuum that can be generated at the pump's inlet; while the theoretical suction lift for a perfect vacuum is about 10 meters of water column, a pump cannot achieve a perfect vacuum. Furthermore, excessive vacuum causes water inside the pump to vaporize, which hinders operation. Consequently, every centrifugal pump has a maximum permissible suction lift, typically ranging from 3 to 8.5 meters. Convenience should not be the sole priority when installing the pump. III. Excessive Resistance Loss in Inlet and Outlet Piping. Some users find that, even though the vertical distance from the reservoir or water tower to the water source surface is within the pump's rated head, the water delivery volume is low or no water is pumped at all. This is often caused by excessively long pipelines or too many bends, resulting in high resistance losses as the water flows through the pipes. Common causes include excessively long pipelines or too many bends, resulting in excessive flow resistance. Generally, a 90-degree bend creates more resistance than a 120-degree bend; each 90-degree bend causes a head loss of approximately 0.5 to 1 meter, and every 20 meters of piping can result in a head loss of about 1 meter. Additionally, some users arbitrarily alter the pipe diameters at the inlet or outlet of the metering pump, which also impacts the pump head. IV. Impact of Other Factors (1) Failure of the foot valve to open. This is usually caused by the pump sitting idle for too long, causing the foot valve gasket to stick shut; foot valves without gaskets may seize due to rust. (2) Clogged foot valve strainer; or the foot valve is submerged in the sludge layer, blocking the strainer. (3) Severe impeller wear. Long-term use wears down the impeller vanes, impairing the pump's performance. (4) Malfunction or blockage of the gate valve or check valve, leading to reduced flow or a failure to pump water. (5) Leakage in the discharge piping also affects the volume of water pumped. The above covers the analysis and repair methods for common metering pump faults—such as low rotational speed, excessive suction lift, and high flow resistance in the inlet/outlet piping. We hope you master this information so that you can easily resolve similar issues in the future. Please credit: Shanghai Shenyin Pump when reposting.
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