Reasons why a chemical pump still leaks after installation

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Chemical pumps are common mechanical devices in both domestic and industrial applications. There are various types of chemical pumps, such as corrosion-resistant chemical pumps, sewage discharge pumps, and circulation pumps. What causes leakage after the installation of acid- and alkali-resistant chemical pumps, and what should be done in such cases? I. Leakage at the flange connection: The cause is generally severe stretching due to the tightening screws. Solution: Tighten the screws diagonally; do not tighten them all at once. The gasket used for sealing between the two flanges should be of the same size as the flanges themselves. II. Leakage from the mechanical seal: Pumping without water in a chemical pump can cause the mechanical seal to burn out. For new pumps, this may be due to operation without water, which leads to damage to the shaft seal; for old pumps, the following possibilities exist: 1. Wear of the moving and stationary rings of the mechanical seal, or excessive tightness during installation. Observe the surfaces of the stationary and rotating rings of the mechanical seal; if there is severe burning, the surfaces appear black with deep marks, and the sealing rubber becomes hard and loses its elasticity. This phenomenon is caused by over-tightening during installation. It’s installed too loosely. By examining the moving and stationary rings of the mechanical seal, a thin layer of scale can be seen on their surfaces; this scale can be wiped off, and the surfaces show little signs of wear. This condition is caused by the spring losing its elasticity or by improper assembly, or it may result from axial movement of the motor. The water quality is poor and contains particles. Due to poor water quality, the presence of small particles and a high content of hydrochlorides in the medium, abrasive wear occurs on the surfaces of the mechanical seals, resulting in grooves, ring-shaped scratches, and other defects. Operation under water shortage causes dry grinding damage. This phenomenon is commonly seen in installations with bottom-valve types, where there is negative pressure at the inlet, air in the water inlet pipe, and air inside the pump chamber. When the pump starts operating, the friction between the mechanical seals generates high temperatures due to their rapid rotation, and no cooling occurs. Upon inspection of the mechanical seals, the spring tension is normal; however, the friction surfaces are burned and blackened, and the rubber has hardened and cracked. Cavitation. Cavitation mainly occurs in hot water pumps. Since the medium is hot water, the high water temperature generates steam; this steam enters the upper parts of the pump chamber, and it is not possible to remove this steam, which leads to operation with insufficient water, failure of the mechanical seal due to dry friction, as well as cavitation. The automatic exhaust valve must be used, and the mechanical seal needs to be replaced. Assembly problem. When installing the pump cover, it may not be aligned properly, resulting in the shaft not being perpendicular to the pump cover and thus preventing the stationary and rotating surfaces from fitting together. As a result, wear occurs on one side after short periods of operation, leading to leakage. It is also possible that the rubber components may be damaged, or the surfaces of the stationary and rotating rings may get scratched during installation. 2. Failure of the mechanical seal adhesive. Reasons for the failure of the mechanical seal adhesive: aging and deformation of rubber components, primarily occurring in hot water pumps. The symptom of failed mechanical sealant is excessively high water temperature, which causes the medium to dissolve the rubber. Visually, the surface of the rubber parts appears loose and rough, losing its elasticity, which leads to the failure of the rubber. 3. It is caused by the pump cover static ring chamber; the main reasons are large machining tolerances of the internal holes in the static ring chamber and rough surfaces. The observed phenomena include water spraying axially, a gap between the stationary ring and the inner hole, or roughness of the inner hole, as well as the stationary ring rotating and the rubber wearing out. 4. Poor machining accuracy, small size, roughness of the motor shaft journals, and corrosion of these journals. The machining dimensions of the motor’s shaft journals (at the location where the rotating ring is situated) are insufficient; in addition, corrosive media can damage the pump. Moreover, when the pump is not in use for an extended period, water acting as a medium leads to differences in electrode potential between the steel shaft and the cast impeller serta pump cover, resulting in a galvanic reaction that causes corrosion of the shaft journals. The observable phenomenon is a pitted corroded surface. III. The motor is running but no water is delivered. Check the rotation direction of the motor. Cause: The motor may be rotating in the wrong direction, or there may be air leaks at the inlet. Solution: Check whether the motor is rotating in the correct direction and whether there is any air leakage at the inlet.