Why does leakage occur in a centrifugal pump? To understand this, we must first understand how a centrifugal pump basically works. As fluid goes through its impeller eye and up the impeller vanes, it starts with low pressure and velocity. As it flows into the volute and gets ready to exit, both the pressure and velocity increase. As the fluid flows out through the discharge, the pressure is high but the velocity gets reduced. The flow then goes out of the pump, which makes the pump exert pressure and raise the energy of the fluid.
When a component of the pump such as static joints and hydraulic malfunction, the whole system might break down. However, a majority of pump failures happen due to the mechanical seal of the pump malfunctioning.
A mechanical seal controls the leakage between a liquid and a rotating shaft. To do this, essentially all seals have to leak in order to maintain a film of fluid over the whole face of the mechanical seal. The leakage from the atmospheric side is quite less. But the leakage between the mechanical seal shafts and sleeves can cause significant issues. Often, the reason these happen is because of the fretting of the O-ring seal on the shaft. You will notice substances dripping from behind the seal close to the drive collar. Polishing the fretted part can provide a temporary fix, but it will not give you a solution. Here are some options you can choose in the short and long term:
Short term solutions
Replacing the shaft could be a practical option given that the maintenance cost is low and you would not have to overhaul the entire pump system.
When repairing or replacing the shaft is proving to be difficult, you can opt for a modified seal but you may have to plan in advance.
You can try relocating the O-ring of the seal sleeve with the help of a local technician. When you get to the bottom of the issue, you can check where the damage on the shaft is and shift the O-ring accordingly. If you still require a new sleeve, the cost will be only a little bit higher.
Long-term solutions
Upgrade the shaft to a higher quality material.
Consult a pump technician and coat the shaft below the seal sleeve with a substance like tungsten carbide. How much of the shaft you may need to coat will depend on the damage. Avoid the area around the drive collar set screws. Make sure to enlist professional support for this.
VEMC, one of the authorized Kirloskar pump dealers in India, supplies industrial water pumps in Mumbai for different industrial applications. We offer a diverse range of pumping solutions including water pumps. For more information on our products and help selecting the right ones for you, please reach out to us on +91 98199 07445. VEMC is ISO 9001:2015 certified and a pioneer in the field of electromechanical engineering products, allied equipment, and services.