When the pump is working, the pump impeller is connected to the centrifugal pump shaft and passes through the pump casing or volute. Without pump seals, vacuum entering the shaft volume will always be a source of leakage.
Over the past 100 years or so, most pumps have relied on packing to prevent the pump from leaking while allowing the shaft to rotate freely. The first seals the packaging within the pump by creating an area called a force seal or stuffing box. The technology has improved over time, and 50 years ago a packing seal consisted of multiple braided threads and graphite washers that could be placed around the shaft and inside the stuffing box. The tanks are tightly packed with surface packers to prevent system water from leaking from the pump housing.
Packing seals require proper lubrication because the friction between the packing and the shaft generates a large amount of heat. This lubrication is provided by system water flowing from the outlet side of the pump through the packing and out of the pump. This creates an "open" system that is used regularly and leaks flushed away. It should "ooze" about one drop of water per second. This water must be replaced with makeup water, which increases the risk of corrosion.
Additionally, manually installing gaskets requires periodic adjustment of the packing seal to maintain the proper amount of lubricant, which can lead to excessive component wear. This type of seal was introduced decades ago and is still used in some industrial applications today.
Mechanical seals are now standard equipment for centrifugal pumps. There is no leakage from the mechanical seal. Instead, an integral spring closes the pump, applying pressure to two highly polished sealing surfaces.
The difference between mechanical seals for internal cleaning and sealants for external cleaning:
Working principle:
Internal mechanical seal: The internal mechanical seal is usually installed inside the pump. The sealing parts of the pump are immersed and come into contact with the system fluid. Upon start-up the sealing parts are automatically immersed in the liquid. Forms a liquid film at the same time they are constantly exposed to liquids during work. Which provides good cooling and lubrication effect.
External mechanical seal: The external mechanical seal is usually mounted on the outside of the pump. The sealing parts are located in the dry area of the pump. The external seal requires cooling and lubrication with external cleaning fluid. (usually clean water) which is passed through the surrounding pipes seal the parts to form a liquid film to reduce friction and corrosion.
Lubrication method:
Mechanical Seal with Internal Flow The internal flow preventer uses system fluid as a lubricant. Therefore, no additional piping or cleaning system is required.
Mechanical Seal with External Supply Mechanical seals that are fed externally require external cleaning fluid to provide cooling and lubrication. It often requires additional tubing and cleaning.
Maintenance and management:
Internal mechanical seal: Compared with the external seal, the internal seal is easy to maintain and use. This is because no additional pipes or systems are needed.
External Mechanical Seal External seals require additional tubing and flushing fluid. They may be more complex to maintain and use.
Area of use:
Internal mechanical seal: The internal seal is suitable for a variety of fluids and adapts well to specific conditions.
External mechanical seals External seals are generally suitable for pumps that must operate in dry environments. But maintaining and managing flow systems can add complexity and cost to the system.
Long life
The mechanical seal is made of stainless steel, graphite and silicon carbide. Carbide, fluororubber, etc. They can withstand long-term tests in high-speed rotation and high-pressure environments, so they have a long life. Package seals are subject to friction and wear. And you need to change and adjust it frequently. Mechanical seals, on the other hand, require less maintenance.
Reliable seal
Mechanical seal uses spring pressure to tightly seal two polished sealing surfaces. Create a reliable seal This design significantly reduces the risk of leakage and ensures stable operation of the system.
High adaptability
Mechanical seals are suitable for many fluids. It is highly adaptable as it can contain various media such as pure water, wastewater, weak alkaline and weak acid chemicals, oil, and water. Fill seals may be limited by fluid properties under certain conditions.
Space saving
When vertical centrifugal pumps use mechanical seals.
A sealing device is usually installed at the top of the pump. Reduces the overall volume of the pump and saves installation space.
Reduce pump room maintenance costs
Mechanical seals require no additional plumbing or cleaning compared to sealing seals. Reduces the cost and complexity of pump room maintenance.
