What is the effect of shaft seal on the efficiency of horizontal centrifugal pump

In the operation system of horizontal centrifugal pumps, the shaft seal device is not large in size, but it plays a vital role in sealing, leakage prevention and energy consumption control. Reasonable selection and maintenance of the shaft seal system is not only related to the stability and safety of equipment operation, but also directly affects the overall operation efficiency of the pump.

Overview of the basic functions and types of shaft seals
The main function of the shaft seal device is to achieve effective sealing at the position where the pump shaft passes through the pump casing to prevent the medium from leaking along the shaft. According to the different sealing principles and structural forms, common shaft seal types mainly include packing seals, mechanical seals and non-contact seals (such as magnetic drive).
The packing seal forms a sealing ring by compressing flexible packing (such as graphite, PTFE), which is generally simple in structure and low in cost; the mechanical seal uses two mutually contacting sealing end faces (dynamic ring and static ring) to maintain sealing in the lubricating liquid film, which has higher efficiency and reliability; the magnetic seal in the magnetic pump achieves true "zero leakage", but the structure is complex and the cost is high.

The impact of packing seals on pump efficiency
The packing seal is a more traditional sealing method. During operation, it relies on the friction between the shaft and the packing to form a seal, but this friction process itself brings energy consumption, especially at high speed or long-term operation, the friction heat increases significantly, causing energy waste. At the same time, the packing has a certain wear on the sleeve, which increases the frequency of equipment maintenance.
In order to avoid the packing from burning due to dry friction, lubricating fluid or cooling water needs to be regularly injected into the sealing chamber. This additional auxiliary system further increases the operating cost and may introduce impurities or dilute the conveying medium, indirectly affecting the overall efficiency of the pump system.

Energy-saving characteristics of mechanical seals
Mechanical seals are more sophisticated in design, and dynamic sealing is achieved under the action of liquid film through the high-precision machined dynamic and static ring end faces. Its friction resistance during operation is significantly lower than that of packing seals, and its energy consumption is lower. It is the mainstream sealing method widely used in modern horizontal centrifugal pumps.
Due to its stable sealing performance and low leakage rate, mechanical seals can reduce the loss of pressure energy inside the pump casing and improve the volumetric efficiency and hydraulic efficiency of the pump body. When conveying high-pressure, high-temperature, toxic or volatile media, the advantages of mechanical seals are more prominent, which can significantly reduce the energy loss and environmental risks caused by leakage.
The lubrication and cooling system of the mechanical seal is also more efficient. The closed-loop design reduces the consumption of coolant and the additional load of the system, which is an important guarantee for the efficient operation of the pump.

The hidden impact of shaft seal leakage on efficiency
Whether it is a packing seal or a mechanical seal, if the seal fails and causes leakage, it will have a negative impact on the pump efficiency. Liquid leakage not only loses the energy of the pump body, but also may cause chain problems such as bearing contamination, pump cavity cavitation, and pump shaft vibration, resulting in an overall decrease in the efficiency of the pump unit.
Long-term micro-leakage will also accelerate corrosion and wear, affect the life and stable operation cycle of the pump, and indirectly cause downtime losses and maintenance energy consumption. Therefore, an efficient shaft seal system is not only a means to reduce direct leakage losses, but also an important part of ensuring the long-term stable efficiency of the pump system.

Energy loss of frictional heat of the shaft seal
The friction of the shaft seal device during operation inevitably generates heat. On the one hand, this part of heat consumes part of the mechanical energy. On the other hand, if the heat removal system is not designed reasonably, it may cause local overheating, causing deformation of the sealing surface, lubrication failure, and even early failure of the sealing system.
Mechanical seals can effectively reduce the friction coefficient and heat loss by optimizing the end face materials (such as silicon carbide, graphite) and precise matching. Some advanced sealing structures use balanced or double end face seals to further reduce the end face pressure and control the generation of friction heat.
In the design of energy-saving pump systems, shaft seal friction heat should be regarded as one of the internal energy consumption sources and controlled through structural optimization and matching of cooling systems.