Mechanical seal of the pump:

operation, assembly, and selection criteria in industrial plants

In the fluid handling sector, mechanical seals are one of the most critical components: they ensure isolation between the inside of the pump and the external environment, prevent leaks, and help maintain the efficiency of the system over time.
A correctly selected and installed seal has a direct impact on operational continuity, especially in systems that handle corrosive, abrasive, or high-temperature fluids.

In this in-depth analysis, we will look at: what a seal is, the main systems used, materials and types, how a mechanical seal works, and the basic rules of installation and maintenance to maximize durability and reliability.

What is meant by pump seal?

A pump seal ensures separation between the process fluid and the external environment at the point where the rotating shaft passes through the pump body.

Without an effective sealing system, the following may occur:

fluid leaks, even if minimal but constant
unwanted infiltration (air or contaminants)
accelerated wear of the shaft and metal components
safety risks, especially with corrosive or toxic fluids

In industrial applications (chemical, electroplating, purification, paints, petrochemical, food), the choice of seal is not a detail: it is a requirement to protect the system, reduce consumption, and extend the life of the pump.

Main sealing systems used in pumps

The most common systems are:

Packing seal (gland)

The packing seal uses braided rings impregnated with lubricants, compressed around the shaft by the gland.

It is a simple and robust solution, still used in systems:
at low pressure
with fluids that are not particularly aggressive
where simple, “on-site” adjustment is required

On the other hand, it requires frequent adjustments, periodic replacement of the rings, and accepts a minimum amount of leakage (necessary for cooling and lubrication).

For this reason, in modern processes it is often replaced by mechanical seals.

Mechanical seals

Mechanical seals are now the most widely used solution in industry because they offer better performance in terms of insulation, durability, and leak reduction.

It consists of two sealing surfaces (planar faces):

one integral with the shaft (rotating)
one fixed to the pump body (counterface)

The faces are kept in contact by springs and/or elastic elements and by the principle of hydraulic/mechanical balance. In practice, it allows:

almost total isolation of the fluid
resistance to high pressures and temperatures
less wear than packing
longer maintenance intervals
compatibility with corrosive fluids

The choice depends on the fluid, pressure, temperature, and operating conditions. The materials are also decisive for chemical compatibility and wear resistance: stainless steel, silicon carbide, graphite, elastomers (EPDM, FKM), etc.

Mechanical seal operation

Operation is based on controlled contact between the rotating face and the counterface. During rotation:

a thin film of fluid lubricates the surfaces and reduces wear
internal pressure and the geometry of the faces limit fluid leakage
springs/elastic elements maintain the closing force even with vibrations or operating variations
the elasticity of the system compensates for minor shaft misalignments

The result is stable and efficient sealing, even under heavy loads.

Editing: common mistakes and essential rules

A mechanical seal only works properly if it is installed according to precise procedures. The most common errors are contamination, incorrect assembly, unsuitable lubricants, or excessive force during assembly.

Essential recommendations

Clean the seats and support surfaces thoroughly before assembly.
Never force the components onto the shaft (risk of scratches/deformations).
Only use lubricants if recommended by the manufacturer.
Check O-rings, springs, and seals before installation.
Check the position and coupling between the rotating face and the counterface.
Start the system in a controlled manner and check for leaks during the first few hours of operation.

Correct assembly increases the service life of the seal and reduces the risk of premature failure.

Maintenance and selection of spare parts

Preventive maintenance is essential in industrial plants. A compromised seal can cause:

fluid leaks
increased energy consumption
shaft wear
unplanned plant downtime

Best practices

Schedule periodic inspections of seal locations
Replace O-rings, gaskets, and worn components promptly
choose materials that are compatible with the fluid chemistry and temperature
use original or perfectly equivalent spare parts
monitor vibrations, noise, and temperature in the seal area

Keeping strategic spare parts in stock allows for quick interventions and reduces downtime.

Conclusions

The correct selection and management of mechanical seals is a key factor in ensuring service continuity, safety, and performance in industrial plants.
Understanding the differences between sealing systems, assessing material compatibility, and following precise assembly procedures can prevent leaks, reduce maintenance costs, and increase pump life.