External factors affecting the mechanical seal of centrifugal pumps

External factors affecting the mechanical seal of centrifugal pumps

1. No auxiliary scouring system or unreasonable setting of auxiliary scouring system

The auxiliary flushing system of mechanical seals is very important as it can effectively protect the sealing surface, play a role in cooling, smoothing, and flushing away debris.

-Sometimes planners do not properly configure the auxiliary flushing system, which fails to achieve sealing effect; 

-Sometimes, although planners have planned an auxiliary system, due to impurities in the flushing fluid,

poor flow and pressure of the flushing fluid, and unreasonable planning of the flushing port orientation, the sealing effect is also not achieved.

2. The axial displacement of the pump shaft is large

The sealing surface of a mechanical seal must have a certain specific pressure in order to have a sealing effect. 

This requires the spring of the mechanical seal to have a certain amount of tightening, 

giving a thrust to the sealing end face, and rotating it to produce the required specific pressure on the sealing surface.

 In order to ensure this specific pressure, the mechanical seal requires that the pump shaft should not have too much displacement, usually within 0.5 mm. 

However, in practical planning, due to unreasonable planning, the pump shaft often experiences significant displacement. 

This phenomenon often occurs in self balancing multi-stage centrifugal pumps, especially during the pump start-up process, where the displacement is relatively large.

3.Excessive oscillation

The mechanical seal oscillates excessively, ultimately leading to the loss of sealing effect. 

However, the reason for the excessive oscillation of mechanical seals is often not due to the mechanical seals themselves. 

Other components of self balancing multi-stage centrifugal pumps are the root cause of oscillation, 

such as unreasonable pump shaft planning, processing reasons, poor bearing accuracy, poor parallelism of couplings, and large radial force.

4. The cause of pump cavitation

Due to unreasonable operation of the device system, poor cavitation function at the pump inlet, 

and high rotation speed of the self multi-stage centrifugal pump, partial cavitation occurs at the inlet of the multi-stage centrifugal pump. 

After cavitation occurs, bubbles will appear in the water, which on the one hand will impact the outer surface of the mechanical seal surface, 

causing damage to its outer surface; On the other hand, it will also cause bubbles in the active film of the dynamic ring's mating surface, 

which cannot form a stable active film, causing dry friction on the mating surface of the dynamic ring and damaging the mechanical sealing device.

5. Excessive axial force

Mechanical seals cannot accept axial force during use, and the presence of axial force can have a severe impact on mechanical seals. 

Sometimes, due to the unreasonable organization and planning of axial force balance in self multi-stage centrifugal pumps, 

as well as reasons such as manufacturing, installation, and operation, the axial force is not balanced. 

The mechanical seal receives an axial force, and the temperature of the sealing gland will be too high during operation. 

For polypropylene like media, it will be melted at high temperatures, so the sealing effect of the multi-stage centrifugal pump will soon be lost after starting. 

When the multi-stage centrifugal pump is stationary, there will be intermittent leakage on the sealing end face.

6. The deflection of the pump shaft is too large

Mechanical seal, also known as end face seal, is a touch type dynamic seal that rotates in the axial direction. 

Under the action of fluid medium and elastic components, two sealing end faces perpendicular to the axis are tightly fitted, 

rotated relative to each other, and then achieve the sealing effect. 

Therefore, it is required that the two seals be evenly stressed between them. 

However, due to the unreasonable product planning of the horizontal multi-stage centrifugal pump, 

the deflection generated at the mechanical sealing device during pump shaft operation is large, 

resulting in uneven stress between the sealing surfaces and poor sealing effect.

7.Poor machining accuracy

There are many reasons for the poor machining accuracy of mechanical seals, some of which are due to the poor machining accuracy of mechanical seals themselves. 

These reasons are easy to attract people's attention and are also easy to find.

 But sometimes the machining accuracy of other components of horizontal multi-stage centrifugal pumps is not good, which is not easy to attract people's attention. 

For example, the increase in precision of pump shaft, shaft sleeve, pump body, and sealing chamber is not sufficient.

By katreenipump