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How To Choose Mechanical Seals Under Different Medio?
Sep 21, 2018

Due to the pressure difference between the fluid in the pump and the atmosphere outside the pump, in order to prevent the external discharge of the slurry, the pump needs to be provided with a sealing device during operation, which is called a shaft seal. Commonly used shaft seal types are: packing seal, mechanical seal, dynamic seal and floating seal. From the current situation of pumps in various industries, mechanical seals have become a common form of sealing in various industries. How to determine what type of mechanical seal is used? We carried out the corresponding working condition analysis through the characteristics of different media, put forward corresponding requirements for the seals of each occasion, and recommended the corresponding types of mechanical seals.

 

A. Corrosive medium: acid

Working conditions: 

The mechanical seal is chemically corroded, and the corrosion rate on the sealing surface is 10-50 times that of the frictionless surface.

On-site sealing requirements: 

The sealing ring is both corrosion-resistant and wear-resistant. The material of the auxiliary sealing ring is both elastic and corrosion-resistant.

Mechanical seal selection:

Choose corrosion-resistant materials and use external mechanical seals. If built-in mechanical seals, the spring surface must be coated with a protective layer.

 

B. high viscosity medium: lubricating oil, gear oil, residual oil, etc.

Working condition: 

Lubrication performance is good when viscosity is high, but too high will affect the floating of the rotary face ring

On-site sealing requirements: 

Friction auxiliary materials wear-resistant, springs must have sufficient capacity to support the resistance generated by high-viscosity media

Mechanical seal selection:

If a rotary seal is used, the design of the drive pin and spring should be increased to increase the shear force against viscosity. Static double-face seal with hard-to-hard friction pair material combination

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C. high temperature medium: hot oil, oil slurry, molten salt, etc.

Working conditions: 

As the temperature increases, the seal wear and corrosion accelerate, the material strength decreases, the medium is easy to vaporize, the sealing ring is easy to deform, the rubber is aging, and the combined ring is loose.

On-site sealing requirements: 

High temperature resistance of sealing materials, good thermal conductivity, low friction factor and expansion coefficient, ensuring that the temperature in the gap of the sealing surface is lower than the vaporization temperature of the medium by 15~30 °C.

Mechanical seal selection:

The sealing material is subjected to stability treatment to eliminate residual stress and the tangential expansion coefficient is similar. If a single-end seal is used, the width of the end face should be as small as possible, and it should be sufficiently cooled and flushed.

 

D. contains solid particles: Tower bottom oil, oil slurry, crude oil, slurry, etc.

Working condition: 

severe wear of the end face of the sealing ring, the solid particles will lose their floating at the moving ring.

On-site sealing requirements: 

Friction pairs should be wear-resistant, to eliminate solid particles or to prevent particle precipitation

Mechanical seal selection:

The double-end machine seal is used to pass the isolation fluid into the sealed chamber. The friction pair adjacent to the medium side should be made of silicon carbide. If a single-end machine seal is used, the fluid with a slightly higher pressure than the seal medium should be introduced from the outside for flushing.