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How to select mechanical seal parameters

作者:Rumi Tech Dept. 浏览:118 发表时间:2020-03-09 13:28:14 来源:Rumi Tech Dept.


Each mechanical seal, only for the specified scope can be effective. Improper selection, will make the sealing performance significantly reduced, shortened life, and even failure. The main parameters of model selection are as follows:



I. medium pressure P of the sealing chamber

 

Medium lubricity is good, high viscosity, P≤ 0.8mpa choose non-equilibrium type. Medium lubricity is poor, low viscosity, P≥ 0.5mpa

 

II. Linear velocity V

 

V≤25m/s is of rotary type. V≥25m/s is a stationary type.

 

III. PV value

 

The PV value relates to the stability (vaporization) of the fluid film between the sealing surfaces and the wear resistance of the friction pair. Examples of PV limit values:

 

End face composite material

 Medium

Non balance

Balance

Cobalt chromium tungsten/graphite

water

2

7

Tungsten carbide/graphite

Water

9

35.5

Tungsten carbide/graphite

water

35.5

142

Silicon carbide/tungsten carbide

water

7

26.6

Silicon carbide/tungsten carbide

water

2

9


IV, sealing medium temperature T


In the absence of external cooling, the maximum temperature of the mechanical seal generally depends on the safe use temperature of the auxiliary sealing material. See the following table:

 

Material

Safe use temp.

Remarks

丁睛橡胶(NBR)

-30~100

Use metal bellows for mechanical seal when over safe operating temperature

硅橡胶(MVQ)

-40~200


乙丙橡胶(EPR)

-10~160


氟橡胶(FPM)

-30~180


聚四氟乙烯(PTFE)

-100~220




V, the particularity of the medium.

1, viscosity: low viscosity medium easy dry friction appropriate to choose the balance type. High viscosity medium, should use forced transmission structure.

2, corrosion and chemical solvents: a, strong corrosion should be sealed with external type of four fluorine bellows.

 

B. the applicable table of auxiliary seals in different chemical media is as follows

Material

Usage

丁腈橡胶(NBR)

Mineral oil, gasoline, volatile oil, potassium carbonate, potassium hydroxide, water, phosphoric acid, etc

硅橡胶(MVQ)

Butanol, low swelling mineral oil, weak acid, weak base, ammonia, etc

乙丙橡胶(EPR)

Acetone, alkali, sulfur dioxide, potassium dichromate, hydrogen peroxide, ammonia, etc

氟橡胶(FPM)

Hot oil, steam, inorganic acid, butanol, chlorine solvent, etc

氯醇橡胶(FCO)

freon


3. Containing suspended solid particles: tungsten carbide/tungsten carbide or silicon carbide/silicon carbide should be used for stationary and static ring materials. When the particles are easy to block the sealing chamber, washing liquid after filtration or separation by auxiliary device should be used to flush the end surface.

4, highly toxic or gas medium: it is appropriate to use double end mechanical seal.

Below Parts notes (translation): 1.static ring,2.dynamic ring, 3.press gland, 4.push ring, 5.spring, 6.positioning ring, 7.shaft sleeve, 8.seal ring for dynamic ring, 9.seal ring for static ring, 10.seal ring for shaft sleeve



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