Each mechanical seal can only function effectively within the specified range. Improper selection will significantly reduce sealing performance, shorten service life, or even cause failure.
The main parameters for selection are as follows
When the medium has good lubricity and high viscosity, choose non-equilibrium type if P≤0.8MPa. When the medium has poor lubricity and low viscosity, P≥0.5Mpa
For V≤25m/s, choose the rotary type. Use the static type when V≥25m/s.
The PV value relates to the stability (vaporization) of the fluid film between the sealing surfaces and the wear resistance of the friction pair. Example of PV limit value:
Selection of mechanical seals and the main parameters of mechanical seals that need to be considered
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 table below:
Selection of mechanical seals and the main parameters of mechanical seals that need to be considered
1. Viscosity: Low viscosity medium is easy to dry and friction should be balanced type. For high viscosity media, a forced transmission structure should be used.
2. Corrosion and chemical solvents: a. For strong corrosion, external PTFE bellows sealing should be used.
b. The application table of auxiliary seals in different chemical media is as follows:
Material Usage
Nitrile rubber (NBR)
Mineral oil, gasoline, volatile oil, potassium carbonate, potassium hydroxide, water, phosphoric acid, etc.
Silicone rubber (MVQ)
Butanol, low swelling mineral oil, weak acid, weak alkali, ammonia, etc.
Ethylene propylene rubber (EPR)
Acetone, alkali, sulfur dioxide, potassium dichromate, hydrogen peroxide, ammonia, etc.
Fluorine rubber (FPM)
Hot oil, steam, inorganic acids, butanol, chlorine solvents, etc.
Chlorohydrin Rubber (FCO)
Freon
Polytetrafluoroethylene (PTFE)
Acids, alkalis, solvents and various media
3. Containing suspended solid particles: The material of the dynamic and static rings should be tungsten carbide/tungsten carbide, or silicon carbide/silicon carbide. When the particles are easy to block the sealing cavity, the flushing fluid filtered or separated by the auxiliary device must be used to flush the end face.
4. Highly toxic or gaseous media: Double-end mechanical seals should be used.
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