The selection of mechanical seals and the main parameters of mechanical seals that need to be considered in the selection1

Every kind of mechanical seal can only function effectively within the specified range. Improper selection will significantly reduce the sealing performance, shorten the service life, or even fail.

The main parameters of the selection are as follows

1. The medium pressure of the sealed chamber P

The medium has good lubricity, and when the viscosity is high, the unbalanced type is selected for P≤0.8MPa. Medium lubricity is poor, when the viscosity is low, P≥0.5Mpa

2. Linear speed V

V≤25m/s selects the rotary type. When V≥25m/s, the static type is selected.

3. 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:

The selection of mechanical seals and the main parameters of mechanical seals that need to be considered in the selection

Four, 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 table below:

The selection of mechanical seals and the main parameters of mechanical seals that need to be considered in the selection

Five, the particularity of the medium.

1. Viscosity: Balanced type should be selected for low-viscosity medium which is easy to dry friction. For high-viscosity medium, forced transmission structure should be adopted.

2. Corrosion and chemical solvents: a. Strong corrosion should be sealed with external PTFE bellows.

b. The applicable table of auxiliary seals in different chemical media is as follows:

Material Purpose

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 base, ammonia water, etc.

Ethylene Propylene Rubber (EPR)

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

Viton (FPM)

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

Chlorohydrin rubber (FCO)

Freon

Polytetrafluoroethylene (PTFE)

Acids, alkalis, solvents and various media

3. Containing suspended solid particles: Tungsten carbide/tungsten carbide, or silicon carbide/silicon carbide should be used as the material of the dynamic and static rings. When the particles are easy to block the sealing cavity, the flushing solution filtered or separated by the auxiliary device must be used to flush the end face.

4. Highly toxic or gaseous medium: Double mechanical seals should be used.