FACTORS AFFECTING THE SELECTION OF MECHANICAL SEALS

Presents

“FACTORS AFFECTING THE SELECTION OF MECHANICAL SEALS” 

1. Media Handled :

Corrosiveness of media decides the material of construction.
• Density of viscosity shows the lubricating properties of the media. This decides the seal arrangement.
                   

• Abrasives in the media decides the type of flushing plan required Corrosiveness of media decides the material of construction.
• Density of viscosity shows the lubricating properties of the media. This
decides the seal arrangement.
• Abrasives in the media decides the type of flushing plan required.

2. Stuffing box pressure :

• When stuffing box pressure < 10 kg. / cm2, unbalanced seals are used.
• When stuffing box pressure . 10 Kg. / cm2 , balanced seals are used.

3. Shaft Speed :

• With increase in speed the chance of seal running dry increases. So proper
flushing plan has to be decided which can give positive flush between the
faces.

4. PV Factor :

• PV factor is defined as the product of the pressure drop across the seal and
the average rubbing velocity. As a general guide, Seal capabilities can be
classified as, Low , if the PV value is 0.7 MPa m/s ( about 20,000 psi ft/min)
Medium, if the PV value is between 0.7 and 10 MPa m/s ( about 285,000 psi
ft/min) High , if the PV value ranges from 10 to 70 MPa m/s (about 2,000,000 psi
ft/min). Balanced seals reduce the pressure acting on the seal faces, therefore they have higher PV values than unbalanced seals.

5. Temperature :

• This decides the material of construction so that the seal does not fail at operating temperature.
• This will decides the seal flushing plan.