SUBJECT : Environmental controls and special seals 3-2

For any given seal application problem there are two generally accepted solutions :

In the following paragraphs I'll be covering each of these environmental controls in detail.

CONTROLLING THE TEMPERATURE IN THE STUFFING BOX AREA.

CONTROLLING THE PRESSURE IN THE STUFFING BOX AREA

PROVIDING A LUBRICANT IF THE SEALING PRODUCT IS A NON LUBRICANT ( Non lubricants have a film thickness less than one micron)

NOTE. If the impeller has been adjusted too close to the back plate the "pump out vanes" can cause a vacuum to occur in the stuffing box. This often happens if the impeller adjustment has been made backwards (as is the case with Duriron pumps). The problem exists with those open impeller designs that adjust towards the volute (Goulds is an example).

DECREASING THE AMOUNT OF LIQUID AGITATION IN THE STUFFING BOX.

This becomes very important if you have to seal a liquid that increases its viscosity with agitation. We call these liquids DILATANTS. Connect the bottom of the stuffing box to the suction side of the pump to allow a single pass of the liquid through the stuffing box. Make sure the connection is very close to the seal faces. You'll be better off using the seal gland flush connection rather than the stuffing box lantern ring connection.

Some liquids decrease their viscosity with agitation. We call these liquids THIXOTROPHIC. In some instances the thinner liquid film can cause more face wear and seal "slip stick". If this problem exists, use one of the environmental controls mentioned above.

HANDLING SLURRY APPLICATIONS.

If you prefer to solve the application problem by using a special seal. the following thoughts might help in deciding your selection.

SEAL DESIGN FEATURES THAT ADDRESS THE PROBLEMS OF EXTREMES IN HOT AND COLD.

If you elect to solve only the sealing problem you must keep in mind that the extremes in heat and cold will also affect the bearing seals as well as the bearing oil. Unless you address these problems separately you will be better off controlling the temperature in the stuffing box area and solving most of the bearing area problems at the same time.

SEAL DESIGN FEATURES THAT ADDRESS THE PROBLEM WITH SLURRIES.

 

®Dupont Dow elastomer

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