SUBJECT: Writing a set of seal specifications 4-3

It is extremely important for any modern process company to have a good set of seal specifications. When written properly the specifications will:

Classify seals by operating conditions.

Speed

Pressure

Temperature

Motion capability

Use dual seals

In each of these configurations the sealed product is at the inside diameter of the seal faces and sliding components. Solids in the fluid will cause problems as centrifugal force throws the solids into the seal faces and restricts the free movement of the sliding and flexing components.

The inner seal should be pressure balanced in both directions to prevent opening of the inner seal if barrier fluid (or system) pressure fluctuates or is lost. Two way balance can easily compensate for vacuum or reversing pressure.

Clearly identify all of the seal materials, otherwise it'll be impossible to troubleshoot a premature seal failure.

Desirable features in any mechanical seal.

Repair kits

Present and more restrictive future legislation will discourage the shipment of seals to outside repair facilities or back to the manufacturer because of personnel hazard problems. Try to select designs that can easily be cleaned and the critical parts replaced at your facility. The following parts must always be replaced:

Relapping of the hard face is acceptable as long as there are no cracks or chips visible.

® E.I.DuPont Dow elastomer

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