MECHANICAL SEALS OR PACKING?

There is an upside to change from packing to mechanical seals, however not all conditions favor seals, so a good general knowledge about sealing systems is important in the decision process.

In order to understand why pumps need to be sealed, we need to go back to some pumping basics and review how a centrifugal pump operates.

The product being pumped enters a centrifugal pump through the suction nozzle at the center of a rotating impeller.  As the impeller rotates, its vanes fill with fluid, then force it out to the pump casing (volute) where it exits the pump at the cutwater through the discharge nozzle.

The discharge pressure will force fluid back behind the impeller, where it attempts to exit by way of the rotating pump shaft. Some pump designs by manufacturers attempt to minimize this leakage, but it can not be stopped entirely. Some form of a sealing method must be applied to stop or minimize the leakage.

PACKING

Packing materials were originally the sealing medium of choice, using soft flexible plant or man-made materials twisted or braided. Today’s packings come in a wide array of materials and configurations, with something for almost every application. It is still a very popular method of sealing pumps because of cost and ease of installation. Depending on the type of packing chosen it needs to leak under and around packing set to lubricate and cool.  Packing also is regarded as a destructive sealing medium due to running directly on the sleeve or shaft causing wear, sometimes extreme wear allowing unacceptable leakage. This becomes a housekeeping problem and loss of product being pumped. These costs are usually not considered when using packing but are actually a part of the total sealing costs.

MECHANICAL SEALS

Mechanical seals are a device used to seal fluids on a rotating shaft, consisting of two flat rings usually of different materials, one of which is rotating, the other stationary, both mounted perpendicular to the shaft. A seal is achieved by keeping the rings in contact with each other usually with a spring arrangement as the shaft turns. There are many engineering configurations and materials used depending on the application.

The greatest benefit of using mechanical seals is the drastic reduction in leakage. That reduction in leakage also has an effect on other things as well. Things like a safer work environment without a wet floor or possible contact with hazardous fluids. Fewer beating failures caused by leaking fluid and no damage from packing to the rotating shaft. The maintenance department also sees savings in time and budget. No more adjusting or replacing packing or sleeve. There also is a large reduction in power consumption versus packing. There is up to 40% reduction in friction loss with seals.

At Priest Electric we have the expertise and technical advice to help you in deciding the best sealing medium and represent some of the best manufacturers in the world.

Have questions about packing or mechanical seals – give us a call, or contact us online!

To Contact Us Call: 1.208.459.6351