It is commonly known that pump mechanical seals are temperamental devices that fail frequently. The fact is, mechanical seals are simple devices that are often misapplied, sometimes installed incorrectly, or perhaps installed on pumps that are not well suited for the application.

Para aquellos que son nuevos en el negocio de la reparación de bombas, los sellos pueden resultar intimidantes, sin embargo, es bien conocido que los sellos mecánicos de las bombas son dispositivos temperamentales que fallan con frecuencia. El hecho es que los sellos mecánicos son dispositivos simples que a menudo son utilizados de forma inadecuada, algunas veces instalados incorrectamente o tal vez montados en bombas que no son aptas para la aplicación. En la mayoría de las aplicaciones, los sellos mecánicos son lo suficientemente macizos para tolerar condiciones de operación y de manejo menos óptimas. Para aplicaciones exigentes todo debe estar bien.

Centrifugal pump failures are most commonly attributed to seal failure, impeller damage and bearing failures. A good understanding of failure modes for seals, impellers and bearings is essential to providing customers with reliable pump repairs.

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One of the most common repairs on centrifugal pumps is replacing worn or damaged wear rings. To restore efficient, reliable operation and prevent catastrophic pump failure, it is critical to restore proper clearances between the stationary casing wear ring and the rotating impeller wear ring. Although many pump manufacturers provide clearances and dimensions, some do not. There are plenty of aging pumps around from now-defunct manufacturers for which dimension data is simply not available.

In such cases, the rule of thumb that follows provides some guidance for acceptable running clearances, or the minimum running clearance chart in American Petroleum Institute (API) Standard 610 can be used as a guide.

A leak rate of one drip per minute equals about a liter (quart) of water in three days. For an O-ring on a submersible pump, that is a major problem. O-rings are often used for static seals on submersible pumps. Understanding what makes a good static seal and what causes one to leak is important for pump maintenance and repair technicians.

For many larger centrifugal pumps, there are options for installing “component” or “cartridge” mechanical seals. Understanding the advantages and limitations of each will allow you to recommend the best solution for customer applications.

One drip per minute amounts to about a liter (quart) of water in 3 days. If that's the leak rate for an O-ring on a submersible pump, that's a big problem. O-rings are common for static seals on submersible pumps. An understanding of what makes a good static seal, and what causes them to leak, is obviously important for pump repair technicians.

Split case pump seals are commonly the most difficult installation of any mechanical seal. The replacement of these seals usually is determined by the type originally found in the pump. The problem is that the existing seal type may not be the best for the fluid pumping application. The fluid to be pumped often is the last thing considered for a system designer specifying a pump for a general application. And if the fluid contains more than just water, problems can start to arise.

Pump packing is a high maintenance item for any centrifugal pump so equipped, and unacceptable for chemical pumping applications. This paper covers how service centers can convert a pump from packing to mechanical seals.