Mechanical Seal Selection

Mechanical Seal Selection

The proper selection of a mechanical seal can be made only if the full operating conditions are known:

1. Liquid
2. Pressure
3. Temperature
4. Characteristics of Liquid
5. Reliability and Emission Concerns

1. Liquid: Identification of the exact liquid to be handled is the first step in seal selection. The metal parts must be corrosion resistant, usually steel, bronze, stainless steel, or Hastelloy. The mating faces must also resist corrosion and wear. Carbon, ceramic, silicon carbide or tungsten carbide may be considered. Stationary sealing members of Buna, EPR, Viton and Teflon are common.
2. Pressure: The proper type of seal, balanced or unbalanced, is based on the pressure on the seal and on the seal size.
3. Temperature: In part, determines the use of the sealing members. Materials must be selected to handle liquid temperature.
4. Characteristics of Liquid: Abrasive liquids create excessive wear and short seal life. Double seals or clear liquid flushing from an external source allow the use of mechanical seals on these difficult liquids. On light hydrocarbons balanced seals are often used for longer seal life even though pressures are low.
5. Reliability and Emission Concerns: The seal type and arrangement selected must meet the desired reliability and emission standards for the pump application. Double seals and double gas barrier seals are becoming the seals of choice.

Seal Environment

The number one cause of pump downtime is failure of the shaft seal. These failures are normally the result of an unfavorable seal environment such as improper heat dissipation (cooling), poor lubrication of seal faces, or seals operating in liquids containing solids, air or vapors. To achieve maximum reliability of a seal application, proper choices of seal housings (standard bore stuffing box, large bore, or large tapered bore seal chamber) and seal environmental controls (CPI and API seal flush plans) must be made.

STANDARD BORE STUFFING BOX COVER

Designed thirty years ago specifically for packing. Also accommodates mechanical seals (clamped seat outside seals and conventional double seals.)

CONVENTIONAL LARGE BORE SEAL CHAMBER

Designed specifically for mechanical seals. Large bore provides Increased life of seals through improved lubrication and cooling of faces. Seal environment should be controlled through use of CPI or API flush plans. Often available with internal bypass to provide circulation of liquid to faces without using external flush. Ideal for conventional or cartridge single mechanical seals in conjunction with a flush and throat bushing in bottom of chamber. Also excellent for conventional or cartridge double or tandem seals.

LARGE BORE SEAL CHAMBERS

Introduced in the mid-8o's, enlarged bore seal chambers with increased radial clearance between the mechanical seal and seal chamber wall, provide better circulation of liquid to and from seal faces. Improved lubrication and heat removal (cooling) of seal faces extend seal life and lower maintenance costs.

BigBore^{TM Seal Chamber}

TaperBore^{TM Seal Chamber}