Tip: Mechanical Shaft Seals

With the evolution of sealing technology over the past few decades we are now able to use mechanical shaft seals on just about any application that handles fluids. However, there are a number of factors to consider when designing these seals:

• The nature of the fluids the mechanical shaft seal will encounter must be taken into consideration for seal design and elastomer choices.
• The shaft seal will need lubrication and cooling because the movement of the rotary seal and hydraulic pressure on the seal faces will generate heat.
• Mechanical shaft seals that are not balanced will generate heat, wear the faces quickly and thus quickly fail.
• If pusher seals are handling fluids which crystallize or coke they will be inclined to hang up on the pump shaft. This happens because the secondary sealing member which needs to compensate for travel when the seal faces wear will not be able to.
• The rotary part of a mechanical shaft seal will be either a positive or friction drive. If the wrong drive is used for your application, the seal will quickly fail.
• The best design for sealing pumps is to use inside mechanical shaft seals but outside seals can be installed if the pump has a stuffing box that is too small for the seals.
• Double mechanical seals can be used if needed for performance optimization and cost effectiveness.
• If it is important for your application to have absolutely no leakage (such as with hazardous materials), tandem seals will allow you to set up a fail safe design with the use of alarms, shut-down devices, etc.
• In applications where you do not have much downtime for replacing seals, cartridge seals can be readied and pre-set so they are available for installation quickly.