Posted on the under Mechanical Engineering , Views 2380 , Add a comment

Mechanical seal,Type ,troubleshooting,

 

mechanical seal

 

stage productmflwt80 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

A mechanical seal is a device which helps join systems or mechanisms together by preventing leakage (e.g., in a plumbing system), containing pressure, or excluding contamination. The effectiveness of a seal is dependent on adhesion in the case of sealants and compression in the case of gaskets.

Metallic bellows mechanical seals are also well suited for high- and low-temperature service, provided the secondary seals are made of a suitable material, e.g. Statotherm

 

Basic Operation


A mechanical seal operates by having two flat faces running against each other. The rotating face is secured to the pump shaft while the stationary face is held in the gland. This is the first of the four possible leak paths that must be secured. The others are shown in Figure 2, and are,

between the Rotating Face and the Shaft,
between the Stationary Face and the Gland, and
between the Gland and the Stuffing Box.

The last two are jointly referred to as the “Tertiary Seal”, and each one comprises a fairly simple sealing challenge as there is no relative motion between the two parts involved.

 

Mechanical Seal Types

.

There are multiple designs available for the mechanical seal configuration. Understanding how they work will help the readers select the appropriate type for their application.

They are:

  • Conventional
  • Pusher
  • Non-pusher
  • Unbalanced
  • Balanced
  • Cartridge

Pusher seals incorporate secondary seals that move axially along a shaft or sleeve to maintain contact at the seal faces, to accommodate wear and to assist in the absorption of shaft misalignment.

 

The Seal Faces

 

For many years, the most popular combination of seal face material was the carbon rotating face running on a ceramic stationary. These are still in popular use, and have been augmented by stainless steel, tungsten carbide and silicon carbide.As the seal faces are machined to a high degree of flatness accuracy, very careful handling of these faces is essential during installation. The seal manufacturers’ installation instructions must also be carefully followed to ensure that the seal faces are suitably protected and precisely located.

 

Seal Flexibility Options

.

Any axial or radial movement of the shaft, will require some flexibility from the spring(s) in order to keep the faces closed. This flexibility however can only be carried to a certain degree, and the mechanical condition of the pump plays an important role in the reliability of the seal.

This seal flexibility is usually supplied by a single large spring, a series of small springs, or a bellows arrangement.

In traditional seal designs the springs were applied to the rotating face, but more recent designs apply the springs or bellows to the stationary face of the seal. In fact, it is now quite common to find both stationary and rotating faces of a mechanical seal having some kind of flexible mounting arrangement.

Although the main closing force is normally provided by the pressure in the stuffing box, the springs and bellows compensate for any shaft movement and keep the seal faces closed during startup and shutdown of the pump.

 

Typical Seal installation Mechanical seal,Type ,troubleshooting And mechanical seal replacement

 

Balanced or Unbalanced Seals

.

An Unbalanced Seal exposes the full cross-sectional area of the rear of the rotating face to the stuffing box pressure and creates a relatively high closing force between the seal faces. Balancing a mechanical seal reduces the closing force which tends to lower wear rate and the temperature buildup, thus extending the life of the seal.

While the balanced seal may appear to be the answer to all sealing problems, certain services may be better served with the unbalanced seal, depending on the need. For example, some light slurry applications may need the additional security of the higher closing force at the seal faces.

Regardless of any other consideration, a balanced seal is usually recommended when the stuffing box pressure exceeds 50 p.s.i.

 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

 

Inside or Outside Seals

 

The more popular arrangement positions the seal inside the stuffing box. Although this requires disassembly of the pump wet end to carry out any maintenance on the seal, the main advantage is that it is possible to control the seal environment inside the stuffing box.

An Outside Seal reverses the orientation of the stationary face as shown above and locates the rotating unit on the shaft outside the stuffing box gland. This simplifies installation and saves maintenance man hours.

An important addition to the Outside Seal in recent years is the Split Seal that eliminates the need to dismantle the pump every time the seal needs to be changed.

 

Component or Cartridge Seals

 

A component seal is one where each part of the seal must be assembled on the pump individually. This requires considerable skill and significant time investment on behalf of the maintenance department.

The cartridge seal is a completely self-contained assembly which includes all the components of the seal, the gland and the sleeve in one unit.

As it does not require any critical installation measurements, it simplifies the seal installation procedures while simultaneously protecting the faces from accidental damage. It also effectively reduces the time spent on maintenance by simplifying seal installation and change-out procedures.

 

Single or Double Seals

 

arrangment Mechanical seal,Type ,troubleshooting And mechanical seal replacement

 

A Double Seal is used instead of a Single Seal when a high degree of leakage protection is desired. It comprises two sets of seal faces combining to increase the security of the environment from the pumpage. They are most frequently used for volatile, toxic, carcinogenic, hazardous and poor lubricating liquids.

Every double seal requires a barrier fluid between the two sets of seal faces and ensure that the outer set of faces receive some lubrication. The recent introduction of Gas Seals uses an inert gas between the seal faces which eliminates any possibility of product contamination.

 

 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

 

CONCLUSION

 

When the mechanical seal is properly selected and correctly installed and supported, all it needs is the protection of appropriate environmental controls to provide extensive and reliable service.

 

Bellows mechanical seal

 

Common feature of all bellows mechanical seals is an elastomer or metallic bellows as dynamic sealing element. Mechanical seals of this type are insensitive to contamination and deposits. The metallic bellows serves in addition as a spring to close the sliding faces

 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

 

Elastomer bellows mechanical seal

 

993450376 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

         Rotating mechanical seal with multiple spring not in contact with the product, mounted on the outside

393960557 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

        Rotating rubber bellows mechanical seal with single spring not in contact with the product

429956916 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

        Stationary rubber bellows mechanical seal with single spring in contact with the product

681566651 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

        Stationary rubber bellows mechanical seal with single spring not in contact with the product

PTFE bellows mechanical seal

568612827 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

         Rotating mechanical seal with multiple spring not in contact with the product, mounted on the outside

Metal bellows mechanical seal

677793016 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

  Rotating bellows mechanical seal

145681440 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

            Rotating bellows mechanical seal for use at high and low temperatures with secondary seals of pure graphite

456370527 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

            Stationary bellows mechanical seal

802517795 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

           Rotating roller bellows mechanical seal

669049533 Mechanical seal,Type ,troubleshooting And mechanical seal replacement

           Stationary roller bellows mechanical seal

To learn more download these Catalog

Click on the image to download

Practical Mechanical Seals

 

articles 200801 Contamination Control Fig1 Mechanical seal,Type ,troubleshooting And mechanical seal replacement
Practical Mechanical Seals

 

Mechanical Seals

 

 Mechanical seal,Type ,troubleshooting And mechanical seal replacement
Mechanical Seals

Program that lets you know what type of mechanical seal

 

 Mechanical seal,Type ,troubleshooting And mechanical seal replacement
BURGMANN ABC-mechanical seal
Program that lets you know what type of mechanical seal

Centrifugal Pumps Seals

 

6 Mechanical seal,Type ,troubleshooting And mechanical seal replacement
Centrifugal Pumps Seals

Troubleshooting Guide

 

Mehanical Seal Mechanical seal,Type ,troubleshooting And mechanical seal replacement
Troubleshooting Guide

 

Mechanical-Seal-Basics

 

 Mechanical seal,Type ,troubleshooting And mechanical seal replacement
See this Flash

 

 And Video

Mechanical Seal Basics and Seal Selection Process Training

Mechanical Seal – Working

 

Mechanical Seals

mechanical seal replacement video

 

 

 

 

 

 

 

 

 

 

 

Leave your opinion

A total of 0 users commented