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Various Seal Designs

Guide to Mechanical Seal Types and Component Properties - Page 2

The basic seal designs have variations that develop seals that meet specific applications. Each seal design has its own strengths and weaknesses.

Cartridge Seal

The cartridge design changes none of the functional components of the basic seal classifications. In a cartridge seal, all items are containerized and only require the tightening of gland bolts, flush connections, and drive screws. The need to scribe lines and make critical measurements is usually eliminated.

Cartridge seals are available in each of the basic types and classifications.

The limiting factor in the designing of a cartridge seal is the space availability in a pump's stuffing box area as they may require greater axial depth and radial cross section.

Pump Seal U Cup Design

"U" Cup Seal

The secondary seal, or "U" cup can be made of PTFE, elastomers or a composite. The large single spring does not drive the rotary but does spread the secondary seal and maintain face loading during pump operations and shutdown.

This seal is a heavy duty balanced design that normally requires greater axial and radial space than does a conventional multi-spring balanced seal.

Pump Seal V Ring Design

"V" Ring Seal

The "V" ring is a sealing device that requires constant loading of the "V" ring in order to seal. If the seal is of the type that will work either inside or outside, then the "V" ring must be turned so that it seals the fluid.

To reduce the clogging of multiple spring types, this design is fairly open and allows fluid circulation to clean the springs as the seal rotates.

Pump Seal O Ring Design

"O" Ring Seal

This particular seal has a dynamic "O" ring secondary seal and a static "O" ring shaft seal. The springs in this design are isolated from the pumped fluid by the "O" ring seals and cannot become clogged unless leakage occurs across the seal face.

This type of seal is normally balanced within its own component parts.

Pump Seal Wedge Design

Wedge Seal

This seal employs a PTFE sliding wedge that mates with a carbon seal face. The wedge makes contact with the shaft and has an interference fit with the carbon.

It contains no close-tolerance fits. This seal is designed for inside use, but may be used outside at low pressures.

Pump Seal Boot Type Design

Boot Type Seal

This seal employs a large single spring that maintains face contact but the drive (the turning of the unit with the shaft) is furnished by the rubber elastomer boot.

Care should be used when installing the seal because the elastomer must grip the shaft if the seal is to drive.

Pump Seal Bellows Design

Bellows Seal

The welded metal bellows design offers a series of thin washers that are welded together on their outside and inside diameters. Each welded set of plates has a fixed amount of axial (along the shaft) movement. The more welded plates that are added to the seal, the greater the ability of the seal to move to adjust for face wear.

The welded plates are usually made of corrosion-resistant material such as Hastelloy* or 300 series stainless. Welded metal bellows designs, which have no sliding elastomers, can be used at elevated temperatures when outfitted with graphite or metal secondary seals. Bellows seals are balanced by design.

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