Mechanical Seals

A mechanical seal is a very effective device. Every centrifugal pump must accommodate a spinning shaft while mechanically maintaining fluid or gas contained in the “wet end” of the pump. Mechanical seals consists primarily of a rotary seal face with a driving mechanism which rotates at the same speed as the pump shaft, a stationary seal face which mates with the rotary and is retained using a gland or in some pump models an integral stuffing box cover, a tension assembly (utillizing springs or a metal bellows) keeps the rotary face firmly positioned against the stationary face preventing, excluding, and containing contamination and leakage, both when the pump is not in operation and when the pump shaft is rotating. Static sealing gaskets, orings or elastomeric bellows are strategically located to complete the seal assembly.

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How Do Mechanical Seals Work?

At the heart of why a mechanical seal works lies the rotating and stationary seal faces. Seal faces are lapped so flat it is impossible for a liquid or gas to flow through them. This allows for a shaft to spin, while a seal is being maintained mechanically. What determines the amount of time a seal will last is selecting the right seal material combination for the application. Hard seal faces for abrasive service, Carbon Vs. Ceramic for simple water (or anti-freeze in the case of automotive applications). Carbon Vs. Silicon Carbide for most applications to reduce energy consumption and provide long life. For critical applications double mechanical seals are usually recommended.

PTFE Seals

PTFE Seals

Split Seals

Split Seals

Mixer Seals

Mixer Seals

Tandem Seals

Tandem Seals

Inboard Seals

Inboard Seals

In-Line Seals

In-Line Seals

Every other leak path within the mechanical seal is blocked with the use off a gasket, o-ring, wedge (Rubber, PTFE or Flexible Graphite). The other key aspect of a mechanical pump seal is how to maintain the seal. Springs (single or multiple), a metal bellows or just compressed elastomers are used to provide the needed energy to keep pressing the seal faces together. The load the seal faces receive are engineered into the design of the seal. The choice of what is the best depends on the temperature, and nature of what is being sealed (viscosity, abrasiveness, weight (is it a slurry?)).


Mechanical seals are engineered for most pumps, mixer and agitator applications in maintenance. In many cases the designs have been proven to be workhorses over years of use. In others seals must be designed for evolving industrial demands. The basic rotating face mechanical seal design is adaptable to serve a wide range of sealing applications including compressors. Standard mechanical seals can suit most requirements to temperatures of 500 degrees F and shaft speeds to 3600 RPM. The selection of secondary seal type often determines the temperature and chemical capabilities of the seal. The combination of materials used in the rotating and stationary faces define the abrasive resistance, and chemical resistance. Seal face combinations will also determine the amount of energy consumed by the pump, mixer, agitator or compressor. Seal faces can be balanced to permit higher pressure sealing. Balanced seals can seal pressures above 200 psi, or used in a multiple stages for higher pressures or especially severe fluid services. Special mechanical seals can be furnished to meet the most demanding of industrial applications considering pressure, temperature, speed or fluid.

Features of Mechanical Seals:

Advanced and Special Features

  • Invisible leakage (vapor only)
  • Requires less energy than packing
  • Seals a pumps shaft while allowing it to rotate
  • Minimal wear on the shafts or sleeves
  • Some designs accommodate shaft deflections and "End Play"
  • No periodic maintenance
  • Up to 20 year life span
Cartridge Seals

Cartridge Seals

Cartridge Seals

Cartridge Seals are pre-assembled package of mechanical seal components making installation much easier with fewer points for potential mechanical pump seal installation errors to occur.

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Seal Pots

Seal Pots

Seal Pots

Mechanical seals occasionally require a seal pot to provide a buffer fluid for your double cartridge seals. Seal pots can not only provide a lubricating buffer, but they can also heat or cool the barrier fluid they contain.

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Seal Details

Single Spring Mechanical Seals

Single spring mechanical seals have the springs coiled in a right of left hand design. The purpose it to prevent unwinding of the spring since pumps can be designed to turn left or right. While some Mechanical seals designs provide for added flexibility to accommodate shaft run out. The rule of thumb is a mechanical seal should have no more than .003" of run out per inch of shaft. On a two inch pump shaft, .006" would be there permissible run out. Misalignment, shaft deflection, and break away shock loading can all damage a mechanical seal. and should be considered prior ro ordering the seal. Single spring seals resists clogging and are commonly used in waste water applications.

Mechanical seals utilize 3 component parts:

  • 1) Seal faces: one that rotates with the pump shaft and one that remains stationary.
  • 2) Secondary seals - Which includes Gaskets, o-rings, rubber bellows, PTFE or Flexible Graphite wedge or V-Rings.
  • 3) The hardware that connects Mechanical Seals into a single rotary piece which has the following hardware gland rings, lock collars, compression rings, set screws, pins, springs, retaining rings/clips and bellows.
    Cartridge Seals are more complicated and include a sleeve and gland.
  • Cartridge Mechanical Seals

    Cartridge seals are by far the easiest seal to install. It requires sliding the gland over the shaft, tightening the gland bolts, using an allen wrench to tighten the set screws to the pump shaft, and removing the setting clips. The purpose of the setting clips is make sure the seal faces are locked into position on the shaft that provides enough force to maintain a seal, but not too much force that would cause premature wear. The cartridge seal cannot be miss installed. 50% of seal failures are caused by Cartridge seals are by far the easiest seal to install. It requires sliding the gland over the shaft, tightening the gland bolts, using an allen wrench to tighten the set screws to the pump shaft, and removing the setting clips. The purpose of the setting clips is make sure the seal faces are locked into position on the shaft that provides enough force to maintain a seal, but not too much force that would cause premature wear. The cartridge seal cannot be miss installed. 50% of seal failures are caused by miss-installation. Cartridge seals nearly eliminate miss-installation (cartridge seals can still be dropped while being installed, causing failure).

    Cartridge seals must fit the stuffing box there is a form Seal Application Data Form to help the make sure the mechanical cartridge seal fits the pump. You can also order our cartridge seals on line.

    Installation of other seal types such as single spring, multiple spring seals, and metal bellows require a careful calculation to assure the seal is placed in the correct position on the shaft. Over compression of the seal will prematurely wear it, while under compression can permit leakage or not seal at all. When installed properly, in the right application, seals often run for as long as 20 years. Mechanical seal life spans will vary greatly depending on the application. Fo help, ask your American Seal & Packing sales representative for installation directions.

    Mechanical Seals can be classified by Arrangement
    Mechanical Seals can be classified by Arrangement

    A mechanical seal works by having two very flat (generally within 2-3 light bands flat) lapped flat faces. This allows a shaft to turn while maintaining a seal. It is very difficult for leakage to occur (beyond a vapor) if installed properly and in good condition. As mentioned above one face is stationary and one rotates with the shaft. One of the two faces is often a non-galling material such as carbon-graphite. The other face will be a harder material (or have a different lapped surface) providing dissimilar materials (or dissimilar surface) making contact and allowing one to be a sacrificial. The softer mechanical seal face usually has the smaller mating surface and is commonly called the "wear nose" of the mechanical Seal. In the case where abrasives are being sealed, two hard faces are used TC vs. SIC or even TC vs. TC or SIC vs. SIC This works as long as the surfaces are lapped differently (mirror finish vs. matt finish).

    Mechanical Seals can be classified by Design
    Mechanical Seals can be classified by Design

    The Easiest seal to install as a replacement for pump packing is a cartridge type mechanical seal:
    The Beauty of cartridge seals are they are self-contained. Holding all the elements of a mechanical seal set:
    *Rotating Face Seal
    *Stationary Seal face or faces
    *Shaft sleeve
    *Gland

    What is Mechanical Seal

    Recent Seal News

    25

    January
    Cartridge Seals - in stock

    We have placed into inventory ANSI standard cartridge seals which we offer at exceptional prices.

    14

    March
    Metal Bellows Seals

    We offer both General Service Metal Bellows seals, and Hastalloy or AM350 bellows.

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