Balanced and Unbalanced Types Of Mechanical Seal

Balanced and Unbalanced Types Of Mechanical Seal

What is the mechanical seal balance?

Mechanical Seal balance is employed to refer the load act across the seal faces. If the load at the seal faces is simply too high, the liquid film between the seal rings might be squeezed out or gasified.

Associate unstable condition from thermoelastic instability might end in a high wear rate of the protected surfaces.

Seal reconciliation will avoid these conditions and result in an increase in the lifetime of mechanical seal and cut back power consumption.

The pressure in any packing box acts equally altogether directions and forces the first ring against the sex ring. The force (F) acts solely on the diameter (Do) across the seal face, it acts as a closing force on the seal faces.

To relieve the force at the seal faces, the diameter of the shoulder on a sleeve or on the seal hardware is decreased . Thereby the seal face pressure will be down. this can be known as seal reconciliation.

A seal while not a shove the look is an associate unbalanced seal. A balanced seal is meant to work with a shoulder. solely metal bellows seal could be a balanced seal that doesn’t need a shoulder.

Seal balance Ratio:

The seal mechanical seal – Balanced and Unbalanced manufacturer shall style the seal faces and seal balance magnitude relation to hiding seal-face-generated heat in keeping with optimum seal life.

As per API 682, the seal balance magnitude relation is calculated as follows,

For seals controlled at the surface diameter, the seal balance magnitude relation, B, is define by the simplified equation:

B= (Do2 – Db2) / (Do2 – Di2)

where

Do – outside diameter of seal face;

Di – within diameter of seal face;

Db – balance diameter of the seal.

For seals controlled at the inner diameter, the seal balance magnitude relation is outlined by the equation:

B= (Db2 – Di2) / (Do2 – Di2)

where

Do – outside diameter of seal face;

Di – within diameter of seal face;

Db – balance diameter of the seal.

For the balanced seal, the balance ratio is adequate to one.

Unbalanced Seals

Virtually all mechanical seals area unit offered in either unbalanced ( referee. Figure) or balanced versions. The term “unbalanced” using once the packing box pressure times the realm exposed to the pumped-up fluid (closing force), acting to shut the seal faces, is larger than the common pressure between the seal faces (pressure gradient)times the realm of contact between the faces.

In different words, unbalanced mechanical seals exhibit web hydraulic closing forces that, generated by the particular pressures to be sealed.

For example, if there have been a packing box pressure of fifty PSIG (3.4barg), the spring load would have to be compelled to be more.

Hence, the “face load” or closing force on the faces would be even beyond fifty PSIG times the face space. This, of course, limits the pressure waterproofing capability of, unbalanced seal.

Unbalanced seals area unit typically a lot of stable than balanced seals once subjected to vibration, placement, and cavitation. The disadvantage is their comparatively unaggressive limit.

If the closing force exerted on the seal faces exceeds the pressure limit, the lubricating film between the faces is squeezed out and also the extremely loaded dry running seal fails.

Balanced Seals

The balanced seal has an equivalent gap (face) space because the unbalanced seal, however the closing space has been reduced in regard to the face space. as a result of force equals pressure times space, reducing the closing space reduces the closing force. Consequently, less heat is generated and also the seal usually features a longer life.

For example, if the packing box pressure were three hundred psig (20.6 barg), then cyberspace closing force would be well reduced to maybe ninety psig (6.2 barg).

To alter the reason, reconciliation a mechanical seal involves a tiny low style modification that reduces the hydraulic forces acting to shut the seal faces. Balanced seals have higher pressure limits, lower seal face loading, and generate less heat. they’re higher able to handle liquids with low lubricity and high vapor pressures.

This is able to embrace lightweight hydrocarbons. Because seal styles vary from manufacturer to manufacturer and from application to application, it’s insufferable to standardize on either configurations or materials that cowl all conceivable services.

Offered basic styles have variations that were typically developed thus on meet specific applications. every seal style has its own strengths and weaknesses.

Conclusion:

Nowadays most of the seal makers area unit used solely balanced mechanical seal. In some special mechanical seals (ie., designed seals) area unit designed with unbalanced mechanical seal.

Balanced mechanical seals ar a lot of most popular than unbalanced mechanical seals.Seal balance magnitude relation may be inside the vary from zero.65 to 1.35, looking on operational conditions.