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Machinery Seals Of The Various Types
May 17, 2017

Machinery Seals have basic types: contact and non-contact Machinery Seals, built-in and exterior Machinery Seals, internal and external Machinery Seals, spring-operated and spring-loaded Machinery Seals, unbalanced and balanced Machinery Seals, single spring and multi-spring mechanical seal, push ring (spring loaded push ring) mechanical seal and bellows seal, etc., the following detailed description of the various mechanical seal concept and related knowledge.

1, contact and non-contact mechanical seal

Contact mechanical end seal is the sealing surface of the asperity contact with the mechanical seal, sealing surface clearance h = 0.5 ~ 1um. Ordinary Machinery Seals are contact Machinery Seals. Non-contact mechanical end seal is the sealing surface of the asperity is not in contact with the mechanical seal, sealing surface clearance for fluid dynamic seal h> 2um, for hydrostatic seal h> 5um. When the work gap changes, its value exceeds the sealing surface lift point clearance (h> hc, contact gap), the sealing surface asperity began to contact, contact mechanical seal will become non-contact mechanical seal, the same H <hc non-contact mechanical seal will become a contact mechanical seal.

Contact mechanical seal friction state is mixed friction, there are boundary friction and dry friction; non-contact mechanical seal friction state is fluid lubrication, but also flexible fluid power lubrication.

Ordinary contact mechanical seal leakage is small, simple structure, widely used. In general, non-contact mechanical seal leakage is large, complex structure, mostly under high parameter conditions or used as a multi-stage seal of the front seal. The use of surface modification technology made of controllable gap non-contact mechanical seal, can achieve zero leakage of process fluid.

In addition, there is a semi-contact mechanical seal that can be adjusted with a balance ratio that can be changed from a contact seal to a non-contact seal or a non-contact seal to a contact seal, as required.

2, built-in and exterior mechanical seal

A mechanical seal mounted on the inside of the gland is called a built-in mechanical seal: a mechanical seal mounted on the outside of the gland is called an external mechanical seal.

A mechanical seal placed inside a sealed fluid is called a built-in mechanical seal; a mechanical seal placed outside the sealed fluid is called an external mechanical seal.

Built-in (built-in) mechanical seal of the spring and dynamic ring installed in the sealed box and the media contact, you can use the media pressure to seal the box. The advantages are: the state of force is good, the leakage is small (due to the direction of leakage and centrifugal force in the opposite direction), cooling and lubrication conditions, the use of a wide range of work (Figure 1-2a).

Outer (external) Machinery Seals of the spring and dynamic ring installed in the sealed box outside the media does not contact, for strong corrosion, high viscosity, easy to crystallization medium. Due to the direction of leakage and centrifugal force in the same direction, the larger the amount of leakage, the use of lower working pressure (Figure 1-2b).

3, the flow and outflow of Machinery Seals

The mechanical seal of the sealing fluid in the direction opposite to the direction of centrifugal force of the sealed fluid is called an internal flow mechanical seal. The mechanical seal in the direction of leakage between the sealing end and the centrifugal force is called an outer flow mechanical seal (Figure 1- 2c and 1-2d).

Since the centrifugal force in the internal flow seal not only prevents the leakage of the fluid, but also prevents the solid particles from entering the sealing surface, the amount of leakage is smaller than that of the outside flow. Usually the inner flow mechanical seal is suitable for high pressure, and the maximum pressure of the external flow mechanical seal is 1 ~ 2MPa.

4, spring-operated and spring-loaded Machinery Seals

The mechanical seal of the elastic element rotates with the shaft is called a spring-mounted mechanical seal; the mechanical seal of the elastic element that does not rotate with the shaft is called a spring-loaded mechanical seal (Figure 1-2e, f).

As the spring-type mechanical seal spring rotating parts by the centrifugal force, it is not suitable for high-speed sealing, but because the structure is simple, radial size is small, commonly used in general mechanical seal. As the spring static mechanical seal of the spring from the centrifugal force, often used in high-speed mechanical seal.





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