BASIC KNOWLEDGE OF PUMP SEALS (1)

With the development of industrial technology and sealing technology, pumps are widely used in many industries such as electric power, chemical industry, petroleum, etc., and requirement for the sealing performance and reliability of pump seals are higher and stricter. The sealing of the chemical pump plays an important role in the operation of the entire equipment. The leakage of the sealing system of the chemical pump will seriously affect the normal operation of the equipment. In particular, the development of high temperature and high pressure pumps has made the sealing of the pumps more strict. Next we mainly introduce the leak parts of chemical pumps and the materials of seals.

1. Leakage Parts of Chemical Pumps

There are many types of mechanical seals for pumps, but there are five main leakage parts:

A. Seals between bush and shaft

B. Seals between moving ring and shaft sleeve

C. Seals between dynamic and static rings

D. Seals between static ring and static ring seat

E. Seals between the sealing end cover and the pump body.

1) Phenomenon: The seal emits a cracking sound during operation (end surface cracking sound)

Possible causes: The sealing liquid vaporizes at the sealing interface, strengthening the cooling of the sealing surface.

Solution: Increase the bypass flush line, expand the bypass flush line and the opening of the gland.

2) Phenomenon: Continuous leakage.

Possible causes: Uneven surface, blistering of graphite sealing surface, thermal deformation of sealing surface.

Solution: During the installation process, the auxiliary seal is scratched and the O-ring is aging. The auxiliary seal becomes hard and brittle due to compression deformation. The auxiliary seal becomes soft and sticky due to chemical action.

3) Phenomenon: Spring failure.

Possible causes: Due to corrosion, metal accessories are damaged and the transmission mechanism is corroded.

Solution: Check the incorrect installation size, check whether the inappropriate material and seal type are used, improve the flushing cooling line, check whether the bolt torque of the gland is too large, causing the gland to deform, and check whether the specific pressure of the gland gasket is appropriate. Check if there are other solid particles between the sealing surfaces, and re-polish the sealing surfaces if necessary.

4) Phenomenon: The seal screams during operation.

Possible causes: Insufficient amount of lubricating fluid at the seal.

Solution: Increase the bypass flush line, expand the bypass flush line and the opening of the gland.

2. Materials of Seals

1) Rubber asbestos gland packing

Rubber asbestos gland packing XS250 (limiting temperature is 250℃), rubber asbestos gland packing XS350 (limiting temperature is 350℃)

Applicable medium: steam, water, alkaline solution.

2) Oil-immersed asbestos gland packing

Oil-immersed asbestos gland packing YS250 (limiting temperature≤250 ℃), YS350 (limiting temperature≤350 ℃). The outstanding features of this kind of products are that the packing contains lubricating oil, the friction coefficient is small, and the compression is large.

Applicable medium: steam, air, industrial water, heavy petroleum products.

3) PTFE asbestos gland packing SMF

Limiting temperature: -100-250℃

Applicable medium: weak acid, strong alkali and other corrosive medium.

4) Oil-impregnated cotton and hemp gland packing YMM

Limiting temperature: ≤120℃

Applicable medium: river water, tap water, ground water, sea water, etc.

5) PTFE fiber braided packing

During use, a small amount of leakage of the gland packing is allowed. After a period of use, when the packing is in a relatively stable state, adjust the packing gland. Never press it too tight at the beginning to prevent it from burning out.

6) Carbon fiber braided gland packing

Carbon fiber braided gland packing is a new material with high strength and high modulus. It has the advantages of high strength, large elastic modulus, high temperature resistance, chemical resistance, good thermal conductivity, low coefficient of thermal expansion, and has self-lubricating properties.

Of course, in addition to the above-mentioned sealing packing, we also have mechanical seals such as spring seals, elastomer bellow seals, etc. The choice of sealing materials needs to be combined with the actual use scenario.