How to Choose the Gaskets of Valves Correctly?
How to Choose the Gaskets of Valves Correctly?

A gasket is a mechanical seal between two objects, which is usually used to prevent pressure, corrosion, and natural thermal expansion, contraction, and leakage of pipelines between two objects. Due to the impossibility of perfect-machined surfaces, the use of gaskets can fill in the irregularity.

1. The correct selection of sealing gaskets is the key to ensuring that the valve is leak-free. For the same working conditions, there are generally several types of pads.

Notes during selection
The correct selection of valve-sealing gaskets is the key to ensuring that the equipment is leak-free. For the same working conditions, there are generally several types of gaskets available for selection. It is necessary to select gaskets reasonably based on the physical properties, pressure, temperature, equipment size, operating conditions, and continuous operating cycle of the medium, to maximize strengths and avoid weaknesses, and fully utilize the characteristics of various gaskets.

When selecting gaskets, the following factors should be fully considered.
(1) It has good elasticity and resilience and can adapt to pressure changes and temperature fluctuations.
(2) It has appropriate softness and can fit well with the contact surface.
(3) Non-polluting process medium
(4) It has sufficient toughness without causing damage due to pressure and tightening force.
(5) At low temperatures, it does not harden and has a small shrinkage.
(6) Good processing performance. It is easy for the installation and compression.
(7) Non-adhesive sealing surface, and it is easy to disassemble.
(8) Cheap price and long service life.

In the use of gaskets, pressure and temperature are mutually constrained. As the temperature increases, the gasket material undergoes softening, creep, and stress relaxation. The mechanical strength also decreases, and the sealing pressure decreases after a period of equipment operation. The reverse is also true. For example, the manual lists high-pressure asbestos rubber sheet XB450 used in water and steam media at a temperature of 450 ℃ and a pressure of less than 6MPa (when conducting sealing performance tests on this material, it is kept under pressure for 30 minutes in steam at 440 degrees to 450 degrees and 12MPa). However, the pressure that can be sealed is only 0.3 to 0.4MPa if the temperature reaches 450 degrees in long-term practical use. For gas media with strong permeability, it is only 0.1 to 0.2MPa. The above situations should be fully considered when selecting.

Summary: Based on the material characteristics and selection criteria of the gasket, there are the following suggestions.

1. High-risk situations must achieve good sealing and safety without danger. High-risk situations include high temperature, high pressure, steam, toxic media, flammability, and explosiveness. Gaskets should be made of high-performance metal ring gaskets, toothed combination gaskets, spiral wound gaskets, wave tooth composite gaskets, etc. The spiral wound gasket ensures the attachment of inner and outer reinforcement rings. The corrugated composite gasket can be the preferred product because of its good comprehensive performance and moderate price. There is no change in working conditions. The tooth-shaped gaskets and metal flat gaskets should be used. Due to manufacturing costs and other factors, the use of metal ring gaskets is not ideal and should be avoided.

2. Asbestos-containing sealing materials should be used sparingly or not, as these materials can generally only be used in low-parameter working conditions such as ordinary water, steam, and oil in unimportant situations. High-strength graphite pads can be used instead of asbestos rubber sheets in low-parameter situations. Although expensive, it has good performance and is currently a common substitute material for asbestos rubber sheets.

3. There are changes in pressure and temperature, vibrations, and impacts (such as flange connections of dynamic equipment such as pumps and compressors). The spiral wound gaskets and corrugated composite gaskets with good rebound performance should be used.

4. The heating medium heating system should use high-strength graphite composite pads, etc., and try not to use asbestos rubber sheets as sealing components. Graphite, which will not swell or expand, and has strong resistance to medium permeability, should be selected as the main body for spiral wound gaskets, wave tooth composite gaskets, etc.

5. The sealing components of pipelines and process equipment that come into contact with production materials should not use asbestos rubber sheet materials as much as possible in industries such as medicine and food. The main material is a PTFE gasket, which is ideal, especially for the better performance of the wrapping gasket. It can overcome the disadvantages of PTFE flat gaskets. It has no elasticity and good elasticity and it is clean and pollution-free.

6. For general corrosive media, stainless steel frame wound gaskets and corrugated composite gaskets can be used. Flat gaskets and PTFE-coated gaskets are used for strong corrosion conditions. 
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