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Valve packing type, selection, leakage causes and solutions, these knowledge please accept


Release time:

2018-01-02

Compression packing is through the compression of the packing gland to produce elastic deformation, and the inner wall of the stuffing box and the valve stem closely match, and produce a layer of oil film in contact with the valve stem to prevent the leakage of the medium. According to its different structure, it can be divided into cotton, molding, rolling, stacking, twisting, weaving and other forming fillers.

1. compression packing

Compression packing is through the compression of the packing gland to produce elastic deformation, and the inner wall of the stuffing box and the valve stem closely match, and produce a layer of oil film in contact with the valve stem to prevent the leakage of the medium. According to its different structure, it can be divided into cotton, molding, rolling, stacking, twisting, weaving and other forming fillers.

According to its different materials, soft filler, semi-metal filler and metal filler.

The use conditions of the compressed packing are introduced below according to the materials composed of the compressed packing.

Made of hemp or cotton impregnated with oil, wax or other impermeable materials for low pressure valves below 100 ℃. Suitable for water, ammonia, acetic acid, caustic soda and other media.

(2) Asbestos fiber filler

Asbestos fiber has good heat resistance, weak acid, strong alkali, high strength, good adsorption performance and so on. Such as adding some acid-resistant and alkali-resistant materials, impregnating materials with small friction coefficients, and adding metal materials with good thermal conductivity, the performance of asbestos fillers can be improved, so that their corrosion resistance, wear resistance, heat resistance, strength, etc. are different Degree of improvement. There are two kinds of asbestos fillers that clamp metal wires and that do not clamp metal. At present, the commonly used asbestos filler is selected according to the JB1712-91. Among them, oil-impregnated asbestos packing (JC68-82) is a sealing material made of asbestos thread (or metal asbestos thread) impregnated with lubricating oil and graphite woven or twisted, and oil-impregnated asbestos packing is divided into three types: square, round and round twisted. There are also rubber asbestos packing (JC67-82), which is a sealing material made of asbestos cloth, asbestos wire (or asbestos metal cloth, wire), rolled or rubber) with rubber adhesive, rolled or rubber adhesive, rubber asbestos packing pressed into a square, coated with high carbon graphite.

(3) Plastic and plastic impregnated filler

YAB type nylon asbestos filler, suitable for corrosive medium, medium temperature ≤ 100 ℃, pressure ≤ 32MPa

PTFE emulsion impregnated asbestos filler, suitable for strong corrosive medium, medium temperature -200~200 ℃ pressure ≤ 35MPa

NFS type PTFE braided packing, suitable for chemicals, medium temperature is -200~260 ℃, pressure ≤ 35MPa

(4) Rubber filler

There are rubber cloth, rubber rod, ring rubber packing, used for temperature ≤ 140 ℃ ammonia, concentrated sulfuric acid and other media.

(5) Carbon fiber filler

The model is TCW type, which is made by impregnating PTFE emulsion with carbon fiber braided rope. Carbon fiber filler has excellent elasticity and flexibility; has excellent self-wetting, high temperature, in the air can be stable in the temperature range of -120~350 ℃, pressure ≤ 35MPa.

(6) Flexible graphite packing

Flexible graphite packing has the following excellent properties:

Unique flexibility and resilience, making incision filler can freely bend more than 90 ° along the axial direction, and will not cause leakage due to temperature and pressure changes, vibration and other factors during use, so it is safe and reliable, and is an ideal sealing material.

② Good temperature resistance. Low temperature can be applied to -200 ° C, in the high temperature oxidizing medium can be used to 500 ° C, in the non-oxidizing medium can be applied to 2000 ° C, and can maintain excellent sealing.

③ strong corrosion resistance. It has good corrosion resistance to acids, alkalis, organic solvents, organic gases and vapors. No aging, no deterioration, in addition to strong oxidizing medium (nitric acid), fuming sulfuric acid, chromic acid, halogen, etc., can resist the corrosion of all media.

④ low friction coefficient, good self-lubrication.

The gas and liquid has excellent impermeability.

The service life is long, can be used repeatedly.

Flexible graphite is widely used in petroleum, chemical industry, power generation, fertilizer, medicine, papermaking, machinery, metallurgy, aerospace and atomic energy industries. Flexible graphite packing can generally be pressed into shape. Applicable nominal pressure ≤ 32MPa.

(7) Expanded PTFE

After expansion treatment of PTFE, to overcome the shortcomings of poor elasticity, with the elasticity of rubber, without losing its original characteristics, performance is greatly improved, with a 100% expansion of PTFE woven packing, mainly used in the valve, applicable temperature -268~288 ℃, the wear of the valve stem has a good sealing effect. In the expansion of polytetrafluoroethylene mixed with certain graphite and high temperature lubricant yarn and woven packing, can be used as a linear speed of 21.8 m/s pump packing.

(8) Ceramic fiber filler

The model is NGW type, which is made of ceramic fiber and metal alloy wire as the main raw material, and then added graphite talc powder. Its temperature resistance is excellent, and it can withstand cryogenic and ultra-high temperature media; corrosion resistance is very good. At present, the domestic application is less. The use temperature of ceramic fiber filler made abroad can reach 1480 ℃.

(9) Metal packing

According to its structure, it can be divided into metal foil winding packing, metal foil kneading and creping packing, metal waveform packing, lead wire twisting packing and lead ring packing.

Metal foil with winding filler and metal foil kneading crepe laminated filler, its advantages are high temperature resistance, erosion resistance, wear resistance, high strength, good thermal conductivity. But the sealing performance is poor, the need for more in the pressing force, must be used in conjunction with the plastic filler. Its use temperature, pressure, corrosion resistance depending on the metal material. Metal waveform filler: the model is BSP-600 type, the wave sheet material is 1 Cr18Ni9Ti, the use temperature is less than or equal to 600 ℃, and the pressure is less than or equal to 20MPa, which is a good filler.

Lead wire twisted filler is mainly used in the temperature of 90 ℃ or less concentrated sulfuric acid and other media.

Lead ring filler is a filler that is cast into a square section after melting lead, and is used in staggered assembly with asbestos filler. Can be used in oil medium with temperature ≤ 500 ℃.

2.V-type packing

V-type packing consists of upper packing, middle packing and lower packing. The upper and middle fillers are made of PTFE or nylon, and the lower filler is made of 1Cr13,1 Cr18Ni9,A3 steel and other materials. PTFE temperature 232 ℃, nylon temperature 93 ℃, general pressure 32MPa, commonly used in corrosive media.

3. O-ring packing

The O-ring section is circular, and its material is rubber, PTFE and metal hollow O-ring. The O-ring is not only used for static sealing, but also for dynamic sealing. Among them, the rubber O-ring is the most widely used. The maximum pressure of O-ring can reach 40MPa.

4. corrugated pipe packing

Bellows used for sealing, can save packing, so called bellows without packing seal. It is a folded round tube body, one end is fixed on the valve stem, the other end is fixed on the valve cover, the valve stem and the valve cover is in a fully closed state, the valve stem can be made up and down movement. Some use bellows in combination with asbestos filler. The bellows are made of 1 Cr18Ni9Ti, high zinc Dutch brass and other materials for toxic media and occasions with high requirements on the sealing surface. The general use pressure is 0.6MPa, and the use temperature is ≤ 150 ℃.

5. liquid packing

Liquid filler is mainly used as a partition between other fillers.

Cause of leakage at 6. packing

1. Packing selection is wrong, not resistant to medium corrosion, not resistant to the valve high pressure or vacuum, high temperature or low temperature use;

2. The packing is installed incorrectly, and there are defects such as replacing large with small, poor spiral winding joints, tightening and loosening;

3. The filler exceeds the use period, has been aging, loss of elasticity;

4. Stem precision is not high, there are bending, corrosion, wear and other defects;

5. The number of packing rings is insufficient, and the gland is not pressed;

6. The gland, bolts and other parts are damaged, so that the gland cannot be compressed;

7. Improper operation, excessive force, etc;

8. The gland is skewed, and the gap between the gland and the valve stem is too small or too large, causing the valve stem to wear,

Solution of 7. packing damage

1. The material and type of filler shall be selected according to the working conditions;

2. Correctly install the packing according to the relevant regulations, the packing should be placed and pressed one by one, and the joint should be 30 ° or 45 °;

3. The use of long, aging, damaged filler should be replaced in a timely manner;

4. stem bending, wear should be straightened, repair, serious damage should be replaced;

5. The packing shall be installed according to the specified number of turns, the gland shall be tightened symmetrically and evenly, and the pressing sleeve shall have a pre-tightening gap of more than 5mm;

6. Damaged glands, bolts and other parts should be repaired or replaced in time;

7. Should comply with the operating procedures, in addition to the impact handwheel, with uniform speed normal force operation;

8. The gland bolts should be tightened evenly and symmetrically. If the gap between the gland and the valve stem is too small, the gap should be appropriately increased;