valve seat Archives

What is the reason for the poor sealing of the valve

February 17, 2022

Where there is a pipeline, the valve is inseparable. The valve is installed on the pipeline and controls the flow of the fluid medium in the pipeline. It is an important control component. But the valve is also a wearable part. A common valve loss in our life is that the valve is not tightly sealed, resulting in leakage. So what is the reason for the poor

marine valve seat

sealing of the valve?
The leakage at the packing of the valve is a part of the valve that is prone to leakage failures. The valve is not tightly sealed, and the reasons are probably as follows.
1. Sealing auxiliary structure
Under the change of temperature or sealing force, the structure of the sealing pair will change. And this change will affect and change the force between the sealing pair, so that the performance of the valve sealing is reduced. Therefore, when choosing a seal, be sure to choose a seal with elastic deformation. At the same time, pay attention to the width of the sealing surface. The reason is that the contact surfaces of the sealing pair cannot be completely matched. When the width of the sealing surface increases, the force required for sealing is increased.
2. Specific pressure of sealing surface
The specific pressure of the sealing surface affects the sealing performance of the valve and the service life of the valve. Therefore, the specific pressure of the sealing surface is also a very important factor. Under the same conditions, too high specific pressure will cause valve damage, but too low specific pressure will cause valve leakage. Therefore, we need to fully consider the appropriateness of the specific pressure when designing
3. Physical properties of the medium
The physical properties of the medium also affect the valve sealing performance. These physical properties include temperature, viscosity, and hydrophilicity of the surface, among others. The temperature change not only affects the slackness of the sealing pair and the change of the size of the parts, but also has an inseparable relationship with the viscosity of the gas. Gas viscosity increases or decreases with increasing or decreasing temperature. Therefore, in order to reduce the influence of temperature on the sealing performance of the valve, when designing the sealing pair, we should design it as a valve with thermal compensation such as an elastic valve seat. Viscosity is related to the permeability of the fluid. When under the same conditions, the higher the viscosity, the lower the permeability of the fluid. The hydrophilicity of the surface means that when there is a film on the metal surface, the film should be removed. Because of this very thin oil film, it will destroy the hydrophilicity of the surface, resulting in blockage of fluid channels.
4. The quality of the sealing pair
The quality of the sealing pair mainly means that we must check the selection, matching and manufacturing accuracy of materials. For example, the valve disc fits well with the valve seat sealing surface, which can improve the sealing performance. The characteristic of many circumferential waviness is that its labyrinth sealing performance is good.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

Video of center-lined butterfly valve:

Evolution of the Sealing Surface of the Triple Eccentric Butterfly Valve

December 9, 2021

The triple eccentric butterfly valve is one of the butterfly valves. Its unique sealing form and sealing structure are continuously improved and upgraded through the product to obtain a better sealing effect. There have been great reforms in high temperature and corrosion resistance. Let’s take a look at its product upgrade process.

triple offset butterfly valve-double flange- (5)

The butterfly valve’s single eccentric soft-seal butterfly valve is the first to be favored by the market. Because of the design of the soft seal, the product has a good sealing effect. Single eccentricity means that the sealing section of the valve seat is eccentric relative to the center of rotation of the valve stem, so that the sealing surface of the butterfly plate gradually separates from the sealing surface of the valve seat during the opening process. When the butterfly plate rotates to 20-25, the sealing surface of the butterfly plate is completely separated from the sealing surface of the valve seat, so that the relative mechanical wear and extrusion between the two sealing surfaces of the butterfly valve is greatly reduced during the opening process, and the sealing performance of the butterfly valve is improved. This design mainly relies on the elastic deformation of the squeezing between the butterfly plate and the valve seat to ensure the sealing of the butterfly valve.
In order to meet the needs of the site, to achieve the effect that the sealing surface of the butterfly plate is separated from the sealing surface of the valve seat faster than the single eccentric structure, the double eccentric sealing butterfly valve is upgraded on the basis of the single eccentric butterfly valve. The lines are relatively offset, so that the butterfly valve forms a cam effect during the opening process. When the butterfly plate rotates to 8°~12°, the two sealing surfaces can be completely separated. The biggest benefit of this structural design is to further reduce the mechanical wear and extrusion deformation between the two sealing surfaces, which improves the sealing performance of the butterfly valve and increases the lifespan.
The triple eccentric sealing butterfly valve is once again upgraded on the basis of the double eccentric butterfly valve. The center line of the seat sealing surface and the valve center line form an angular eccentricity, and a third eccentricity appears. In this way, during the opening process, the sealing surface of the butterfly plate can be separated from the sealing surface of the valve seat immediately, and will contact and compress the sealing surface of the valve seat at the moment of closing. This unique eccentric design makes full use of the benefits of the cam, so that the mechanical friction and scratches between the two sealing surfaces of the butterfly valve seal pair can be completely eliminated when opening and closing, so that the possibility of wear and leakage is eliminated. The product changes the extrusion seal into a torque seal. By adjusting the external driving torque, the adjustment of the seal specific pressure is realized, so that the sealing performance and service life of the triple eccentric structure sealing butterfly valve are greatly improved. At the same time, while ensuring a tight seal, it also improves the characteristics of the sealing sub-materials of the single-eccentric soft-seal butterfly valve and the double-eccentric soft-seal butterfly valve that cannot withstand high temperature and wear.
Now, the triple eccentric sealing butterfly valve is widely used as the best device to cut off or adjust the flow of the medium pipeline in the urban construction, petrochemical, metallurgy, electric power and other industries. Its structure itself is the most ideal opening and closing part in pipelines, and it is the development direction of today’s pipeline opening and closing parts. If you need butterfly valve products, look for Tanghai Valve. 24 years of experience in butterfly valve production is more assured.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D
Video of triple eccentric butterfly valve: https://youtu.be/AkRwg2X1Wh0

factors affecting the sealing performance of resilient butterfly valve seat

October 21, 2021

Rubber butterfly valve is an important part of regulating flow medium, and tight sealing is the most important quality of the product. The sealing performance of rubber butterfly valves is affected by many factors, and the most important influence is still closely related to the sealing surface. Today we will focus on three factors. Let’s take a

Wafer type butterfly valve with worm gear

look at the main factors that affect the sealing performance of rubber butterfly valves:

1. Quality of the sealing surface/valve seat
First of all, we must make it clear that the sealing surface refers to the part where the valve seat and the disc are in contact with each other for medium opening and closing control, and only which part of the valve seat and the disc are in contact instead of the entire sealing pair. The quality of the sealing surface is mainly related to the quality of the sealing material. The quality of the sealing material should be produced by the brand manufacturer and qualified in process. In addition, the choice of sealing material should be in line with the medium. For example, rubber butterfly valves cannot be used for highly corrosive media.

2. Width of sealing surface/valve seat
The width of the sealing surface mainly affects the movement resistance of the fluid. The larger the sealing surface, the lower the resistance, and the narrower the resistance is relatively large. Therefore, the increase in the width of the sealing surface can reduce the erosion and wear of the sealing surface by the fluid. At the same time, because the increase in the width of the sealing surface increases the length of the leakage stroke proportionally, the leakage can be reduced proportionally. However, the width of the sealing surface must not be excessively increased, because an increase in the width of the sealing surface, under the same sealing force, the reduction of the specific pressure of the seal will increase the possibility of leakage.

3. The pressure difference between before and after the valve
The specific pressure on the sealing surface is caused by the pressure difference between the front and rear of the valve and the applied sealing force, which refers to the pressure acting on a unit area of the sealing surface. The specific pressure directly affects the sealing performance, reliability and service life of the rubber butterfly valve. When the specific pressure on the sealing surface is small and the surface roughness is low, the leakage increases rapidly. When the specific pressure on the sealing surface is large, the effect of surface roughness on the leakage is significantly reduced.

In addition, the sealing performance of the rubber butterfly valve is related to the sealing surface material of the butterfly valve and its processing state, the nature of the medium, the existence of the sealing oil film, the rigidity and structural characteristics of the closing part, and so on. For more information, please call Tanghai for inquiries, and we will have professionals to answer your questions about butterfly valves.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

Commonly Used Seat Materials for Butterfly Valve

August 30, 2021

The valve seat is a detachable part inside the valve. Its main function is to support the valve core to be fully closed or fully closed, and to form a sealing pair. Under normal circumstances, the diameter of the valve seat is the size of the valve. The butterfly valve seat is made of a wide range of materials, but the commonly used materials include soft-seal EPDM, nitrile rubber (NBR), polytetrafluoroethylene (PTFE), and metal hard-seal hard alloy materials. kind. Let’s introduce them one by one below.

wafer type butterfly valve, EPDM seat (10)

1. EPDM: Compared with other general-purpose rubbers, EPDM has great advantages.
①The cost performance is very high. Among the commonly used rubbers, EPDM has the lightest raw rubber density and can be filled in a large amount, reducing the cost of the rubber.
②EPDM material is resistant to aging, sun exposure, heat resistance, moisture resistance, and radiation resistance, and is suitable for weak acid and weak alkali media. Good insulation properties.
③The applicable temperature range can be as low as -40℃–60℃, and it can be used for a long time under the temperature condition of 130℃.
2. Nitrile rubber (NBR): oil resistance, heat resistance, abrasion resistance and good water resistance, air tightness and excellent bonding properties. It is widely used in petroleum pipelines. The disadvantage is that it is not resistant to low temperature, ozone, poor insulation performance, and general elasticity.
3. Polytetrafluoroethylene (PTFE): A fluoroplastic, this material has strong resistance to acids, alkalis, and various organic solvents. At the same time, the material is resistant to high temperatures and can be used continuously at 260°C, and the maximum use temperature can reach 290-320°C. The emergence of PTFE has successfully solved many problems in the chemical, petroleum, pharmaceutical and other industries.

Fluorine lined butterfly valve-PTFE-WAFER (8)

4. Metal hard seal (hard alloy): The material of the metal hard seal valve seat has very good high temperature and high pressure resistance, corrosion resistance, wear resistance and other characteristics, which makes up for the defects of soft seal material that is not resistant to high temperature and high pressure. However, the hard seal material has high requirements on the processing technology. The only disadvantage of the metal hard seal valve seat is that the sealing performance is poor, and leakage will occur after a long time of operation.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

Valve seal (ring) material usage range comparison table

June 4, 2021

Valve seal (ring) material usage range comparison table
The selection of valve sealing material is determined according to the operating conditions of the valve, such as:

marine valve seat

pipeline medium, temperature range (high and low temperature), pressure, and internal structure of the valve. For different occasions, the selected seals are also different. Valve seals can generally be divided into two categories, soft seals and hard seals. Users should have a detailed understanding of their codes, operating temperature, pressure, medium and other parameters.

Comparison table of valve sealing material usage range:

Valve sealing material	Use range of valve sealing material
Rubber (X)	Nominal pressure PN ≤ 1 MPa, operating temperature t ≤ 150℃, applicable valves: globe valve, diaphragm valve, butterfly valve, check valve, etc.
Nylon (N)	Nominal pressure PN ≤ 32 MPa, operating temperature t ≤ 90℃, applicable valves: globe valves, ball valves, etc.
Polytetrafluoroethylene (F)	Nominal pressure PN ≤ 6.4 MPa, operating temperature t ≤ 180℃, applicable valves: globe valve, ball valve, gate valve, diaphragm valve, butterfly valve, check valve, etc.
Bus alloy (B)	Nominal pressure PN ≤ 2.5 MPa, operating temperature t ≤ 150℃, applicable valves: stop valves for ammonia, etc.
Ceramics (G)	Nominal pressure PN ≤ 1.6 MPa, operating temperature t ≤ 150℃, applicable valves: ball valves, plug valves, etc.
Enamel (C)	Nominal pressure PN ≤ 1.0 MPa, operating temperature t ≤ 80℃, applicable valves: globe valve, diaphragm valve, check valve, discharge valve, etc.
Copper alloy (T)	Nominal pressure PN ≤ 1.6 MPa, operating temperature t ≤ 200℃, applicable valves: gate valve, globe valve, check valve, plug valve, etc.
Stainless steel (H)	Nominal pressure PN ≤ 32 MPa, operating temperature t ≤ 450°C, applicable valves: globe valves, ball valves (medium and high pressure valves), etc.
Nitrided steel (D)	Nominal pressure PN ≤ 10 MPa, operating temperature t ≤ 540℃, applicable valve: power station gate valve, only for general use
Cemented carbide (Y)	Nominal pressure (PN) and operating temperature (t) are determined according to the material of the valve body. Applicable valves: high-pressure, ultra-high-pressure valves, high-temperature and low-temperature valves

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

The chemical composition, characteristics and applications of rubbers

December 30, 2020

Here we will introduce Rubber variety (abbreviated symbol) with their Chemical composition, Performance characteristics and Main application.

1. Natural rubber (NR) is mainly rubber hydrocarbon (polyisoprene), containing a small amount of protein, moisture, resin acid, sugar and inorganic salt. Large elasticity, high tensile strength, excellent tear resistance and electrical insulation, good wear resistance and drought resistance, good processability, easy to bond with other materials, and superior to most synthetic rubbers in comprehensive performance. Disadvantages are poor resistance to oxygen and ozone, easy to aging and deterioration; poor resistance to oil and solvents, low resistance to acid and alkali, and low heat resistance. Operating temperature range: about -60℃~+80℃. Production of tires, rubber shoes, hoses, tapes, insulation layers and sheaths of wires and cables, and other general products. It is especially suitable for manufacturing torsional vibration eliminators, engine shock absorbers, machine supports, rubber-metal

lug type butterfly valve-ductile iron

suspension components, diaphragms, and molded products.

2. Styrene butadiene rubber (SBR) is a copolymer of butadiene and styrene.
The performance is close to natural rubber, and it is currently the largest output of general-purpose synthetic rubber. It is characterized by abrasion resistance, aging resistance and heat resistance exceeding natural rubber, and its texture is more uniform than natural rubber. The disadvantages are: low elasticity, poor flex resistance and tear resistance; poor processing performance, especially poor self-adhesiveness and low green rubber strength. Operating temperature range: about -50℃~＋100℃.
Mainly used to replace natural rubber to make tires, rubber sheets, hoses, rubber shoes and other general products.

3. Butadiene rubber (BR)
It is a cis-structure rubber formed by polymerization of butadiene. The advantages are: excellent elasticity and wear resistance, good aging resistance, excellent low temperature resistance, low heat generation under dynamic load, and easy metal bonding. The disadvantages are low strength, poor tear resistance, poor processing performance and self-adhesiveness. Operating temperature range: about -60℃~＋100℃.
Generally used together with natural rubber or styrene-butadiene rubber, mainly to make tire treads, conveyor belts and special cold-resistant products.

4. Isoprene rubber (IR) is a kind of cis structure rubber made by polymerization of isoprene monomer. The che

Wafer butterfly valve-PN20-WCB-ANSI-150 (4)

mical composition and three-dimensional structure are similar to natural rubber, and the performance is very close to natural rubber, so it is called synthetic natural rubber. It has most of the advantages of natural rubber. Due to its aging resistance, natural rubber has slightly lower elasticity and strength than natural rubber, poor processing performance and higher cost. Operating temperature range: about -50℃~+100℃ It can replace natural rubber to make tires, rubber shoes, hoses, tapes and other general products.

5. Chloroprene rubber (CR) is a polymer formed by emulsion polymerization of chloroprene as monomer.
This kind of rubber contains chlorine atoms in its molecule, so compared with other general rubbers: it has excellent antioxidant, ozone resistance, non-flammable, self-extinguishing after fire, oil resistance, solvent resistance, acid and alkali resistance, aging and gas resistance. Advantages such as good tightness;
Its physical and mechanical properties are also better than natural rubber, so it can be used as general-purpose rubber as well as special rubber. The main disadvantages are poor cold resistance, large specific gravity, high relative cost, poor electrical insulation, and easy sticking, scorching, and mold sticking during processing. In addition, the raw rubber has poor stability and is not easy to store. Operating temperature range: about -45℃~＋100℃. It is mainly used to manufacture cable sheaths and various protective covers and protective covers that require high ozone resistance and high aging resistance; oil and chemical resistance hoses, tapes and chemical linings; flame-resistant rubber products for underground mining, and various moldings Products, sealing rings, gaskets, adhesives, etc.

6. Butyl rubber (IIR) is a copolymer of isobutylene and a small amount of isoprene or butadiene. The biggest feature is good air tightness, good ozone resistance, good aging resistance, high heat resistance, long-term working temperature can be below 130 ℃; resistance to strong inorganic acids (such as sulfuric acid, nitric acid, etc.) and general organic solvents, vibration absorption and damping characteristics Good and very good electrical insulation. The disadvantages are poor elasticity, poor processing performance, slow vulcanization speed, and poor adhesion and oil resistance. Operating temperature range: about -40℃~+120℃. Mainly used as inner tube, water tyre, balloon, wire and cable insulation layer, chemical equipment lining and shockproof products, heat-resistant conveyor belt, heat-resistant aging tape products.

7. Butadiene rubber (NBR) Copolymer of butadiene and acrylonitrile. It is characterized by its excellent resistance to gasoline and aliphatic hydrocarbon oils, second only to polysulfide rubber, acrylic ester and fluorine rubber, but better than other general rubbers. Good heat resistance, good air tightness, abrasion resistance and water resistance, and strong adhesion. The disadvantages are poor cold resistance and ozone resistance, low strength and elasticity, poor acid resistance, poor electrical insulation, and poor resistance to polar solvents. Operating temperature range: about -30℃~＋100℃. Mainly used to manufacture various oil-resistant products, such as hoses, sealing products, etc.

8. Hydrogenated butadiene rubber (HNBR) is a copolymer of butadiene and acrylonitrile. It is obtained by fully or partially hydrogenating the double bonds in the butadiene of NBR.
It is characterized by high mechanical strength and abrasion resistance, and its heat resistance is better than NBR when crosslinked with peroxide
Good, other properties are the same as nitrile rubber. The disadvantage is that the price is higher. Operating temperature range: about -30℃~+150℃. Mainly used for oil and high temperature resistant sealing products.

9. Ethylene propylene rubber (EPM\\EPDM)
The copolymer of ethylene and propylene is generally divided into two yuan ethylene propylene rubber and three yuan ethylene propylene rubber.
It is characterized by excellent ozone resistance, ultraviolet resistance, weather resistance and aging resistance, ranking first in general rubber. Electrical insulation, chemical resistance, impact elasticity, acid and alkali resistance, low specific gravity, high filling compounding is possible. Heat resistance up to 150°C, resistance to polar solvents-ketones, esters, etc., but not to aliphatic and aromatic hydrocarbons. Other physical and mechanical properties are slightly inferior to natural rubber and superior to styrene butadiene rubber. The disadvantage is that the self-adhesion and mutual adhesion are very poor, and it is not easy to bond. Operating temperature range: about -50℃~+150℃. Mainly used as chemical equipment lining, wire and cable sheathing, steam hose, heat-resistant conveyor belt, rubber products for automobiles and other industrial products.

10. Silicone rubber (Q)
It is a special rubber with silicon and oxygen atoms in the main chain, of which silicon element plays a major role. Its main feature is high temperature resistance (maximum 300℃) and low temperature resistance (minimum -100℃). It is currently the best high temperature resistant rubber. It has excellent electrical insulation and high stability to thermal oxidation and ozone. , Chemically inert. The disadvantage is that the mechanical strength is low, oil resistance, solvent resistance, acid and alkali resistance are poor, it is difficult to vulcanize, and the price is more expensive. Operating temperature: -60℃~+200℃.

Tanghai Valve is the best manufacturer of butterfly valve, check valve, knife gate valve in China. We produce the best quality products with competitive low prices.

Tianjin Tanghai Valve Manufacturing Co., Ltd. is one of the largest butterfly valve manufacturers in China, main products are butterfly valves, check valves, gate valve and globe valves. Key words: butterfly valve, lug type butterfly valve, wafer type butterfly valve, U-type butterfly valve, double flange butterfly valve, gate valves, check valves, globe valves, valve parts (Valve body, Valve disc, Valve shaft, Valve seat…)

URL: http://www.tanghaivalve.com

Name: Harry Li

Email: harry@tanghaivalve.com

Code of valve sealing or lining material

September 16, 2020

The sealing surface of the valve mainly refers to the contact surface of the valve disc and the valve seat. The sealing

marine valve seat

element plays the role of cutting off and connecting, adjusting and distributing, separating and mixing the medium on the valve passage, and improving the quality and service life of the valve sealing surface. Appropriate sealing surface materials and reasonable sealing structure must be selected. Valve sealing ring materials are mostly mixed materials, and seals of different components have different effects. When selecting valves, customers should choose corresponding seals according to the actual conditions of the medium, temperature and pressure.

code	sealing material/lining material
T	Copper alloy
X	Rubber
N	Nylon plastic
F	Fluoroplastic
B	Babbitt alloy
H	Alloy steel
D	Nitrided steel
Y	Hard alloy
J	Lining
Q	Lead lining
C	Enamel
P	Boronized steel

Note:

1. The code of the valve seat sealing material directly processed by the valve body is coded by “W”.
2. When the sealing materials of the valve seat and the valve disc (valve plate) are different, it is indicated by the code of low hardness material (except for diaphragm valves).

What are the main factors affecting valve sealing?

September 11, 2020

Valve leakage is very common in daily life and industrial production, and the impact is very large. It will cause waste or bring danger to life. For example, the leakage of tap water valve will lead to serious consequences, such as the

ductile iron, DI, butterfly valve, manufacturer, center line, TH valve

chemical industry. Toxic, harmful, flammable, explosive and corrosive media leakage, etc., serious threats to personal safety, property safety and environmental pollution accidents. A valve that relies on external force to rotate and drive to open and close is designed with a sealing device. It is used to install a certain number of packing seals in the packing culvert to achieve a sealing effect, but how about the sealing? Leakage at the packing of the valve is one of the most prone to leakage failure in the valve, but the reasons are largely the following reasons.

1. The structure of the sealing pair

The structure of the sealing pair will change when the temperature or sealing force changes. Moreover, this change will affect and change the mutual force between the sealing pairs, thereby reducing the performance of the valve sealing. Therefore, when choosing a seal, be sure to choose a seal with elastic deformation. At the same time, pay attention to the width of the sealing surface. The reason is that the contact surfaces of the sealing pair cannot be completely matched. When the width of the sealing surface increases, the force required for sealing must be increased.

2. The specific pressure of the sealing surface

The specific pressure of the sealing surface affects the sealing performance of the valve and the service life of the valve. Therefore, the specific pressure of the sealing surface is also a very important factor. Under the same conditions, too much specific pressure will cause damage to the valve, but too little wine will cause valve leakage. Therefore, we need to fully consider the appropriateness of the specific pressure when designing.

3. The physical properties of the medium

The physical properties of the medium also affect the sealing performance of the valve. These physical properties include temperature, viscosity and surface hydrophilicity. The temperature change not only affects the slackness of the sealing pair and changes in the size of the parts, but also has an inseparable relationship with the viscosity of the gas. The gas viscosity increases or decreases as the temperature increases or decreases. Therefore, in order to reduce the influence of temperature on the sealing performance of the valve, when we design the sealing pair, we must design it into a valve with thermal compensation such as an elastic valve seat. Viscosity is related to the permeability of the fluid. When under the same conditions, the greater the viscosity, the smaller the permeability of the fluid. The hydrophilicity of the surface means that when there is a thin film on the metal surface, the thin film should be removed. Because this thin oil film will destroy the hydrophilicity of the surface and block the fluid channel.

4. The quality of the sealing pair

The quality of the sealing pair mainly refers to the selection, matching, and manufacturing accuracy of materials. For example, the valve disc and the sealing surface of the valve seat are very consistent, which can improve the sealing performance. The characteristic of many hoop waviness is its good labyrinth sealing performance.

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

Reasons and solutions for leakage of valve sealing surface

September 11, 2020

The valve is the most used control component in the fluid system. It can be used to switch or control the flow

U-type-flange-butterfly-valve-2

direction and adjust the function. From the simplest cut-off function, the valve is sealed in the machine. Its function is to prevent the medium from In the cavity where the part is located, the joint between the parts leaks outward or prevents external substances from entering the inside. The collar and parts that play a sealing role are called seals or sealing structures, or seals for short. The two joint surfaces are in contact with the seal and play a sealing role. The surface is called the sealing surface. The valve sealing surface is the core part of the valve, and its leakage can generally be divided into the following types, namely, leakage of the sealing surface, leakage at the joint of the sealing ring, leakage caused by the fall of the closure member, and leakage of foreign objects embedded between the sealing surfaces. One of the most extensive uses of valves in pipelines and equipment is to cut off the flow of media. Therefore, its tightness is the main factor that determines whether internal leakage occurs. The valve sealing surface is generally composed of a pair of sealing pairs, one on the valve body and the other on the disc.

The reasons for the leakage of the sealing surface are generally as follows:
1. The sealing surface is unevenly ground and cannot form a tight line;
Second, the top center of the connection between the valve stem and the closing member is suspended, incorrect or worn;
3. The valve stem is bent or incorrectly assembled, which makes the closing part skewed or out of alignment;
4. Improper selection of the sealing surface material or failure to select the valve according to the working conditions, the sealing surface is prone to corrosion, erosion and wear;
5. Surfacing and heat treatment are not operated in accordance with the regulations, due to low hardness, wear, corrosion due to burning of alloy elements, and cracks due to excessive internal stress;
Six, the sealing surface after the surface treatment peels off or loses its original performance due to excessive grinding; Seven, the sealing surface is not tightly closed or the crevices appearing due to cold shrinkage after closing, resulting in intermediate corrosion; Eight, treat the shut-off valve as When the throttle valve and pressure reducing valve are used, the sealing surface is eroded and damaged;
9. The valve has reached the fully closed position and continued to apply excessive closing force, including incorrect use of long levers, and the sealing surface was crushed and deformed;
10. Excessive wear of the sealing surface causes disconnection, that is, the sealing pair cannot be tightly sealed;

Prevention and elimination methods of valve sealing surface leakage:
1. When grinding the sealing surface, the grinding tools, abrasives, emery cloth, sandpaper and other objects should use a reasonable grinding method to be correct, and color inspection should be carried out after grinding. The sealing surface should be free of indentation, cracks, scratches and other defects;
2. The connection between the valve stem and the closing member should meet the design requirements. If the top center does not meet the requirements, it should be trimmed. The top center should have a certain movable clearance, especially the axial gap between the valve stem shoulder and the closing member should not be less than 2 Mm;
3. The bend of the valve stem should be straightened. After the valve stem, stem nut, closing parts and valve seat are adjusted, they should be on a common axis;
Fourth, when selecting a valve or replacing the sealing surface, it should meet the working conditions. After the sealing surface is processed, its corrosion resistance, resistance and scratch resistance should be good;
5. The surfacing welding and heat treatment process should meet the technical requirements of the regulations and specifications. After the sealing surface is processed, the acceptance should be carried out. No defects that affect the use are allowed;
Six, the sealing surface surface firing, nitriding, shed infiltration, plating and other processes must be carried out in strict accordance with the technical requirements of its regulations and specifications. The penetration layer of the sealing surface should not exceed one-third of this layer to damage the plating and penetration layer. In serious cases, the plating layer and penetration layer should be removed and the surface treatment should be performed again. The sealing surface of the surface with high frequency smashing can be repeatedly fired and repaired;
Seven, the valve should be marked when it is closed or opened, and it should be repaired in time if the valve is not tightly closed. For high-temperature valves, some slits that appear to be cold-shrinked after closing should be closed more than once at a certain interval after closing;
8. The valve used as a shut-off valve is not allowed to be used as a throttle valve or a pressure reducing valve. The closing part should be in the fully open or fully closed position. When the flow and pressure of the medium need to be adjusted, the throttle valve and reducing valve should be set separately. Pressure valve;
9. The front opening and closing of the valve should comply with the section “Operation of the valve”. The closing force of the valve is appropriate. The diameter of the handwheel is less than 320mm. Only one person is allowed to operate. For handwheels with a diameter equal to or greater than 320mm, two persons or one person are allowed to operate. Operate with leverage within 500 mm;
10. After the waterline drops, it should be adjusted, and the sealing surface that cannot be adjusted should be replaced;

TH Valve is a professional manufacturer of butterfly valve, gate valve, check valve, globe valve, knife gate valve, ball valve with API, JIS, DIN standard, used in Oil, Gas, Marine industry, Water supply and drainage, fire fighting, shipbuilding, water treatment and other systems, with Nominal Diameter of DN50 to DN1200, NBR/EPDM/VITON, Certificates & Approvals: DNV-GL, Lloyds, DNV, BV, API, ABS, CCS. Standards: EN 593, API609, API6D

The main classification and use conditions of valve sealing materials

September 10, 2020

The valve seal is the most important part of the entire valve. Its main purpose is to prevent leakage. The valve sealing

soft sealing marine valve, rubber sealing, valve seat parts

seat is also called a sealing ring. It is an organization that directly contacts the medium in the pipeline and prevents the medium from flowing. When the valve is in use, there are a variety of different media in the pipeline, such as liquid, gas, oil, corrosive media, etc., and different valve seals are used in different places and can adapt to various medium.
Then, valve seal materials can be divided into two major categories, namely, metallic materials and non-metallic materials. Non-metallic seals are generally used for pipelines at room temperature and pressure, while metal seals are widely used and can be used for high temperature and high pressure!
The following briefly introduces the use conditions of various sealing materials and the commonly used valve types.

1. Synthetic rubber
Synthetic rubber is better than natural rubber in oil resistance, temperature resistance and corrosion resistance. Generally, the use temperature of synthetic rubber t≤150℃, natural rubber t≤60℃, and rubber is used for the sealing of stop valves, gate valves, diaphragm valves, butterfly valves, check valves, pinch valves and other valves with a nominal pressure of PN≤1MPa. Commonly used types of synthetic rubber: NBR, EPDM, VITON.
2. Nylon
Nylon has the characteristics of low friction coefficient and good corrosion resistance. Nylon is mostly used for ball valves and globe valves with temperature t≤90℃ and nominal pressure PN≤32MPa.
3. Polytetrafluoroethylene Polytetrafluoroethylene is mostly used for globe valves, gate valves, and ball valves with a temperature t≤232℃ and a nominal pressure of PN≤6.4MPa. Short name: PTFE
4. Cast iron
Cast iron is used for gate valves, stop valves, cock valves, etc. for temperature t≤100℃, nominal pressure PN≤1.6MPa, gas and oil. main types: GI, DI
5. Babbitt alloy
Babbitt alloy is used for ammonia stop valves with temperature t-70~150℃ and nominal pressure PN≤2.5MPa.
6. Copper alloy
Commonly used copper alloy materials include 6-6-3 tin bronze and 58-2-2 manganese brass. Copper alloy has good wear resistance, suitable for water and steam with temperature t≤200℃ and nominal pressure PN≤1.6MPa. It is often used in gate valves, globe valves, check valves, plug valves, etc.
7. Chromium stainless steel
Commonly used grades of chromium stainless steel are 2Cr13 and 3Cr13 after quenching and tempering treatment, which has good corrosion resistance. It is commonly used on valves of water, steam, petroleum and other media with temperature t≤450℃ and nominal pressure PN≤32MPa.
8. Chromium nickel titanium stainless steel
The commonly used grade of chromium nickel titanium stainless steel is 1Cr18Ni9ti, which has good corrosion resistance, erosion resistance and heat resistance. It is suitable for steam, nitric acid and other media with temperature t≤600℃ and nominal pressure PN≤6.4MPa, used in stop valves, ball valves, etc.
9. Nitrided steel
The commonly used grade of nitriding steel is 38CrMoAlA, which has good corrosion resistance and scratch resistance after carburizing treatment. Commonly used for power station gate valves with temperature t≤540℃ and nominal pressure PN≤10MPa.
10. Boronizing
Boronizing is directly processed from the valve body or valve clack body material to form the sealing surface, and then boronizing surface treatment, the sealing surface has good wear resistance. Used in power station blowdown valves. To
When the valve is in use, the matters that should be paid attention to are:
1. The sealing performance of the valve should be tested to ensure its performance.

2. Check whether the sealing surface of the valve is worn, and repair or replace it according to the situation.

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