Tag Archive for: valve

Posts

What are the commonly used valves

The valve is a pipeline accessory, used to open and close the pipeline and control the flow of fluid medium in the pipeline. The functions of the valve in the pipeline include cut-off, regulation, diversion, prevention of reverse flow, stabilization, diversion or overflow and pressure relief. There are many types of valves. As the control components of fluid control systems, from the simplest butterfly valves and gate valves to the various valves used in extremely complex automatic control systems, there are many varieties and specifications.

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

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

Valves can be used to control the flow of various types of fluids, such as air, water, steam, various corrosive media, mud, oil, liquid metal, and radioactive media. The application range covers various industries. Although there are many types of valves, what are the commonly used valves? This article introduces you one by one:

There are five types of commonly used valves: butterfly valves, gate valves, check valves, ball valves, and stop valves.

Butterfly valve:
The butterfly valve, also known as the flap valve, is a simple and easy-to-use regulating valve. The butterfly plate in the body of the butterfly valve is the closing part of the valve, which is in the shape of a disc. The working principle is that the butterfly plate rotates around the valve shaft to realize the valve. Open and close, usually, the butterfly plate is driven by the valve stem and rotates 90° to complete one opening and closing, and achieve the purpose of interception. If you change the deflection angle of the butterfly plate, it can also be used as a flow control. Under normal circumstances, butterfly valves are often used for on-off control of low-pressure pipeline media.
Wafer butterfly valve and flange butterfly valve are the two connection forms of butterfly valve. The butterfly valve is suitable for making large-diameter valves, suitable for natural gas, liquefied petroleum gas, city gas, cold and hot air, chemical smelting and power generation, environmental protection, building water supply and drainage, etc. It is used to regulate and cut off the flow of media on the pipelines that transport various corrosive and non-corrosive fluid media in the system.

gate valve:

non-rising-stem-gate-valve-IS&Y

non-rising-stem-gate-valve-IS&Y

Gate valves are usually used for interception in pipeline systems. Its opening and closing parts are gates. The movement direction of the gate is perpendicular to the direction of the medium flow in the pipeline. The gate rises and the valve opens to realize the flow of the pipeline medium; the gate falls, The valve is closed, and the flow of the pipeline medium is cut off. The gate valve can only be fully opened or fully closed to cut off the flow of the medium, and cannot be used for adjustment and throttling. Therefore, the gate valve is generally used to keep the gate valve gate plate fully open and fully closed, and is used in a pipeline environment that does not need to be opened and closed frequently.
According to the structure of the gate, the gate valve can be divided into two types: wedge gate valve and parallel gate valve. Wedge gate valves can be divided into three types: single gate valve, double gate valve and elastic gate valve.

Check valve:
The check valve is also a list valve or check valve, which is an automatic valve, which

double-wing-check-valve-3

double-wing-check-valve-3

means that the check valve works automatically and does not require manual operation. When the medium flows through the check valve, under the pressure impact of the fluid medium, the check valve The valve flap of the return valve opens automatically and the medium passes through; after the medium flow is cut off, the valve flap automatically closes under the force of its own spring device to prevent the medium from flowing back and backflow.
Check valves are only suitable for installation in pipelines where the medium flows in one direction. The main function is to prevent the medium from flowing backwards, to prevent the pump and drive motor from reversing, and to discharge the container medium.

Globe valve:
The globe valve, also known as the shut-off valve, is a forced-sealing valve. That is to say, unlike the automatic operation of a check valve, the shut-off valve must apply pressure to the disc when it is closed to force the sealing

globe valve body

globe valve body

surface to not leak. When the medium enters the valve from below the disc, the flow direction changes, so the resistance that needs to be overcome to close the shut-off valve is the friction between the valve stem and the packing, as well as the thrust generated by the pressure of the medium, and the force to close the valve. The force is larger than that of opening the valve, so the diameter of the valve stem should be larger, otherwise the valve stem will bend failure. The flow resistance of the stop valve is higher than other valves.
The shut-off valve can be used to cut off the medium like a gate valve, but more often, people use the shut-off valve to adjust the flow.

Ball valve:
The ball valve evolved from the rotary valve. It is the same as the butterfly valve in that it also needs to be rotated 90 degrees to open and close. The difference is that the butterfly

ball valve (8)

ball valve (8)

valve is a butterfly plate, and the cock of the ball valve is a sphere, with a circular through hole or channel passing through its axis.
The ball valve can cut off, distribute and change the flow direction of the medium in the pipeline, and only need to rotate 90 degrees and a small torque can be closed tightly. Therefore, the ball valve is most suitable for use as a switch and shut-off valve. At present, it has been widely used in petroleum refining, long-distance pipeline, chemical industry, papermaking and other industries.

TH Valve is a professional manufacturer of butterfly valvegate valvecheck valveglobe valveknife 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

Related news/knowledge:
O type |V type ball valve structure principle;
The difference between globe valve and check valve;
The working principle and characteristics of the globe valve;
Electric globe valve selection and application

How to choose a valve in the chemical industry

The media transported in various pipelines in the chemical industry are usually corrosive, such as sulfuric acid, hydrochloric acid, nitric acid and other corrosive media. All corrosion protection is the most basic requirement of chemical equipment. Chemical valves are of course no exception, and the selection of valve materials must be corrosion-resistant. If the chemical valve is wrongly selected, it will damage the equipment at the slightest level, or cause serious accidents, causing injury to machinery, equipment and even people. However, for different corrosive media, the selection of valves is also different. This article will talk about the key points of valve material selection for some common chemical media:

lug type butterfly valve, ductile iron, center lined,

lug type butterfly valve, ductile iron, center lined,

Hydrochloric acid: Most metal materials, including various stainless steel materials, are not resistant to hydrochloric acid corrosion, and high-silicon ferro-molybdenum can only be used in hydrochloric acid below 50°C and 30%. Contrary to metal materials, most non-metal materials have good corrosion resistance to hydrochloric acid, so rubber-lined valves (such as fluoroplastics, etc.) are the best choice for transporting hydrochloric acid. But if the temperature of the medium exceeds 150°C, or the pressure is greater than 16 kg, any plastics (including fluoroplastics and even polytetrafluoroethylene) will be difficult to handle. For hydrochloric acid exceeding this condition, there is no ideal valve currently on the market.

Sulfuric acid: As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. Different concentrations and temperatures of sulfuric acid have great differences in the corrosion of materials. For concentrated sulfuric acid with a concentration of more than 80% and a temperature of less than 80°C, carbon steel and cast iron have good corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. Not suitable for use as a valve material; ordinary stainless steels such as 304 and 316 have limited use for sulfuric acid media. Therefore, pump valves for transporting sulfuric acid are usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (20 alloy valve). Fluoroplastics have better resistance to sulfuric acid, and fluorine-lined valves (recommended by Tanghai Valves) are a more economical choice. If the pressure is too high and the temperature rises, the point of use of the plastic valve will be impacted, and you can only choose the more expensive ceramic ball valve.

Nitric acid: Most metals are rapidly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid resistant material. It has good corrosion resistance to all concentrations of nitric acid at room temperature. Note that stainless steel containing molybdenum (such as 316, The corrosion resistance of 316L) to nitric acid is not better than that of ordinary stainless steel (such as 304, 321), and sometimes even worse.

Acetic acid: Acetic acid is one of the most corrosive substances in organic acids. Ordinary steel will be severely corroded in acetic acid at all concentrations and temperatures. Stainless steel is an excellent acetic acid resistant material. 316 stainless steel containing molybdenum is also suitable for high temperature and rarefied materials. Acetic acid vapor. For demanding requirements such as high temperature and high concentration of acetic acid or other corrosive media, high alloy stainless steel or fluoroplastic pumps can be used.

Salt water/sea water: The corrosion rate of ordinary steel in sodium chloride solution, sea water and salt water is not very high, and generally must be protected by paint; all kinds of stainless steel also have a very low uniform corrosion rate, but may cause local corrosion due to chloride ions. It is usually better to use 316 stainless steel.

TH Valve is a professional manufacturer of butterfly valvegate valvecheck valveglobe valveknife 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

Related news/knowledge:
Main application areas of 10 major types of valves;
Types and selection of electric valves;
Prevention and treatment of valve corrosion;
Uses and characteristics of manual butterfly valve (2)

Pneumatic butterfly valve working principle diagram

Pneumatic butterfly valve working principle diagram
Pneumatic butterfly valve is a kind of general-purpose valve that is particularly widely used. Nowadays, many chemical industry, paper industry, coal industry, petroleum, medical, etc. will use valves, especially pneumatic valves, and if the use is relatively large, it must be Pneumatic butterfly valves are extremely common on many pneumatic pipelines! Especially in low-pressure large and medium-caliber pipelines, it is used more and more. The larger the diameter, the more economical and economical than other valves.

Double offset-butterfly valve-D972F-150lbC (1)

Double offset-butterfly valve-D972F-150lbC (1)

Pneumatic butterfly valves are so widely used because of their simple structure, easy maintenance, and rapid switching, which can not only improve work efficiency, but also reduce maintenance time. According to customer requirements, seal rings of different materials and parts of different materials can be selected to be suitable for different media and working conditions, so that the pneumatic butterfly valve can achieve great results.
Working principle of pneumatic butterfly valve:
The pneumatic butterfly valve uses compressed air as the power source, and drives the valve stem to control the disc-shaped butterfly plate to rotate around the axis. The initial position of the valve is determined according to actual needs. When the valve rotates 90° from the initial position, an action ends (by opening To off, or from off to on), otherwise, another action (from off to on, or from on to off) ends.
The execution speed of the pneumatic butterfly valve is relatively fast, it is not easy to be damaged due to jamming during the movement process, and does not require the hands of workers. It can not only be used as a cut-off valve, but also can be equipped with a valve positioner to achieve the function of regulating and controlling the pipeline medium. Pneumatic butterfly valve actuators are divided into single-acting and double-acting forms. The double-acting is vent opening and vent closing! Among them, the single-acting actuator has a spring return function, which can be

U-type flange butterfly valve, ductile iron, DI, center line,

U-type flange butterfly valve, ductile iron, DI, center line,

automatically closed or opened in the case of gas or power failure, with a high safety factor!
Related knowledge: dynamic diagram of butterfly valve working principle
Recommended products: Pneumatic regulating butterfly valve Pneumatic triple eccentric butterfly valve

TH Valve is a professional manufacturer of butterfly valvegate valvecheck valveglobe valveknife 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

electric hard seal butterfly valve vs electric soft seal butterfly valve

The difference between electric hard seal butterfly valve and electric soft seal butterfly valve
With the rapid development of many industrial fields in our country, industrial automation has gradually replaced the manual operating system, especially the use of various automatic control valves. With its unique structural

wafer type butterfly valve, EPDM seat (10)

wafer type butterfly valve, EPDM seat (10)

characteristics, electric butterfly valves have become one of the most used valve types. First, the scope of application is also the most extensive. However, in different working conditions, it is particularly important to choose different electric butterfly valves, not to waste costs, and to save resources. From the valve sealing structure, electric butterfly valves can be divided into two categories: soft seal and hard seal. What is the difference between them? Which one has more advantages? How should we distinguish between them?

The difference between the electric hard-sealed butterfly valve and the electric soft-sealed butterfly valve is mainly reflected in the performance and structure. The two seals can complement each other. Both have advantages and disadvantages. The advantage of one side may be the disadvantage of the other. When choosing, you should analyze your own needs, working conditions, etc., and choose the right product.
The main differences are as follows:
1. From the structure: the electric soft sealing butterfly valve is mostly in the middle line structure, and the sealing material is generally fluorine plastic, rubber, resin, etc., which has good corrosion resistance and sealing. Choose different parts and materials, which can be suitable for use. In a variety of media. Electric hard-sealed butterfly valves are mostly single-eccentric, double-eccentric and triple-eccentric butterfly valves. The seals are mostly stainless steel + cemented carbide. Among them, the three-eccentric butterfly valve has no friction transmission between the sealing surfaces, and has the characteristics of high temperature resistance, wear resistance, and good mechanical properties.

D673H-16C-stainless steel pneumatic triple eccentric butterfly valve

D673H-16C-stainless steel pneumatic triple eccentric butterfly valve

2. Temperature resistance: soft seal is used in normal temperature environment, hard seal can be used in low temperature, normal temperature, high temperature and other environments;
3. In terms of pressure: soft seal low pressure-normal pressure, hard seal can also be used in working conditions such as medium and high pressure;
4. Sealing performance: The soft sealing butterfly valve has better sealing performance and can reach zero leakage. The disadvantage is that it is easy to age, wear, and has a short service life. The hard-sealed butterfly valve can maintain good operation under high pressure and high temperature, is relatively resistant to wear, has good mechanical properties, and has a long service life, but the sealing performance is poor!
When the electric butterfly valve is opened and closed, it not only saves effort, but also has low flow resistance. It is convenient and quick to operate, light in weight, small in size, and has a relatively simple structure. Customers can choose a soft-seal or hard-seal butterfly valve reasonably according to economic conditions, the conditions of the medium used, and the on-site environment.

TH Valve is a professional manufacturer of butterfly valvegate valvecheck valveglobe valveknife 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

Related news/knowledge:
Valve seal (ring) material usage range comparison table;
Ball valve model preparation method/code name establishment;
Vulcanized vs soft seated/back-up butterfly valve;
Main application areas of 10 major types of valves

Wafer butterfly valve installation instructions and steps

Wafer butterfly valve is one of the most common types of valves in industrial pipelines. The wafer butterfly valve itself has a relatively small structure. You only need to put the butterfly valve in the middle of the flanges at both ends of the pipeline, and use stud bolts to pass through the pipeline flange and the The clip-on butterfly valve is locked to control the fluid medium in the pipeline. Wafer butterfly valve is especially suitable for places with narrow space or short distance between pipelines. When the butterfly valve is in the fully open position, the thickness of the butterfly plate is the only resistance when the medium flows through the valve body. Therefore, the pressure drop generated by the valve is very high. Small, so it has better flow control characteristics.

wafer type butterfly valve, with handle (13)

wafer type butterfly valve, with handle (13)

1. Instructions before installation of wafer butterfly valve:
1. Before installation and operation, use air spray to remove foreign objects on the piping, and clean the inner surface of the piping with clean water.
2. Carefully check whether the valve usage is consistent with its performance specifications; (temperature, pressure)
3. Check the valve channel and sealing surface for debris, and remove it in time;
4. The valve must be installed in time after unpacking, please do not loosen any fastening screws or nuts on the valve at will;
5. Wafer butterfly valves must use special butterfly valve flanges.
6. The electric butterfly valve can be installed on the pipeline at any angle. For the convenience of maintenance, it is recommended not to install it upside down.
7. When installing the butterfly valve flange, it must be ensured that the flange surface and the sealing rubber are aligned, the screws are evenly tightened, and the sealing surface must fit completely; if the screw tightening force is uneven, the rubber bumps will block the butterfly plate, or the top Staying on the butterfly plate causes leakage at the valve stem. To
2. The installation steps of the wafer butterfly valve: The correct installation of the wafer butterfly valve is related to the sealing degree of the butterfly valve, and whether it will leak or not, including the safety in working conditions. The user should understand the installation process.

wafer & lug type butterfly valve (7)

wafer & lug type butterfly valve (7)

1. As shown, place the valve between the two pre-installed flanges, paying attention to the alignment of the bolt holes.
2. Gently insert four pairs of bolts and nuts into the flange holes, and tighten the nuts slightly to correct the flatness of the flange surface;
3. Fix the flange to the pipeline by spot welding;
4. Remove the valve;
5. Fully weld and fix the flange on the pipeline;
6. Install the valve after the welding port has cooled down. Ensure that the valve has enough space in the flange to prevent the valve from being damaged, and ensure that the valve plate has a certain degree of opening;
7. Correct the valve position and tighten the four pairs of bolts (be careful not to over tighten)
8. Open the valve to ensure that the valve plate can be opened and closed freely, and then slightly open the valve plate;
9. Tighten all nuts in cross balance;
10. Reconfirm that the valve can open and close freely. Note: Confirm that the valve plate does not touch the pipeline.
The installation of the wafer butterfly valve must be laid flat before installation, remember not to bump it at will, after it is drawn to the installation length during installation, in the design of the on-site pipeline, it is not possible without special permission Disassemble the wafer butterfly valve at will, this is what we need to know before installation. At the same time, everyone should know that the wafer butterfly valve can be installed in any position, but after the wafer butterfly valve is installed, the butterfly valve needs to be laid along the line, and a bracket is made for the wafer butterfly valve. Once the bracket is made, it will be used At that time, it is strictly forbidden to remove the bracket.
Related products: Electric wafer butterfly valve Pneumatic wafer butterfly valve

TH Valve is a professional manufacturer of butterfly valvegate valvecheck valveglobe valveknife 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 difference between internally and externally threaded valves

Threaded valve (also called  internal threaded valve) generally refers to a valve with internal or external thread on the valve body. It is mainly divided into internal threaded valve and external threaded valve. Corresponding to the pipeline. Usually threaded valves can only be manufactured with small diameters and are used for normal pressure or low pressure projects. If they are not available for high pressure work, they need to be used with welded link valves or flanged valves.

internally threaded valve and externally threaded valve

internally threaded valve and externally threaded valve

Common threaded valves are: threaded gate valve, threaded ball valve, threaded globe valve, threaded check valve.
The difference between internal threaded valve and external threaded valve:
From the point of use: Due to price and working flow requirements, most of the valves on the market use internal threaded valves. From the channel: Taking into account the thread connection, the passage of the external thread of the same caliber is smaller than the internal thread, the flow rate is faster, and the flow rate is small.
From the appearance: Most of the internal threads are pipe threads, the external threads are mostly taper threads, and the bite-type external threads are pipe threads.
In terms of pressure resistance: The wall of the valve with external thread of the same material is usually thicker than that of the internal thread (the smaller the passage, the thicker the wall), and the pressure resistance is greater. This is the reason why valves with high pressure ratings are all external threads. To
Sealing form of threaded valve:
1. Direct sealing: internal and external threads directly play a sealing role. In order to ensure that the joints are not leaking, they are often filled with lead oil, thread hemp and PTFE raw material tape; among them, PTFE raw material tape is widely used every day; this material has good corrosion resistance and extremely sealing effect. Good, it is convenient to use and store. When disassembling, it can be completely removed, because it is a non-sticky film, which is much better than lead oil and hemp.
2. Indirect sealing: the tightening force of the thread is transmitted to the gasket between the two planes, so that the gasket plays a sealing role.
Thread standard of threaded valve:
1. International standards ISO228/1, DIN259, are internal and external parallel threads, code G or PF (BSP.F);
2. German standard ISO7/1, DIN2999, BS21, taper external thread, parallel internal thread;
3. British standard ISO7/1, BS21, internal and external tapered thread, code PT or BSP.Tr or Rc;
4. American standard ANSIB21, internal and external tapered thread, code name NPT.

TH Valve is a professional manufacturer of butterfly valvegate valvecheck valveglobe valveknife 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

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

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)

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

Classification and introduction of pipe thread-(3)

Sealing pipe thread (R)

The basic dimensions and tolerances of inch sealing pipe threads

Cooperate way

There are two matching methods for inch seal pipe threads: cylindrical internal thread and conical external thread form a “column/cone” fit; conical internal thread and conical external threa

NPT thread picture

NPT thread picture

d form a “cone/cone” fit.

European countries mainly use “column/cone” matching threads; countries outside Europe mainly use “cone/cone” matching threads. The inspection gauges for the two types of threads are somewhat different; the current ISO inch seal pipe thread gauge standard (ISO 7- 2:2000) is designed according to the “column/cone” coordination system.

mark

The complete mark of inch seal pipe thread is composed of thread feature code, thread size code and rotation direction code.

The characteristic code of inch sealed cylindrical internal thread is: RP;

left &right hand thread

left &right hand thread

The characteristic code of the inch sealing cone internal thread is: RC;

The characteristic code of the inch sealing cone external thread is: R1 (used with the inch sealing cylindrical internal thread);

R2 (used in conjunction with inch sealing cone internal thread);

The rotation code of the left-hand thread is LH; the rotation code of the right-hand thread is omitted and not marked.

For sealing pipe threads, use RP/R1 and RC/R2 to indicate “column/cone” and “cone/cone” thread pairs respectively.

Unsealed pipe thread

The basic size and limit deviation of the imperial unsealed pipe

mark:

The complete mark of inch unsealed pipe thread is composed of thread feature code, thread size code, pitch diameter tolerance grade code and rotation direction code.

The characteristic code of inch unsealed cylindrical thread is: G

For inch non-sealed cylindrical internal threads, the codes for the tolerance grades of the median diameter are omitted and not marked; while the codes for the pitch diameter and metric grades of the inch non-sealed cylindrical external threads are A and B respectively.

When indicating the thread pair of the inch unsealed pipe thread, only the marking code of the external thread is marked.

Example:

Right-handed, non-sealed cylindrical female thread with size code 2: G2

Class A with size code 3, right-handed, unsealed cylindrical external thread: G3A

Grade B with size code 4, left-handed, unsealed cylindrical external thread: G4 B-LH

Thread pair consisting of a right-handed, non-sealed cylindrical internal thread and a grade A cylindrical external thread with a dimension code of 2: G2A

The inner thread is processed by pipe thread taps, and the outer thread has die.

Note: 2, 3, 4 above are code names, not inch sizes, don’t confuse

other

Conversion of 55° tapered pipe thread

55° tapered pipe thread means that the thread angle is 55° and the thread has a taper of 1:16. This series of thread is widely used in the world, and its code is different from country to country.

China UK France Japan iso

Code ZG R (outside) G PT R

R (external thread) Rc (internal) R R Rc

Conversion of 60° Conical Pipe Thread

The 60° tapered pipe thread refers to a pipe thread with a tooth profile angle of 60° and a thread taper of 1:16. This series of threads is used in the machine tool industry in my country, the United States and the former Soviet Union. Its code name was previously designated as K in our country, and later designated as Z, now it is changed to NPT.

Classification and introduction of pipe thread-(2)

“Cylinder/cone” and “cone/cone”. Two inch seal pipe threads use different thread ring gauges (cylindrical thread ring gauge and tapered thread ring gauge) and thread plug gauge (the position of the datum plane is different, the two datum planes are different Half-tooth apart). Pipe threads that pass the inspection in European countries may be unqualified if they are inspected by countries outside of Europe. In international trade, you must pay attention to this difference, otherwise there may be waste. Before 1994, the ISO standard for sealed pipe threads and their gauges The standard is designed according to the “cone/cone” coordination system. China’s imperial sealed pipe thread products can directly enter the international market. However, the pipe thread products of European countries are in a disadvantageous position. After 2000, ISO’s imperial seal The pipe thread standard and its gauge standard are designed according to the “column/cone” matching question system. Our country’s original inch seal pipe thread products will encounter difficulties when entering the international market. For this reason, China revised the inch seal pipe in 2000 Thread national standard. Change the original one thread standard into two thread standards to remind the designer to pay attention to the difference and correct selection of the two mating threads. Japan still insisted on adopting 1994 when it revised the inch seal pipe thread standard in 1999 The ISO standard a year ago. Therefore, the international inch seal pipe thread market after 2000 is more complicated, and domestic

NPT thread picture

NPT thread picture

manufacturers must be careful.

Inch sealing pipe thread is a general purpose sealing pipe thread. Sealing filler should be added to the thread pair during use. Its characteristics are economical and the processing accuracy requirements are moderate. Without sealing fillers, it can ensure that the sealed connection thread is dry sealed Pipe thread. There is no dry seal pipe thread in the inch pipe thread system.

Sealed pipe threads have two functions: mechanical connection and sealing; non-sealed pipe threads have only one function of mechanical connection. Therefore, the accuracy of sealed pipe threads is stricter than that of unsealed pipe threads. Some people see unsealed pipe threads The tolerance of the pitch diameter is half of the tolerance of the sealed pipe thread. It is considered that the accuracy of the unsealed pipe thread is higher than that of the sealed pipe thread. This view is incorrect. The sealed pipe thread has requirements for the accuracy of the tooth shape. Its large diameter, The tolerances of the pitch diameter and the minor diameter are the same; the flank angle and pitch error have a greater impact on the sealing performance. The non-sealed pipe thread basically has no requirements for the accuracy of the tooth form. The top diameter tolerance is greater than the pitch diameter tolerance; the bottom diameter There is no tolerance requirement. In addition, some people think that it is possible to use non-sealed cylindrical internal threads and sealed cylindrical external threads to form a fit. This view is also wrong. This is equivalent to relaxing the accuracy requirements of sealed internal threads, and the sealing of pipe threads There may be a problem.

Due to differences in the use of sealed pipe threads, processing accuracy, assembly and testing techniques, the pipe thread standard cannot guarantee that all threaded parts that meet the standard can be sealed. In the imperial sealed pipe thread standard, a unified thread item cannot be proposed. The accuracy requirements of the parameters. These individual thread parameters have a direct impact on the sealing performance. The fundamental way to solve the problem is to formulate their own internal control measures for their specific products. Each industry or company formulates its own internal control measures. The internal control indicators of these parameters are generally confidential. Companies in other industries are not universal, and manufacturers must have a clear understanding of this. Sealing pipe thread standards are not omnipotent, and sealing problems may require manufacturers to pay attention to them. Before 1987, China did not have American and British pipe thread standards. But In production, these two internationally commonly used pipe thread standards cannot be avoided. For this reason, the old mechanical drawing standards once stipulated the marking codes for American and British pipe threads. These thread codes are derived from the Chinese Pinyin alphabet, and have not considered the foreign Whether the standard codes of standard pipe threads are consistent. Since this standard only specifies the thread codes and not the thread parameters, the same thread code may have different thread parameters in different companies or industries. There is no basis for judging who is right and who is wrong when there is a scrap .From 1987 to 1991, China promulgated the British pipe thread standard. From then on, the pipe thread code and marking should comply with the pipe thread standard. The pipe thread code specified in the old mechanical drawing standard should be abolished immediately.

Classification and introduction of pipe thread-(1)

Pipe thread is a thread used for connection on the pipe wall to the valves. There are 55-degree unsealed pipe threads and 55-degree sealed pipe threads. Mainly used to connect pipes to make the internal and external threads fit tightly. There are two types which are straight pipes thread and tapered pipes thread.
Common pipe threads mainly include the following types: NPT, PT, G, etc.

NPT thread picture

NPT thread picture

1) NPT is the abbreviation of National (American) Pipe Thread, which belongs to the American standard 60-degree tapered pipe thread and is used in North America. Refer to GB/T12716-1991 for the national standard.

2) PT (BSPT) is the abbreviation of Pipe Thread. It is a 55-degree sealed tapered pipe thread. It belongs to the Wyeth thread family. It is mostly used in Europe and the Commonwealth countries. It is often used in the water and gas pipe industry. The taper is 1:16. Refer to GB/ T7306-2000. The domestic name is ZG.

3) G is a 55-degree non-sealed pipe thread, which belongs to the Wyeth thread family. Marked as G stands for cylindrical thread. Refer to GB/T7307-2001 for the national standard.

Metric and inch threads

Metric threads are expressed by pitch, while American and British threads are expressed by the number of threads per inch;

Metric thread is 60-degree equilateral profile, inch thread is isosceles 55-degree profile, and American thread is isosceles 60-degree profile;

Use metric units (such as mm) for metric threads, and use imperial units (such as inches) for American and British threads;

“Insiders” usually use “minutes” to refer to the thread size, one inch equals 8 points, 1/4 inch equals 2 points, and so on.

In addition, there are: ISO—Metric Thread Standard 60°; UN—Unified Thread Standard 60°; API—American Petroleum Pipe Thread Standard 60°; W—British Wyeth Thread Standard 55°.

The difference between various threads

NPT, PT, G  are all pipe threads.

NPT is the abbreviation of National (American) Pipe Thread, which belongs to the American standard 60-degree tapered pipe thread and is used in North America. National standards can be found in GB/T12716-1991

PT is the abbreviation of Pipe Thread. It is a 55-degree sealed tapered pipe thread. It belongs to the Wyeth thread family and is mostly used in Europe and Commonwealth countries. Commonly used in water and gas pipe industry, the taper is 1:16. National standards can be found in GB/T7306-2000

G is a 55-degree non-thread sealed pipe thread, which belongs to the Wyeth thread family. Marked as G stands for cylindrical thread. National standards can be found in GB/T7307-2001

In addition, the 1/4, 1/2, and 1/8 marks in the thread refer to the diameter of the thread size, and the unit is inch. Insiders usually use points to refer to the thread size, one inch equals 8 points, 1/4 inch equals 2 points, and so on. G is the general name of pipe thread (Guan). The division of 55 and 60 degrees is functional, commonly known as pipe circle. That is, the thread is processed by a cylindrical surface.

ZG is commonly known as pipe cone, that is, the thread is processed by a conical surface. The general water pipe joints are like this. The national standard is marked as Rc metric thread to indicate the pitch, and the American thread is 60 degrees. Metric units are used for metric threads, and imperial units are used for American and British threads. Pipe thread is mainly used to connect pipelines. The internal and external threads are closely matched. There are two types of straight pipes and tapered pipes. The nominal diameter refers to the diameter of the connected pipe, obviously the thread diameter is larger than the nominal diameter. 1/4, 1/2, 1/8 are the nominal diameters of inch threads, and the unit is inches.

Inch pipe threads are derived from British Wyeth threads. The combination of Wyeth threaded pipe series and Wyeth thread profiles establishes the basic dimensions of British pipe threads. According to the 1/16 taper relationship, the radial diameter tolerance of Wyeth threads is converted into British sealed tubes. Tolerance of the axial number of threads (there is a certain amount of rounding and adjustment). Then refer to the tolerance value of the inch seal pipe thread to propose the tolerance of the inch unsealed pipe thread (the tolerance changes from one-way distribution to one-way distribution, relax the top Diameter tolerance, let go of the bottom diameter tolerance). The time for the three types of threads is:

In 1841, the British Wyeth thread was proposed, and in 1905, the new Wyeth thread standard (BS 84) was promulgated.

In 1905, the British Sealed Pipe Thread Standard (BS 21) was promulgated.

From 1905 to 1940, Wyeth Thread performed the responsibility of the imperial unsealed pipe. In 1940, the unsealed pipe thread series (BSP series) of Wyeth Thread was proposed; in 1956, the British unsealed pipe thread standard (BS 2779) was issued separately.

European countries and Commonwealth countries first accepted the imperial pipe thread standard. The ISO/TC5/SC5 Pipe Thread Standardization Technical Committee and its secretariat are controlled by European countries, and the imperial pipe thread standard was adopted by the ISO standard. In 1955, the ISO proposed the imperial sealed pipe thread Standard (ISO R 7); In 1961, ISO proposed the standard for imperial unsealed pipe threads (ISO R 228). In 1978, ISO promulgated two official standards for imperial pipe threads (ISO7-1 and ISO228-1). Threads have been generally accepted by countries outside North America and are widely used in international trade.

The inch pipe thread in the ISO standard has been converted to the metric system. The metric method of the inch pipe thread is very simple. Multiply the inch size of the original pipe thread by 25.4 to convert it to the millimeter size. The inch pipe thread size is being eliminated. The so-called use of real pipe thread standards is unrealistic. There is no distinction between real metric pipe threads and fake metric pipe threads.