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The difference between internally and externally threaded valves

June 1, 2021

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

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 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℃.

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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…)

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Name: Harry Li

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Classification and introduction of pipe thread-(3)

December 7, 2020

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

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

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)

December 7, 2020

“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

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)

December 7, 2020

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

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.

Resilient seated socket end gate valve

November 18, 2020

GATE VALVE-resilient seated SOCKET END
Standard: EN1074; EN1171

Socket ended resilient seated wedge gate valve-ductile iron (1)

CAST IRON / DUCTILE IRON GATE VALVE SOCKET END
NON RISING STEM
Pressure: PN10 / PN16
Connection ends: Socked ends, for PVC pipes, uPVC pipes
FACE TO FACE: ACCORDING TO BS, DIN, ANSI, AWWA, SABS STANDARD ETC.
BODY:CAST IRON/DUCTILE IRON
BONNET:CAST IRON/DUCTILE IRON
WEDGE:CAST IRON/DUCTILE IRON, fully vulcanized with EPDM rubber
STEM: SS/BRASS
Coating: fusion bonded expoxy coating

The opening and closing part of the socket gate valve is a gate. The movement direction of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and fully closed, and cannot be adjusted or throttled. The gate has two sealing surfaces. The two sealing surfaces of the most commonly used mode gate valve form a wedge. The wedge angle varies with valve parameters, usually 50, and 2°52′ when the medium temperature is not high. The gate of the wedge gate valve can be made into a whole, called a rigid gate; it can also be made into a gate that can produce slight deformation to improve its manufacturability and compensate for the deviation of the sealing surface angle during the processing. The plate is called an elastic gate.

Socket gate valve can be divided into wedge gate valve and parallel gate valve according to the sealing surface configuration. The wedge gate valve can be divided into: single gate, double gate and elastic gate; parallel gate valve can be divided into It is single gate type and double gate type. According to the thread position of the valve stem, it can be divided into two types: rising stem gate valve and non-rising stem gate valve.

When the socket gate valve is closed, the sealing surface can only rely on the medium pressure to seal, that is, rely on the medium pressure to press the sealing surface of the gate against the valve seat on the other side to ensure the sealing of the sealing surface, which is self-sealing. Most gate valves use forced sealing, that is, when the valve is closed, the gate must be forced against the seat by external force to ensure the sealing performance of the sealing surface.

The gate of the socket gate valve moves linearly with the valve stem, which is called rising stem gate valve (also called rising stem gate valve). Usually there is a trapezoidal thread on the lifting rod, through the nut on the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is, the operating torque is changed into operating thrust.

When the valve is opened, when the lifting height of the gate is equal to 1:1 times the valve diameter, the fluid passage is completely unblocked, but this position cannot be monitored during operation. In actual use, the apex of the valve stem is used as a mark, that is, the position where it cannot be opened, as its fully open position. In order to take into account the locking phenomenon of the temperature change, it is usually at the top position of the opening, and then rewind 1/2-1 turn as the position of the fully open valve. Therefore, the fully open position of the valve is determined by the position of the gate (that is, the stroke).

Socket ended resilient seated wedge gate valve-ductile iron (2)

In some gate valves, the stem nut is set on the gate, and the rotation of the handwheel drives the rotation of the valve stem to lift the gate. This kind of valve is called a rotating stem gate valve or a dark stem gate valve.

advantage:
The fluid resistance is small, and the sealing surface is less brushed and corroded by the medium.
It is easier to open and close.
The flow direction of the medium is not restricted, does not disturb the flow, and does not reduce the pressure.
The shape is simple, the length of the structure is short, the manufacturing process is good, and the scope of application is wide.

Disadvantages:
It is easy to cause erosion and scratches between the sealing surfaces, which makes maintenance difficult.
The overall size is large, opening requires a certain amount of space, and the opening and closing time is long.
The structure is more complicated.

The types of socket gate valves can be divided into wedge gate valves and parallel gate valves according to the sealing surface configuration. Wedge gate valves can be divided into: single gate type, double gate type and elastic gate type; parallel gate type Gate valves can be divided into single gate type and double gate type. Divided according to the thread position of the valve stem, it can be divided into two types: open stem gate valve and dark stem gate valve.

Matters needing attention in installation and maintenance
Handwheels, handles and transmission mechanisms are not allowed to be used for lifting, and collisions are strictly prohibited.
The double gate valve should be installed vertically (that is, the valve stem is in the vertical position and the handwheel is at the top).
The gate valve with bypass valve should be opened before opening (to balance the pressure difference between inlet and outlet and reduce the opening force).
The gate valve with transmission mechanism should be installed according to the product manual.
If the valve is frequently opened and closed, lubricate at least once a month.

Structural features:
The general gate valves used on the market for a long time generally have water leakage or rust. The company introduces the elastic seat seal gate valve produced by European high-tech rubber and valve manufacturing technology, which overcomes the defects of poor sealing and rust of general gate valves. The sealing gate valve uses the compensation effect of the elastic gate plate to produce a small amount of elastic deformation to achieve a good sealing effect. The valve has the obvious advantages of light switch, reliable sealing, good elastic memory and service life. It can be widely used as a regulating and intercepting device on the pipelines of tap water, sewage, construction, petroleum, chemical industry, food, medicine, textile, electric power, shipbuilding, metallurgy, energy system, etc.

Valve material comparison table-valve pressure-temperature

October 27, 2020

The relationship between valve temperature and pressure:
The valve operating temperature and pressure have a certain internal connection and influence each other. Among them, temperature is the dominant factor affecting the valve. A valve with a certain pressure is only suitable for a

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

certain temperature range, and changes in valve temperature can affect the valve’s operating pressure. E.g:
The nominal pressure of a carbon steel valve is 10MPa. When the medium working temperature is 200℃, its maximum working pressure P20 is 10MPa; when the medium working temperature is 400℃, its maximum working pressure P40 is 5.4MPa; when the medium works When the temperature is 450℃, the maximum working pressure P20 is 4.5MPa.

Valve material temperature and pressure comparison table:
Valve material and applicable pressure, temperature and grade
Gray cast iron is suitable for water, steam, air, gas, oil and other media with nominal pressure PN≤1.0MPa and temperature -10℃～200℃. Commonly used grades are: HT200, HT250, HT300, HT350.
Malleable cast iron Suitable for water, steam, air and oil media with nominal pressure PN≤2.5MPa and temperature -30～300℃. Commonly used grades are: KTH300-06, KTH330-08, KTH350-10.
Nodular cast iron is suitable for water, steam, air and oil with PN≤4.0MPa and temperature of -30～350℃. Commonly used grades are: QT400-15, QT450-10, QT500-7. At present, the level of domestic technology varies among factories, and it is often difficult for users to inspect. It is recommended that PN≤2.5MPa, and steel valves are used for safety.
Acid-resistant high-silica ductile iron Suitable for nominal pressure PN≤0.25MPa, suitable for corrosive media with temperature lower than 120℃.
Carbon steel is suitable for water, steam, air, hydrogen, ammonia, nitrogen and petroleum products with a nominal pressure of PN≤32.0MPa and a temperature of -30～425℃. Commonly used grades are WC1, WCB, ZG25, high-quality steel 20, 25, 30 and low-alloy structural steel 16Mn.
Copper alloy is suitable for water, sea water, oxygen, air, oil and other media with PN≤2.5MPa and steam media with temperature of -40～250℃. Commonly used grades are ZGnSn10Zn2 (tin bronze), H62, Hpb59-1 (brass) , QAZ19-2, QA19-4 (aluminum bronze).
High-temperature copper is suitable for steam and petroleum products with nominal pressure PN≤17.0MPA and temperature≤570℃. The specific selection must be in accordance with the valve pressure and temperature specifications. Commonly used grades are ZGCr5Mo, 1Cr5M0.ZG20CrMoV, ZG15Gr1Mo1V, 12CrMoV, WC6, WC9, etc.
Low-temperature steel is suitable for media with nominal pressure PN≤6.4Mpa and temperature≥-196℃ ethylene, propylene, liquid natural gas, liquid nitrogen, etc. Commonly used grades are ZG1Cr18Ni9, 0Cr18Ni9, 1Cr18Ni9Ti, ZG0Cr18Ni9
Stainless and acid-resistant steel Suitable for media such as nitric acid and acetic acid with nominal pressure PN≤6.4Mpa and temperature≤200℃. Commonly used grades are ZG0Cr18Ni9Ti, ZG0Cr18Ni10<nitric acid>, ZG0Cr18Ni12Mo2Ti, ZG1Cr18Ni12Mo2Ti<acid and urea>

Valve seal (ring) material usage range comparison table

October 27, 2020

The selection of valve sealing material is determined according to the operating conditions of the valve, such as: pipeline medium, temperature range (high and low temperature), pressure and internal structure of the valve. For

soft sealing marine valve, rubber sealing, valve seat parts

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 and valve sealing material use range:
Rubber (X) Nominal pressure PN ≤ 1 MPa, operating temperature t ≤ 150℃, applicable valves: globe valves, diaphragm valves, butterfly valves, check valves, etc.
Nylon (N) Nominal pressure PN ≤ 32 MPa, operating temperature t ≤ 90°C, applicable valves: globe valves, ball valves, etc.
PTFE (F) Nominal pressure PN ≤ 6.4 MPa, operating temperature t ≤ 180°C, applicable valves: globe valves, ball valves, gate valves, diaphragm valves, butterfly valves, check valves, etc.
Bus alloy (B) Nominal pressure PN ≤ 2.5 MPa, operating temperature t ≤ 150°C, applicable valves: stop valves for ammonia, etc.
Ceramic (G) Nominal pressure PN ≤ 1.6 MPa, operating temperature t ≤ 150°C, applicable valves: ball valves, plug valves, etc.
Enamel (C) Nominal pressure PN ≤ 1.0 MPa, operating temperature t ≤ 80°C, 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 valves: power station gate valves, 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

What is the positive transmission of gears

October 23, 2020

When the total displacement coefficient of a pair of gears is greater than 0, it is a positive transmission.
Positive transmission refers to the positive displacement design of the gear. If two gears meshing with each other are in positive displacement, their center distance is greater than (the pair of gears) standard center distance. Conversely, if both gears use negative displacement, the center distance is smaller than the standard center distance. To judge whether the position is shifted, it is mainly to compare the measured gear parameters (including center distance) with the standard parameters of the gear to draw a conclusion.
Gear transmission is the most widely used transmission form in mechanical transmission. It has relatively

accurate transmission, high efficiency, compact structure, reliable work and long life. At present, the achievable indexes of gear technology: peripheral speed v=300m/s, rotation speed n=105r/min, transmitted power P=105KW, modulus m=0.004~100mm, diameter d=1mm~152.3mm
Features
1, the instantaneous transmission ratio is constant. The instantaneous transmission ratio of non-circular gear transmission can be designed according to the required change law.
2, the transmission ratio range is large, which can be used to decelerate or increase speed.
3, the range of speed (pitch circle speed) and transmission power is wide, and it can be used for high-speed (v>40m/s), medium-speed and low-speed (v<25m/s) transmission; power is from less than 1W to 105KW.
4, high transmission efficiency. A pair of high-precision involute cylindrical gears has an efficiency of over 99%.
5, compact structure, suitable for short-distance transmission.
6, the manufacturing cost is higher. Certain gears with special tooth shapes or high precision require special or high-precision machine tools, cutting tools and measuring instruments, so the manufacturing process is complicated and the cost is high.
7, low-precision gears, noise, vibration and shock during transmission, pollute the environment.
8, no overload protection
According to the relative position of the two shafts and the direction of the gear teeth, it can be divided into the following types:
<1>Straight tooth cylindrical gear drive;
<2> Helical cylindrical gear drive
<3> herringbone gear transmission;
<4> bevel gear transmission;

bevel gear

<5> cross-axis helical gear transmission.
According to the working conditions of the gear, it can be divided into:
<1>; Open gear transmission type gear transmission, the gears are exposed, and good lubrication cannot be guaranteed.
<2>; half-open gear transmission, the gear is immersed in the oil pool, with a protective cover, but not closed.
<3>; closed gear transmission, gears, shafts and bearings are all installed in a closed box, with good lubrication conditions, difficult for dust and sand to enter, accurate installation,
Gear transmission has good working conditions and is the most widely used gear transmission.
Gear transmission can be classified according to the relative position of its axis.
Gear drive can be divided into cylindrical gear drive, bevel gear drive, non-circular gear drive, rack drive and worm drive according to the shape of the gear.
According to the tooth profile curve, it can be divided into involute gear transmission, cycloid gear transmission and arc gear transmission. A transmission composed of more than two gears is called a gear train. The gear transmission can be divided into ordinary gear transmission and planetary gear transmission according to whether there are gears with axis movement in the gear train. The gears with axis movement in the gear train are called planetary gears. Gear transmission can be divided into closed type according to its working conditions
Gear transmission calculation
Open and semi-open transmission. Sealing the transmission in a rigid case and ensuring good lubrication is called closed transmission, which is more commonly used, especially for higher-speed gear transmissions, which must be closed transmission. Open transmission is exposed and cannot guarantee good lubrication. It is only used for low speed or unimportant transmission. Half-open transmission is somewhere in between.
The law of meshing: 　The smoothness of gear transmission requires the instantaneous transmission ratio in the process of gear tooth meshing i=angular speed of driving wheel/angular speed of driven wheel=ω1/ω2=constant, this requirement is guaranteed by tooth profile. Figure 2 shows that the two meshing tooth profiles E1 and E2 are in contact at any point K, and the common normal line N1N2 of the two tooth profiles is made through the point K, which intersects the connecting center line O1O2 at point C. The condition for maintaining contact during the meshing process of the two tooth profiles is that the velocity of the K point on the tooth profile E1, vK1, and the K point velocity on the tooth profile E2, vK2, are equal in the direction of the common normal line N1N2, that is, vKn1=vKn2=vKn. Make perpendicular lines from O1 and O2 to the N1N2 line and intersect at points N1 and N2. The above formula shows that the two-wheel tooth profile must meet the following conditions: “No matter where the two-wheel tooth profile is in contact at any position, the common normal line passing through the contact point must pass the fixed point C ─ ─ node on the connecting center line.” This is a circular gear. The basic law of tooth profile meshing. There are many curves that can meet this law. In fact, the requirements of manufacturing, installation and load-bearing capacity should be considered. Generally, only involute, cycloid and arc are used as the working tooth profile of the gear. Part of the tooth profile is involute.
For involute gears, the base radius rb1 and rb2 of wheel 1 and wheel 2 are respectively. The N1N2 line is the internal common tangent of the two base circles, that is, the common normal of any contact point of the two tooth profiles coincides with it. Because the two base circles have only one internal common tangent in one direction, the common normal of any contact point passes through the fixed point C, which shows that using an involute as the tooth profile conforms to the basic law of tooth profile meshing.
The two circles drawn through node C with O1 and O2 as the centers are called pitch circles. The pitch radius of wheel 1 and the pitch radius of wheel 2 Involute gears have the following characteristics: ①N1N2 is the trajectory of the contact points of the two tooth profiles, called the meshing line, which is a straight line. ②The common tangent line tt of the two pitch circles of gear transmission through node C is called the meshing angle α’between it and the meshing line N1N2, which is a constant. ③The pressure between the tooth surfaces is always along the direction of the common normal line N1N2 of the contact point, so the pressure direction between the tooth surfaces does not change when the involute gear transmits power. ④The transmission ratio is inversely proportional to the radius of the base circle of the two wheels. After the gear is made, the base circle is determined. Therefore, even if the center distance is slightly deviated from the design during operation, the transmission ratio will not be affected. This feature is called the separability of the transmission. It affects the processing, assembly and Maintenance is very beneficial. ⑤The two tooth profiles only have no sliding between the tooth surfaces when the node C is in contact, and there is sliding between the tooth surfaces when they are in contact at other points, and the farther away from the node, the greater the sliding. ⑥Since the involute gear can mesh with a rack with a linear tooth profile, it can be processed by a tool with a linear tooth profile. The tool is easy to manufacture and the machining accuracy can be high.
Coincidence degree: Coincidence degree is an important parameter that affects the continuous transmission of gears. As shown in Figure 2, gear tooth meshing starts from the contact between the tooth root of the driving wheel and the tooth tip of the driven wheel, that is, the intersection A of the tooth tip circle of the driven wheel and the meshing line is the starting point of meshing. As the wheel 1 rotates, the wheel 2 is pushed to rotate, and the contact point moves along the meshing line. When the contact point moves to the intersection E of the addendum circle of the wheel 1 and the meshing line (the dotted line in the figure), the tooth profile When the meshing ends, the two tooth profiles begin to separate. Point E is the meshing end point, which is the actual meshing line length. If the front pair of teeth are still in contact at point D before point E, and the latter pair of teeth are in contact at point A, then the transmission is continuous; if the front pair of teeth has left at point E, and the latter pair has not yet entered meshing , Then the transmission is interrupted. Considering the influence of gear manufacturing, installation errors and deformation, ε≥1.1～1.4 is often required in practice. The greater the coincidence degree, the more stable the transmission. The above refers to the coincidence degree of the end face of the cylindrical gear, and there is a longitudinal coincidence degree for the helical cylindrical gear.
The condition for a pair of gears to be able to mesh correctly is that they must have equal modulus and equal pressure angle.

Accuracy requirements of Equipment installation

October 23, 2020

1. For static equipment
The vertical deviation of vertical equipment should not be greater than L/1000 and not greater than 10mm. Unless the drawings have special requirements.

lug type butterfly valve, ductile iron, center lined,

The horizontal deviation of horizontal equipment should not be greater than L/1000 in the axial direction and 2D/1000 in the radial direction.

2. For moving equipment
When the pump is aligned, the selection of the installation datum and the allowable deviation of the level must meet the requirements of the “special specification” or the pump technical file. Generally, the allowable deviation of horizontal horizontality is 0.10mm/m, and the allowable deviation of vertical horizontality of the installation datum part is 0.05mm/m. The leveling and alignment values must not be adjusted by loosening the anchor bolts.
1. The pump that is disassembled and installed is based on the processing surface of the pump body, and the allowable deviation of the horizontality of the pump in the vertical and horizontal directions is 0.05mm/m.
2. The integrally installed pump should be leveled based on the inlet and outlet flange surface or other horizontal processing datum plane. The allowable deviation of horizontality is 0.05mm/m in the longitudinal direction and 0.10mm/m in the transverse direction.
3. When the driving shaft and the driven shaft are connected by a coupling, the centering deviation of the two shafts and the gap between the end faces of the two shafts should be:
Centering deviation: the radial displacement is not more than 0.03mm.
The axial tilt should not be greater than 0.05/1000.
The end face gap is 1.00~3.5mm.

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