What are valves?

What are valves?

Valves are piping accessories used to open and close piping, control flow, and regulate and control the parameters (temperature, pressure, and flow) of the medium being transported. According to its function, it can be divided into shut-off valve, check valve, regulating valve and so on.
The valve is a control component in the fluid delivery system and has functions such as cut-off, regulation, diversion, prevention of backflow, regulation, shunting or overflow relief. Valves for fluid control systems range from the simplest shut-off valves to the extremely complex self-control systems available in a wide variety of sizes and sizes.
Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metals, and radioactive media. According to the material, the valve is also divided into cast iron valve, cast steel valve, stainless steel valve (201, 304, 316, etc.), chrome molybdenum steel valve, chrome molybdenum vanadium steel valve, dual phase steel valve, plastic valve, non-standard custom valve.

1 Introduction  4 Requirements 
Standard Manufacturing process
Types Connection

Introduction of valve

A valve is a device used in a fluid system to control the direction, pressure, and flow of a fluid. It is a device that allows a pipe or a medium (liquid, gas, powder) to flow or stop and control its flow.
The valve is a control component in the pipeline fluid delivery system. It is used to change the passage section and the flow direction of the medium, and has the functions of diversion, cutoff, throttling, check, diversion or overflow relief. Valves for fluid control, from the simplest shut-off valves to the wide variety of valves used in extremely complex automatic control systems, the variety and specifications of the valve, the nominal diameter of the valve from a very small instrument valve to a diameter of up to 10m Valves for industrial piping. It can be used to control various types of fluids such as water, steam, oil, gas, mud, various corrosive media, liquid metal and radioactive fluid. The working pressure of the valve can be from 0.13MPa to 1000MPa. The working temperature can be C-270 ° C ultra-low temperature to 1430 ° C high temperature.
The valve can be controlled by various transmission methods, such as manual, electric, hydraulic, pneumatic, turbo, electromagnetic, electromagnetic hydraulic, electrohydraulic, gas-hydraulic, spur gear, bevel gear drive, etc.; can be under pressure, temperature Under the action of other forms of sensing signals, according to predetermined requirements, or simply open or close without relying on the sensing signal, the valve relies on a driving or automatic mechanism to cause the opening and closing member to be lifted, slid, swiveled or swiveled. Movement, thereby changing the size of its flow path area to achieve its control function.

Domestic and foreign valve standard comparison

China’s valve industry’s current national standards are equivalent, equivalent or non-equivalent foreign advanced standards

China’s current national standards Equivalent, equivalent or non-equivalent foreign standard
Standard Name Standard Name
GB/T 12220-1989 通用阀门  标志 ISO 5209-1977 通用阀门  标志
GB/T 12221-1989 法兰连接金属阀门  结构长度 ISO 5752-1982 法兰连接金属阀门的结构长度
GB/T 12222-1989 多回转阀门  驱动装置的连接 ISO 5210-1~5211.3-1982 多回转阀门驱动装置的连接
GB/T 12223-1989 部分回转阀门 驱动装置的连接 ISO5211-1~5211.3-1982 部分回转阀门驱动装置的连接
GB/T 122241-1989 安全阀  一般要求 ISO 4126-1984 安全阀 一般要求
GB/T 122247-1989 蒸汽疏水阀  分类 ISO 6704-1982 蒸汽疏水阀  分类
GB/T 12248-1989 蒸汽疏水阀  术语 ISO 6552-1982 蒸汽疏水阀  术语
GB/T 12249-1989 蒸汽疏水阀  标志 ISO 6553-1980 蒸汽疏水阀  标志
GB/T 12250-1989 蒸汽疏水阀 结构 ISO 6554-1980 法兰连接蒸汽疏水阀 结构长度
GB/T 12251-1989 蒸汽疏水阀 试验方法 ISO6948-1981 蒸汽疏水阀出厂检验和工作特性测试
GB/T 12224-1989 钢制阀门  一般要求 ANSIB 16.34-1996 阀门  法兰连接和对焊连接
JB/T 7927-1999 阀门铸钢件  外观质量要求 MSS SO55-1996 阀门、法兰。管件及其它管件的铸钢件质量标准
GB/T 12226-1989 通用阀门 灰铸铁件技术条件 ISO/DIS 185-1981
BS1452-1982
灰铸铁分级
灰铸铁件技术条件
GB/T 12228-1989 通用阀门  碳素钢锻件技术件 ASTM A105-1992
ASTM A181-1990
管路附件用碳钢锻件技术规范
常用管路碳钢锻件规范
GB/T 12229-1989 通用阀门  碳素钢铸件条件 ANSI/ASTM A216-1989
ASTM A703-1990
高温用可溶焊碳钢铸件
受压铸钢件技术条件
GB/T 12230-1989 通用阀门  奥氏体钢铸件技术条件 ASTM A351-1991
ASTM A703-1990
高温用奥式体钢铸件规范
受压铸钢件技术条件
GB/T 12242-1989 安全阀  性能试验方法 ANSI/ASME PTC 25.3-1989 安全阀和泄压阀性能试验规范
GB/T 12245-1989 减压阀  性能试验方法 JIS 8372-1981
JIS B8410-1990
DSS 405-1981
空气减压阀
水道用减压阀
蒸汽减压阀
GB/T 12232-1989 通用阀门  法兰连接铁制闸阀 BS 5150-1992
ISO/DIS 5996-1984
普通铸铁楔式闸阀及双闸板闸阀铸铁闸阀
GB/T 12234-1989 通用阀门  法兰和对焊连接钢制闸阀 ANSI/API 600-2001 法兰或对焊连接钢制闸阀
GB/T 12235-1989 通用阀门  法兰连接钢制截止阀和升降式止回阀 ANSI/API 600-2001 法兰或对焊连接钢制闸阀
GB/T 12236-1989 通用阀门 钢制旋启式止回阀 ANSI/API 600-2001 法兰或对焊连接钢制闸阀
GB/T 12237-1989 通用阀门 法兰和对焊连接钢制球阀 ISO/DIS 7121-1986
API 607-1991
法兰或对焊连接钢制球阀
1/4回转阀门软密封座的耐火试验
GB/T 12238-1989 通用阀门 法兰和对夹连接蝶阀 BS 5155-1992 一般用途的铸铁和碳钢蝶阀
GB/T 12239-1989 通用阀门  隔膜阀 BS 5156-1992 一般用途的隔膜阀
GB/T 12240-1989 通用阀门  铁制旋塞阀 API 593-1984 球墨铸铁法兰旋塞网
GB/T 12243-1989 弹簧直接载荷式安全阀 JIS B8210-1986 蒸汽及气体用弹簧安全阀
GB/T 12244-1989 减压阀  一般要求 JIS 8372-1981
JIS B8410-1990
DSS 405-1981
空气减压阀
水道用减压阀
蒸汽减压阀
GB/T 12246-1989 先导式减压阀 JIS 8372-1981
JIS B8410-1990
DSS 405-1981
空气减压阀
水道用减压阀
蒸汽减压阀

Types of valves

Ball Valve

Evolving from plug valves, ball valves are a kind of quarter-turn valves whose disc is ball shape. They are mainly used for blocking off, distributing and changing the direction of flow, of which, ball valves with V-type opening have a better flow rate moderating function.

Advantages:

  • The lowest flow resistance (zero).
  • Ball valves won’t get stuck during working even without lubricant, so they are reliable for controlling the flow of corrosive and low-boiling-point media.
  • Fully sealed ability under conditions with relatively high pressure and temperature.
  • Fast shut-off (speeds of some structures are merely 0.05-0.1s), no impact when automatic system operating.
  • The disc can automatically position on the margin.
  • When fully opening or closing, the sealing surfaces of the ball and valve body are separated with the medium, so the sealing surfaces won’t be eroded when the medium is speedily passing the valve.
  • Compact structure, lightweight – so it is considered as the most suitable valve for low-temperature system.
  • Symmetrical shape, especially welded body, being able to withstand the pressure from pipeline.
  • Disc can withstand high-pressure difference when closing.
  • Ball valves with all-welded valve body can directly be buried in the ground, and prevent the inner part of valves from being eroded. Ball valves, whose service life can reach to 30 years, are an ideal option for petroleum, natural gas pipelines.

Disadvantages:

The major material of the sealing ring of valve body is PTEF, which won’t have chemical reactions with almost all other materials. In addition, PTEF has characteristics such as small friction coefficient, stable performance, aging resistance, being able to withstand a wide range of temperature, excellent sealing performance. But, its physical properties, including large expansion coefficient, cold stream sensitivity, poor thermal conductivity, restrain the design of valve body. As the material of sealing ring hardens, its sealing ability weakens. Moreover, PTEF is unable to with high temperature and can’t be used in conditions with temperature higher than 180℃, otherwise the sealing part will deteriorate. 
Weak adjustment performance compared to globe valves, especially pneumatic or electric valves

Plug Valve

It is a rotary valve whose disc is plunger shape (cylindrical shape or conical shape), which can be rotated to control the flow of media. The working principle of plug valves is basically the same with that of ball valves, which evolves from plug valves and mainly used in oil field exploitation, and petrochemical field.

Relief Valve

It is a protective device for pressure vessel, equipment, or pipeline. When the pressure of equipment, vessel or pipeline exceeds the allowed value, the valve will automatically open and discharge media, so as to prevent the pressure continue to go up. If the pressure is lower than the allowed value, valve should close automatically and timely in order to guarantee safe operation of equipment, vessel or pipeline.

Steam trap valve

Media like vapor, compressed air will generate condensate water during transporting that needs to discharge in time for stabilizing the working efficiency and operation of devices.
Steam traps have the following functions:

  • To prevent vapor leakage
  • To discharge air, or other incondensable gases

Check Valve

Check valves, which are also known as non-return valves, one-way valves, reflux valves, can be divided into swing type and lift type. They are a kind of automatic valves that open and close by the force produced by the flow of media. The main function of check valves is to prevent media from flowing backward, pumps and drive motor from reversing, vessel media from venting. 

Gate Valve

It is a valve that vertically moves along the axis of tunnel, and is used for on/off control of the flow of medium rather than moderating flow rate. Gate valves are able to withstand high or low temperature or pressure and convey a wide range of media, but not including mud type media generally.

Advantages:

  • Small flow resistance force.
  • Small torque required for on/off control.
  • The direction of flow is not restricted – gate valves can be used in a bidirectional loop network.
  • The impact of erosion caused by media is less than that of globe valves when gate valves are fully open.
  • Simple structure, good manufacturability.
  • Short structural length.

Disadvantages:

  • Relatively large installation space – big external dimension, long open length required.
  • High-frequency rubbing during opening and closing; Scrapes may occur in high-temperature conditions.
  • Generally, gate valves have two sealing surfaces, which bring a little more difficulty to machining, grinding and maintenance.
  • Long on/off time.

Butterfly Valve

Butterfly valves are a kind of valves that block off or moderate the flow of medium by quarter-turning (the disc is rotated a quarter turn).

Advantages:

  • Simple structure, volume, lightweight, low material consumption.
  • Quick shut-off, small flow resistance.
  • Being able to be used in controlling the flow of media with suspended solid, or, according to the solidity of the sealing surface, powdery or granular media. Butterfly valves are suitable for blocking off and moderating flow (bi-direction) in ventilating and dedusting pipeline, as well as gas pipe, waterway in metallurgy industry, light industrial field, power plant, petrochemical system.

Disadvantages:

  • Small scope of flow moderating – 95% of flow won’t be blocked off even the valve is only open 30%.
  • Being unable to withstand pipeline system with high temperature and pressure due to the restriction of its structure and sealing surface materials (temperature ≤ 300℃, pressure ≤ PN40).
  • Poor sealability compared with ball valves, globe valves (So it can only be installed on places where require low sealabilty.)

Globe Valve

It is a valve whose disc moves along the center line of valve body. According to this kind of movement mode, the variation of the opening of valve body is proportional to disc travel. Besides, the fact that the valve stem of globe valve has a relatively short travel of opening and closing, its reliable blocking-off function, these three factors are why globe valves are a suitable option for flow moderating, blocking off, and throttling.

Advantages:

  • Wear resistance – small friction compared with gate valves during the processes of opening and closing.
  • Short open length (a quarter of the channel within the valve body).
  • Only one sealing surface, good manufacturability, easy maintenance.
  • High-temperature resistance – Globe valves’ packing materials are normally asbestos and graphite.

Disadvantages:

Because globe valves will change the flow direction of medium, their minimum flow resistance is higher than that of most other valves.
Slow opening speed

Reducing Valve

Reducing valves are used for reducing the upstream pressure to the required downstream pressure and stabilizing the downstream pressure by consuming the energy of medium.

Requirements

Valve installation requirements

  1. Before installing the valve, carefully check whether the model and specifications of the valve used are consistent with the design;
  2. According to the model of the valve and the factory manual, check whether the valve can be applied under the required conditions;
  3. When the valve is hoisted, the rope should be tied to the flange connection between the valve body and the valve cover, and should not be placed on the hand wheel or the valve stem to avoid damage to the valve stem and the hand wheel;
  4. When installing the valve on the horizontal pipe, the valve stem should be vertical upwards, and the valve stem should not be installed downward;
  5. When installing the valve, it is forbidden to use the forced-to-mouth connection method of pulling and pulling hard to avoid damage caused by uneven force;
  6. The open gate valve should not be installed in the wet place in the ground, so as to avoid valve stem corrosion.

Valve assembly requirements

The cleaned parts must be sealed and stored for installation.
The requirements for the installation process are as follows:

  1. The installation workshop must be clean, or set up a temporary clean area, such as the use of newly purchased color strips or plastic film to prevent dust from entering during the installation process.
  2. The assembly workers must be dressed in clean cotton overalls, wearing a cotton cap, hair can not leak, wear clean shoes, hand wearing plastic gloves, skim.
  3. The assembly tool must be degreased and cleaned before assembly to ensure cleanliness.

Valve specifications

  1. The model number of the valve should indicate the national standard number requirement. If it is an enterprise standard, the relevant description of the model number should be indicated.
  2. The working pressure of the valve requires ≥ the working pressure of the pipeline. Under the premise of not affecting the price, the working pressure of the valve should be greater than the actual working pressure of the pipeline.
  3. Valve manufacturing standards, should be based on the national standard number, if it is an enterprise standard, the procurement contract should be accompanied by corporate documents.

Valve performance testing requirements

  1. When a certain specification of a valve is manufactured in batches, an official agency shall be entrusted to carry out the following performance tests: 1 the opening and closing torque of the valve under the working pressure condition; 2 the detection of the flow resistance coefficient of the valve under the condition of pipeline water delivery.
  2. The valve should be tested before leaving the factory: 1 valve in the open condition, the valve body should withstand the internal pressure of the valve pressure value twice; 2 valve in the closed condition, the two sides respectively with 11 times the valve pressure Value, no leakage; but the metal-sealed butterfly valve, the leakage value is not greater than the relevant requirements.

Valve sealing requirements

The sealing performance of the valve refers to the ability of the sealing parts of the valve to prevent the leakage of the medium. It is the most important technical performance index of the valve. There are three sealing parts of the valve: the contact between the sealing surface of the opening and closing parts and the valve seat; the joint of the packing with the valve stem and the stuffing box; the connection between the valve body and the valve cover. The leak in the former place is called endoleak, which is commonly referred to as the lack of tightness, which will affect the ability of the valve to cut off the medium. For shut-off valves, internal leakage is not allowed. The latter two leaks are called leaks, that is, the medium leaks from the valve to the outside of the valve. External leakage can cause material loss, pollute the environment, and cause accidents in severe cases. For flammable, explosive, toxic or radioactive media, external leakage is not allowed, so the valve must have a reliable sealing performance.

Other requirements for valves

  1. The assembled valve is purged with nitrogen for at least 1 minute.
  2. The airtight test must be pure nitrogen.
  3. After the airtight test is passed, encapsulation is carried out, sealed with a clean polyethylene cap, and the polyethylene cap is soaked with an organic solvent before use and wiped clean.
  4. Then seal with a vacuum bag.
  5. Fnally packing.
  6. Measures should be taken during transportation to ensure that the envelope is not damaged.

The valve parts are few, the structure is simple, the precision is general, and it is a simple component in the mechanical industry, but the core sealing part of the valve is required to be particularly high. The valve manufacturing process is complicated and the technical difficulty is also great.

What process characteristics do we need to pay attention to?

1. Valve manufacturing materials

Due to the variety of valve specifications, such as general valves have gate valves, globe valves, check valves, ball valves, butterfly valves, hydraulic control valves; industrial valves have solenoid valves, regulating valves, pressure reducing valves, high temperature and high pressure valves, low temperature valves and other special valves They are used in various fields of the national economy, and their use occasions vary widely, such as high temperature and high pressure, low temperature cryogenic, flammable and explosive, highly toxic, strong corrosive medium and other working conditions, which imposes stringent requirements on the material of the valve.
In addition to cast iron, carbon steel and alloy structural steel, the valve manufacturing materials also use CrNi stainless steel, CrMoAl nitrided steel, CrMoV heat resistant steel, CrMnN acid resistant steel, precipitation hardened steel, duplex stainless steel, low temperature steel, titanium alloy and Mongolian. Nyle alloy, Inconel alloy, Hastelloy and G0CrW cemented carbide. The casting, welding and processing properties of these high-alloy materials are very poor, which brings great difficulty to the manufacturing process. In addition, most of these materials are high-alloy, high-strength, high-hardness precious materials, and there are many difficulties in material selection, preparation, and procurement. Some materials are difficult to purchase due to their small amount of use.

2. Structure of the cast blank

Most of the valve blanks are made of thin shell castings with complex structure, which not only requires good appearance quality, but also has dense internal quality and good metallographic structure. It cannot have defects such as pores, shrinkage holes, sand inclusions, cracks, etc. . Therefore, the casting process is complicated and the heat treatment technology is difficult. In the machinery industry, the casting of pressure-bearing thin-shell casting blanks of valves is much more complicated and difficult than castings of other mechanical components.

3. Mechanical processing technology

Because most of the high-strength, high-hardness, high-corrosion materials have poor cutting performance, such as high-alloy stainless steel and acid-resistant steel, they have the disadvantages of high toughness, high strength, poor heat dissipation, large chip viscosity and strong work hardening tendency. Difficult to achieve the required dimensional accuracy and finish, it presents certain difficulties for machined tools, processes and equipment. In addition, the valve sealing surface is also very high in machining accuracy, mating angle, smoothness and matching sealing pair, which brings great difficulty to machining.

4. Process arrangement of valve parts

The number of main parts of the valve is small, the structure is relatively simple, the processing precision of most sizes is not high, and the outside is rough, which gives the impression of being a simple machine. In fact, the heart seal of the valve can be extremely precise, the “three degrees” (flatness, smoothness, hardness) of the sealing surface is very high, and the sealing degree of the sealing faces composed of two sealing surfaces must reach zero to zero. To meet the zero leakage of the airtight test. This rough reference to ensure the precise zero-to-zero requirements of the heart is the biggest process difficulty in valve processing.

5. Valve test and inspection

The valve is an important opening and closing and regulating component of the pressure pipeline, and the working conditions of the pressure pipeline are different, high temperature and high pressure, low temperature cryogenic, flammable and explosive, highly toxic and strong corrosion. However, the test and inspection conditions for valve manufacturing are unlikely to meet the same requirements for working conditions. The international and domestic various valve test standards are tested under the condition of near normal temperature with gas or water as the medium. There is a fundamental hidden danger, that is, the valve products that have passed the normal factory test may have difficulty in meeting the requirements of use due to problems such as material selection, casting quality and sealing damage under severe actual working conditions. Quality accident. It is no wonder that some old valve experts who have worked for a lifetime are more and more cautious and more worried.

Manufacturing process of valves

The first step: valve body manufacturing

Valve body (casting, sealing surface surfacing)
Casting purchase (according to standard) into factory inspection (according to standard) ➱ surfacing welding ➱ ultrasonic flaw detection (according to the pattern) ➱ surfacing and post-weld heat treatment ➱ finishing ➱ grinding sealing surface ➱ sealing surface hardness test, coloring flaw detection.

The second step: the valve internals manufacturing process

A. Internal parts such as valve discs, valve seats, etc.

Purchasing raw materials (according to the standard), entering the factory inspection (according to the standard), making blanks (round steel or forgings, according to the technical requirements of the drawings), roughing the ultrasonic flaw detection surface (when the pattern is required), roughing the surfacing, welding, welding and welding Post-heat treatment ➱ Finishing of all parts ➱ grinding sealing surface ➱ sealing surface hardness test, coloring flaw detection.

B. Valve stem

Purchasing raw materials (according to standards), entering the factory inspection (according to the standard), making blanks (round steel or forgings, according to the technical requirements of the drawings), roughing, surfacing, welding, post-weld heat treatment, finishing, machining, grinding, grinding ➱ valve stem surface treatment (nitriding, quenching, electroless plating) ➱ final treatment (polishing, grinding, etc.) ➱ grinding sealing surface ➱ sealing surface hardness test, coloring flaw detection.

C. Do not need to weld the inner surface of the sealing surface, etc.

Purchasing raw materials (according to the standard), entering the factory inspection (according to the standard), making blanks (round steel or forgings, according to the technical requirements of the drawings), roughing the ultrasonic inspection surface (when the drawings are required), finishing the various parts.

The third step: fastener manufacturing

Fastener manufacturing standard DL439-1991.
Purchasing raw materials (according to standards), entering the factory inspection (according to the standard), making blanks (round steel or forgings, according to the technical requirements of the drawings) and sampling for necessary inspection, roughing, finishing, and spectral inspection.

The fourth step: final assembly

After receiving parts, cleaning, cleaning, rough assembly (according to the drawings), water pressure test (according to drawings, processes), after passing, disassembling, wiping, final assembly, and electrical installation or actuator debugging (for electric valves) The package is shipped.
1504662865119111 - What are valves?
Valve product production and inspection flow chart

Step 5: Valve product production and inspection process

  1. The company purchases raw materials of various specifications.
  2. The material is tested by a spectrum analyzer, and the raw material material test report is printed for backup.
  3. Raw material cutting with a cutting machine.
  4. The inspector checks the diameter and length of the raw material cut.
  5. The forging workshop processes the raw materials by forging.
  6. The inspector performs various dimensional inspections of the blank for forming.
  7. The worker is cutting the waste edge.
  8. The sand blaster sandblasts the surface of the blank.
  9. The inspector performs surface treatment inspection after sandblasting.
  10. Workers carry out rough machining.
  11. Valve body sealing thread processing—Employees are inspected after processing by the inspection and inspection personnel.
  12. The valve body is connected to the thread for machining.
  13. Middle hole machining.
  14. The inspector conducts a general inspection.
  15. Qualified semi-finished products are sent to the semi-finished warehouse.
  16. Semi-finished products are plated.
  17. Semi-finished plating surface treatment inspection.
  18. Inspection of various accessories (ball, valve stem, sealed seat).
  19. Product assembly in the assembly shop—assembly line inspection personnel inspect the product.
  20. The assembled product is subjected to pressure testing and drying to the next process.
  21. The assembly shop is responsible for product packaging—-packaging line inspection personnel to check the sealing, appearance and torque of the product. Unqualified products must never be packaged.
  22. Qualified products are packaged and sent to the finished product warehouse.
  23. All inspection records will be stored in the computer for easy access.
  24. Qualified products are sent to and from the country through containers.

Valve cleaning step

Valve components must be processed through the following processes before assembly:

  1. According to the processing requirements, some parts need to be polished, and the surface cannot be processed with burrs;
  2. All parts are degreased;
  3. After the degreasing is completed, the acid washing passivation is carried out, and the cleaning agent does not contain phosphorus;
  4. After pickling and purification, rinse with pure water, there can be no drug residue, carbon steel parts save this step;
  5. Dry the parts one by one with a non-woven fabric, and do not leave the surface of the parts such as wire wool, or blow dry with clean nitrogen;
  6. Use a non-woven fabric or a precision filter paper to analyze the pure alcohol and wipe each component one by one until there is no dirty color.

Daily maintenance of valves

  1. The valve storage environment should be noted. It should be stored in a dry and ventilated room and block both ends of the passage.
  2. The valve should be regularly inspected, and remove the dirt on it, apply anti-rust oil on its surface.
  3. Install the applied valve and perform regular maintenance to ensure its normal operation.
  4. Check the valve sealing surface for wear and repair or replace it according to the situation.
  5. Check the trapezoidal thread wear of the stem and stem nut, whether the packing is out of date, etc., and make necessary replacements.
  6. Test the sealing performance of the valve to ensure its performance.
  7. The valve in operation should be in good condition, the bolts on the flange and the bracket are complete, the thread is not damaged, and there is no looseness.
  8. If the handwheel is lost, it should be timely and cannot be replaced with a spanner wrench.
  9. The packing gland is not allowed to be skewed or has no pre-tightening clearance.
  10. If the valve is used in a harsh environment and is susceptible to dirt such as rain, snow, dust, sand, etc., a protective cover should be installed for the valve stem.
  11. The scale on the valve should be kept intact, accurate and clear, and the valve seals and caps.
  12. The insulation jacket should be free from dents and cracks.
  13. the valve in operation, to avoid hitting it, or supporting heavy objects.

Valve connection

Flange connection

This is the most used form of connection in the valve. According to the shape of the joint surface, it can be divided into the following types:

  1. Smooth type: used for valves with low pressure. More convenient processing
  2. Concave and convex type: high working pressure, can use medium hard washer
  3. Gutter type: It can be used with gaskets with large plastic deformation. It is widely used in corrosive media and has good sealing effect.
  4. Trapezoidal trough type: use oval metal ring as a gasket, used for valves with working pressure ≥ 64 kg / cm 2 , or high temperature valves.
  5. lens type: the gasket is a lens shape, made of metal. For high pressure valves with working pressure ≥100 kg/cm 2 or high temperature valves.
  6. O-ring type: This is a newer form of flange connection, which developed with the appearance of various rubber O-rings, it is in the form of a sealed connection.

Clip connection

A connection form in which the valve and the two pipes are directly clamped together by bolts.

Butt weld connection

A connection that is directly welded to the pipe.

Threaded connection

This is a simple connection method and is often used for small valves. There are two cases:

  1. Direct sealing: The internal and external threads directly seal. In order to ensure that the joints are not leaking, they are often filled with lead oil, wire hemp and polytetrafluoroethylene raw material tape; among them, the polytetrafluoroethylene raw material tape is widely used; this material has good corrosion resistance and excellent sealing effect. It is easy to use and store. When disassembling, it can be completely removed, because it is a non-stick film, which is superior to lead oil and wire.
  2. Indirect sealing: the force of screwing is transmitted to the gasket between the two planes, so that the gasket acts as a seal.

Card sleeve connection

The ferrule connection, the connection and sealing principle is that when the nut is tightened, the ferrule is subjected to pressure, and the blade portion bites into the outer wall of the tube, and the outer tapered surface of the ferrule is tightly pressed against the tapered surface of the joint body under pressure, thereby It can reliably prevent leakage.
The advantages of this form of connection are:

  1. Small size, light weight, simple structure, easy assembly and disassembly;
  2. Strong connection, wide range of use, can withstand high pressure (1000 kg / cm), high temperature (650 ° C) and shock vibration
  3. Can choose a variety of materials, suitable for anti-corrosion;
  4. Processing accuracy requirements are not high; easy to install at high altitude.
  5. The ferrule connection form has been adopted in some small diameter valve products in China.

Clamp connection

This is a quick connection method that requires only two bolts for low pressure valves that are often removed.

Self-tightening connection

All of the above connection forms use external force to offset the medium pressure and achieve sealing. The following describes the connection form that uses the medium pressure for self-tightening. Its sealing ring is installed at the inner cone, at an angle to the opposite side of the medium, the medium pressure is transmitted to the inner cone, and is transmitted to the sealing ring. At a certain angle of the cone surface, two component forces are generated, one and The centerline of the valve body is parallel to the outside and the other is pressed against the inner wall of the valve body. The latter part of the force is self-tightening. The greater the medium pressure, the greater the self-tightening force. Therefore, this type of connection is suitable for high pressure valves. It is more connected to the flange and saves a lot of material and manpower, but it also requires a certain pre-tightening force, so that it can be used reliably when the pressure inside the valve is not high. Valves made using the principle of self-tightening are generally high pressure valves.
There are many forms of valve connections, such as small valves that do not have to be removed, welded to the pipe; some non-metallic valves, socketed connections, and so on. Valve users should be treated according to the circumstances of the break.

Valve related accessories

There are valves and fittings, they are used in the connection or control system of the pipeline. Valves and fittings cannot exist independently and complement each other. Valve fittings are made of carbon steel and stainless steel, as well as PVC, or other materials. The first two are commonly used. In recent years, with the improvement of people’s living standards, the demand for non-staple foods has also increased. It’s up. Therefore, the rapid development of food machinery has been promoted, so the stainless steel sanitary valve fittings production industry has become popular. People usually say that the valve fittings are mostly stainless steel sanitary grade.

Valve maintenance

Claim

  1. The valve should be stored in a dry and ventilated room, and both ends of the passage must be blocked.
  2. Valves stored for a long time should be inspected regularly to remove dirt and apply anti-rust oil on the processing surface.
  3. After installation, it should be inspected regularly, mainly for inspection items:
  • Wear of the sealing surface.
  • Trapezoidal thread wear of the stem and stem nut.
  • Whether the filler is out of date or not, and if it is damaged, it should be replaced in time.
  • After the valve is overhauled and assembled, the sealing performance test shall be carried out.

Valves in operation, all valve parts should be complete and intact. The bolts on the flange and the bracket are indispensable, the thread should be intact and no looseness is allowed. The tightening nut on the hand wheel should be tightened if it is loose, so as not to wear the joint or lose the handwheel and nameplate. If the handwheel is lost, it is not allowed to replace it with a wrench. It should be timely. The packing gland is not allowed to be skewed or has no pre-tightening clearance. For valves in environments that are susceptible to contamination by rain, snow, dust, sand, etc., the valve stem should be fitted with a protective cover. The scale on the valve should be complete, accurate and clear. The seals, caps and pneumatic accessories of the valve should be completed. The insulation jacket should be free from dents and cracks. It is not allowed to tap, stand or support heavy objects on a running valve; especially non-metallic valves and cast iron valves are prohibited.

Valve grease maintenance

The professional maintenance work of the valve before and after the production before the welding plays a vital role in the service of the valve. The correct and orderly maintenance will protect the valve, make the valve function properly and extend the valve. life. Valve maintenance work seems simple, but it is not. There are often neglected aspects of work.

  • First, when the valve is greased, the problem of the amount of grease is often ignored. After the grease gun is refueled, the operator selects the valve and the grease injection method to perform the grease filling operation. There are two cases: on the one hand, the amount of grease is less than that of the grease, and the sealing surface is accelerated by the lack of lubricant. On the other hand, excessive fat injection causes waste. There is no accurate calculation of the different valve sealing capacities based on the valve type category. The sealing capacity can be calculated in terms of valve size and type, and a proper amount of grease can be injected reasonably.
  • Second, when the valve is greased, the pressure problem is often ignored. During the grease injection operation, the grease injection pressure changes regularly in the peaks and valleys. The pressure is too low, the seal leaks or fails, the pressure is too high, the grease injection port is blocked, the seal grease hardens or the seal ring and the valve ball and the valve plate are locked. Usually, when the grease pressure is too low, the injected grease flows into the bottom of the valve chamber, which usually occurs in a small gate valve. On the one hand, the grease injection pressure is too high. On the one hand, the grease injection nozzle is checked. If the grease hole is blocked, the situation is replaced. On the other hand, the grease is hardened. The cleaning fluid is used to repeatedly soften the failed sealing grease and inject a new grease. . In addition, the sealing type and sealing material also affect the grease filling pressure. Different sealing forms have different grease filling pressures. Generally, the hard sealing grease pressure is higher than the soft sealing.
  • Third, when the valve is greased, pay attention to the problem that the valve is in the switch position. Ball valve maintenance is generally in the open position, in special circumstances, choose to turn off maintenance. Other valves cannot be discussed in terms of opening. The gate valve must be closed during maintenance to ensure that the grease fills the seal groove along the seal. If it is open, the seal grease will fall directly into the runner or valve cavity, causing waste.
  • Fourth, when the valve is greased, the problem of grease injection is often ignored. The pressure, grease injection amount and switch position are normal during the grease filling operation. However, in order to ensure the grease filling effect of the valve, it is sometimes necessary to open or close the valve to check the lubrication effect and confirm that the valve ball or the surface of the valve is evenly lubricated.
  • Fifth, when filling grease, pay attention to the problem of valve body sewage discharge and wire plug pressure relief. After the valve pressure test, the gas and moisture in the valve chamber of the sealed chamber are boosted due to the increase of the ambient temperature. When the grease is injected, the drain and pressure should be drained first, so as to facilitate the smooth operation of the grease injection work. After the grease is applied, the air and moisture in the sealed chamber are sufficiently replaced. Timely discharge of the valve chamber pressure also ensures the safety of the valve. After the grease is applied, be sure to tighten the drain and pressure relief plug to prevent accidents.
  • Sixth, when filling the grease, pay attention to the problem of uniform grease. In normal fat injection, the fat-producing hole closest to the grease injection port first comes out of fat, then to the low point, and finally to the high point, and the fat is successively produced. If it is not in accordance with the law or does not produce fat, it proves that there is clogging and clearing treatment in time.
  • Seventh, when filling the grease, also observe the problem that the valve diameter and the seal ring are flush. For example, if there is a ball valve, if there is an open position, the position limiter can be adjusted inward to confirm that the path is straight and locked. Adjusting the limit can not only pursue the opening or closing of a position, but should be considered as a whole. If the opening position is flush and not closed, the valve will not be closed. In the same way, if the adjustment is in place, it is also necessary to consider the corresponding adjustment. Make sure the valve is at right angles.
  • Eighth, after the grease is applied, the grease injection port must be sealed. Avoid the entry of impurities, or the oxidation of lipids at the grease injection port. Apply anti-rust grease to the cover to avoid rust. So that it will be applied the next time.
  • Ninth, when filling grease, it is also necessary to consider the specific issues in the future delivery of oil products. In view of the different qualities of diesel and gasoline, the ability to flush and decompose gasoline should be considered. In the future valve operation, when encountering the gasoline section, timely replenish the grease to prevent wear.
  • Tenth, when filling grease, do not ignore the grease filling on the stem. There is a sliding bushing or packing on the valve shaft, and it is also necessary to maintain the lubrication state to reduce the frictional resistance during operation. If the lubrication cannot be ensured, the torque is increased during the electric operation, and the switch is laborious during manual operation.
  • Eleventh, some ball valve body is marked with an arrow, if there is no English FIOW handwriting, it is the sealing seat action direction, not as a medium flow direction reference, the valve is in the opposite direction. Typically, a two-seat sealed ball valve has a two-way flow direction.
  • Twelfth, when the valve is maintained, pay attention to the water in the motor and its transmission mechanism. Especially the rain that infiltrates during the rainy season. One is to rust the transmission mechanism or the transmission bushing, and the other is to freeze in winter. The torque caused by the operation of the electric valve is too large. Damage to the transmission components may cause the motor to be unloaded or the over-torque protection may not be electrically operated. The drive components are damaged and manual operation is not possible. After the over-torque protection action, the manual operation also fails to switch. For example, forced operation will damage the internal alloy parts.

Common problem

Why does the double seal valve not be used as a shut-off valve?

The advantage of the double seat valve spool is the force balance structure, which allows a large differential pressure, and its outstanding disadvantage is that the two sealing faces cannot be in good contact at the same time, resulting in a large leak. If it is artificially and forcibly used to cut off the occasion, it is obviously not effective, even if it has made many improvements (such as double-sealed sleeve valves), it is not advisable.

Why does the two-seat valve easily oscillate when working at a small opening?

For a single core, the valve stability is good when the medium is flow-opening; the stability of the valve is poor when the medium is flow-closed. The double seat valve has two spools, the lower spool is closed, and the upper spool is open. Thus, when working at a small opening, the flow-closed spool is liable to cause vibration of the valve. This is a double seat valve. Can not be used for small opening work.

What kind of straight stroke control valve has poor anti-blocking performance, and the anti-blocking performance of the angular stroke valve is good?

The straight-stroke valve spool is vertically throttled, and the medium flows horizontally in and out, and the flow passage in the valve chamber is inevitably turned and inverted, making the flow path of the valve quite complicated (shape is inverted S-type). In this way, there are many dead zones that provide space for the precipitation of the medium, which in the long run causes blockage. The direction of the angular stroke valve throttling is the horizontal direction. The medium flows horizontally and horizontally, which makes it easy to take away the dirty medium. At the same time, the flow path is simple, and the space for the medium to precipitate is also small, so the anti-blocking performance of the angular stroke valve is good.

Why is the cut-off pressure difference of the angular stroke type valve larger?

The cut-off pressure difference of the angular stroke type valve is large because the resultant force of the medium on the valve core or the valve plate generates a very small torque to the rotating shaft, and therefore, it can withstand a large pressure difference.

Why is the straight stroke control valve stem thin?

It involves a simple mechanical principle: large sliding friction and low rolling friction. The valve stem of the straight stroke valve moves up and down, and the packing is slightly pressed tightly, which will tightly seal the valve stem and produce a large backlash. For this reason, the valve stem is designed to be very small, and the filler is also commonly used with a small friction coefficient of PTFE filler to reduce the backlash, but the problem is that the valve stem is thin, the bend is easy, and the filler life is short. The best way to solve this problem is to use the travel valve stem, that is, the angular stroke type regulating valve. Its valve stem is 2 to 3 times thicker than the straight stroke valve stem, and the graphite packing with long life is selected. Well, the filler has a long life and what is a hard seal?
The shut-off valve requires that the leakage is as low as possible, the leakage of the soft-sealed valve is the lowest, and the cutting effect is of course good, but it is not wear-resistant and has poor reliability. From the double standard of small leakage, sealing and reliability, the soft seal cut is not as good as the hard seal cut. Such as full-featured ultra-light regulating valve, sealed and protected by wear-resistant alloy, high reliability, leakage rate of 10 to 7, has been able to meet the requirements of the shut-off valve.

Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

Please notice that you might be interested in the other technical articles we’ve published:

  • Sealing Tests for Valves

  • The Origin and Development of the Valve

  • Nine Anti-Corrosion Measures of Valves

  • The Selection of Control Valve

  • Operation and Maintenance Manuals for Gate Valves

  • When the control valves are used in liquid service

  • Choosing Valves Based on Industry Characteristics

  • Designs and Uses of Ball Valves for Submarine Pipelines

  • Corrosion Fatigue of Valves

  • How to choose valves

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