What is a complete knowledge of valves?

Valve is a pipeline accessory, which is used to open and close the pipeline, control the flow direction, and adjust and control the parameters (temperature, pressure and flow) of the conveying medium. According to its function, it can be divided into cut-off valve, check valve and regulating valve.

Valve is the control part in the fluid conveying system, which has the functions of cutting off, regulating, shunting, backflow prevention, pressure stabilization, shunting or overflow pressure relief. The valves used in the fluid control system, from the simplest cut-off valve to various valves used in the extremely complicated automatic control system, have quite a variety of varieties and specifications.

Valves can be used to control the flow of various fluids, such as air, water, steam, corrosive media, mud, oil, liquid metal and radioactive media. Valves are divided into cast iron valves, cast steel valves and stainless steel valves (20 1, 304, 3 16, etc. ), chrome-molybdenum steel valves, chrome-molybdenum steel valves, dual-phase steel valves, plastic valves, non-standard customized valves, etc.

Valve is a device used to control the direction, pressure and flow of fluid in fluid system, and it is a device to make the media (liquid, gas and powder) in pipelines and equipment flow or stop and control their flow.

Valve is the control part in the pipeline fluid transportation system, which is used to change the cross section of the channel and the flow direction of the medium, and has the functions of shunting, cutoff, throttling, check, shunting or overflow pressure relief. Valves used for fluid control range from the simplest shut-off valve to various valves used in extremely complicated automatic control systems, with nominal diameters ranging from extremely tiny instrument valves to industrial pipeline valves with diameters of 10m. It can be used to control the flow of various types of fluids, such as water, steam, oil, gas, mud, various corrosive media, liquid metal and radioactive fluids. The working pressure range of the valve is 0.00 13MPa to 1000MPa, and the working temperature range is from ultra-low temperature of c-270℃ to high temperature of 1430℃.

The valve can be controlled by various transmission modes, such as manual, electric, hydraulic, pneumatic, turbine, electromagnetic, electromagnetic hydraulic, electrohydraulic, pneumatic hydraulic, spur gear and bevel gear drive. Under the action of pressure, temperature or other forms of sensing signals, it can act according to predetermined requirements, or it can be simply turned on or off without relying on sensing signals. The valve moves, slides, swings or rotates the opening and closing parts up and down by driving or automatic mechanism, thus changing the size of its flow area to realize its control function.

According to the function and purpose

(1) Close the valve

This kind of valve is used for opening and closing. Standing on the inlet and outlet of cold and heat sources, equipment and pipeline branches (including risers), it can also be used as a drain valve and a vent valve. Common cut-off valves are gate valves, globe valves, ball valves and butterfly valves.

Gate valves can be divided into exposed and hidden rods, single and double rams, wedge rams and parallel rams. The sealing performance of gate valve is not good, and it is difficult to open large-diameter gate valve; The size of the valve body along the water flow direction is small, the flow resistance is small, and the nominal diameter span of the gate valve is large.

Cut-off valves are divided into three types according to the flow direction of the medium: straight-through, right-angle and direct-flow, and also divided into open-stem and hidden-stem. The sealing performance of globe valve is better than that of gate valve, with long valve body, large flow resistance and maximum nominal diameter DN200.

The valve core of the ball valve is a sphere with an opening. Move the valve stem so that the ball hole is fully open when facing the pipeline axis, and fully closed when turning 90. The ball valve has certain adjustment performance and is tightly closed.

The valve core of the butterfly valve is a circular valve plate, which can rotate along the vertical axis perpendicular to the pipeline axis. When the plane of the valve plate is consistent with the axis of the pipeline, it is fully open; When the gate plane is perpendicular to the pipeline axis, the gate is completely closed. Butterfly valve body has small length and low flow resistance, which is higher than gate valve and globe valve. [ 1]

(2) Check valve

This kind of valve is used to prevent the medium from flowing backwards. It opens itself by using the kinetic energy of the fluid and closes automatically when it flows backwards. Stand at the outlet of the water pump, the outlet of the steam trap and other places where the fluid is not allowed to flow backwards. Check valves are divided into swing type, lift type and clip type. For swing check valves, the fluid can only flow from left to right, and automatically closes when it flows in the opposite direction. For the lift check valve, when the fluid flows from left to right, the valve core is lifted to form a channel, and when the fluid flows in the opposite direction, the valve core is pressed against the valve seat and closed. For the wafer check valve, when the fluid flows from left to right, the valve core opens to form a channel, and when the fluid flows reversely, the valve core presses on the valve seat and closes. Wafer check valves can be installed in multiple positions, with small volume, light weight and compact structure. [ 1]

(3) Control valve

The pressure difference before and after the valve is constant. When the opening of ordinary valve changes in a large range, its flow rate changes little, but when it reaches a certain opening, the flow rate changes sharply, that is, the regulation performance is not good. The regulating valve can change the resistance of the valve by changing the stroke of the valve core according to the direction and magnitude of the signal, so as to achieve the purpose of regulating the flow. Regulating valves are divided into manual regulating valves and automatic regulating valves. Manual or automatic regulating valves are divided into many types, and their regulating performance is also different. Automatic control valves include self-operated flow control valves and self-operated differential pressure control valves. [ 1]

(4) vacuum class

Vacuum includes vacuum ball valve, vacuum baffle valve, vacuum inflation valve, pneumatic vacuum valve, etc. Its function is to change the direction of air flow, adjust the size of air flow and cut off or connect the pipeline in vacuum system, which is called vacuum valve.

(5) Special purpose category

Special purpose categories include pigging valves, exhaust valves, sewage valves, exhaust valves, filters, etc.

Exhaust valve is an indispensable auxiliary component in pipeline system, which is widely used in boilers, air conditioners, oil and gas, water supply and drainage pipelines. It is often installed at commanding heights or bends to remove excess gas in the pipeline, improve the efficiency of the pipeline and reduce energy consumption.

According to the main parameters

At nominal pressure:

(1) vacuum valve: refers to the valve whose working pressure is lower than the standard atmospheric pressure.

(2) Low pressure valve: refers to the valve with nominal pressure PN ≤ 1.6Mpa.

(3) Medium-pressure valves: refer to valves with nominal pressure PN of 2.5Mpa, 4.0Mpa and 6.4Mpa.

(4) High-pressure valve: refers to the valve with the nominal pressure PN of 10.0 MPa ~ 80.0 MPa.

(5) Ultra-high pressure valve: refers to the valve with nominal pressure pn ≥ 100.0mpa. ..

Depending on the operating temperature:

(1) ultra-low temperature valve: used for working temperature t of medium.

(2) Normal temperature valve: used for medium with working temperature of -29℃

(3) Intermediate temperature valve: used for working temperature of medium of 120℃

(4) High temperature valve: used for working temperature of medium t >；; 425℃ valve.

According to the driving mode:

According to the driving mode, it can be divided into automatic valve, electric valve and manual valve.

diameter

(1) Small valves: valves with nominal diameter DN≤40mm.

(2) Intermediate diameter valve: a valve with a nominal diameter DN of 50 ~ 300mm.

(3) Large-diameter valves: valves with a nominal diameter DN of 350 ~ 1200mm.

(4) Extra-large-diameter valves: valves with nominal diameter dn ≥1400 mm.

According to the structural characteristics

Structural characteristics of valves

Structural characteristics of valves

The structural feature of the valve is that according to the movement direction of the closing part relative to the valve seat, it can be divided into:

(1) truncated door shape: the closing piece moves along the center of the valve seat; Such as stop valves

(2) cock and ball: the closing part is a plunger or ball, which rotates around its own center line; Such as plug valves, ball valves

(3) gate shape: the closing piece moves along the center of the vertical valve seat; Such as gate valves, gates, etc.

(4) Swing shape: the closing part rotates around the shaft outside the valve seat; Such as swing check valves.

(5) Butterfly: the disc of the closing part rotates around the shaft in the valve seat; Such as butterfly valves and butterfly check valves.

(6) Slide valve shape: the closing piece slides in the direction perpendicular to the channel. sly/tricky

According to the connection method

(1) Threaded connection valve: The valve body has internal thread or external thread, which is connected with the pipeline by thread. ..

(2) Flange valve: The valve body is connected by flange and connected with the pipeline flange.

(3) Welding connecting valve: The valve body has a welding groove and is welded with the pipeline.

(4) Clamp connection valve: The valve body has a clamp and is connected with the pipe clamp.

(5) Socket-type connecting valve: connected to the pipeline through a ferrule.

(6) Clamping valve: a connection form that directly clamps the valve and two pipelines together with bolts.

According to the valve body material

(1) metal valve: Its valve body and other parts are made of metal. Such as cast iron valves, cast steel valves, alloy steel valves, copper alloy valves, aluminum alloy valves, lead alloy valves, titanium alloy valves, Monel alloy valves, etc.

(2) Non-metallic valve: Its valve body and other parts are made of non-metallic materials. Such as plastic valves, enamel valves, ceramic valves, FRP valves, etc.

Installation requirements

1. Before installing the valve, carefully check whether the model and specification of the valve used are in line with the design;

2. According to the valve model and factory instructions, check whether the valve can be used under the required conditions;

3. When lifting the valve, the rope should be tied to the flange joint between the valve body and the bonnet, not to the handwheel or valve stem, so as to avoid damaging the valve stem and handwheel;

4. When installing a valve on a horizontal pipeline, the valve stem should be vertically upward, and it is not allowed to install the valve stem downward;

5. When installing the valve, it is not allowed to use the forced docking method of pulling to avoid uneven stress and damage;

6. Open-stem gate valves should not be installed in underground damp places to avoid valve stem corrosion.

Assembly requirements

Clean parts must be sealed during installation.

The installation process requirements are as follows:

1. The installation workshop must be kept clean, or a temporary cleaning area must be set up, such as using newly bought colored striped cloth or plastic film to prevent dust from entering during installation.

2, assembly workers must wear clean cotton overalls, cotton caps, hair can't leak, feet wear clean shoes, plastic gloves, degreasing.

3. Assembly tools must be degreased and cleaned before assembly to ensure cleanliness.

acceptance requirement (AR)

Acceptance shall be carried out according to HG 20202-2000 Code for Construction and Acceptance of Degreasing Engineering. Before assembly, wipe all parts with clean precision filter paper, select the dead angle of parts, and the color of filter paper is consistent and qualified.

Valve specification requirements

1, and the model of the valve shall indicate the requirements of the national standard number. If it is an enterprise standard, it shall indicate the relevant description of the model.

2. The working pressure of the valve shall be equal to or higher than that of the pipeline. Under the premise of not affecting the price, the working pressure that the valve can bear should be greater than the actual working pressure of the pipeline.

3. The valve manufacturing standard shall indicate the number of the national standard on which it is based. If it is an enterprise standard, the purchase contract shall be accompanied by enterprise documents.

Performance test requirements

1. When a valve of a certain specification is manufactured in batch, an official institution shall be entrusted to test the following performance: ① the opening and closing torque of the valve under working pressure; ② Detection of valve flow resistance coefficient under the condition of pipeline water delivery.

2. Before the valve leaves the factory, the following tests should be carried out: ① When the valve is opened, the valve body should bear an internal pressure test twice the working pressure of the valve; ② When the valve is closed, both sides bear 1 1 times the working pressure of the valve without leakage; However, the leakage value of metal sealing butterfly valve is not greater than the relevant requirements.

Sealing requirements

The sealing performance of the valve refers to the ability of each sealing part of the valve to prevent medium leakage, which is the most important technical performance index of the valve. There are three sealing parts of the valve: the contact between the opening and closing part and the two sealing surfaces of the valve seat; Joint of packing with valve stem and stuffing box; The joint of valve body and bonnet. The former leakage is called internal leakage, which is usually called lax closure, which will affect the valve's ability to cut off the medium. For block valves, internal leakage is not allowed. The latter two kinds of leakage are called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve. Leakage will cause material losses, pollute the environment, and even cause accidents in serious cases. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.

Other requirements

1. Purge the assembled valve with nitrogen for at least 65438 0 minutes.

2. The air tightness test must use pure nitrogen.

3. After passing the air tightness test, package it and seal it with a clean polyethylene cover. Polyethylene cover should be soaked in organic solvent and wiped clean before use.

4. Then seal it with a vacuum bag.

5. Final packaging.

6. Measures should be taken to ensure that the package is not damaged during transportation.

Before assembly, the valve parts must go through the following processes:

1, according to the machining requirements, some parts need to be polished, and the surface should not have machining burrs.

2. All parts are degreased;

3. After degreasing, pickling and passivation, and the cleaning agent does not contain phosphorus;

4. Rinse with pure water after pickling and purification, and there can be no chemical residue, so this step is omitted for carbon steel parts;

5. Dry the parts one by one with non-woven fabrics, and do not leave steel wool on the surface of the parts or dry them with clean nitrogen;

6. Wipe the parts one by one with non-woven fabric or precision filter paper dipped in analytical pure alcohol until there is no dirty color.

1, valve storage environment should be paid attention to, should be stored in a dry and ventilated room, and block both ends of the channel.

2, the valve should be checked regularly, and remove the dirt on it, and apply antirust oil on its surface.

3. After the valve is installed and used, it should be overhauled regularly to ensure its normal operation.

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

5, check the valve stem and valve stem nut trapezoidal thread wear, packing whether expired failure, etc. , and make the necessary replacement.

6. Test the sealing performance of the valve to ensure its performance.

7, the valve should be in good condition in operation, the bolts on the flange and bracket are complete, the thread is in good condition, and there is no looseness.

8. If the handwheel is lost, it should be filled in time and cannot be replaced by a wrench.

9, packing gland is not allowed to skew or no pre-tightening clearance.

10. If the valve is used in harsh environment and easily polluted by rain, snow, dust and sand, a protective cover should be installed for the valve stem.

1 1. The scale on the valve should be complete, accurate and clear, and the valve should be sealed and stamped.

12, and the insulation sleeve shall be free of depressions and cracks.

13. When the valve is running, avoid knocking it or supporting heavy objects.

Preface of valve model compilation

The valve model should usually indicate the valve type, driving mode, connection form, structural characteristics, sealing surface material, valve body material and nominal pressure. The standardization of valve models provides convenience for the design, selection and sale of valves. Nowadays, there are more and more types and materials of valves, and the model compilation of valves is becoming more and more complicated. Although there is a unified standard for valve model compilation in China, it is increasingly unable to meet the needs of the development of the valve industry. If the standard quantity of new valves cannot be adopted, each manufacturer can make a model according to his own needs.

Understanding the left picture is the first step to understand various valve models. Let's give you an example to give you a general idea:

Valve model: "Z 9665438+Y-100IDN150" This is a complete gate valve model. It is easy to understand that the final "DN 150" was not included in the compilation. Front: "Z96 1Y- 100I" is installed according to the above sequence diagram, as shown below:

"Z" is the unit1; "9" is unit 2; "6" is the third unit; "1" is 4 units; "y" is unit 5; "100" is 6 units; "I" is Unit 7.

The significance of this valve model is: gate valve, electric drive, welded connection, wedge-shaped single gate, cemented carbide seal, 10Mpa pressure, chromium-molybdenum steel valve body material.

For valves with other functions or special mechanisms, add a Chinese word before the valve type code.