The maintenance of valves is an important measure to ensure their long-term stable operation and extend their service life. Here are some key steps to note for valve maintenance:

1.Preservation and maintenance

a.Orderly storage: Valves should be stored in categories, with small valves placed on shelves and large valves neatly arranged on the ground to avoid disorderly stacking and damage caused by flange connection surfaces coming into contact with the ground.

b.Cleaning and Protection：

(1)Seal the inlet and outlet of the valve with wax paper or plastic sheets to prevent dirt from entering.

(2)Apply anti rust oil to the machined surface that can rust in the atmosphere for protection.

(3)Valves placed outdoors should be covered with oil felt or cloth to prevent dust and rain.

c.Regular inspection:

(1)For valves that are not used for a long time, asbestos packing should be removed to avoid chemical corrosion.

(2)The valves newly added to the warehouse should be checked for rainwater or dirt and wiped clean in a timely manner.

2.Usage and maintenance.

a.Keep clean: Regularly keep the valve clean and lubricate the transmission threads regularly.

b.Correct operation:

(1)The valve stem thread needs to be coated with lubricant (such as yellow dry oil, molybdenum disulfide, or graphite powder) to reduce wear.

(2)Valves that are not frequently opened or closed should also have their handwheel turned regularly to prevent the valve stem threads from biting.

(3)Outdoor valves require protective sleeves for the valve stem to prevent rain, snow, dust, and rust.

c.Inspection and maintenance

(1).Regularly check the sealing performance and operational flexibility of the valve to ensure no leakage or blockage.

(2).Check whether the connecting components (such as bolts and nuts) are loose or damaged, and tighten or replace them in a timely manner.

d.Packing maintenance

(1).Packing is the key to valve sealing and requires regular inspection and timely replacement of failed packing.

(2).After the valve is installed in the pipeline, if there is leakage, the packing gland nut should be tightened, but it should not be tightened all at once to avoid losing elasticity.

3.Lubrication and grease injection

a.grease injection volume and pressure:

(1)When injecting grease, the amount should be accurately calculated based on the sealing capacity of the valve type to avoid excessive or insufficient grease.

(2)The grease injection pressure needs to be lost. If it is too high, it may block the grease injection port, and if it is too low, the sealing effect will be poor.

b.Injection timing:

(1)During the use of valves, due to the loss and drying of lubricating grease, regular replenishment is required.

(2)Especially during the process of valve opening and closing, the lubrication condition of the transmission parts should be checked in a timely manner.

4.Special maintenance for different valves

a.Gate valve

(1)When fully open, the operating pressure loss of the medium is minimized, making it suitable for situations that do not require frequent opening and closing.

(2)Not suitable for use as a regulator or throttle to avoid damaging the sealing surface.

b.Globe valve

(1)After opening, there is no contact between the valve seat and the sealing surface of the valve disc, and the wear of the sealing surface is small.

(2)Attention should be paid to the flow direction of the medium during installation, generally from bottom to top.

c.ball valve

(1)The structure is simple, the operation is convenient, and it is suitable for situations with fast opening and closing.

(2)When in use, only fully open or fully closed, not used to regulate flow.

In the valve industry, after manufacturing, in order to better distinguish the types of various valves and the working conditions and environments they are suitable for, the valve body and other components of the valve often have several differences.

In the valve industry, after manufacturing, in order to better distinguish the types of various valves and the working conditions they are suitable for, the valve bodies and other components of the valves often have several differences. Looking at the current industry, the valve materials include carbon steel, low temperature Carbon steel, nickel steel, molybdenum steel, stainless steel, alloy steel, Monel, nickel alloy and other materials. Various manufacturing processes are used to compile models, including gate valve code Z, globe valve code J, throttle valve code L, etc. Generally, transmission mode codes are represented by Arabic numerals, such as electromagnetic ones written 0; turbine ones. 3; Choose 6 for pneumatic valves. Generally speaking, the structure of each valve is different.

Valve materials that use carbon steel are generally used in a temperature range of -30°C to +425°C and are non-corrosive applications, including water, oil and gas; for low-temperature carbon steel valves, the temperature can be as low as - WC6 The material used (1.25% chromium 0.5% molybdenum steel) can be used in non-corrosive applications, including water, oil and gas, and the temperature range is -30°C to +593°C; the valve oil grade made of chromium is WC9 and gas, the same Non-corrosive applications, including water, operating temperature range from -30°C to +593°C; products made of 5% chromium and 0.5% molybdenum alloy valves can be used in mildly corrosive or corrosive applications and non-corrosive applications, while 9% Valve products made of 1% chromium molybdenum alloy have a service temperature range of -30°C to +649°C, and are suitable for mildly corrosive or corrosive applications and non-corrosive applications; valves made of 12% chromium steel are also relatively corrosion-resistant ; Secondly, for stainless steel products, it is also an indispensable metal element in valve manufacturing. Stainless steel valves must specify a carbon content of 0.04% and above when the temperature is above +425°C, and can be used in corrosive or ultra-low or high temperature non-corrosive applications; while Monel materials The valve has good resistance to all common organic acids and salt water, can be welded, and also has high corrosion resistance to most alkaline solutions, with temperatures up to +400°C; secondly, the valve is made of Hastelloy nickel alloy valve material It has good resistance to sulfuric acid and phosphoric acid corrosion, and is especially suitable for use in various concentrations and temperatures of hydrofluoric acid in the processor, with temperatures up to +649°C.

As industrial manufacturing technology advances rapidly today, the materials of valves are also changing rapidly. In order to adapt to the needs of different working conditions, more valves made of alloy valves are slowly being developed and popularized.

Ball valve structure



Datong ball valve has many kinds of structure, but the basic is much the same, All the opening and closing parts are circular spherical cores, mainly composed of valves, spheres, sealing rings, valve bars and other drive devices, and the valve bars are rotated 90 degrees to achieve the opening and shutting of the valve, and are used in the pipe for shutting, dispensing, adjusting the flow size and changing the direction of the medium. Valve seat according to different conditions using different valve seat sealing form. O-ball valve body inside the installation of the middle through the ball, the ball is open with a diameter and pipe diameter equal to the through hole, the ball can be rotated in the sealing seat, in the direction of the pipeline on both sides of a circular elastomer to achieve sealing. V type ball valve ball core with V type structure, valve core is 1 / 4 ball shell, open with V type gap, large circulation capacity, adjustable range, with shear force, can close tight and other characteristics, especially suitable for fluid material with fibrous working conditions. I. Structure of O-type ball valve

O-ball valve body inside the installation of the middle through the ball, the ball is open with a diameter and pipe diameter equal to the through hole, the ball can be rotated in the sealing seat, in the direction of the pipeline on both sides of a circular elastomer to achieve sealing.By rotating the ball 90 °, the direction of the through hole can be changed, so as to realize the switch of the ball valve.O-type ball valve with floating or fixed design, phase motion parts are used Friction coefficient of small self-lubricating materials, Therefore, the operation torque is small, in addition to the long-term sealing of the sealing grease, which makes the operation more flexible. Its product advantages are as follows: 1. Type O ball valve has small fluid resistanceBall valves generally have two types of aperture and shrinkage structures. No matter which type of structure, the flow resistance coefficient of the ball valve is relatively small. Conventional ball valve for straight-through, also known as full-flow type ball valve, channel diameter is equal to the inner diameter of the pipeline, the resistance loss is only the same length of the pipeline friction resistance. This ball valve has the least fluid resistance of all valves. There are two ways to reduce the resistance of the pipeline system: First, to reduce the flow rate, the method is to increase the pipe diameter and valve diameter, which will greatly increase the cost of the pipeline system. The second is to reduce the local resistance of the valve, the ball valve is the best choice. 2, O ball valve switch quickly, convenient ball valve only need to rotate 90 degrees to complete the full open or full closed, so it can quickly open and close. 3, O-type ball valve sealing performance of the vast majority of the ball valve seat are made of polyethylene tetraethylene (PTFE) and other elastic materials, usually called soft sealing ball valve. Soft seal ball valve has good sealing performance, and the roughness of the valve sealing surface and processing accuracy requirements are not very high. 4, O-type ball valve long life due to polytetrafluoroethylene (PTFE or F4) has good self-lubricating, and the ball friction coefficient is small. Due to the improvement of processing technology to reduce the ball roughness, thereby greatly improving the service life of the ball valve. 5, O ball valve reliability high ball and seat a pair of sealing pair will not occur abrasion, rapid friction and other faults; After the valve stem is changed to the internal type, the hidden trouble of the valve stem flying out due to the loosening of packing gland under the action of fluid pressure is eliminated; The ball valve with anti-static and fire-resistant structure can be used to transport oil, natural gas and gas pipelines. O-type ball valve spool (ball) for spherical, from the structural point of view, when sealing the ball seat embedded in the body side seat. The relative moving parts are self-lubricating materials with minimal friction coefficient, so the operating torque is small. In addition, the long-term sealing of the sealing grease makes the operation more flexible. Generally used for two adjustment, flow characteristics for fast opening. O-ball valve fully open, on both sides of the unimpeded valve, forming a straight pipe channel, two-way sealing, with “self-cleaning” performance of the best characteristics, suitable for particularly unclean, containing fiber media two cut off occasions. The ball core always generates friction with the valve during the opening and closing of the valve, and at the same time, the seal between the valve core and the valve seat is achieved by the pre-tight sealing force of the valve seat towards the ball core, but due to the excellent mechanical and physical properties of the flexible sealed valve seat, its sealability is particularly good. II. V-type ball valve structure

V type ball valve ball core with V type structure, valve core is 1 / 4 ball shell, open with V type gap, large circulation capacity, adjustable range, with shear force, can close tight and other characteristics, especially suitable for fluid material with fibrous working conditions. Under normal circumstances, V-shaped ball valves are single-sealed ball valves. Not suitable for two-way use. V-shaped edge, cut off impurities. In the process of rotation of the ball, the ball V-shaped knife edge and the valve seat tangent, thereby cutting off the fiber and solid material in the fluid, and the general ball valve does not have this function, so it is easy to lead to the closure of the fiber impurities stuck, to repair and maintenance of great inconvenience. The valve core of the V-type ball valve will not be stuck by the fiber. In addition, because the flange connection form is adopted, it is easy to disassemble and install, no special tools are needed, and maintenance is also simple and easy. When the valve is closed. The V-shaped gap creates a chisel-like scissor effect between the valve and the valve, and it has both self-cleaning function and prevents the spherical core from being stuck. The valve body, valve cover and valve are respectively made of metal point-to-point structures, and a smaller friction factor is used for the spring spring, so the operation torque is small and stable. V-ball valve is a right angle rotary structure, can achieve flow regulation, according to the V-angle of the V-ball, to achieve different degrees of proportion, The V-type ball valve is generally used in conjunction with the valve actuator and positioner, and can achieve proportional adjustment. The V-Type valve core is best suitable for various adjustment situations, has a large rated flow factor, a large variable ratio, good sealing effect, zero sensitivity of adjustment performance, small size, and can be mounted vertically. Suitable for controlling gas, steam, liquid and other media. V ball valve for right-angle rotary structure, by V valve body, pneumatic actuator, positioner and other accessories; There is an inherent flow characteristic that is approximately equal to one hundred percent; Double bearing structure, small starting torque, excellent sensitivity and induction speed, super shear capacity.

With the continuous improvement of technology, pneumatic valves and electric valves have replaced the use of manual valves in many working conditions. Many users do not know how to choose between pneumatic valves and electric valves. In order to correctly choose pneumatic valves and electric valves, you must first understand the use and comparison of pneumatic valves and electric valves. With the continuous improvement of technology, pneumatic valves and electric valves have replaced the use of manual valves in many working conditions. Many users do not know how to choose between pneumatic valves and electric valves. In order to correctly choose pneumatic valves and electric valves, you must first understand the use and comparison of pneumatic valves and electric valves. Pneumatic valves and electric valves are composed of electric actuators and pneumatic actuators equipped with various types of valves, which are used to replace manual valves in working conditions to achieve automatic control. The biggest difference between the two valves is the driving source. How to choose these two valves in actual use mainly depends on which valve is suitable for the actual working conditions. The following introduces the general differences in the use of these two valves. First of all, the action time of pneumatic valves is faster than that of electric valves. Moreover, pneumatic valves can be opened repeatedly in a short period of time, and electric valves with too high switching frequency will cause the motor to heat up. Therefore, pneumatic valves are more suitable for occasions that require quick shutoff. Because electric valve actuators are all electronic components, they are prone to sparks when a failure occurs. Therefore, pneumatic valves are more suitable for use in flammable and explosive situations than electric valves. In terms of maintenance, pneumatic valves are easy to maintain and do not require high professional skills from maintenance personnel. The opposite is true for electric valves. However, the maintenance cost of pneumatic valves is much higher than that of electric valves. In terms of on-site conditions, the use of pneumatic valves requires an air source on site, while electric valves can be used after being connected to the power supply. This is much more convenient than pneumatic valves.

With the progress of the times and continuous reform, my countries valve products have also innovated with the changes of the times. Currently, in the valve market where environmental protection and safety are increasingly vocal, the use of automatic control devices such as electric valves and pneumatic valves has gradually become more and more popular. of. The use of automatic control valves is more energy-saving and safer and more reliable. Compared with traditional manual valves, it moves faster than ordinary valves, which not only reduces manual manpower, but also greatly improves work efficiency. (1) 1. Advantages of electric valves: good effect on liquid media and large diameter gases, and not affected by climate. Not affected by air pressure. Disadvantages: high cost, not good in humid environment. 2. Advantages of pneumatic valves: good effect on gas media and small diameter liquids, low cost, and easy maintenance. Disadvantages: Affected by fluctuations in air pressure, the air is easily affected by water content in the northern winter, causing the transmission part to freeze and become inoperable. (2) Generally, pneumatic ones are faster than electric ones, and electric ones can be used as flashlights. The pneumatic ones, which are both hand-operated and gas-operated, are relatively expensive. Electric valves move slowly. There are not many brands of electric valves that can be explosion-proof; pneumatic valves move quickly, and explosion-proof prices are relatively lower than electric valves (the key is what accessories are equipped with pneumatic valves, and the accessories will be more expensive than electric valves). (3) Electric valves are used in some places with large pipe diameters, because pneumatic valves are difficult to operate, but the stability of electric valve doors is not as good as pneumatic valves, the switching speed is slow, and the actuator may jam for a long time. Pneumatic valve doors open and close quickly and with high precision, but they require a stable air source. (4) The operating force distance ratio of pneumatic valves is that of electric valves. The opening and closing speed of pneumatic valves can be adjusted. The structure is simple and easy to maintain. Due to the buffering characteristics of the gas itself during the action process, it is not easy to be damaged due to jamming, but there must be a gas source. And its control system is also more complex than electric valves. (5) Electric valves are driven by electricity and are not suitable for occasions with explosion-proof requirements. For example, when a large amount of easily contaminated gases are dispersed in the surrounding environment, they can only rely on pneumatic valves. Pneumatic response time is slower than electric and not as accurate as electric. Pneumatic valves are powered by gas. Electric valves use electricity converted into electromagnetic energy as power. Electric valves are more sensitive than pneumatic valves, are not as safe and reliable as pneumatic valves, are not as easy to maintain as pneumatic valves, and are not as powerful as pneumatic valves. The control of pneumatic valves is more complicated than that of electric valves. Moreover, all aspects of the cost are very expensive. If automatic control is involved, an electromagnetic reversing valve must be added, and the sensitivity of the electromagnetic reversing valve directly affects the pneumatic valve. Compared with pneumatic valves, electric valves have a simple structure and reliable operation, and their power source (power supply or air source) is easy to solve for remote operating points. The disadvantage is that the price is higher and the explosion-proof requirements are also higher. When selecting, factors such as the availability, price, and control requirements of the power source should be comprehensively considered. When selecting a valve, you generally first confirm parameters such as valve material, valve diameter, medium type, pipeline pressure, connection method, control method, medium temperature, etc.

1 To determine the nominal pressure, instead of using Pmax to set the PN, find the corresponding PN from the table based on the three conditions of temperature, pressure, and material and satisfy the PN value of the selected valve. Valve type selection

Selection of valve type: (1) To determine the nominal pressure, instead of using Pmax to set the PN, find the corresponding PN from the table based on the three conditions of temperature, pressure, and material and satisfy the PN value of the selected valve. (2) The leakage amount of the determined valve type meets the process requirements. (3) The working pressure difference of the determined valve type should be smaller than the allowable pressure difference of the valve. If this is not possible, special considerations must be made or another valve must be selected. (4) The temperature of the medium is within the operating temperature range of the valve, and the ambient temperature meets the requirements. (5) Consider the anti-blocking problem of the valve according to the unclean condition of the medium. (6) Consider the corrosion resistance of the valve based on the chemical properties of the medium. (7) According to the pressure difference and medium containing hard objects, consider the erosion.

Selection of actuators: (1) The simplest is the pneumatic diaphragm type, followed by the piston type, and finally the electric type. (2) The main advantage of electric actuators is that the driving source (power supply) is convenient, but the price is high, and the reliability, waterproof and explosion-proof are not as good as pneumatic actuators, so pneumatic actuators should be preferred. (3) The old electric actuators are bulky and bulky. We already provide electronic precision, small and high-reliability electric actuators (the price is correspondingly high). (4) The old ZMA and ZMB membrane actuators can be eliminated and replaced by multi-spring lightweight actuators (performance improved, weight and height reduced by about 30%). (5) There are many varieties and specifications of piston actuators. It is recommended that the old, big and stupid ones be no longer used, and new light structures should be used.

Selection of materials: (1) The pressure rating, operating temperature and corrosion resistance of the valve body should not be lower than the requirements of the process connection pipeline, and the manufacturer's finalized products should be given priority. (2) Cast iron valves should not be used for water vapor or wet gases containing more water and flammable and explosive media. (3) When the ambient temperature is lower than -20°C (especially in the north), cast iron valves should not be used. (4) For media with severe cavitation and erosion, in the rectangular coordinates formed by temperature and pressure difference, when the temperature is 300°C and the pressure difference is 1.5MPa in the area outside the two-point line, the throttling sealing surface should be Use wear-resistant materials, such as cobalt-based alloys or surface surfacing Stellite alloys. (5) For highly corrosive media, when selecting corrosion-resistant alloys, appropriate corrosion-resistant materials must be selected based on

Selection of flow characteristics: The following is a preliminary selection. For detailed selection, please see the special information: (1) Select logarithmic characteristics when S>0.6. (2) Select logarithmic characteristics when working with small openings and large changes in unbalanced force. (3) When the required adjusted parameter reflection speed is fast, choose a straight line, and when it is slow, choose a logarithm. (4) Linear characteristics are optional for the pressure regulation system. (5) The liquid level adjustment system has optional linear characteristics.

Mode of action selection: (1) In foreign countries, faults are often expressed as open or closed, that is, fault open and fault closed, which is exactly the opposite of the air open and air closed expressions in our country. Fault open corresponds to an air closed valve, and failure close corresponds to an air open valve. (2) New light valves and fine small valves no longer emphasize the positive and negative effects of the execution machinery, so they must be marked on the endnote.

Selection of spring range: (1) First, select the spring range, and also determine the working spring range. (2) Determining the working spring range involves calculating the output force to overcome the unbalanced force. If there are difficulties, the conditions (mainly the pressure difference when the valve is closed) should be informed to the manufacturer to help calculate and adjust the spring and working range before leaving the factory (currently, many manufacturers do not do calculations at all).

Selection of flow direction: (1) At the orifice, the medium flowing in the opening direction of the valve core is called flow open, and the medium flowing in the closing direction is called flow closed. (2) The main choice of flow direction is single-seal regulating valves, which include single-seat valves, angle valves, and single-seal sleeve valves. It is based on specified flow direction (such as double-seat valve, V ball) and arbitrary flow (such as O ball). (3) When dg＞15, flow open is usually selected. When dg≤15, small-diameter valves, especially high-pressure valves, can choose flow closed to improve service life. (4) Flow closing is optional for the two-position switch valve. (5) If the closed-flow valve oscillates, change it and the open-flow valve will be eliminated.

Selection of packing: (1) The commonly used control valves are PTFE -shaped packing and graphite -shaped packing. (2) PTFE packing has low friction, but is resistant to temperature differences and has a short service life; graphite packing has high friction, but has good temperature resistance and long service life; graphite packing is recommended for high temperatures and valves with positioners. (3) If the PTFE packing is frequently replaced, graphite packing may be considered.

Selection of accessories: (1) The accessories of the control valve mainly include: positioner, converter, relay, booster valve, retaining valve, pressure reducing valve, filter, oil mist, travel switch, position transmitter , solenoid valve, handwheel mechanism. (2) Accessories serve to supplement functions and ensure valve operation. Increase what is necessary and do not increase what is unnecessary. Adding accessories when unnecessary increases price and reduces reliability. (3) The main function of the positioner is to increase the output force and movement speed. When these functions are not needed, it is not necessary to use the positioner. (4) For fast response systems, if the valve does not act quickly, a converter is optional. (5) In strict explosion-proof situations, optional: electrical converter + pneumatic positioner. (6) The solenoid valve should choose a reliable product to prevent it from not acting when it is required to act. (7) It is recommended not to use the handwheel mechanism in import.

    The working principle of three-way ball valve is to rotate the valve love to make the valve open or closed. Ball valve switch lightweight, small size, can be made into a large caliber, reliable sealing, simple structure, easy maintenance, sealing surface and the ball surface is often in the closed state, is not easy to be eroded by the media, in various industries have been widely used.

    Three-way ball valve in the pipeline is mainly used to do cutting, distribution and change the direction of flow of media. Three-way ball valve is a relatively new type of ball valve category, it has its own structure unique to some of the advantages, such as switching without friction, sealing is not easy to wear, opening and closing torque is small. This can reduce the specifications of the matching actuator.

    Three-way ball valves have T-type and L-type. T-type can make three orthogonal pipeline interconnection and cut off the third channel, play the role of shunt, merge. L-type three-way ball valves can only be connected to each other orthogonal to the two pipelines, can not keep the third pipeline at the same time connected to each other, and only play the role of distribution.

     1, three-way ball valve in the structure of the integrated structure, 4-sided seat sealing type, less flange connection, high reliability, design to achieve a lightweight

     2、Three way ball valve has long service life, large flow capacity and low resistance.

     3, three-way ball valve according to the role of single-acting and double-acting two types, single-acting type is characterized by once the power source failure, the ball valve will be in the control system requirements of the state

    Ball valves and gate valves are the same type of valve, the difference is that its closing member is a sphere, the sphere around the center line of the valve body for rotation to achieve open, close a valve. Ball valve in the pipeline is mainly used to do cut off, distribution and change the direction of flow of media. Ball valves are widely used in a new type of valve, it has the following advantages:

Valve basic knowledge

1, the basic parameters of the valve: nominal pressure PN, nominal diameter DN

2, the basic function of the valve: cut off the medium, adjust the flow, change the direction of flow.

3, the valve connection methods are mainly flange, threaded, welded, clamps

4, the valve’s pressure-temperature level: different materials, different operating temperatures, allowing no impact on the working pressure is different.

5、Pipe flange standards are mainly two systems: the European system and the U.S. system.

Two systems of pipe flange connection size is completely different, not interchangeable.

According to the pressure level to distinguish between the more appropriate:

European system for PN0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3, 10.0, 16.0, 25.0, 32.0, 40.0 MPa.

American system is PN1.0 (CIass75), 2.0 (CIass150), 5.0 (CIass300), 11.0 (CIass600), 15.0 (CIass900), 26.0 (CIass1500), 42.0 (CIass2500) MPa.

The main types of pipe flanges are: Integral (IF), Plate Plain Welding (PL), Necked Plain Welding (SO), Necked Butt Welding (WN), Socket Welding (SW), Screw (Th), Butt Welding Ring Loose Sleeve (PJ/SE)/(LF/SE), Flat Welding Ring Loose Sleeve (PJ/RJ), Flange Cover (BL).

Types of flange sealing surfaces are full-flat (FF), raised face (RF), concave face (FM) convex face (M), tongue-and-groove (T) groove (G) surface, ring bonding surface (RJ) and so on.

6、Cast iron valve body is not suitable for use in the following occasions

1）Water vapor or wet gas with high water content;

2）Flammable and explosive liquids;

3) Ambient temperature below -20℃;

4) Compressed gas

Control valve
1、Control valve consists of valve body and actuator and its accessories.
2、Pneumatic thin-film actuator has two forms of positive and negative action; with the increase of signal pressure, the actuator downward for positive action, and vice versa, the actuator upward for negative action; usually accepts the standard signal pressure of 20-100KPa; with the locator when the pressure is higher than 250KPa. six basic strokes (mm): 10; 16; 25; 40; 60; 100.
3、What are the characteristics of electric actuator compared with pneumatic actuator, and what kinds of output forms are there?
The driving source is electric power, simple and convenient, large thrust and torque, high rigidity. However, the structure is complex, poor reliability. In small and medium-sized specifications, pneumatic expensive. Commonly used in applications where there is no air source or where strict explosion-proof or explosion-proof is not required.
Provide three types of output: angle stroke, straight stroke and multi-turn.
4、What are the characteristics of straight-through single-seat adjustment valve? Applicable to what occasions?
(1) As there is only one spool, the drain flow is small and easy to seal. The standard drain flow is 0.01% KV, and further design can be used as a globe valve.
(2) Due to the large unbalanced force thrust, the permissible differential pressure is small. DN100 valve △ P is only 120KPa.
(3) small flow capacity. DN100 KV is only 120. suitable for use in small leakage, differential pressure occasions.
5、What are the characteristics of straight-through double-seat adjustment valve? Applicable to what occasions?
(1) the allowable differential pressure is large, because it can offset many unbalanced forces. DN100 valve △ P is 280KPa.
(2) The flow capacity is large. DN100 is 160 KV.
(3) The two spools cannot be sealed at the same time, and the leakage is large. The standard leakage rate is 0.1% KV, which is 10 times that of single-seat valve.
Mainly used in high differential pressure, leakage requirements are not strict occasions
6、What are the main advantages of sleeve adjustment valve?
Combines the advantages of single-seated and double-seated valves. The main ones are:
(1) good stability. As the spool throttling instead of the slide valve seat throttling, and the spool is equipped with a balance hole, which can reduce the unbalanced force of the medium acting on the spool. At the same time, the guiding surface of the sleeve and the spool, coupled with small changes in the unbalance force, so it is not easy to cause spool vibration.
(2) Interchangeability, versatility. Only need to replace the sleeve to obtain different flow coefficients and different flow characteristics.
3）Large permissible differential pressure and small influence of thermal expansion. The balancing principle of sleeve valve with balancing hole is the same as that of double-seat valve, so the allowable differential pressure is larger. And because the sleeve and valve plug are made of the same material, the expansion caused by temperature change is basically the same.
(4) The sleeve provides two kinds of throttling windows: large hole and small hole (injection type). The latter has the effect of reducing noise and vibration, and is further improved to be a specialized low-noise valve.
It is suitable for occasions where the pressure difference between the front and rear of the valve is large and the noise requirement is low.
7, in addition to single and double seat valves and sleeve valves, what other valves have regulatory functions?
Diaphragm valves, butterfly valves, O-type ball valves (mainly cut-off), V-type ball valves (regulation ratio, with shear effect), eccentric rotary valves.
8, the adjustment ratio of the control valve R, the ideal adjustment ratio, the actual adjustment ratio is how much?
Control valve can control the ratio of large flow and small flow is called the adjustment ratio R.
When the pressure difference between the two ends of the valve to maintain a constant, the larger flow rate and the smaller flow rate of the ratio known as the ideal adjustment ratio.
In practice, the pressure difference between the two ends of the valve is variable, the adjustable ratio is called the actual adjustable ratio.
9, what is the flow coefficient of the control valve C, Cv, KV value?
Control valve flow capacity of the size of the flow coefficient to indicate.
(1) engineering unit system Cv definition: when the control valve is fully open, the pressure difference between the valve before and after 1kgf/cm2, the number of cubic meters of water per hour through the temperature of 5 ~ 40 ℃.
(2) British system of units C definition: when the regulator valve is fully open, the valve before and after the pressure difference of 1bf/in2 (1 degree 60.F of water per minute through the US gallons of water.
(3) International System of Units KV: when the control valve is fully open, before and after the valve pressure difference of 100kPa, the temperature is 5 ~ 40 ℃, the number of cubic meters of water through the hour.
CV = 1.17KV
Voltage = 1.01°C

Installation og valves

1.1 Maintenance, Installation, and Use Precautions

1) The valve should be placed in a dry and ventilated room, and both ends of the diameter should be sealed to prevent dust; 2) Long term storage should be regularly inspected and oil should be applied to the processing surface to prevent rusting; 3）Before installing the valve, carefully check whether the markings match the usage requirements;

4) During installation, the inner cavity and sealing surface should be cleaned, and the packing should be checked for tightness and the connecting bolts should be evenly tightened;

5) Valves should be installed in the allowed working position, but attention should be paid to the convenience of maintenance and operation;

6) During use, do not partially open the gate valve to adjust the flow rate, in order to avoid damaging the sealing surface when the medium flow rate is high. It is recommended to fully open or fully close it;

7) Rotate the handwheel when opening or closing, and do not use other auxiliary levers;

8) Transmission components should be regularly lubricated with oil; When using the valve, the rotating part should be regularly oiled, and the trapezoidal thread part of the valve stem should be oiled.

9) After installation, regular maintenance should be carried out to remove dirt from the inner cavity, check the sealing surface, and inspect the wear of the valve stem nut;

10) There should be a set of scientifically correct installation and operation standards. Sealing performance tests should be conducted during maintenance, and detailed records should be kept for inspection.

11) Other precautions:

1) Valves should generally be positioned before pipeline installation. The piping should be natural, and if the position is not correct, it cannot be forcefully pulled to avoid leaving prestress;

2) Before positioning, low-temperature valves should undergo opening and closing tests in a cold state (such as in liquid nitrogen) as much as possible, requiring flexibility and no jamming phenomenon;

3) Liquid valves should be configured with a 10 ° inclination angle between the valve stem and the horizontal to prevent liquid from flowing out along the valve stem and increasing cold loss; More importantly, it is necessary to avoid the liquid from touching the sealing surface of the packing, causing it to harden and lose its sealing effect, resulting in leakage;

4) The connection of the safety valve should have an elbow to avoid direct impact on the valve; In addition, it is necessary to ensure that the safety valve does not frost to prevent failure during operation;

5) The installation of the globe valve should ensure that the flow direction of the medium is consistent with the arrow marked on the valve body, so that when the valve is closed, pressure is applied to the cone at the top of the valve, and the packing is not loaded. But for valves that are not frequently opened and closed but require strict assurance of no leakage in the closed state (such as heating valves), they can be consciously reversed to be tightly closed with the help of medium pressure;

6) Large scale gate valves and pneumatic control valves should be installed vertically to avoid tilting towards one side due to the heavy weight of the valve core, which increases mechanical wear between the valve core and the liner and causes leakage;

7) When tightening the compression screw, the valve should be in a slightly open position to avoid damaging the sealing surface of the valve top;

8) After all valves are in place, they should be opened and closed again, and it is qualified if they are flexible and not stuck;

9) After bare cooling, the connecting valve flange of a large air separation tower is pre tightened once in the cold state to prevent leakage at room temperature but at low temperature;

10) It is strictly prohibited to use the valve stem as a scaffold to climb high temperature valves above 200 ℃ during installation. As the installation is at room temperature, after normal use, the temperature rises, the bolts expand due to heat, and the gap increases. Therefore, they must be tightened again, which is called "hot tightening".

11) Operators should pay attention to this work, otherwise leakage may occur.

12) When the weather is cold and the water valve is closed for a long time, the accumulated water behind the valve should be drained.

1.2 Homework System and Homework Site

1.2.1 During construction, the construction contractor, safety department, factory production department, and construction unit should fully coordinate to clarify the scope of work responsibilities.

1.2.2 Full time responsible persons shall work on-site in their respective work responsibility areas.

1.2.3 When dismantling or installing valves, corresponding changes and arrangements should be made to the daily production within a certain range affected by such operations, and the medium in the pipeline should be cleared and cut off.

1.2.4 The necessary work site should be ensured at the work site.

1.2.5 Support components that are compatible with the weight of the valve should be installed at the work site to prevent the valve from sinking and the center of the piping from shifting.

1.2.6 After completing the homework, preparations should be made for inspection items such as pressure resistance test, air tightness test, and non-destructive inspection.

1.2.7 Before entering production operation after completing the homework, the interior of the pipeline network should be cleaned, and it should be confirmed whether the blind plates on the pipeline have been removed, as well as whether the valves operated during construction should be restored to their pre construction open and closed states.

1.3 Precautions for valve installation

1.3.1 Before valve installation, it is necessary to confirm that the valve meets the design requirements and relevant standards. 1.3.2 When handling and installing valves, precautions should be taken to prevent accidents such as collisions and scratches. 1.3.3 Before installing valves, the interior of the pipeline should be cleaned to remove impurities such as iron filings and prevent foreign objects from entering the valve sealing seat. In addition, the valve during installation should be in the closed state.

1.3.4 During valve lifting operations. Valves should be lifted correctly at the designated lifting position, and should not be lifted or pulled only under local stress.

1.3.5When installing valves, it is necessary to confirm whether the flow direction of the medium, installation form, and handwheel position comply with regulations.

1.3.6 Installation of flange connected valves.

1) The flange surfaces of valves and piping should be free of damage, scratches, etc., and kept clean. Especially when using metal gaskets (oval or octagonal cross-section), the groove of the flange should match the gasket and be coated with red lead for matching to ensure good sealing.

(2) The perpendicularity between the flange surface on the piping and the centerline of the piping, as well as the error of the flange bolt holes, should be within the allowable range. Valves and piping centerlines must be aligned before installation. (3) When connecting two flanges, the first step is to evenly press the sealing surface of the flange against the gasket, ensuring that the flange is connected with equal bolt stress.

(4) When tightening bolts, use a wrench that matches the nut. When using hydraulic or pneumatic tools for tightening, be careful not to exceed the specified torque.

(5) The fastening of flanges should avoid uneven force and should be tightened in a symmetrical and intersecting direction. (6) After installing the flange, it is necessary to confirm the firmness and uniformity of all bolts and nuts.

(7) The material of bolts and nuts must comply with regulations. After tightening, it is advisable for the bolt head to protrude two pitches from the nut.

(8) To prevent loosening caused by vibration during the fastening of bolts and spirals, washers should be used. To avoid adhesion between threads at high temperatures, anti sticking agent (molybdenum disulfide) should be applied to the threaded area during installation.

(9) For valves above 200 degrees Celsius, after the temperature rises, the flange connecting bolts, valve cover fastening bolts, pressure sealing bolts, and packing pressure cover bolts must be tightened again.

(10) Low temperature valves are installed at atmospheric temperature. In practical applications, when the medium passes through, it becomes a low-temperature state. Due to the formation of temperature differences, flanges, gaskets, bolts, and nuts will shrink. Moreover, due to the different materials of these components, their coefficients of linear expansion are also different, creating an environment that is very prone to leakage. Starting from this objective situation, when tightening bolts at atmospheric temperature, it is necessary to use torque that takes into account the shrinkage factors of each component at low temperatures.

1.3.7 Installation of welded connection valves

(1) The socket of socket welding and the groove processing of butt welding should be correct and comply with relevant standards and regulations.

(2) During welding, it is necessary to prevent iron filings and welding beans from entering the piping, and tungsten inert gas shielded welding should be used.

(3) When welding, the valve should be in a slightly open state.

(4) Welding materials should be selected correctly based on the valve and piping materials. When using coated welding electrodes, it is necessary to check the storage condition of the electrodes and confirm whether a suitable drying treatment for the type of coated welding electrode has been adopted.

(5) Personnel engaged in welding operations should meet the requirements of welding technicians.

(6) When heat treatment is required after welding, the time and temperature curve records of the heat treatment should be checked.

(7) The welding area should undergo visual inspection or non-destructive testing to confirm the absence of harmful defects such as cracks, weld beads, and undercutting.

Five connection methods for valves: 

1. Flange connection valve: The valve body has a flange and is connected to the pipeline using a flange. 

2. Threaded connection valve: The valve body has internal or external threads and is connected to the pipeline using threads. 

3. Welded connection valve: The valve body has a welded joint and is connected to the pipeline by welding. 

4. Clamp connected valve: The valve body has a clamp mouth and is connected to the pipeline using clamps. 

5. Card sleeve connected valve: a valve that uses a card sleeve to connect to the pipeline.

Welding and Silver Brazing.

In the industrial field and in many piping systems, stainless steel valves are a common equipment. However, many people have a certain misunderstanding of the name "stainless steel valve," thinking that since it is stainless steel, it will never rust. But is that really the case?

Stainless steel is an alloy, the main components include: iron, chromium, nickel and other elements. Among them, chromium is a key factor in making stainless steel corrosion resistant. Chromium forms an extremely thin and strong chromium-rich oxide film on the surface of stainless steel, which can prevent corrosive media such as oxygen and moisture from further invading the interior of stainless steel, thus playing a protective role. When this layer of oxide film is destroyed, stainless steel is likely to rust.

1. If the stainless steel valve in the high concentration of chloride ions in the environment, such as the sea water treatment system or the use of chlorine disinfectant industrial environment. Chloride ion has a strong penetration ability, which can penetrate the oxide film on the surface of stainless steel and destroy the integrity of the oxide film. Once the oxide film is broken, the iron atoms are exposed and react with oxygen and moisture from the outside world, causing rust. For example, a small seaside seawater desalting plant, the use of stainless steel valve in operation for a period of time, the valve surface appeared rust. After testing, it is due to the continuous erosion of chloride ions in the sea water valve surface, although it is stainless steel material, but it is difficult to resist the long-term role of high concentration of chloride ions. Influence of pH: Stainless steel valves may also rust in strong acidic or alkaline environments. For example, in some chemical companies, stainless steel valves are used in piping systems that handle strong acids or alkalis. Extreme pH will change the chemical state of the stainless steel surface, so that the oxide film can not be maintained normally, which in turn causes corrosion and rust. For example, a chemical company in the production process of stainless steel valves, due to exposure to strong acidic chemicals, the valve inside the sealing parts soon appeared rust phenomenon, affecting the normal sealing performance of the valve. High temperature environment: In high temperature environment, the stability of stainless steel will be affected. High temperature may lead to changes in the internal structure of stainless steel, making the distribution of chromium in stainless steel uneven, reducing the ability of chromium to form an effective oxide film. At the same time, high temperatures may also accelerate the speed of chemical reactions, making stainless steel more susceptible to reacting with the surrounding corrosive medium. There is a high temperature steam pipe system in the stainless steel valve, in a high temperature environment for a long time, the surface of the valve corrosion, because the high temperature changes the internal structure of stainless steel, reducing its corrosion resistance.

2. Material factors Types of stainless steel: Not all stainless steels have the same corrosion resistance. Common stainless steel austenitic stainless steel, martensitic stainless steel and ferritic stainless steel. Austenitic stainless steel contains a higher proportion of nickel, its corrosion resistance is relatively strong, but the price is also high. The corrosion resistance of martensitic stainless steel and ferritic stainless steel is relatively weak, and the risk of rust will increase if used in some harsh environments. If you do not choose the appropriate stainless steel type according to the actual use environment when selecting stainless steel valves, it may lead to rust problems. For example, in an ordinary industrial environment containing a certain amount of chloride ions, in order to save costs, a martensitic stainless steel valve was selected, and the valve rusted before long. Impurity content: The impurity content in stainless steel will also affect its corrosion resistance. If the stainless steel contains too much sulfur, phosphorus and other impurities, these impurities will form a local micro-battery inside the stainless steel, accelerating the corrosion process. Some low-quality stainless steel materials may be due to the production process, high impurity content, when used to manufacture the valve is easy to rust.

3. Processing and use factors surface damage: In the process of stainless steel valve processing, such as cutting, welding, grinding and other operations, if improper operation, may cause damage to the oxide film on the surface of stainless steel. For example, the high temperature generated during welding will destroy the oxide film of the welding part, and if there is no timely treatment, such as pickling and passivation, this part is easy to rust. In the process of use, by the impact of external objects or scratching, will also destroy the surface of the valve oxide film, thus creating conditions for rust. For example, when a factory installed a stainless steel valve, due to careless operation, the surface of the valve was scratched by a sharp object, and then in the process of use, the scratched part soon rusted. Stress concentration: If there is stress concentration in the stainless steel valve during installation or use, it will also affect its corrosion resistance. The distribution of element Cr in local area is changed and the corrosion resistance of these areas is decreased. For example, in the connection of the valve, if the bolt tightening force is uneven, it may cause stress concentration, which in turn causes rust.

How to prevent stainless steel valve rust 1. Choose the right stainless steel material according to the specific use of the environment to choose the appropriate stainless steel valve. If it is in the marine environment or chlorine-containing environment, the austenitic stainless steel valve with strong corrosion resistance to chloride ion is preferred, and the higher the nickel content, the stronger the corrosion resistance. For acidic or alkaline environments, choose a stainless steel type that can withstand the corresponding pH. 2. Optimization of processing and installation In the process of processing, appropriate processing technology should be adopted to minimize the damage to the oxide film on the surface of stainless steel. After welding, pickling and passivation treatment should be carried out in time to restore the corrosion resistance of the welded parts. During installation, make sure the valve is installed correctly to avoid stress concentration. For example, tighten the bolt evenly to avoid excessive tightening of the valve deformation. 3. Environmental Control For the environment in which the stainless steel valve is located, if possible, minimize the concentration of chloride ions, acid-base substances and other corrosive media. In chemical enterprises, some protective measures can be adopted, such as setting an isolation layer around the valve to prevent corrosive substances from directly contacting the valve. 4. Check and maintain the stainless steel valve regularly to find out whether there is damage or rust on the surface of the valve. If slight rust is found, suitable rust removal techniques, such as mechanical rust removal or chemical rust removal, can be applied, followed by protective treatments, such as rust preventive oil or passivation. Although the stainless steel valve has a certain corrosion resistance due to its stainless steel material, it is still likely to rust under the influence of a variety of adverse factors. Understanding the causes of rust in stainless steel valves and taking corresponding preventive measures are of great significance to ensure their normal use in various environments and prolong their service life. Whether in industrial production or daily life in the pipeline system, the correct treatment of stainless steel valve rust problem is to ensure the safe and stable operation of the system key link.

The advantages of ceramic valves are that metal valves are limited by the conditions of the metal material itself, making it difficult to meet the needs of harsh working conditions such as high wear and strong corrosion. Mainly manifested as short service life and severe leakage, greatly affecting the stability of system operation. Traditional metal valves urgently need to be thoroughly innovated in terms of materials, design, and manufacturing processes. Wear resistant ceramic valves made of special ceramic materials are mainly used in industrial fields such as power, petroleum, chemical, metallurgy, mining, and sewage treatment. Especially in the face of harsh working conditions such as high wear, strong corrosion, high temperature, and high pressure, their excellent performance is demonstrated. It can meet the high wear and strong corrosion usage environment, and its outstanding feature is the ultra long service life. Its cost-effectiveness is far superior to other similar metal valves, and ceramic valves are increasingly recognized by industry insiders for their excellent performance.

Advantages of ceramic valves:
① The sealing and vulnerable components of the valve are made of high-tech new ceramic structural materials to extend its service life, which improves the wear resistance, corrosion resistance, and sealing performance of the valve product, greatly extending its service life.
② The use of ceramic valves can greatly reduce the maintenance and replacement frequency of valves, improve the safety and stability of supporting equipment operation systems, reduce the labor intensity of workers, and save equipment repair costs.
③ The promotion of the use of ceramic valves for environmental protection has improved the sealing performance of industrial pipelines, while minimizing leakage and playing a positive role in promoting environmental protection.
④ Low raw material cost: The raw materials for manufacturing ceramics are widely available and cost-effective. Ordinary elements such as aluminum, carbon, and silicon can be used to produce high-performance ceramic materials, which can save a large amount of metal materials and rare mineral resources.

Ceramic ball valve：
Ball valves can be used for flow control of corrosive or high-temperature fluids containing solid substances. Depending on the application, all flow components can be made of ceramic, or only important parts can be sprayed with ceramic. If the channel of the ball valve changes from a circular hole to a triangular hole, the flow characteristics are roughly equal in percentage. Therefore, when the valve positioner is installed, it can be used as a regulating valve. If the vertex of a triangular hole is made into an angle shape, the range of amplitude variation will be large, making it ideal as a regulating valve. However, if the corner is not a fillet, it will cause stress concentration and easy to crack. Therefore, although the adjustment performance of the regulating valve will be slightly reduced after the fillet is made, it should be made into a fillet shape. At this point, the fluid flow rate through the regulating valve also increases, which exacerbates corrosion and wear. Therefore, it is more important to utilize and utilize the characteristics of ceramics.

Ceramic gate valve：
It is necessary to use this type of valve under extremely harsh conditions in coal gasification equipment, where the high temperature and high pressure gas contains hard particle corrosive gas streams of coal powder and ash powder. In the past, valves made of metal with cobalt chromium tungsten hard alloy deposited on the sealing surface could not meet the requirements for use. Nowadays, metal is used for the high-temperature and pressure resistant parts of the shell, while ceramic is used for the sealing parts. Due to the development of a unique structure to prevent micro powder abrasion, the service life of the valve has been greatly improved.

Ceramic diaphragm valve：
The structure of the diaphragm valve is very simple, and its contact medium part is composed of a ceramic valve body and a PTFE diaphragm. After precision grinding and polishing treatment, the ceramic valve seat surface is completely pressed against the diaphragm without leakage. As a supporting rubber lining material, fluororubber is used. The channel of the ceramic valve body has a smooth surface and minimal friction with the medium.