Continuous high temperature hard sealed ball valve fault diagnosis and solution general gate valve globe valve, gate valve selection and application introduction

Continuous high temperature hard sealed ball valve fault diagnosis and solution general gate valve globe valve,

gate valve selection and application introduction

        Hard seal ball valve use conditions are much stricter than soft seal gate valve, continuous high temperature, strong corrosion and soot, particulate matter, sand and other substances on the continuous use of hard seal ball valve caused a very big obstacle. In the use of hard sealed ball valves, it is often due to working conditions or human factors caused by abnormal gate valves and have to be repaired. It is necessary and efficient to master the causes of common gate valve failures and then find ways to prevent failures for the valve industry staff and product users.
Hard seal ball valve use conditions are much stricter than soft seal gate valve, continuous high temperature, strong corrosion and soot, particulate matter, sand and other substances on the continuous use of hard seal ball valve caused a very big obstacle. In the use of hard sealed ball valves, it is often due to working conditions or human factors caused by abnormal gate valves and have to be repaired. It is necessary and efficient to master the causes of common gate valve failures and then find ways to prevent failures for the valve industry staff and product users.
The purpose is to analyze the hard sealed ball valve and the problems found in the whole process of user use, expand the hard sealed ball valve product appearance design and the configuration of the equipment need to pay attention to the problems, and give the direction of improvement.
From the perspective of product use to classify, hard sealed ball valve common faults can be roughly divided into the following two categories: non-technical professional common faults and technical professional common faults.
1 Common faults in non-technical majors
This kind of common failure is irrelevant to technology, that is, it is not the internal structure of the gate valve or internal structure parts operation failure. Thus, the failure phenomena are usually caused by external standards.
1.1 Wrong valve selection
Some customers choose gate valve models, because of insufficient understanding of the product working condition, or in consideration of cost, the selected gate valve can not meet the requirements of operating temperature, pressure, material corrosion, abrasion, resulting in the gate valve once delivery, soon abnormal.
Therefore, in the selection process, the customer side or the planning institute must put the stability of the use of the product in place, so the cost of selecting excessive low-end goods, resulting in common failures caused by harm, but penny wise and pound foolish. This point in strict conditions of hard sealed ball valve model selection, is very important.
1.1.1 Incorrect material selection of painted carbide tool surface on ball seat sealing surface
Hard sealed ball valve performance focus on steel ball, seat surface hardening solution. In order to ensure metal to metal sealing, the hard seal ball seat middle seal is much higher than the working pressure of the general gate valve, which makes it easy for the metal composite material to be occluded or contusion, both of which can cause the gate valve to not be used properly. At this stage of use, the effect is also good ball seat surface hardening method is what paint carbide tool technology (usually nickel base superalloy and chromium cobalt alloy), hard sealing ball valve ball and valve seat paint layer to a large extent depends on the ball seat sealing surface performance indicators and service life, so in the specific complex working conditions, to select the actual situation of carbide tool layer.
The selection of hard alloy cutting tool layer is about two routes: one is to pursue its strength, high toughness aluminum alloy layer wear resistance, abrasion resistance is very strong, mainly used for fine, hard suspended particle material conditions (such as energy chemical industry, photovoltaic cell field); The other is to pursue its corrosion resistance. With some volatile substances, the corrosion resistant aluminum alloy layer can effectively control the internal structural plate of the ball seat, thus extending the life. It is mainly used in the working condition of volatile substances (such as petrochemical industry and paper industry). Hard sealed ball valve material selection, the ball seat sealing surface of the paint carbide tool layer of raw materials is very important, must not be selected and working conditions, application material standards inconsistent with the hard alloy tool.
1.1.2 Material selection of some main parts of gate valve is inconsistent with the ambient temperature of working condition
Hard sealed ball valve, there are some internal parts of the material selection is not so much the application conditions of the ambient temperature or the temperature of the physical environment is closely related, such as filling material, sealing ring, seat wire sleeve, etc. There are generally two reasons for selecting hard sealed ball valves. One is that the working temperature is high, and the soft sealing seat is difficult to bear. The other is that the material etch level and abrasion ability are very strong, and the soft sealing seat is not hard enough. Thus, hard sealed ball valves are not equal to high temperature ball valves. In some working conditions, the ambient temperature of the product is not necessarily very high.
When the material temperature is too low by 200℃, synthetic plastics can be used for filling material, sealing ring (including the body cover sealing ring, the lower seat sealing ring, the middle flange sealing ring, etc.), the seat liner sleeve, etc. This kind of equipment is similar to the equipment of relevant parts in the soft seal gate valve.
When the material temperature exceeds 200℃, the filling material must be made of high purity graphite (high purity graphite has strong heat resistance, and the high temperature environment characteristics basically do not change), the sealing ring is generally made of iron wire wrapped in high purity graphite ring ** (sealed with high purity graphite, shaped by iron wire), and the seat liner also needs to be changed into metal composite material.
Therefore, in the hard sealing ball valve model selection link, working condition environment temperature or physical environment temperature is one of the necessary factors must be used to determine the model selection Angle. Incorrect selection of main parts will lead to cost consumption at least, and even cause invalid gate valve and can not be used.
1.2 Common faults in the model selection of accessory parts
The accessory parts of the valve include the driving mechanism, the supporting facilities and equipment of the driving mechanism and the supporting frame and connecting shaft of the connecting driving mechanism. According to its power source, the driving mechanism of hard sealed ball valve can be divided into: financial lever rocker, seamless steel pipe rocker, turbocharged actuator, spindle clutch reducer (for manual control or automatic operation), fully automatic actuator (including electric actuator, electric actuator, electro-hydraulic actuator, etc.).
For the financial lever rocker, seamless steel pipe rocker, gear mechanism and other driving mechanisms with manual control, according to the actual working torque value to calculate the torque, and then choose their own length or specifications, the torsional and compressive strength of natural raw materials are to be considered.
The model selection of the fully automatic actuator is relatively complex. Take the electric actuator as an example, the electric actuator is divided into single effect type and double effect type. Double effect electric actuator power switch is spring force effect, torque is consistent. Single-effect electric actuator must get rid of spring elastic effect when it is opened, and turn off by spring force when it is cancelled. In that case, its output torque is a category torque value, which enhances the difficulty of model selection. Generally, electric actuator must be assembled under the premise of torque value in the work of valve, multiplied by a safety performance. Avoid the situation of insufficient operating force due to the output torque of the actuator with category variation.
Generally, when leaving the factory, its working practice torque value can not be effectively detected before the specific working condition. The common standard is to estimate their working torque value based on the full load torque value multiplied by a material index. For hard sealed ball valve, the material index should be selected according to the difference of working conditions. If it is particulate matter, soot, sand material, the index needs to be as large as possible, generally in the range of 1.5 ~ 2 selection.
In addition to the model selection of the actuator itself, the model selection of its additional parts should also be combined with the actual situation, such as relays, pressure regulating valves, valve position power switches, etc. For example, an electric actuator with a large air flow rate is configured with a relay with a small total gas flow rate, so that the air inlet of the electric actuator will be relatively slow, and the gate valve will be closed and slowed down. The longer the sealing surface is worn, it is not conducive to the life of gate valve. And, the advantage of the valve of the protection device is that the opening and closing speed is fast. Many people have stipulated that the opening and closing position is in N seconds, which puts forward higher requirements for the reasonable layout of the relevant parts.
1.3 Common non-technical faults
In addition to the above common model selection caused by incorrect non-technical common faults, in the specific use of hard sealed ball valves, because the installation position, process, etc., is not in accordance with the standard, it may also produce common application faults, so in the use of gate valves, should follow the instructions, to connect the parts to be connected well, to ensure that there is no mistake.
2 Common faults in technical specialties
The common faults of non-technical majors mentioned above are all caused by human factors and come from subjective factors. If you are prudent or have rich working experience, you can actually deal with them. The cause of common faults has nothing to do with the internal structure of gate valve. And technical professional common failure. To put it bluntly, this is because the professional technology of hard and tight gate valve is not mature enough. Sometimes we only try to reduce its impact as much as possible, but it is difficult to solve it completely. Naturally, if a hard sealed ball valve with a service life of 3 months can be used for more than half a year through fault handling or prevention, even if common faults can not be completely avoided, it can also be called a success.
2.1 Leakage caused by damage of sealing surface
For the gate valve, and even for the gate valve, the sealing surface is the most important part that affects the related work of the whole gate valve. From the working principle of gate valve, gate valve is opening and closing parts, its operation process is the whole process of steel ball opening or canceling on the valve seat, if the sealing surface is damaged in the process of opening or closing, the sealing surface may leak, leading to the leakage of the valve, the gate valve is invalid.
2.1.1 Effective use of seat springs
The very big difference between hard sealed ball valves and soft sealed gate valves is that the steel ball and seat are all metal composite materials, which is different from the soft sealed steel ball is metal material, and the seat is non-metallic material. Therefore, the sealing principle will be different, soft seal gate valve sealing principle is: The sealing force between the ball and the seat causes the non-metallic material valve seat to bend, and converts the uneven line contact between the valve seat and the ball into contact. At the same time, after the soft sealing valve seat is distorted and deformed, it is further connected with the surface surface of the ball to compensate for the uneven pothole of the surface surface of the ball. If the distortion of the ball and the valve seat is larger or smaller, the sealing characteristics will not be affected. The sealing principle of hard sealed ball valve is that the sealing force between the steel ball and the seat is difficult to bend the metal material valve seat, so more sealing force (compared with soft sealing gate valve) should be used to bend the sealing surface of the valve seat, so as to achieve the connection between the steel ball and the valve seat, so as to achieve the seal, but the bending is small, if the force of the ball seat is slightly changed, It might not seal. The difference between the two principles is not too difficult to get two results: first, hard sealed ball valve steel ball and seat extrusion pressure is very large; Two, hard seal ball valve for the seal of the adjustment system is inferior to the soft seal gate valve.
Because the extrusion pressure between the hard sealed ball valve ball and the valve seat is very large, rolling friction occurs between the metal steel ball and the metal seat when the gate valve is opened and closed. According to engineering mechanics, rolling friction between metal materials with similar strength is likely to bruise the sealing surface (causing scratches on the sealing surface). In hard sealed ball valves, the torsion spring (disc spring or column spring) is generally connected after the seat to compare the working pressure to adjust. That, to a certain extent, the sealing force in a certain range, have reached the seal.
2.1.2 Cushioning effect of valve seat pressure ring
The cushioning effect of spring is described above. The elastic force and compression of spring are linear or conic function relations, and the amplitude range is relatively short, so it can be adjusted in a very small range. When a gate valve leaks or is larger than or below the operating pressure specification, it must be adjusted by the thickness of the seat pressure ring installed behind the seat.
2.1.3 Leakage of sealing surface caused by working condition
In fact, for the efficacy of hard sealed ball valves, leading to greater confusion is not a technical problem, even customized enough high precision, in the specific use, there will still be some problems, such problems generally appear in the coal chemical industry, photovoltaic cell field, the consistent characteristics of this condition is that the substance is not composed of a single vapor or liquid, in which there are a large number of suspended particles, Such suspended particles lead to strong washing of the flow gate of the steel ball and the valve seat, and even cross the flow gate into the sealing surface, which can lead to fatal damage to the sealing surface.
In the face of this situation, the maintenance status of gate valve accounts for 20% of the maintenance volume. British sealing gate valve ball and seat sealing surface requirements are relatively high, once the scratch exceeds 0.1mm, most of the grinding is not likely to be used, once such a situation occurs, often the ball seat is damaged at the same time. So keep these things as low as possible.
The two sides of the sealing surface of the valve seat are trimmed out of 2 steps, that is, the “double scraper” structure. The steps on both sides are like two scraping plates. In the process of opening and closing the steel ball, the suspended particles attached to the steel ball can be effectively shaved to prevent them from entering the sealing surface. Naturally, this kind of seat is generally used in the condition of suspended particles, for water, steam material, scraper structure to reduce the compression strength of the seat, and improve the production cost, without.