The regulating valve is directly installed on the process pipeline, the use of poor conditions, such as high temperature and pressure, deep freezing, extremely toxic, flammable, explosive, easy to penetrate, easy to crystallize, strong corrosion and high viscosity, its quality directly affects the quality of the system. Thus affect the quality of the final product and the efficiency of the system operation. Problems can occur if not properly selected or maintained. For example, some regulating circuits are not stable: they oscillate all the time, and if the selection is improved, the quality of regulation is greatly improved after changing the linear characteristic spool to the logarithmic characteristic spool or changing the flow direction. For example, some continuous oscillations occur in the adjustment process, not because the proportion of the regulator is too large or too small, but because the dry friction of the valve stuffing box is too large, and the action is not flexible. For example, the leakage of the regulating valve will cause factory pollution and even cause accidents. Therefore, attention should be paid to the role of the regulating valve, and maintenance and maintenance should be strengthened. What are the problems with manual control?

Above is a schematic diagram of a manually controlled level. The liquid continuously flows through the inlet valve 2 into the storage tank 1, and continuously flows out through the outlet valve 4. We can see that the liquid level in the tank will fluctuate with the inflow or outflow. When the fluctuation is serious, the liquid in the tank may overflow or be evacuated. To solve this problem and keep the level within a certain range, the simplest way is to install a glass tube level gauge 3. With the upper and lower limits of the level gauge as the standard, when the liquid level rises to close to the upper limit scale, you can open the export valve, or close the inlet valve opening; When the liquid level drops to the lower limit scale, you can close the outlet valve or open the opening of the inlet valve, so as to avoid the tank overflow due to excessive liquid level, or because of the liquid level down and the evacuation of the accident occurred, so that the liquid level remains within a certain range. This process is directly controlled by people, so it is called manual control. It can be seen that manual control has at least the following problems and thus cannot meet the requirements of modern industry for process control. 1. Poor control accuracy. When the liquid level requirements are more accurate, that is, the upper and lower limits of the liquid level change range requirements are small, because of human reflection to manual operation there is a process, resulting in excessive liquid level control. 2. Slow response time. 3. Fatigue failure. 

The pneumatic regulating valve is to use compressed gas as the power source, the cylinder as the actuator, and drive the valve with the help of valve positioner, converter, solenoid valve, position valve, gas storage tank, gas filter and other accessories to realize the switching quantity or proportional adjustment, and receive the control signal of the industrial automation control system to complete the regulating pipeline. Medium: flow, pressure, temperature, liquid level and other process parameters. The characteristics of pneumatic regulating valves are simple control, fast response, and intrinsically safe, and there is no need to take additional explosion-proof measures.

The International Electrotechnical Commission IEC defines the control valve (known as Control Valve in foreign countries) as: "The terminal component formed by a power-operated device in the industrial process control system, which includes a valve body component. There is a component inside that changes the flow rate of the process, and the valve body component It is also connected with one or more executive agencies. The actuator is used to respond to the signals sent by the control. It can be seen that the regulating valve is composed of two parts: the actuator and the valve body parts, namely:

Regulating valve = actuator + valve body parts + accessories

Among them, the actuator is the propulsion device of the regulating valve, which generates a corresponding thrust according to the size of the signal pressure, so that the putter produces a corresponding displacement, thus driving the core action of the regulating valve; the valve body component is the regulating part of the regulating valve, which is directly in contact with the medium and changes the joints of the regulating valve through the displacement of the putter rod of the actuator. Flow area, to achieve the purpose of adjustment.

Butterfly valves provide an effective closing method for the switching and regulation of fluids. They are the successor to traditional gate valve technology, which is heavy and difficult to install and does not provide the tight shutoff performance needed to prevent leakage and increase productivity. The earliest use of butterfly valves dates back to the late 18th century and was improved in the 1950s to a smaller, lighter design that effectively solved the problem of leakage.

Emerson's Keystone brand developed the flexible seat butterfly valve family in the 1950s, a more compact, lighter design to meet user needs for leakage and safety challenges. Butterfly valve is mainly used in low pressure, low temperature environment to replace the gate valve, such as plant utilities, building HVAC and other industrial industries need bubble class sealing conditions. It features a rubber-lined, centering disc design, which means the disc and stem are centered on the body and pipe. Disc rotation 90 completes the full closed to full open travel and can be matched with manual, electric and pneumatic actuators. The actuator controls the valve plate action to limit or allow fluid to pass through the pipeline, and the user can adjust the flow of the pipeline medium through the control system.

In response to the sustainable development policies of today's society, we reduce the dependence on metal raw materials while being lightweight and able to apply in corrosion-resistant conditions such as construction equipment, transport and cargo containers, plastic or glass-steel pipelines, and purification, ozone or demining. Keystone has developed the CompoSeal series of composite valve products, elastic seat valves made of high quality engineered composite materials to provide good internal and external chemical corrosion resistance.

With the continuous development of rubber lining elastic seat butterfly valve, its application field is further expanded. End users are able to apply it to hotter, more corrosive applications such as mildly corrosive environments, food and beverage and hot air applications. Emerson's representative product, the Keystone F990 / 920 with TFE seat, is well suited to replace other types of valves in the food and beverage industry.

However, there is still a gap in this market. Customer demand for more efficient and safer butterfly valves is driving the need for metal seated valves with tight shutoff performance, which neither gate valves nor high-performance butterfly valves can meet.

To meet these customer needs, a new valve type - tri-eccentric butterfly valve was developed and introduced to the market. According to international standards, the Triple Eccentric Valve (TOV) is the first valve capable of achieving two-way zero leakage performance, achieving zero leakage tight shutdown through metal-to-metal torque sealing and angular travel non-frictional rotation. The tri-eccentric valve can be used in extreme temperature and pressure conditions, while providing zero leakage, metal sealing.

One of the challenges faced by customers using butterfly valves today is the compatibility of the materials used with the application conditions. To address this challenge, valve manufacturers are increasingly applying new advanced technologies to the coating of valve bodies and plates, enabling them to be used in aggressive media.
Butterfly valves are not recommended for applications where large pressure drops are required. In addition, because the butterfly valve plate is located in the flow path, it cannot be used in applications requiring straight line valves. They are suitable for regulating conditions, but not for conditions requiring minimal regulation.
Butterfly valves provide an effective closing method for the switching and regulation of fluids. They are the successor to traditional gate valve technology, which is heavy and difficult to install and does not provide the tight shutoff performance needed to prevent leakage and increase productivity. The earliest use of butterfly valves dates back to the late 18th century and was improved in the 1950s to a smaller, lighter design that effectively solved the problem of leakage.

Emerson's Keystone brand developed the flexible seat butterfly valve family in the 1950s, a more compact, lighter design to meet user needs for leakage and safety challenges. Butterfly valve is mainly used in low pressure, low temperature environment to replace the gate valve, such as plant utilities, building HVAC and other industrial industries need bubble class sealing conditions. It features a rubber-lined, centering disc design, which means the disc and stem are centered on the body and pipe. Disc rotation 90 completes the full closed to full open travel and can be matched with manual, electric and pneumatic actuators. The actuator controls the valve plate action to limit or allow fluid to pass through the pipeline, and the user can adjust the flow of the pipeline medium through the control system.

1、 Installation

1）. Preparation before installation:

Check valve parameters: Carefully verify the diameter, pressure range, spring pressure, and other parameters of the steam pressure reducing valve to ensure they match the selected data.

Cleaning the pipeline system: Before installation, the pipeline system needs to be thoroughly cleaned to remove impurities such as welding slag, debris, and oxide scale. A 100 mesh steam filter can be installed in front of the pressure reducing valve. The filter screen is made of corrosion-resistant double-layer stainless steel filter, and the filter head is installed on the side to avoid water accumulation.

Prepare installation tools and materials: Ensure that the necessary tools for installation are complete, such as wrenches, screwdrivers, etc., and prepare suitable connecting fittings, gaskets, and other materials.

2. Installation position and direction
Horizontal installation is preferred: Steam pressure reducing valves are generally recommended to be installed on horizontal pipelines, with the valve cover facing upwards for easy operation and maintenance. They should be installed in the direction of the arrow on the valve body, so that they are consistent with the direction of fluid flow and cannot be installed in reverse.

Attention to straight pipe section requirements: There should be a certain straight pipe section before and after the installation of the pressure reducing valve. The length of the straight pipe in front of the valve is about 600 millimeters, and the length of the straight pipe behind the valve is about 1000 millimeters.

3. Installation of supporting facilities

Install bypass valve: Install an adjustable steam shut-off valve on the bypass pipeline of the pressure reducing valve. The diameter of the bypass valve should be the same as that of the pressure reducing valve, and it should be installed on the top of the pressure reducing valve as much as possible to avoid corrosion caused by water accumulation. Installation pressure

Gauge and safety valve: Install a pressure gauge before and after the pressure reducing valve for pressure setting and monitoring. At the same time, a steam safety valve should be installed downstream of the pressure reducing valve. The set pressure of the safety valve should be higher than the upper deviation of the pressure reducing valve, but lower than the maximum pressure at which the equipment or control valve closes.
Installation of steam water separator and drain valve: Install a steam water separator or drain valve at the inlet of the pressure reducing valve to reduce and eliminate water hammer and erosion, or install a drain valve at the outlet of the pressure reducing valve.

4、 Maintenance
1). Daily maintenance to maintain cleanliness: Regularly clean the dust, oil stains, and other dirt on the surface of the pressure reducing valve to prevent impurities from entering the valve body and affecting its performance. Check the connection parts: Regularly check the connection parts between the pressure reducing valve and the pipeline for looseness, leakage, etc. If there are any problems, tighten or replace the seals in a timely manner. Observing the operating status: During operation, closely observe the working status of the pressure reducing valve, including whether the pressure regulation is stable, whether the valve action is flexible, etc. If there are any abnormalities, they should be dealt with in a timely manner.

2). Regular maintenance and inspection of filters: Regularly clean or replace the filter screen before the pressure reducing valve to prevent impurities from blocking the filter screen and affecting the filtration effect. Check the seals and springs: Every certain time, check whether the seals of the pressure reducing valve are worn or aged, and whether the springs are deformed or broken. If there are any problems, replace them in a timely manner. Calibration of pressure gauge: Regularly calibrate the pressure gauge before and after the pressure reducing valve to ensure accurate pressure display, in order to facilitate correct adjustment and monitoring of pressure.

3). Long term shutdown maintenance emptying pipeline: When the steam pressure reducing valve is not in use for a long time, the front and rear shut-off valves should be closed to empty the steam and condensate in the pipeline, to prevent water accumulation from corroding the valve components. Apply protective oil: Apply protective oil to the exposed machined surface of the pressure reducing valve to prevent rust and store it properly.

working principle:

1. Direct acting solenoid valve

Principle: When a normally closed direct acting solenoid valve is energized, the solenoid coil generates electromagnetic suction to lift the valve core, causing the sealing element on the valve core to leave the valve seat and open the valve; When the power is cut off, the electromagnetic force disappears, and the sealing element on the valve core is pressed against the valve seat by the spring force, causing the valve to close. Characteristics of the normally open type: It can work normally under vacuum, negative pressure, and zero pressure difference. The larger the valve diameter, the larger the volume and power of the electromagnetic head. The direct acting solenoid valve produced by our company with imported technology can be used for 1.33 × 10-4 Mpa vacuum.

2. Step by step direct acting solenoid valve (i.e. recoil type)

Principle: Its principle is a combination of direct action and pilot action. When powered on, the solenoid valve first opens the auxiliary valve. The lower chamber pressure of the main valve is greater than the upper chamber pressure, and the valve is opened by the simultaneous action of pressure difference and electromagnetic force; When the power is cut off, the auxiliary valve uses spring force or medium pressure to push the sealing element to close and move downwards to close the valve port. Characteristics: It can work reliably even at zero pressure difference or at a certain pressure. Generally, the working pressure difference does not exceed 0.6 MPa, but the electromagnetic head has a large power and volume, requiring vertical installation.

3. Pilot operated solenoid valve

Principle: When powered on, the electromagnetic force drives the pilot valve to open the pilot valve. The pressure in the upper chamber of the main valve rapidly decreases, forming a pressure difference in the upper and lower chambers of the main valve. With the help of the medium pressure, the main valve closing member moves upward, and the valve opens; When the power is cut off, the spring force closes the pilot valve, and the inlet medium pressure quickly enters the upper chamber of the main valve through the throttle hole, forming a pressure difference in the upper chamber and causing the main valve to close. Features: Small size, low power, but limited range of medium pressure difference, meeting the pressure difference condition (0.01MPa).

Electromagnetic valve is an industrial equipment controlled by electromagnetic force, used as an automation basic component for controlling fluids. It belongs to actuators and is not limited to hydraulic and pneumatic systems. Electromagnetic valves are widely used in many products due to their precision and flexibility in control. As a gatekeeper for circuit safety, the selection and application of solenoid valves should be safe and reliable. The required model and function of solenoid valves may vary in different control systems, so choose the appropriate solenoid valve based on practical requirements.

Four major selection principles

Security:
1. Corrosive media: Plastic king solenoid valves and all stainless steel (316) should be selected; For strongly corrosive media, use isolation membrane type. Neutral medium, copper alloy can also be used as the valve body material for solenoid valves. Ammonia valves cannot use copper materials.

2. High temperature steam medium: Stainless steel or cast steel valve bodies should be selected, and polytetrafluoroethylene seals should be used. Copper alloy valve bodies can also be used for ordinary high temperatures (below 180 degrees). High temperature (350 degrees) thermal oil and steam are sealed with hard seals and heat sinks are added.

3. Explosive environment: Choose products with corresponding explosion-proof levels, and choose waterproof and dustproof varieties for outdoor installation or dusty occasions.

4. The working pressure of the solenoid valve should exceed the high working pressure inside the pipe

Applicability：

1. The selection of electromagnetic coils for products with different medium temperatures will also vary (for example, high-temperature solenoid valves must be equipped with high-temperature coils), otherwise the coils will burn out, seriously affecting their lifespan.

2. Working pressure difference: Pilot operated solenoid valves can be selected for low working pressure differences above 0.03Mpa; Select direct acting or step-by-step direct acting solenoid valves for low working pressure differentials close to or less than zero.

3. Select the nominal diameter (DN) based on the flow rate and valve Kv value, or choose the same pipe inner diameter.

4. In environments with high relative humidity and water droplets and rain, waterproof solenoid valves should be selected.

5. The voltage specification should preferably use AC220V or DC24V.

The regulating valve positioner is the main accessory of the pneumatic actuator, which is used in conjunction with the pneumatic actuator to improve the position accuracy of the valve, overcome the influence of valve stem friction and medium imbalance force, and ensure that the valve is correctly positioned according to the signal from the regulator.

In the following situations, a locator should be equipped:
1. When the medium pressure is high and the pressure difference is large;
2. When the diameter of the regulating valve is large (DN>100); 3. High or low temperature regulating valve;
4. When it is necessary to increase the operating speed of the regulating valve;
5. When using standard signals and operating non-standard spring actuators (spring range outside 20-100KPa);
6. When used for split range control;
7. When the valve is operated in reverse (switching between gas closed and gas open);
8. When it is necessary to change the flow characteristics of the valve (the locator cam can be changed);
9. No spring execution
When the mechanism or piston actuator needs to achieve proportional action;

10. When using electrical signals to operate pneumatic actuators, it is necessary to use an electrical valve positioner.

Solenoid valve:
When the system needs to implement program control or two position control, an electromagnetic valve is required. When selecting solenoid valves, in addition to considering AC and DC power sources, voltage, and frequency, attention must be paid to the relationship between the type of action of the solenoid valve and the regulating valve. "Normally open" or "normally closed" types can be used.If it is required to increase the capacity of the solenoid valve to shorten the action time, two solenoid valves can be used in parallel or combined with a large capacity pneumatic relay as a pilot valve.

Pneumatic relay:
Pneumatic relay is a power amplifier that can send air pressure signals to distant places, eliminating hysteresis caused by extended signal pipelines. It is mainly used between field transmitters and regulating instruments in the central control room, or between regulators and field regulating valves. Another function is to amplify or reduce signals.

converter:
Transformers are divided into gas electric converters and electric gas converters, whose function is to achieve a certain relationship between gas and electrical signals and convert them into each other. They are mainly used to convert 0-10mA or 4-20mA electrical signals or 0-100KPa gas signals into 0-10mA or 4-20mA electrical signals when operating pneumatic actuators with electrical signals.

Air filter pressure reducing valve:
Air filter pressure reducing valve is an accessory in industrial automation instruments. Its main function is to filter and purify the compressed air from the air compressor and stabilize the pressure at the required value. It can be used as a gas supply source and stabilizing device for various pneumatic instruments, solenoid valves, cylinders, spraying equipment, and small pneumatic tools.

Self locking valve (retaining valve):
A self-locking valve is a device that maintains the valve position. When the air source fails, the pneumatic control valve can cut off the air source signal, keeping the pressure signal of the diaphragm chamber or cylinder in the state before the fault, so that the valve position is also maintained at the position before the fault, playing a protective role.

Valve position transmitter:
When the regulating valve is far away from the control room, in order to accurately understand the position of the valve switch without going to the site, a valve position transmitter should be equipped, which converts the displacement of the valve opening mechanism into an electrical signal according to a certain rule and sends it to the control room. This signal can be a continuous signal reflecting any opening of the valve, or it can be considered as the reverse action of the valve positioner.

Travel switch (feedback device):
The travel switch is a device that reflects the two extreme positions of the valve switch and sends out indication signals at the same time. The control room can use this signal to trip the valve switch status in order to take corresponding measures.

The maintenance techniques for chemical pumps are as follows:

1. Check whether the pipelines and joints of the chemical pump are loose. Rotate the chemical pump by hand and test if it is soft.

2. Remove the water intake plug of the chemical pump body and inject water (or slurry).

3. When abnormal noise is detected in the chemical pump, it should be stopped immediately to check the cause.

4. Effectively close the gate valve, outlet pressure gauge, and inlet vacuum gauge of the water outlet pipeline.

5. Move the motor and try to check if the direction of the motor is correct.

6. After starting the motor and the chemical pump working normally, turn on the outlet pressure gauge and the inlet vacuum pump, display the appropriate pressure, slowly open the gate valve, and check the load condition of the motor.

7. The flow rate and head of the chemical pump should be controlled within the range indicated on the nameplate as much as possible.

8. During the operation of chemical pumps, the bearing temperature shall not exceed 35 degrees Celsius of the ambient temperature, and the temperature shall not exceed 80 degrees Celsius.

9. Add bearing lubricating oil into the bearing body and observe the oil level, which must be located at the centerline of the oil level. Lubricating oil should be replaced or replenished in a timely manner.

10. When stopping the use of the chemical pump, please close the gate valve and pressure gauge before stopping the motor.

11. During one month of operation, the chemical pump needs to replace the lubricating oil every 100 hours, and then replace the oil every 500 hours.

12. Regularly adjust the sealing pressure plate to ensure that the dripping condition inside the sealing chamber is normal.

13. Regularly check the wear of the sleeve and replace it promptly if there is significant wear.

14. When using chemical industry pumps in winter, after parking, the drain plug at the lower part of the pump body must be loosened to clean the medium. Prevent frostbite.

15. The chemical pump has been out of service for a long time and needs to be completely disassembled, wiped off of moisture, and installed with grease applied to the rotating and joint parts, and properly stored.

After the installation of various newly purchased and installed centrifugal pump products, it is necessary to conduct centrifugal pump testing in advance. When conducting centrifugal pump testing, the following centrifugal pump testing methods and precautions should be followed.

1. Before starting the centrifugal pump, it is prohibited to conduct idle and no-load testing. The liquid test should be carried out according to the operating procedures specified in the centrifugal pump operating instructions. For the forced lubrication system, the temperature rise of the centrifugal pump bearing oil should not exceed 28 degrees, and the temperature of the bearing metal should be less than 93 ℃.

2. For centrifugal pumps with oil ring lubrication or splash lubrication systems, the temperature of the lubricating oil should not exceed 39 degrees, and the temperature of the bearing components should be less than 82 degrees.
3. When testing the centrifugal pump, the vibration value of the centrifugal pump bearings should also be checked. The vibration standard of the centrifugal pump bearings can refer to the vibration standards of relevant petrochemical rotating machinery.

4. During the centrifugal pump testing process, the operation of the centrifugal pump should be very balanced and noiseless, the coolant and lubricating oil systems should be normal, and there should be no leakage in the centrifugal pump and its ancillary pipelines.

5. During the process of testing the centrifugal pump, attention should be paid to whether the current of the centrifugal pump motor is operating within the specified range. If the current exceeds the limit, it indicates that the actual working head is lower than the pump head. In this case, it is recommended to close the outlet valve to control the flow rate of the centrifugal pump and use it within the rated current range.

6. Various seals and medium leaks of centrifugal pumps must not exceed the following standard requirements:

(1) Clean water centrifugal pump with mechanical seal: 10 drops/min for light oil and 5 drops/min for heavy oil

(2) Multi stage centrifugal pump product with packing seal: 20 drops/min for light oil and 10 drops/min for heavy oil

(3) For magnetic driven pumps transporting toxic, harmful, flammable, and explosive media, visible leaks are not allowed.

Virtual reality technology has been widely used in engineering structure design and manu2facture due to its high efficiency and obvious characteristics which are different from traditional way.The paper gave a detailed introduction of its application in valve design. A virtual experiment was con2ducted to calculate the extreme stress in order to optimize the valve structure. Stress concentration ofopenings on valve is discussed and the relationship between sealing face and seal pressure is establishedby employing effective seal pressure. The simulation results show that the virtual reality technologycan provide a quantitative evaluation for valve strength and seal properties , which is necessary forvalve design both theoretically and practically.

Simulation test steps The valve product has a high degree of structural similarity and is suitable for using modules Normalization and parameterization design have the same or similar design calculation modes Like. In addition, there are many standard and universal parts for valves, which facilitates the application of group technology and feature modeling technology in CAD systems. In valve installation During the development process, virtual design and simulation experiments are used to conduct valve testing Door optimization can not only obtain high-quality products, but also reduce costs. For valve testing, the strength of the valve body and the sealing of the sealing surface Performance is within the main scope of testing. Stress and sealing on the valve body The distribution of pressure on the sealing surface is used in practical design Testing or correcting formulas, although this method has a high safety factor, is difficult To meet the requirements of valve design development. Using practical means, these two The parameters are difficult to accurately measure. By conducting simulation experiments, designers can To obtain precise separation of stress and sealing ratio pressure on the valve body and sealing surface The distribution of results makes the design and improvement of valves more targeted and accurate Accuracy. Valve simulation belongs to static structural analysis, and its testing steps are as follows As shown in Figure 1. During the valve simulation test, it is necessary to establish a valve Door solid model, finite element model mesh division, defining boundary conditions The work of analyzing and calculating results 

(1) establishes a solid model of the valve from the purpose of analysis Establish a model and make necessary changes to the model structure, such as analyzing The target is the flow characteristics when the valve is fully open and the fluid inside the flow channel The velocity distribution is irrelevant to the characteristics of the valve outer wall and the analysis target It can be completely omitted or simplified. 

(2) The quality of mesh division in finite element models affects the calculation time The spacing and accuracy are greatly affected. Generally, before ensuring the quality of grid generation The finer the grid, the higher the computational accuracy, but the required calculations The longer the time. The analysis of the contact relationship between valve components requires multiple iterations Proxy solving consumes a lot of computation time and resources. For large Calculate the sealing pressure ratio of the sealing surface of the caliber butterfly valve, and compare it with the diameter size, The width of the sealing surface is relatively small, as it is the focus of analysis, Therefore, the grid at this location should be appropriately refined for other positions of the valve Placing a grid can reduce distribution density and save computation time. 

(3) The definition of boundary conditions and virtual operating conditions is mainly based on the actual operating conditions of the valve, which constrains and loads its model. For valves with simple structures, the plane formed by the operating axis and the centerline of the flow channel can serve as the symmetry plane of the valve structure. Applying constraints on the valve body section at this position can make the results more accurate. When considering the stress caused by temperature difference on the valve body, the displacement constraint applied on the symmetrical section can completely eliminate the stress concentration caused by the constraint. Without affecting the analysis results, some components unrelated to the analysis target can be omitted to reduce calculation time, which is particularly effective in situations with large computational loads. For example, when calculating the specific pressure of the sealing surface, equivalent constraints can be applied to the sealing components (valve seat, sealing ring, etc.), and fastening components can be omitted according to the situation.

 (4) For the final analysis and calculation results, targeted data extraction and analysis should be carried out. If a hydraulic strength test is conducted on a hard sealed butterfly valve to obtain the stress distribution of the entire valve, the main focus is usually on the stress distribution on the valve body, and only the stress results of the valve body need to be extracted. To observe the sealing effect of the valve, it is necessary to extract the pressure distribution data on the sealing surface.

Water hammer, also known as water hammer, is a hydraulic transition phenomenon in pressure pipelines caused by sudden changes in water flow velocity, also known as transient flow. In pressure pipelines, when there is a sudden change in flow velocity due to certain reasons, the pressure of the liquid inside the pipeline increases or decreases due to the inertia of the fluid. It poses great harm to water pump units and pipeline systems. In general, water hammer does not occur during normal operation and shutdown of the water pump.

From different perspectives, water hammer phenomena can be divided into four categories:
(1) According to the relationship between the duration of valve closure and water hammer, it can be divided into direct water hammer phenomenon and indirect water hammer phenomenon;

(2) According to the fluctuation of water hammer, it can be divided into continuous water hammer phenomenon and separated water hammer phenomenon;

(3) According to the hydraulic characteristics of water hammer, it can be divided into rigid water hammer phenomenon and elastic water hammer phenomenon;
(4) According to the external conditions causing water hammer, it can be divided into startup water hammer phenomenon, valve closing water hammer phenomenon, and pump stopping water hammer phenomenon.

What are the hazards of pump shutdown water hammer:
Pump shutdown water hammer is a type of water hammer phenomenon, which occurs in the pump station and pipeline system due to the sudden power outage of the pump unit caused by misoperation by pump station staff, external power grid accidents tripping, and natural disasters (strong winds, lightning strikes, earthquakes).
According to the investigation, many water hammer accidents belong to pump shutdown water hammer accidents, which pose a great threat to the safety of pump rooms and pipelines. Several pump rooms in China have experienced pump shutdown water hammer, resulting in pump room flooding or pipeline rupture. Although the duration of water hammer phenomenon is short, the engineering accidents it causes cannot be ignored, ranging from vibration and hydraulic impact noise generated by water pump units; In severe cases, the water pump unit may be damaged by vibration, and the pipeline may crack due to hammering, resulting in a water outage accident. If the pump is stopped due to an accident and causes water column separation and flow interruption in the pipeline to bridge the water hammer, its destructive power will be more severe.

How to protect against water hammer when stopping the pump

Due to the possibility of serious accidents in pump stations and water delivery systems caused by pump shutdown water hammer, it is necessary to take corresponding measures according to the specific situation to eliminate pump shutdown water hammer or reduce water hammer pressure. So far, there have been various measures to prevent water hammer during pump shutdown,

It can be roughly divided into:
1. Water replenishment (gas injection) and pressure stabilization can prevent water column separation or high pressure interruption to bridge water hammer. There are bidirectional pressure regulating chambers, unidirectional pressure regulating chambers, and pressure tanks belonging to this type.
(1) Bidirectional pressure regulating tower: Built near the pump station or at an appropriate location on the pipeline, the water surface height of the bidirectional pressure regulating tower should be higher than the water surface height of the receiving pool at the end of the water transmission pipeline, taking into account the head loss along the pipeline. The pressure regulating tower will replenish water or release excessive pressure in the pipeline as the pressure changes, effectively avoiding or reducing water hammer pressure.
(2) Unidirectional pressure regulating tower: Built near the pump station or at an appropriate location in the pipeline, the height of the one-way pressure regulating tower is lower than the pipeline pressure at that location. When the pressure inside the pipeline is lower than the water level inside the tower, the regulating tower replenishes water to the pipeline to prevent the water column from breaking and to avoid bridging water hammer.
(3) Pressure tank: There is not much experience in using it domestically, but it is widely used abroad. It works using specific laws of gas volume and pressure. As the pressure in the pipeline changes, the pressure tank replenishes water to the pipeline or absorbs excessive pressure in the pipeline, similar to a bidirectional pressure regulating tower.

2. Water release and pressure reduction can prevent a sudden increase in pressure

This type includes pump stop water hammer eliminators, slow closing check valves, rupture discs, etc.

(1) There are three main types of pump stop water hammer eliminators: bottom opening pump stop water hammer eliminators, self closing pump stop water hammer eliminators, and automatic reset pump stop water hammer eliminators. They work similarly in principle, that is, when the outlet pressure drops to a certain value during the pump shutdown process, the eliminator opens. When the water hammer pressure rise wave returns to the water pump, the eliminator discharges water outward to eliminate the water hammer. The length of the main pipe protected by the water hammer eliminator generally does not exceed 800m.
(2) Slow closing check valve is a type of check valve that eliminates water hammer through slow closing. It has many forms, is simple and feasible, and has been widely used. There are two types of slow closing check valves: heavy hammer type and accumulator type. This type of valve can adjust the valve closing time within a certain range as needed. Generally, the valve closes 70% to 80% within 3-7 seconds after a power outage, and the remaining 20% to 30% of the closing time is adjusted according to the situation of the water pump and pipeline, usually within the range of 10-30 seconds.
(3) Blasting diaphragm is similar to installing fuses on circuits. When the pressure in the pipeline exceeds the predetermined value due to water hammer, the diaphragm automatically ruptures, causing water flow to leak out and eliminating water hammer.

3. Other types

(1) Appropriately increasing the diameter and wall thickness of the pipeline and reducing the flow velocity of the water transmission pipeline can to some extent reduce the water hammer pressure.
(2) Reduce pipeline length from one pump station to two pump stations, and connect the two pump stations with suction wells.
(3) Choosing a water pump unit with a large moment of inertia or installing a flywheel with sufficient inertia can reduce the water hammer value to a certain extent.
(4) Change the longitudinal section layout of the pipeline. When arranging water pipelines, efforts should be made to avoid sudden changes in slope.

The steps and basis of valve selection before procurement

In a fluid piping system, a valve is a control element whose main role is to isolate equipment and piping systems, regulate flow, prevent backflow, and regulate and discharge pressure. Since it is very important to select the most suitable valve for the piping system, it is also important to understand the characteristics of the valve and the steps and basis for selecting the valve. So far, the valve industry has been able to produce a complete range of gate valves, globe valves, throttle valves, plug valves, ball valves, electric valves, diaphragm valves, check valves, safety valves, pressure reducing valves, steam traps and emergency shut-off valves and other 12 categories, more than 3,000 models, more than 4,000 specifications of valve products; The maximum working pressure is 600MPa, the maximum nominal diameter is 5350mm, the maximum working temperature is 1200 °C, the minimum working temperature is -196 °C, and the applicable medium is water, steam, oil, natural gas, strong corrosive media (such as concentrated nitric acid, medium concentration sulfuric acid, etc.), flammable media (such as benz, ethylene, etc.), toxic media (such as hydrogen sulfide), explosive media and radioactive media (metal sodium, -loop pure water, etc.). Valve pressure parts are made of cast copper, cast iron, ductile iron, high silicon cast iron, cast steel, forged steel, high and low alloy steel, stainless acid resistant steel, Hastelloy, Inconel, Monel alloy, duplex stainless steel, titanium alloy, etc. And it is able to produce a variety of electric, pneumatic and hydraulic valve drives. In the face of so many valve varieties and such complex working conditions, to choose the most suitable valve products for the installation of the pipeline system, I think that the first thing to do is to understand the characteristics of the valve; Secondly, we should grasp the steps and basis for selecting valves; Furthermore, the principle of valve selection should be followed. 1

Characteristics of the valve (use characteristics and structural characteristics) use characteristics: it determines the main use performance and use range of the valve, and the characteristics of the valve are: the category of valves (closed circuit valves, regulating valves, safety valves, etc.); Product type (gate valve, globe valve, butterfly valve, ball valve, etc.); The material of the main parts of the valve (valve body, valve cover, valve stem, valve disc, sealing surface); valve transmission mode, etc. Structural characteristics: It determines some structural characteristics of the installation, repair, maintenance and other methods of the valve, which belong to the structural characteristics: the structural length and overall height of the valve, and the connection form with the pipeline (flange connection, threaded connection, clamp connection, external threaded connection, welded end connection, etc.); The form of sealing surface (inlay ring, threaded ring, surfacing welding, spray welding, valve body body); Stem structure form (rotating rod, lifting rod), etc. 2 Steps and basis for selecting valves (1) Select step 1.Clarify the purpose of the valve in the equipment or device, and determine the working conditions of the valve: applicable medium, working pressure, working temperature, etc. 2. Determine the nominal diameter and connection method of the pipeline connected to the valve: flange, thread, welding, etc. 3. Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc. 4. According to the medium, working pressure and working temperature of the pipeline, determine the materials of the shell and internal parts of the selected valve: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc. 5. Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc. 6. Determine the parameters of the valve: for automatic valves, first determine the allowable flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole. 7. Determine the geometric parameters of the selected valve: structural length, flange connection form and size, the size of the valve height direction after opening and closing, the size and number of bolt holes connected, the overall valve appearance, etc. 8. Use the existing information: valve product catalog, valve product sample, etc. to select appropriate valve products. (2) The basis for selecting valves: while understanding and mastering the steps of selecting valves, we should also further understand the basis for selecting valves. 1. The purpose of the selected valve, the working conditions and the operation control mode. 2. The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable and explosive medium, viscosity of the medium, etc. 3. Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing level, etc. 4. Installation size and overall size requirements: nominal diameter, andThe connection method of the pipe and the connection size, external dimensions or weight limits, etc. 5. Additional requirements for the reliability, service life and explosion-proof performance of the valve product. (When selecting parameters, it should be noted that if the valve is to be used for control purposes, the following additional parameters must be determined: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop when closed, maximum and minimum inlet pressure for the valve.) According to the above-mentioned basis and steps for selecting valves, the internal structure of various types of valves must be detailed in detail when selecting valves reasonably and correctly, so as to make a correct choice for the preferred valves. The ultimate control of the pipeline is the valve. The valve opening and closing control the flow of the medium in the pipeline, and the shape of the valve flow channel gives the valve a certain flow characteristic, which must be taken into account when selecting the most suitable valve for installation in the piping system. 3



The following are the principles that should be followed in the selection of valves: (1) The valve flow channel for shut-off and open medium is a straight-through valve, and its flow resistance is small, and the valve for shut-off and open medium is usually selected. Downward closed valves (globe valves, piston valves) are rarely used because of their tortuous flow channels and higher flow resistance than other valves. Where high flow resistance is permitted, a closed valve can be used. (2) The valve for flow control is usually selected as the valve that is easy to adjust the flow rate as the flow control. Downward closing valves, such as globe valves, are suitable for this purpose because the size of the seat is proportional to the stroke of the shut-off. Rotary valves (plugs, butterfly, ball) and flexural body valves (clamp valves, diaphragm valves) can also be used for throttle control, but usually only within a limited range of valve diameters. The gate valve is a disc-shaped gate to the circular valve seat mouth to do a cross-cutting movement, it can only control the flow well when it is close to the closed position, so it is usually not used for flow control. (3) The valve for reversing the diversion can have three or more channels according to the needs of the reversing shunt. Plug and ball valves are more suitable for this purpose, so most valves used for reversing diverters are selected as one of these valves. However, in some cases, other types of valves can also be used for reversing diverts as long as two or more valves are properly connected to each other. (4) Valves for medium with suspended particlesWhen there are suspended particles in the medium, it is most suitable to use the valve with wiping effect along the sliding of the sealing surface of its closing parts. If the back and forth motion of the shut-off to the seat is vertical, it is possible to hold the particles, so the valve is only suitable for basic clean media unless the sealing face material allows for the particles to be embedded. Ball valves and plug valves have a wiping effect on the sealing surface during the opening and closing process, so they are suitable for use in media with suspended particles. At present, whether in the petroleum, chemical industry, or in the pipeline system of other industries, valve applications, operating frequencies and services are ever-changing, to control or eliminate even small leakage, the most important and critical equipment is the valve. The ultimate control of the pipeline is the valve, and the valve’s service and reliable performance in various areas is unique.

Valve inspection and maintenance after purchase

The valve is not repaired and maintained in a timely manner, resulting in valve disrepair leakage or ineffective switching; The valve is not regularly overhauled and tested for pressure testing, and even has not been cleaned, tested and technically identified for many years, resulting in debris being deposited in the valve, not closing tightly, and serious oil seepage and oil channeling; The valve is not closed after overhaul, or the nozzle is not blocked after the valve is removed; The valve dust orchid gasket is made of materials that are not resistant to oil and pressure. Therefore, it is necessary to strengthen the inspection of the valve and strive to prevent problems before they occur.

The main content of the valve inspection

1. Whether there is leakage at the dynamic seal of the valve stem and the static seal of the flange gasket 2, whether the opening and closing state is normal 3, whether there is any damage and leakage of the valve body and other abnormal phenomena 4, rotate the normally open or normally closed valve for 1~2 times or do a lifting test 5, lubricate the valve stem of the normally open or normally closed valve 6, check and debug the power head and electrical system of the pneumatic valve
   
   What are the 10 problems that are often encountered in the use of valves?
   
2. Why is it easy to oscillate when the double seat valve is working with a small opening?
   
   For a single core, when the medium is a flow-open type, the valve stability is good; When the medium is a flow-closed type, the stability of the valve is poor. The double-seat valve has two spools, the lower spool is in the flow closed, and the upper spool is in the flow open, whichIn the case of small opening work, the flow closed valve core is easy to cause valve vibration, which is why the double-seat valve cannot be used for small opening work.
   
3. Why can’t the double seal valve be used as a shut-off valve?
   
   The advantage of the double-seat valve spool is that the force balance structure allows a large pressure difference, and its outstanding disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used for shut-off occasions, it is obviously not effective, even if many improvements have been made to it (such as double sealed sleeve valves), it is not desirable.
   
4. What kind of linear control valve has poor anti-blocking performance and good anti-blocking performance of quarter-turn valve?
   
   The spool of the linear valve is vertically throttled, and the medium is horizontally flowing in and out, and the flow channel in the valve cavity must turn backwards, making the flow path of the valve quite complex (shaped like an inverted “S” shape). In this way, there are many dead zones that provide space for the media to settle and in the long run, causing clogging. The throttling direction of the quarter-turn valve is horizontal, the medium flows in horizontally and flows out horizontally, which is easy to take away the unclean medium, and the flow path is simple, and the space for medium precipitation is also very small, so the quarter-turn valve has good anti-blocking performance.
   
5. Why is the stem of the linear control valve thinner?
   
   It involves a simple mechanical principle: high sliding friction and low rolling friction. The stem of the linear valve moves up and down, and the packing is slightly compressed, which will wrap the stem very tightly, resulting in a large return difference. For this reason, the valve stem is designed to be very small, and the packing is often used with a small coefficient of friction PTFE packing to reduce the backlash, but the problem is that the valve stem is small, it is easy to bend, and the packing life is also short. To solve this problem, the best way is to use the stem of the travel valve, that is, the quarter-stroke type of control valve, its stem is 2~3 times thicker than the straight-stroke valve stem, and the graphite packing with long life is selected, the stem stiffness is good, the packing life is long, and the friction torque is small and the return difference is small.
   
6. Why is the shut-off pressure difference of quarter-turn valves larger?
   
   The shut-off pressure difference of quarter-turn valves is large because the resultant force generated by the medium on the spool or valve plate on the rotating shaft is very small, so it can withstand a large pressure difference.
   
7. Why do demineralized water media use rubber-lined butterfly valves and fluorine-lined diaphragm valves with short service life?
   
   Demineralized water media contain low concentrations of acids or alkalis, which are highly corrosive to rubber. The corrosion of rubber is manifested as expansion, aging, and low strength, and the butterfly valve and diaphragm valve with rubber lining are poorly used, which is essentially caused by the lack of corrosion resistance of rubber. The back-lined diaphragm valve is improved to a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve cannot withstand folding up and down and is broken, resulting in mechanical damage and shortening the life of the valve.     Now the best way is a special ball valve for water treatment, which can be used for 5~8 years.
   
8. Why should the shut-off valve be hard sealed as much as possible?
   
   The shut-off valve requires the lower the leakage, the better, the leakage of the soft seal valve is the lowest, and the shut-off effect is of course good, but it is not wear-resistant and has poor reliability. From the double standard of small leakage and reliable sealing, soft seal cutting is not as good as hard seal cutting. For example, the full-function ultra-light control valve, sealed and stacked with wear-resistant alloy protection, high reliability, leakage rate of 10-7, has been able to meet the requirements of the shut-off valve.
   
9. Why did the sleeve valve replace the single and double seat valves but not get the wish?
   
   The sleeve valve that came out in the 60s, was widely used at home and abroad in the 70s, and the sleeve valve accounted for a large proportion of the petrochemical plant introduced in the 80s. Today, this is not the case, and single-seat valves, double-seat valves, and sleeve valves are all used equally. This is because the sleeve valve only improves the throttling form, stability and maintenance is better than the single-seat valve, but it is consistent with the single-seat and double-seat valves in terms of weight, anti-blocking and leakage indicators, how can it replace the single-seat and double-seat valves? Therefore, it can only be used together.
   
10. Why is selection more important than calculation?
    
    Calculation is much more important and complex than sizing. Because the calculation is just a simple formula calculation, it itself does not depend on the accuracy of the formula, but on the accuracy of the given process parameters. There is a lot of content involved in the selection, and if you are not careful, it will lead to improper selection, which will not only cause a waste of manpower, material and financial resources, but also use efficiencyIf the result is not ideal, it will bring several use problems, such as reliability, life, operation quality, etc.
    
11. Why is the piston actuator used more and more in pneumatic valves?
    

    For pneumatic valves, the piston actuator can make full use of the air supply pressure, making the actuator smaller in size and thrust than the diaphragm type, and the O-ring in the piston is also more reliable than the diaphragm, so it will be used more and more.