There are many types of valves used in water treatment, such as: gate valves, globe valves, butterfly valves, check valves, plug valves, valves, safety valves, and pressure reducing valves.

1. Gate Valve

Usages:

This is the most commonly used on-off valve, which uses a gate (i.e., the opening and closing member, referred to as a or door in a gate valve, and the valve seat is referred to as a gate seat or door seat) to connect (fully open) and shut off ( closed) the medium in the pipeline. It is not allowed to be used as a throttle, and during use, it should avoid partially opening the gate because the of high-speed flowing media can accelerate the damage to the sealing surface. The gate moves up and down in a plane perpendicular to the centerline of the gate seat, like a door, to shut off the medium in the pipeline, hence it is called a gate valve.

Features:

1. Low fluid resistance. The internal medium passage of the valve body is straight, the medium flows in a straight line, and fluid resistance is small.
2. Less force required for opening and closing. Compared with globe valves, gate valves require less force to open and close because the gate perpendicular to the direction of the medium flow, whether opening or closing.
3. High height and long opening and closing time. The gate has a large travel distance and the lifting is done through a screw.
4. Water hammer is unlikely to occur. This is due to the long closing time.
5. The medium can in any direction on both sides, making it easy to install. The passages on both sides of the gate valve are symmetrical.
6. Short structural length (the between the two connection ends of the shell).
7. The sealing surface is prone to wear, affecting the service life. During opening and closing, the gate and valve seat's two sealing surfaces rub against each other, and under the action of medium pressure, they are prone to wear, affecting the sealing performance and shortening service life.
8. High price. There are many contact sealing surfaces, the processing is complex, especially the sealing surface on the gate seat is difficult to process and there are many parts.

2. Globe Valve

Usages:

The globe valve is a type of closed circuit valve that controls the opening and closing of pipelines by moving the valve disc (the closing element the globe valve) along the centerline of the valve seat passage. The globe valve is generally suitable for various pressures and temperatures within the specified standard range, for liquid and gas media, but it is not suitable for conveying liquids containing solid precipitates or crystalline substances. In low-pressure pipelines, globe valves can also be to regulate the flow of media in the pipeline. Due to structural limitations, the nominal diameter of globe valves is below 250mm. In pipelines with media pressure and higher flow velocity, the sealing surface will wear out quickly. Therefore, when flow regulation is required, a throttle valve must be used.

Features:

1. The wear and scratch of the sealing surface are not serious, so the work is more reliable and the service life is long.
2. The sealing surface area is small, the structure is simple, the working hours required to manufacture the sealing surface and the expensive materials required for the sealing ring are than those of the gate valve.
3. The valve disc travel is small when opening and closing, so the height of the globe valve is small. It is to operate.
4. The valve disc is moved by the screw thread, so there is no sudden opening and closing phenomenon, and it is not easy to cause "water hammer" phenomenon.
5. The opening and closing torque is large and it is laborious to open and close. When closing, the movement direction of valve disc is opposite to the direction of the medium movement pressure, so it is necessary to overcome the action force of the medium, thus the opening and closing torque large, which affects the application of large diameter globe valves.
6. The flow resistance is large. Among various shut-off valves, the flow resistance of the globe is the largest (the medium passage is more tortuous).
7. The structure is more complex.
8. The medium flow direction is unidirectional. It ensure that the medium flows from bottom to top.

3. Butterfly Valve

Usages:

A butterfly valve is a rotary valve that uses a disc-shaped (also known as a butterfly plate) closure member to open and close the passage rotating it 90° or approximately 90°. The movement of the butterfly valve's closure member has a wiping action, making most butterfly valves suitable media with suspended solid particles. There are two common types of butterfly valves: wafer type and flanged type. Wafer type butterfly valves are connected between two flanges using double-headed bolts, while flanged type butterfly valves have flanges on the valve itself, and are connected to the pipeline flanges using bolts.

Features:

1. Compact size, short length, simple structure, and light weight.
2. Easy operation, quick opening and closing, only need rotate the valve flap 90°.
3. Good sealing and regulating performance, using rubber as the sealing ring, with good compression and resilience (i., will not harden), so the sealing performance is good. The valve flap can perform sensitive flow control when opened from 15° to 70.
4. Small operating torque and fluid resistance. According to measurements, the fluid resistance of butterfly valves is less than that of other types of valves except ball.
5. Due to the limitations of the sealing material, the operating pressure and working temperature range of butterfly valves are relatively small.

4. Check Valve

Usages and Features:

A check valve, also known as a non-return valve, is a type of valve that prevents the backflow of media in pipelines. opens when the media flows in the forward direction and automatically closes when the media flows in the reverse direction. It is typically used in pipelines where media is not allowed flow in the opposite direction, to prevent damage to equipment and machinery from reverse flow. When a pump stops running, it prevents the rotation of the pump in the direction. In pipelines, check valves are often used in series with shut-off valves. This is because the seal of a check valve is relatively poor, and when media pressure is low, a small amount of media may leak, so a shut-off valve is needed to ensure the pipeline is closed. A foot valve is also type of check valve that must be submerged in water and is specifically installed at the front end of the suction pipe of a pump that cannot self-prime or does have a vacuum suction to draw water.

5. Cock Valve

Usages:

The plug valve refers to a type of valve where the closure member (a plug with a passage) rotates around the centerline of the valve to achieve opening or closing. It is widely used in pipelines conveying media with temperatures ≤120℃. Due to the thermal expansion of the plug and the body, it may cause jamming, so it is less used at high temperatures. The plug valve can be used to cut off the flow of media, and can also be used as a control valve, three-way valve, four-way valve, or distribution valve, as well as to change the direction of the media flow.

Features:

1. The resistance is relatively small when the medium passes through, especially for the straight-through type.
2. Simple structure, light weight, size, convenient and fast operation.
3. When there is considerable pressure of the medium in the pipeline, "water hammer" may occur due to rapid closure.
4. Turning the plug is laborious (large sealing surface).
5. Can be installed horizontally or vertically.
6. The cone surface in contact between the valve body the plug is large, which is prone to wear during use and affects the seal. If a sealed structure is adopted, injecting grease into the sealing surface to form oil film can improve the sealing performance.

6. Throttle Valve

Usages and Features:

The throttle valve regulates the flow and pressure of the pipeline medium by changing the cross-sectional area of the valve passage. The smaller the cross area, the greater the resistance to the medium, and the smaller the flow. In fact, all kinds of shut-off valves can regulate flow, but because the between the closure member and the valve stem is movable, there is a gap at the connection, so during the process of change, the rise and fall of the member is not easily proportional to the change in passage area, resulting in poor regulation performance. Therefore, a special throttle valve is used for regulation. The throttle valve be used as a shut-off valve, generally it does not have a sealing surface, even if it has a sealing surface, the sealing surface is quickly eroded the action of high-speed medium, losing its sealing property. Therefore, the throttle valve on the pipeline cannot replace the function of a shut-off valve.

7. Safety Valve

Usages and Features:

A safety valve is a protective valve. It is installed on pressurized equipment, containers, and pipelines. The safety valve remains closed under conditions. When the pressure of the medium in the protected pipeline exceeds the specified value, the valve disc automatically opens to discharge the excess medium, thereby reducing the; and when the medium pressure returns to within the specified range, it automatically closes. The safety valve ensures the safe operation of the system and equipment on the pipeline Safety valves are widely used on boilers, compressor air receivers, high-pressure containers, and pipelines where the working pressure of the medium may exceed the allowed value and cause hazards.

8. Pressure Reducing Valve

Usages and Features:

The pressure reducing valve reduces the pressure of the medium in the equipment container or pipeline to the specified pressure, and maintains the outlet pressure within a range despite changes in inlet pressure or outlet flow. The pressure reducing valve achieves pressure reduction by regulating the flow, making it suitable for the needs of various production processes.

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.