The opening and closing part of knife gate valve is wedge. The movement direction of the wedge is perpendicular to the fluid direction. Knife gate valve can only be fully opened and closed, can’t be adjusted or throttled. Next, let's learn about the common malfunctions and solutions of knife gate valve in the application process with Dervos! 1. Leakage of Closing Parts of Knife Gate Valve (1) Reasons of Leakage ① The sealing surface of knife gate valve is not well ground; ② The sealing ring is not tightly matched with the valve seat and disc; ③ Valve disc and valve rod are not firmly connected; ④ The valve rod is bent and twisted to make the upper and lower closing parts misaligned; ⑤ Closing too fast, resulting in poor contact or damage of sealing surface; ⑥ Improper material selection makes the valve unable to withstand medium corrosion; ⑦ Some media gradually cool down after the valve is closed, resulting in fine cracks on the sealing surface and erosion; ⑧ The valve can’t be closed tightly due to the embedding of welding slag, rust, dust and other impurities, or the valve core is blocked due to the falling off of mechanical parts in the production system. (2) Solutions ① Conduct pressure test carefully before use. If leakage is found on the sealing surface or the root of the sealing ring, handle it before use； ② Check whether all parts of the valve are in good condition in advance. Do not use the valve with bent valve rod or the valve disc is not firmly connected with the valve rod; ③ The valve should be closed firmly without strong force. In case of poor contact or obstruction between sealing surfaces, it should be opened a little immediately to let sundries flow out, then closed tightly; ④ When selecting the valve, we should consider the corrosion resistance of the valve body and closing parts; ⑤ It should be used correctly according to the structural characteristics of the valve; ⑥ In case of medium cooling and large temperature difference after valve closing, close the valve after cooling; ⑦ A filter should be added to the valve that may enter impurities. 2. Filler Leakage of Knife Gate Valve (1) Reasons of Leakage ① The filler does not adapt to the corrosion, temperature and pressure of the working medium; ② The filling method is wrong. In particular, the whole filler is placed in a spiral, which is most likely to cause leakage; ③ The machining accuracy or surface finish of the valve rod is not enough, there are ellipses or nicks; ④ The valve rod has pitted or rusted due to open air; ⑤ The valve stem is bent; ⑥ The filler has been used too long and aged; ⑦ Operation is too fierce. (2) Solutions ① Proper filler selection; ② Correct method of filling; ③ If the processing of valve rod is unqualified, repair or replace it; ④ Protective measures should be taken to prevent corrosion; ⑤ The bent valve rod should be straightened or renewed; ⑥ The filler should be replaced after a certain period of use; ⑦ Pay attention to stable operation. Open a...

Ball valve is a new type of valve widely used in recent years.Three-way ball valve is a relatively new type of ball valve. It has unique advantages in its own structure. It is widely used in petroleum, chemical industry, urban water supply and drainage and other working conditions requiring cut-off, diversion and confluence. Features of Three-way Ball Valve: 1. Integrated structure, less flange connection and high reliability; 2. Long service life and large circulation capacity; 3. According to the structural form, the three-way ball valve can be divided into L-type, T-type and Y-type. Different structural forms are selected according to different working conditions. Advantages of Three-way Ball Valve: 1. Low fluid resistance. Its resistance coefficient is equal to the pipe section with the same length; 2. Simple structure, small volume and light weight; 3. Tight and reliable, good sealing performance. It has been widely used in vacuum system; 4. Easy operation and quick opening and closing.It only needs to rotate 90° from full open to full close. It facilitates remote control; 5. Convenient maintenance. The sealing ring is generally movable, which is convenient for disassembly and replacement; 6. When the valve is fully open or closed, the sealing surface of the ball and valve seat is isolated from the medium. When the medium passes through, the valve sealing surface won’t be eroded. 7. Wide range of application. The diameter of three-way ball valve is as small as a few millimeters and as large as a few meters. It can be used in high vacuum and high pressure environments. Precautions for Maintenance of Three-way Ball Valve: 1. The valve handle rotation position should be reserved; 2. It can’t be used as throttling; 3. Ball valve with transmission mechanism should be installed vertically.

Forged steel gate valve is a gate valve forged with metal steel materials. Forged steel gate valves are widely used. They are mainly used for cutting off in pipelines. They can only be fully opened and fully closed, can’t be used for regulation and throttling. Design Form of Forged Steel Gate Valve Bonnet: (1) Bolted bonnet. According to this design form, the valve body and bonnet are connected with bolts and nuts and sealed with spiral wound gaskets (316 clamp flexible graphite manufacturing). Metal ring connection can also be adopted for customers' special requirements; (2) Welded bonnet. According to this design form, the valve body and bonnet are connected by thread and sealed by full welding. Full penetration connection can also be adopted for customers' special requirements; (3) Pressure self-tightening bonnet. According to this design form, the valve body and bonnet are connected by thread and sealed by internal pressure self-sealing ring. Structural Features of Forged Steel Gate Valves: (1) Low fluid resistance; (2) Small size, light weight; (3) Good sealing performance, widely used in vacuum system; (4) Simple structure, easy disassembly and replacement. Precautions for Forged Steel Gate Valve: (1) Pay attention to the pressure and temperature of forged steel gate valve; (2) Pay attention to the switch position of forged steel gate valve; (3) Pay attention to the blowdown and blockage of forged steel gate valve body; (4) Pay attention to the diameter of forged steel gate valve is flush with the seal ring seat.

1、Classification of Stainless Steel Gate Valves: 2、Advantages of Stainless Steel Gate Valve: 1. It has low fluid resistance, the sealing surface is little scoured and eroded by the medium; 2. Opening and closing is labor-saving; 3. The flow direction of media is unrestricted; 4. Good manufacturing technology, reliable sealing performance, corrosion resistance and wide application range. 3、Disadvantages of Stainless Steel Gate Valve: 1. It is easy to cause erosion and scratch between sealing surfaces； 2. The overall dimension is large, so it needs a certain space for opening, the opening and closing time is long； 3. Complex structure. 4、Precautions for Installation of Stainless Steel Gate Valve: 1. It is generally installed horizontally in the pipeline; 2. Hand wheel, handle and transmission mechanism are not allowed to be used for lifting, and collision is strictly prohibited; 3. The bypass valve should be opened before the gate valve with bypass valve is opened (To balance the pressure difference between the inlet and outlet and reduce the opening force); 4. The gate valve with transmission mechanism should be installed according to the provisions of the product operation manual; 5. If the valve is opened and closed frequently, lubricate it at least once a month.

Butterfly valves are divided into concentric butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve and three eccentric butterfly valve. What are the main differences between these four butterfly valves? Now, Dervos will introduce to you: 1. Concentric Butterfly Valve (Midline Butterfly Valve) The structural feature of the concentric butterfly valve is that the valve stem axis, the center of the butterfly plate and the center of the body are in the same position. It has the advantages of simple structure and convenient manufacture. The disadvantage is that the butterfly plate and valve seat are always in the state of extrusion and scratch, with large resistance distance and fast wear. In order to overcome extrusion and scratch and ensure sealing performance, the valve seat basically adopts elastic materials such as rubber or polytetrafluoroethylene, but the use of sealing materials is limited by temperature. 2. Single Eccentric Butterfly Valve The structural feature of the single eccentric butterfly valve is that the axis of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the rotation axis, which disperses and reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat, and solves the extrusion problem between the butterfly plate and the valve seat of the concentric butterfly valve. However, the scratch phenomenon between the butterfly plate and the valve seat has not disappeared in the whole opening and closing process of the valve. Therefore, the application range of single eccentric butterfly valve is similar to concentric butterfly valve, and there are few applications. 3. Double Eccentric Butterfly Valve The double eccentric butterfly valve is further improved on the basis of the single eccentric butterfly valve. Its structural feature is that the axis of the valve rod deviates from the center of the butterfly plate and the center of the body. The effect of double eccentricity enables the butterfly plate to leave the valve seat immediately after the valve is opened, which greatly eliminates the unnecessary excessive extrusion and scratch between the butterfly plate and the valve seat, reduces the opening resistance and wear, improves the service life of the valve seat. The scratch is greatly reduced, so that the double eccentric butterfly valve can adopt metal seat, which improves the application of butterfly valve in high temperature field. However, the sealing effect is produced by the elastic deformation caused by the extrusion of butterfly plate and valve seat. It has high requirements for the closing position (especially the metal valve seat), low pressure bearing capacity and large leakage. 4. Three Eccentric Butterfly Valve To withstand high temperature, hard seal must be used, but the leakage is large; to achieve zero leakage, soft seal must be used, but it is not resista...

Plug valve is one of the earliest used valves with simple structure, fast opening and closing and low fluid resistance. Ordinary plug valves are sealed by the direct contact between the finished metal plug body and the valve body, which has the disadvantages of poor sealing, large opening and closing force and easy wear. They can only be used in low (not higher than 1 MPa) and small diameter (less than 100 mm). In order to expand the application range of plug valve, many new structures have been developed. Oil seal plug valve is the most important one. Special grease is injected from the top of the plug body between the taper hole of the valve body and the plug body to form an oil film to reduce the opening and closing torque and improve the sealing performance and service life. Its working pressure can reach 64 MPa, the maximum working temperature can reach 325℃, and the maximum diameter can reach 600 mm. The closing part of the plug valve is a cylinder with holes, which rotates around the axis perpendicular to the channel, so as to open and close the channel. Advantages of plug valve: 1. Easy for frequent operation, quick opening and closing; 2. Low fluid resistance; 3. Simple structure, relatively small volume, light weight and easy maintenance; 4. Good sealing performance; 5. The installation direction is unrestricted, the flow direction of media can be arbitrary; 6. No vibration and low noise. Classification of plug valves: 1. By structure: tight set plug valve, self-sealing plug valve, pressure balance plug valve and oil seal plug valve; 2. By channel: straight plug valve, three-way plug valve and four-way plug valve. The channel of plug valve has many forms. The common straight through type is mainly used to cut off the fluid; Three-way and four-way plug valve are suitable for fluid reversing.