What are gate valves?
Gate valves are gates with opening and closing parts. The movement direction of gate is perpendicular to the direction of fluid. Gate valve can only be fully opened and closed, and can not be adjusted and throttled. Gate valves are sealed by contact between the valve seat and gate plate. Metal materials are usually overlaid on the sealing surface to increase wear resistance, such as 1Cr13, STL6, stainless steel, etc. There are rigid gate and elastic gate. According to the difference of gate, gate valves are divided into rigid gate and elastic gate.
|Characteristics of gate valves||Cautions for Gate Valve Use|
|The working principle of gate valve||Moving mode of gate valve|
|Types of gate valve||Applications of gate valve|
|Advantages and disadvantages||Gate Valve Installation|
The body is made of high-grade ductile iron, and its weight is reduced by 20%~30% compared with the traditional gate valve. It is easy to install and maintain.
Flat-bottomed brake pedestal
Traditional gate valves often accumulate in the groove of the bottom of the valve due to the deposit of foreign materials such as stone, wood, cement, iron chips and sundries after water washing. It is easy to cause water leakage because they can not close closely. The flat bottom design of the elastic seat gate valve is the same as that of the water pipe machine. It is not easy to cause the accumulation of sundries and make the fluid smooth and unimpeded.
High-quality rubber is used for internal and external rubber. The rubber vulcanization technology in Europe ensures the precise geometric size of the vulcanized gate, and the rubber and nodular graphite cast gate are then reliable, not easy to fall off and have good elastic memory.
Precision casting valve body
Precision casting is used for the valve body. The precise geometric dimension ensures the sealing of the valve without any finishing.
- Handwheels, handles and transmission mechanisms are not allowed to be lifted and collisions are strictly prohibited.
- Double gate valves should be installed vertically (i.e. the stem is in the vertical position and the handwheel is at the top).
- Gate valves with bypass valves should be opened before opening (in order to balance the pressure difference between inlet and outlet and reduce the opening force).
- Gate valves with belt drive mechanism shall be installed according to the specifications of the product.
- Lubricate the valve at least once a month if it is frequently switched on and off.
- Gate valves are only used for medium operation on all kinds of pipelines or equipment, and are not allowed to be used for throttling.
- No additional auxiliary bars shall be added to the gate valve with handwheel or handle during operation (if the seal is not tight, the sealing surface or other parts shall be inspected and repaired). The handwheel and handle rotate clockwise to close, otherwise open. Gate valves of belt drive mechanism shall be used in accordance with the specifications of the product.
The opening and closing part of the gate valve is the gate. The movement direction of the gate is perpendicular to the direction of the fluid. The gate valve can only be fully opened and closed, and can not be used for regulation and throttling. The gate has two sealing surfaces. Its sealing form is wedge-shaped and wedge-shaped angle varies with the parameters of the gate valve. Usually it is 5 degrees. The wedge-shaped gate can be made into a whole, called rigid gate. It is generally hard-sealed gate valve. This type of gate valve has many extensions, such as stainless steel gate valve, knife gate valve, pneumatic gate valve, electric gate valve and so on. Below is a brief introduction to the structure and principle of these gate valves, more gate valve specifications and model parameters, please check the inside page. Gate valve dynamic diagram
Stainless steel gate valve open stem and concealed stem introduction:
The gate plate of stainless steel gate valve moves in a straight line with the stem. This type of gate valve is also called open bar gate valve. Usually there are trapezoidal threads on the lifting rod. Through the nut at the top of the gate valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is to say, the operating torque is changed into the operating thrust. When the stainless steel gate valve is used in practice, it is marked by the vertex of the stem, i.e. the position where it does not move, as its full open position. In order to consider the lock phenomenon of temperature change, it is usual to turn back 1/2-1 turn at the top position as the position of the fully opened gate valve. Some gate valves, stem nuts set on the gate plate, hand wheel rotation to drive the rotation of the valve stem, and make the gate lift, this kind of gate valve is called concealed stem gate valve.
The working principle of pneumatic gate valve:
Pneumatic gate valve is driven by compressed air and driven by cylinder. When the gate valve closes, the sealing surface can be sealed only by medium pressure. Pneumatic gate valve is forced to seal. When the gate valve closes, the gate must be forced to the seat by external force to ensure the sealing surface. Pneumatic gate valves can be divided into pneumatic knife gate valves, pneumatic open bar gate valves, pneumatic stainless steel gate valves and so on. Selection is based on open selection, but most of the series of pneumatic gate valves can only be used for truncation, starting and closing.
Principle and characteristics of electric gate valve:
Electric gate valve works by the electric actuator to control the gate valve to do lifting motion, thus realizing the function of automatic switching and opening and closing. The electric gate valve has the characteristics of adjustable switching speed, simple structure, sensitive response, safety, reliability and easy maintenance. It is an ideal switching valve in pipeline. The valve seat adopts hard sealing form and can be used as throttle valve in various high temperature and high pressure situations such as steam and heat conducting oil. Taichen brand electric gate valves can also be divided into electric knife gate valves, electric stainless steel gate valves, electric high temperature and high pressure gate valves and other products according to their structure.
When the gate valve closes, the sealing surface can be sealed only by medium pressure, that is, only by medium.
Pressure will pressure the sealing surface of the gate to the seat on the other side to ensure the sealing of the sealing surface, which is self-sealing. Most gate valves are forced to seal, that is, when the valve closes, the gate must be forced to the seat by external force to ensure the sealing surface.
Motion mode: The gate of the gate valve moves in a straight line with the stem, also known as the open bar gate valve. Usually there are trapezoidal threads on the lifting rod. Through the nut at the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is to say, the operating torque is changed into the operating thrust. When opening the valve, when the gate lifting height is equal to 1:1 times the valve diameter, the flow passage is completely open, but in operation, this position can not be monitored. In practical use, the vertex of the valve stem is used as the sign, that is, the position of the valve stem that is not moving is used as its full open position. In order to consider the locking phenomenon of temperature change, the valve is usually opened to the vertex position and reversed to 1/2-1 turn as the position of the fully open valve. Therefore, the full open position of the valve is determined by the position of the gate (i.e. stroke). Some gate valve stem nuts are set on the gate plate. Handwheel rotation drives the stem to rotate, which lifts the gate plate. This kind of valve is called rotary stem gate valve or dark stem gate valve.
There are many manufacturers of gate valves in China, and the connection dimensions are not uniform. Mainly divided into the following categories:
- Machinery Department standard valves produced according to JB/T 203-1999 “Structural Length of Gate Valves”;
- National standard valves manufactured according to GB/T 12221-2005 “Structural Length of Metal Valves”;
- American standard valves manufactured according to ASME B16.10-2009 “Face-to-Face and End-to-Face Size of Valves“.
- Gate valves are divided into wedge type and parallel type according to the structure of gate plate. Wedge gate has three structures: single gate, double gate and elastic gate.
- Gate valves can be divided into flat gate valves and knife gate valves according to different structural types.
- The working principle of manual gate valve: turning the handwheel, lifting or dropping the valve plate connected with the stem through the threads of the handwheel and the stem to open and close.
According to the classification of shell/main body materials, gate valves can be divided into:
- Metal material valves: such as carbon steel valves, alloy steel valves, stainless steel valves, cast iron valves, titanium alloy valves, Monel valves, copper alloy valves, lead alloy valves, etc.
- Metal body lined valves: such as rubber-lined valves, fluorine-lined valves, lead-lined valves, plastic-lined valves, enamel-lined valves.
- Non-metallic material valves: such as ceramic valves, glass valves, plastic valves.
1. Electric gate valve:
The electric gate valve is composed of electric actuator and tine gate valve. The work is driven by electric power, and the electric actuator drives the valve stem to do lifting motion. Electric actuator has torque control mechanism, field operation mechanism and hand, electric switching mechanism. In addition to local operation, it can also carry out remote operation, PLC control, intelligent control of 4 ~ 20mA current input and output, etc. The diamond gate valve disc adopts the universal top structure with double gate plates in the middle, which can automatically adjust the coincidence between the disc and the sealing surface of the valve seat to ensure the sealing of the valve. At the same time, the structure is easy to maintain, cost-saving and disc interchangeability is good. The electric gate valve is a common electric switch valve in remote automation system.
Brief Introduction of Electric Knife Gate Valve:
Electric knife gate valve is also known as electric knife gate valve, electric slurry valve and electric slurry valve. Its opening and closing parts are gates. The movement direction of the gate is perpendicular to the fluid direction. The medium can be cut off by the knife-edge gate which can cut the fibre material, but it can only be fully opened and closed, and can not be adjusted and throttled. The knife gate valve is made into two forms of hidden rod and open rod according to different structures. The gate of electric knife gate valve has shearing function. It can scrape the adhesion on the sealing surface and automatically remove debris. The stainless steel gate can prevent seal leakage caused by corrosion. It is widely used in coal preparation, gangue discharge, slag discharge, pulp, sewage, coal slurry, ash, slag-water mixture medium as shutoff valve.
2. Pneumatic gate valve:
Pneumatic gate valve is composed of pneumatic piston actuator, gate valve, accessories and other parts. It works with compressed air as driving force, and uses cylinder to drive valve stem to do lifting motion, so as to realize the switch control of pipeline medium. When the pneumatic gate valve is forced to seal, that is, when the gate valve closes, it must rely on external force to force the gate to the seat to ensure the sealing surface. Pneumatic gate valve can be divided into pneumatic stainless steel gate valve, pneumatic flange gate valve, pneumatic knife gate valve, etc. The pneumatic gate valve has the advantages of small fluid resistance, compact structure, high temperature resistance and long service life. Widely used in petroleum, chemical, metallurgical, steel and other industries as on-off valves.
Pneumatic knife gate valve uses:
The opening and closing parts of pneumatic knife gate valve are gates. The moving direction of the gate is perpendicular to the direction of fluid. It works with the knife gate valve driven by compressed air. The valve can only be fully opened and closed, and can not be adjusted and throttled. Pneumatic knife gate valve has the advantages of simple and compact structure, reasonable design, light material saving, reliable sealing, convenient and flexible operation, small volume, smooth passage, small flow resistance, light weight, easy installation, easy disassembly and so on. It can be used in various serious wear and tear switching occasions such as powder, sludge and coal sludge. Pneumatic knife gate valve has shearing function. It can scrape the adhesion on the sealing surface and automatically remove debris. Stainless steel gate can prevent seal leakage caused by corrosion.
Gate valves are designed for fully open or fully closed operation. They are installed in pipelines as isolating valves, and should not be used as control or regulating valves. The operation of a gate valve is either turning the handle clockwise to close or to open. Gate valves are used with almost all fluid such as air, fuel gas, feedwater, steam, lube oil, hydrocarbon. Some special gate valves are used in slurry and powder products too, such as knife gate valve.
Advantages of gate valve
- Small flow resistance. The medium passage inside the valve body is straight through, the medium flows in a straight line, and the flow resistance is small.
- It is more labor-saving when opening and closing. Compared with globe valves, gate motion is perpendicular to the direction of medium flow, whether open or closed.
- High altitude, long opening and closing time. The opening and closing journey of the gate is large, and the lifting is carried out by screw.
- Water hammer is not easy to occur. The reason is the long closure time.
- The medium can flow in any direction on both sides and is easy to install. Both sides of gate valve passage are symmetrical.
- The length of the structure (the distance between the two connecting ends of the mooring shell) is small.
- Simple in shape, short in length, good in manufacturing technology and wide in application.
- Compact structure, good rigidity of valve, smooth passage, small flow resistance, stainless steel and cemented carbide sealing surface, long service life, PTFE packing, reliable sealing, easy and flexible operation.
Disadvantages of gate valve
- It cannot be used to control the flow.
- A gate valve is slow in operation. Opening and closing take times which is good as it reduces the chance of hammering.
- When partially open, it creates vibration and noise.
- Repairs, such as lapping and grinding of seats are more difficult due to limited access.
- 1) Installation location, height, import and export direction must meet the design requirements, the connection should be firm and tight.
- 2) All kinds of manual valves installed on the insulation pipeline shall not have downward handles.
- 3) Appearance inspection must be carried out before the valve is installed. The nameplate of the valve should conform to the current national standard “General Valve Mark” GB 12220. For valves with working pressure greater than 1.0 MPa and cutting off effect on main pipe, strength and tightness performance tests should be carried out before installation. Qualified valves are allowed to be used. In the strength test, the test pressure is 1.5 times of the nominal pressure, and the duration is not less than 5 minutes. The valve shell and packing should be qualified without leakage. The test pressure is 1.1 times of the nominal pressure in the tightness test, and the test pressure should meet the requirements of GB 50243 standard for the duration of the test, with no leakage on the valve sealing surface as the qualification.
- 4) Handwheel, handle and transmission mechanism are not allowed to be hoisted and collision is strictly prohibited.
- 5) Gate valves with belt drive mechanism shall be installed according to the specifications of the product.
Source: China Gate Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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