A gate valve is a commonly used valve called a knife gate valve. It has a simple structure and is mainly composed of the valve body, cover, stem, plate and sealing device. The gate valve is characterized by a small opening and closing torque, good sealing performance, low flow resistance and long service life.
The gate valve controls the flow of the medium through the lifting and lowering of the valve plate. When the valve plate is raised, the medium flows smoothly; when the valve plate is lowered, the valve plate is closely fitted to the valve seat to stop the flow of the medium.
The working principle of the gate valve:
The working principle of the gate valve is to control the flow of the medium through the lifting and lowering of the valve plate.
When the gate valve is closed, the valve plate is completely lowered and fits closely to the valve seat, forming a good seal and stopping the flow of the medium.
When the gate valve needs to be opened, turn the handwheel or operating handle to lift the stem upwards by means of a screw. The stem drives the valve plate upwards and gradually separates from the valve seat, thus opening the passage, and the medium starts to flow.
When the gate valve needs to be closed, the stem is lowered downwards by rotating the handwheel or operating handle. The valve stem drives the valve plate downwards and presses against the valve seat, stopping the flow of the medium.
The gate valve’s opening and closing process is relatively slow because the contact area between the valve plate and the valve seat is large, and a larger force is required to move the plate. However, due to the large contact area between the valve plate and the valve seat, the gate valve has a better sealing performance and can withstand higher pressures.
Gate valve construction:
It is generally composed of valve body, valve seat, valve stem, gate plate, valve cover, and sealing ring. It can be transformed into a variety of electric gate valves and pneumatic gate valves by equipping the transmission device and gate valve.
The difference between rising stem gate valve and dark stem gate valve：
The open stem gate valve is different from the dark stem gate valve in terms of transmission mode. The open stem gate valve is driven by the handwheel to rotate the nut in situ, and the valve stem rises and falls in a straight line to complete the switch; for the dark stem gate valve, the handwheel drives the valve stem to rotate. The thread (equivalent to a nut) moves up and down to complete the switch.
#1 The open rod gate valve can see the lead screw, but the dark rod can not see the lead screw;
#2 The open stem gate valve lifts or lowers the valve disc through the threaded transmission of the valve stem and the steering wheel; the dark stem gate valve is connected with the steering wheel and the valve stem when it is switched on and off, and it is rotated by the valve stem at a fixed point. Drive the valve disc to lift up and down to complete the opening and closing;
#3 The transmission thread of the dark stem gate valve is located inside the valve body. During the opening and closing process, the valve stem only rotates, and the gate moves up and down in the valve body; the stem of the open stem gate valve drives the gate to rise and fall together, and the The drive thread is outside the valve body, and the opening and closing and position of the gate can be visually judged according to the movement direction and position of the valve stem.
Gate valves have the following characteristics:
1. Simple structure:
The gate valve has a relatively simple structure, consisting of a few parts, and is relatively easy to install and maintain.
2. Good sealing performance:
The gate valve adopts the metal-to-metal sealing method between the valve plate and the valve seat, with good sealing performance, which can effectively prevent the leakage of the medium.
3. Small flow resistance:
Gate valve channel diameter and pipe diameter is basically the same. Small flow resistance will not have a significant impact on the flow rate of the medium.
4. Small opening and closing torque:
As the valve plate of the gate valve and the valve seat are sealed with a flat surface, the friction in the opening and closing process is small, so the opening and closing torque is relatively small.
5. Long service life:
Because of the simple structure of the gate valve, good sealing performance, and small friction in the process of opening and closing, the service life is long.
6. Wide range of applications:
Gate valves are suitable for a variety of media, including liquids, gases, etc., and can withstand high pressure and temperature.
Gate valves can be classified according to different classifications;
The following are some of the common classifications:
1. Classified by the shape of the valve plate:
– Flat plate gate valve: the valve plate is flat in shape, suitable for the flow requirements of larger occasions.
– Wedge gate valve: both sides of the valve plate have a beveled angle, which can reduce the impact when opening and closing and is suitable for the high-speed flow of media. 2.
2. Classified by transmission mode:
– Manual gate valve: through the hand wheel, handle, and other manual operations to open and close.
– Electric gate valve: through the motor drive to open and close, can achieve remote control.
– Pneumatic gate valve: through the pneumatic device to open and close, suitable for the need for fast opening and closing occasions.
3. Classified by working pressure:
-Low-pressuree gate valve: applicable to the working pressure is low, generally below 0.6MPa.
– Medium pressure gate valve: suitable for working pressure between 0.6MPa and 6.4MPa.
-High-pressuree gate valves: for applications with higher working pressures, generally above 6.4MPa.
The choice of main materials for gate valves depends on the nature of the medium, working conditions, and requirements.
The following are common gate valve main materials:
1. Cast iron:
Cast iron gate valves are suitable for general industrial applications and have good mechanical properties and corrosion resistance.
2. Carbon steel:
Carbon steel gate valves are suitable for higher working temperatures and have good resistance to high temperatures and corrosion.
3. Stainless steel:
Stainless steel gate valve is suitable for corrosive media with high requirements, such as chemical, food, pharmaceutical, and other industries.
4. Copper alloy:
Copper alloy gate valves are suitable for occasions with high requirements for seawater and acidic media, such as marine engineering, etc.
5. Nickel-based alloy:
Nickel-based alloy gate valve is suitable for high temperature, high pressure, corrosive media, and other special working conditions of the occasion, such as oil refining, chemical industry, and other industries.
6. Titanium alloy:
Titanium alloy gate valve is suitable for occasions with extremely high requirements for corrosive media, such as marine engineering, the chemical industry, etc.
7. Polytetrafluoroethylene (PTFE):
PTFE gate valve is suitable for high-temperature, corrosive media with high requirements for occasions, such as chemical, pharmaceutical, and other industries.
Gate valves are widely used in various industrial fields, including the following:
1. Petrochemical industry:
Gate valves are commonly used in oil, natural gas, chemical and other industries on the transmission pipeline, used to control the opening and closing of the fluid and regulation.
2. Electric power industry:
Gate valves are used in the water supply system of electric power stations, circulating water systems, etc., used to control the opening and closing of water flow and regulation.
3. Metallurgical industry:
Gate valves are commonly used in metallurgical industry on high temperature and high pressure media pipelines, such as steel making, iron making and other process fluid control.
4. Sewage treatment industry:
Gate valves can be used on the inlet and outlet pipelines of sewage treatment plants to control the flow and treatment of sewage.
5. Urban water supply and drainage system:
Gate valves are commonly used in urban water supply and drainage system on the pipeline, used to control the flow of water opening and closing and regulation.
6. Air conditioning and heating systems:
Gate valves can be used on pipes in air conditioning and heating systems to control the flow of hot and cold media.