Four commonly used valves are introduced.

1, gate valve

Also known as gate valve or gate, gate valve movement direction is perpendicular to the direction of the fluid, gate valve can only be fully opened and full, can not be adjusted and throttling. According to the close cover configuration, it can be divided into wedge-shaped gate valve and parallel gate valve, and the wedge type gate valve can be divided into single gate type, double sluice plate type and elastic gate type, and parallel gate type gate valve can be divided into single sluice plate type and double sluice type plate type. According to the screw thread position of the stem, it can be divided into two kinds: the open gate valve and the hidden pole gate valve. Classification of gate valves: manual gate valves, pneumatic gate valves, and electric gate valves.

Gate valve advantages: small fluid resistance, sealing surface of the medium scour and erosion small; open and close more labor-saving; medium flow is not restricted, no flow, no pressure; simple shape, short structure length, good manufacturing technology, wide range of application. Gate valve shortcomings: easy to cause erosion and abrasion between the sealing surface, the maintenance is more difficult; the shape size is larger, the opening needs a certain space, the opening and closing time is long; the structure is more complex; the seat slot is easily deposited solid material and is not strictly shut. Therefore, it is not suitable for pipelines containing fibers or solids. Commonly used in air, steam, oil medium pipeline, also used as vent valve and low vacuum system valve.

Gate valve is one of the commonly used cut-off valves, mainly used to connect or cut off the medium in the pipeline, and is not suitable for regulating the medium flow rate. Gate valves are suitable for pressure, temperature and caliber range, especially for medium and large diameter pipes.

The installation and maintenance of gate valves should be paid attention to:

(1) handwheel, handle and transmission mechanism are not allowed to be used for lifting, and no collision is strictly prohibited.

(2) double gate valve should be installed vertically (that is, the valve stem is in a vertical position and the handwheel is at the top).

(3) gate valve with bypass valve should be opened before bypass to balance the pressure difference between inlet and outlet and reduce opening force.

(4) gate valves with transmission mechanisms shall be installed according to the requirements of the product manual.

(5) if the valve is frequently switched on, lubricate at least once a month.

2, ball valve

Ball valve, standard GB/T21465-2008 "valve terminology" is defined as: opening and closing parts (spheres) driven by the stem, and revolving around the stem axis of the valve. It is mainly used to truncate or connect the medium in the pipeline, and can also be used to regulate and control the fluid. The hard sealed V ball valve has a strong shear force between the V core and the metal valve seat of the hardfacing hard alloy. It is especially suitable for the medium containing the fiber and the tiny solid material. The multi - ball valve can not only flexibly control the switching of the flow, shunt and flow of the medium, but also close any channel and connect the other two channels. Valves of this type should be installed horizontally in pipes. Classification of ball valves: pneumatic ball valves, electric ball valves and manual ball valves.

The main features of the ball valve are compact structure, reliable seal, simple structure, convenient maintenance, closed seal surface and spherical surface, not easy to be eroded by medium, easy to operate and maintenance, suitable for water, solvent, acid, natural gas and other general working medium, and also suitable for poor working conditions, such as oxygen. Hydrogen peroxide, methane and ethylene have been widely applied in various industries. The ball valve body can be integral or modular.

Advantage：

1. the fluid resistance is small, and the full diameter ball valve basically has no flow resistance.

The 2. is simple in structure, small in size and light in weight.

3. is closely dependable. It has two sealing surfaces, and the sealing materials of ball valves are widely used in various kinds of plastics. The sealing performance is good and can be completely sealed. It has also been widely used in the vacuum system.

4. easy operation, quick opening and closing, and full turn to full clearance as long as 90 degrees of rotation to facilitate remote control.

5. maintenance is convenient, the ball valve structure is simple, the seal ring is generally active, dismantling and replacement are more convenient.

6. when fully open or fully closed, the sealing surface of the ball and valve seat is separated from the medium. When the medium is passed, the sealing surface of the valve will not be eroded.

7. it has wide application range, small to several millimeters, large to several meters, and can be applied from high vacuum to high pressure.

8. because the ball valve is wiped in the process of opening and closing, it can be used in the medium with suspended solids.

Ball valves are classified according to function:

1. Bypass valve: the ball valve is normally opened for static water, so the bypass valve is first pressed, that is, both sides are filled with water.

2, the air valve: when filling the water, remove the air and use the float to shut the valve by itself; when draining, replenish the air, the buoy will fall down on its own.

3. Pressure relief valve: when opening and closing the valve, remove the pressure water between the valve and the sealing cover so as not to wear the sealing cap tightly.

4. Drain valve: drain the sewage from the lower part of the shell.

The ball valve with transmission mechanism can be divided into: (1) pneumatic ball valve; (2) electric ball valve; (3) hydraulic ball valve; (4) pneumatic and liquid ball valve; (5) electro-hydraulic ball valve; (6) turbine drive ball valve.

3, butterfly valve

Butterfly valve, also known as disc valve, opens and close the disc as a disc and can rotate around the valve body axis. It is mainly composed of valve body, stem, disc and sealing ring. The valve body is cylindrical, with short axial length and built-in disc. The disc is driven by the stem. If it turns 90 degrees, it will be able to complete the opening and closing. Changing the deflection angle of the disc can control the flow of the medium. The main seal is the sealing ring. Its materials are two kinds of butterfly valves, butterfly valves and butterfly valves, which are commonly used according to the purpose and medium. The pinch butterfly valve is connected with a double head bolt.