1, valve characteristics

1.1 features:

It determines the main performance of the valve and the scope of use, belong to the valve use characteristics: valve type (closed valve, regulating valve, safety valve, etc.);Type of products (gate valve, globe valve, butterfly valve, ball valve, etc.);Material of main parts of valve (body, cover, stem, disc, sealing surface);Valve transmission, etc.

1.2 structural characteristics:

It determines the valve installation, repair, maintenance and other methods of some structural characteristics, structural characteristics are: the structural length and overall height of the valve, and the pipeline connection form (flange connection, thread connection, clamp connection, thread connection, welding end connection, etc.);Sealing surface form (insert ring, thread ring, surfacing welding, spray welding, valve body body);Valve stem structure (rotary rod, lifting rod), etc.

2、Valve selection procedure

①Specify the purpose of the valve in the equipment or device, determine the working conditions of the valve: applicable medium, working pressure, working temperature and so on.

②Determine nominal size and connection of pipe to valve: flange, thread, weld, etc.

③Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical or electro-hydraulic linkage.

④According to the pipeline transmission medium, working pressure, working temperature to determine the selected valve shell and internal parts of the material: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid steel, copper alloy.

⑤Select valve type: closed circuit valve, regulating valve, safety valve, etc.

⑥Type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.

⑦Determine the parameters of the valve: for the automatic valve, according to different needs to determine the allowable flow resistance, discharge capacity, back pressure, and then determine the nominal size of the pipe and the diameter of the seat hole.

⑧Determine the geometric parameters of the selected valve: length of structure, flange connection form and size, size of valve height after opening and closing, size and number of connecting bolt holes, size of the entire valve shape, etc.

⑨Use available data: valve product catalog, valve product samples and so on to select the appropriate valve products.

3、Valve selection

(1) the use of the selected valve, operating conditions and control mode.
(2) the nature of the working medium: working pressure, working temperature, corrosion performance, whether there are solid particles, whether the medium is toxic, whether it is flammable, explosive medium, the viscosity of the medium and so on.
(3)Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, seal grade and so on.
(4) installation size and shape size requirements: nominal size, and pipe connection and connection size, shape size or weight restrictions.
(5) additional requirements on the reliability, service life of valve products and the explosion-proof performance of electric devices.

According to the above selection of valve basis and steps, reasonable, correct selection of the valve must also be a variety of types of valves for detailed understanding of the internal structure, in order to give priority to the selection of the valve to make the right choice.The ultimate control of the pipe is the valve.The opening and closing parts of the valve control the flow pattern of the medium in the pipeline. The shape of the valve runner enables the valve to have certain flow characteristics, which must be taken into account when selecting the most suitable valve for installation in the pipeline system.

4.Valve selection should follow the principle

4.1 Valves for cut-off and open media

The flow path for the straight valve, its flow resistance is small, usually choose as cut-off and open medium valve.Downward closed valve (globe valve, plunger valve) due to its tortuous flow path, flow resistance than other valves, so less choice.Closed valves are available where high flow resistance is permitted.

4.2 A valve for controlling flow

Valves that are easy to regulate flow are usually chosen for flow control.A downward-closed valve (such as a globe valve) is suitable for this purpose because its seat size is proportional to the stroke of the closing member.Rotary valves (plug valves, butterfly valves, ball valves) and flex body valves (clamping valves, diaphragm valves) may also be used for throttling control but are usually limited to a limited valve size range.Gate valve is disc gate to the circular seat mouth do crosscutting movement, it only close to the closed position, to better control the flow, it is not usually used for flow control.

4.3 Reverse shunt valve

These valves may have three or more channels depending on the need for reverse shunt.Plug and ball valves are more suitable for this purpose, so most valves used for reversing shunt are selected for one of these valves.In some cases, however, other types of valves may also be used for commutative shunt as long as two or more valves are properly joined to each other.

4.4 Valves for media with suspended particles

When there are suspended particles in the medium, it is best to use its closing parts along the sealing surface of the sliding valve with the role of wiping.Particles may be trapped if the shutoff member moves vertically back and forth against the seat, so the valve is only suitable for basic clean media unless sealing material permits the insertion of particles.Ball valve and plug valve can wipe the sealing surface in the opening and closing process, so it is suitable to be used in medium with suspended particles.

At present, whether in oil, chemical, or other industries in the pipeline system, valve applications, operating frequency and service of the ever-changing, to control or put an end to even the small leakage, the most important, the most critical equipment is also a number of valves.The ultimate control of the pipeline is the valve, which is unique in all areas of service and reliability.