1 CHARACTERISTICS OF VALVES
1.1 Usage
It determines the main performance of the valve and the use of the range of characteristics of the valve are: Valve type (closed-circuit Valves, control valves, safety valves, etc.) ; product type (Gate Valves, Globe Valves, butterfly valves, ball valves, etc.) ; Valve main parts (body, cover, stem, disc, sealing surface) of the material, valve transmission mode.
1.2 Structural Characteristics
It determines some of the structural characteristics of valve installation, repair, maintenance, etc. Structural characteristics include: The structural length and overall height of the valve, and pipe connection form (flange connection, thread connection, clamp connection, external thread connection, welding end connection, etc.) ; Sealing surface form (insert ring, thread ring, build-up welding, spray welding, Valve Body) ; Valve Stem Structure Form (rotating Rod, lifting Rod) and so on.
2 VALVE SELECTION STEPS
2.1 Specify the use of the valve in the equipment or device, determine the working conditions of the valve: applicable medium, working pressure, working temperature and so on.
2.2 Determine the nominal diameter of the pipe connecting the valve and the connecting method: Flange, thread, welding, etc. .
2.3 Determine the way to operate the valve: Manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage and so on.
2.4 According to the medium of pipeline transportation, working pressure and working temperature, the materials of the Shell and inner parts of the selected valve are determined: Gray cast iron, Malleable cast iron, Ductile Iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc. .
2.5 Select the type of Valve: Closed Valve, Control Valve, safety valve, etc. .
2.6 Determine the type of Valve: Gate Valve, Globe Valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc. .
2.7 Determine valve parameters: for automatic valves, according to different needs to first determine the allowable flow resistance, discharge capacity, back pressure, and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole.
2.8 Determine the selected valve geometric parameters: structural length, flange connection form and size, after opening and closing the size of the valve height direction, connecting the size and number of bolt hole, the overall size of the valve shape.
2.9 Use The available information: Valve Product Catalog, valve product sample, etc. to select the appropriate valve product.
3 CHOICE OF VALVE
3.1 The use, operating condition and operating control mode of the valve selected.
3.2 The nature of the working medium: Working Pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is flammable, explosive medium, medium viscosity and so on.
3.3 Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, seal grade, etc. .
3.4 Installation size and outline size requirements: nominal diameter, connection with the pipe and connecting size, outline size or weight restrictions, etc. .
3.5 Additional requirements for reliability, service life of valve products and explosion-proof performance of electric devices.
3.6 According to the above selection of valve basis and steps, reasonable and correct selection of valves must also be a detailed understanding of the internal structure of various types of valves, in order to be able to select the preferred valve to make the right choice.
3.7 The final control of the pipeline is the valve. The opening and closing part of the valve controls the flow pattern of the medium in the pipeline, and the shape of the valve channel makes the valve have certain flow characteristics, which must be taken into account when selecting the most suitable valve for the pipeline system.
4 THE CHOICE OF VALVE SHOULD FOLLOW THE PRICIPLES
4.1 Valves For Cut-Off And Open Media
The flow channel for the straight-through Valve, its flow resistance is small, usually chooses as the cut-off and the open medium uses the valve. Downward closed Valve (Globe Valve, plunger valve) because of its winding flow channel, flow resistance higher than other valves, so less choice. In allowing a higher flow resistance of the occasion, you can choose to close the valve.
4.2 Valves For Flow Control
Usually choose easy to adjust the flow of the valve as a control flow. A downward closing 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, butterfly, ball) and flex body valves (pinch, diaphragm) can also be used for throttling control, but usually only in a limited valve size range. Gate Valve is a disc-shaped gate to a circular valve seat for cross-cutting movement, it only close to the closed position, it can better control the flow, it is usually not used for flow control.
4.3 Valves For Reverse Shunting
The valve may have three or more channels, depending on the need for reverse shunting. Plug and ball valves are more suitable for this purpose, therefore, the majority of the valve used in reverse flow are selected in one of these valves. In some cases, however, other types of valves may also be used as reverse shunts, provided that two or more valves are properly connected to each other.
4.4 Valves For Media With Suspended Particles
When the medium with suspended particles, the most suitable for its closure parts along the sealing surface of the sliding with the role of wiping the valve. If the closure moves vertically back and forth against the seat, particles may be trapped, so the valve is intended for only moderately clean media unless the sealing surface material permits embedding of particles. Ball Valve and plug valve in the opening and closing process of the sealing surface have the role of wiping, it is suitable for use in the medium with suspended particles.
At present, whether in the petroleum, chemical industry, or in other industries pipeline system, valve application, operating frequency and service ever-changing, to control or eliminate even the slightest leakage, the most important, the most critical equipment is also the valve. The final control of the pipeline is the valve, the valve in each field of service and reliable performance is unique.
Post time: Jul-28-2021