The Importance of Valves in Industry.

The Importance of Valves in industry

In fluid piping systems, valves are control components. Their main functions are to isolate equipment and piping systems, regulate flow, prevent backflow, and regulate and discharge pressure. Since choosing the most suitable valve for the piping system is crucial, understanding valve characteristics, the steps for selecting valves, and the basis for making the right choice becomes essential.

As of now, the valve industry can produce a wide variety of valves, including gate valves, globe valves, throttling valves, plug valves, ball valves, electric valves, diaphragm valves, check valves, safety valves, pressure relief valves, steam traps, and emergency shut-off valves, among over 3,000 models and 4,000 specifications. The highest working pressure can reach 600 MPa, the largest nominal diameter can be 5350 mm, the maximum working temperature is 1200°C, and the minimum working temperature is -196°C. Valves are suitable for a wide range of media, including water, steam, oils, natural gas, highly corrosive media (such as concentrated nitric acid and moderately concentrated sulfuric acid), flammable media (such as benzene, ethylene), toxic media (such as hydrogen sulfide), explosive media, and radioactive media (such as sodium metal and pure water in nuclear loops). The materials used for valve pressure-bearing parts include cast copper, cast iron, ductile cast iron, high-silicon cast iron, cast steel, forged steel, high and low alloy steels, stainless steel, Hastelloy, Inconel, Monel, duplex stainless steel, titanium alloy, and others. Additionally, electric, pneumatic, and hydraulic valve actuators are available.

With such a wide variety of valve types and the complex working conditions, selecting the most suitable valve for the piping system is essential. To make the right choice, it is important to first understand the characteristics of valves, followed by mastering the steps and criteria for valve selection, and then adhering to the principles for valve selection.

1. Characteristics of Valves

There are two main types of valve characteristics: functional characteristics and structural characteristics.

Functional Characteristics: These determine the main performance and application range of the valve. Functional characteristics include:

• Valve type (e.g., shut-off valve, control valve, safety valve)
• Valve product types (e.g., gate valve, globe valve, butterfly valve, ball valve)
• Materials used for key valve components (e.g., valve body, valve cover, valve stem, valve disc, sealing surfaces)
• Valve actuation method (manual, electric, pneumatic, hydraulic, etc.)

Structural Characteristics: These define the installation, maintenance, and operational characteristics of the valve. Structural characteristics include:

• Valve structural length and overall height
• Connection types with pipelines (flanged, threaded, clamp, external thread, welded, etc.)
• Sealing surface types (e.g., welded rings, threaded rings, spray welding, valve body)
• Valve stem structure (rotating stem, rising stem)

2. Steps and Criteria for Selecting Valves

(1) Steps for Selecting Valves

1. Clarify the valve’s purpose and working conditions: Determine the medium, working pressure, temperature, and other operational parameters.
2. Determine the nominal diameter and connection method of the pipeline that connects to the valve: flanged, threaded, welded, etc.
3. Determine the method for operating the valve: manual, electric, electromagnetic, pneumatic, hydraulic, electric-hydraulic linkage, etc.
4. Select materials for the valve’s shell and internal parts: Depending on the medium, working pressure, and temperature, select appropriate materials such as cast iron, carbon steel, alloy steel, stainless steel, copper alloys, etc.
5. Choose the valve type: Shut-off valve, control valve, safety valve, etc.
6. Determine the valve’s style: Gate valve, globe valve, ball valve, butterfly valve, throttling valve, safety valve, pressure relief valve, steam trap, etc.
7. Determine the valve’s parameters: For automatic valves, consider factors like allowable flow resistance, discharge capacity, back pressure, nominal diameter, and valve seat hole size.
8. Confirm the valve’s geometric parameters: Structural length, flange connection form and dimensions, valve height when open or closed, dimensions of bolt holes, and overall valve dimensions.
9. Refer to available resources: Use valve product catalogs, product samples, and other references to select the most appropriate valve.

(2) Criteria for Selecting Valves

While mastering the steps for selecting valves, it’s also important to understand the criteria that guide valve selection:

1. Purpose, operating conditions, and control method: What is the valve’s intended purpose, and under what conditions will it operate?
2. Characteristics of the working medium: Pressure, temperature, corrosiveness, presence of solid particles, toxicity, flammability, explosiveness, viscosity, and other properties.
3. Fluid characteristics for the valve: Flow resistance, discharge capacity, flow rate characteristics, sealing performance, and other specific fluid needs.
4. Installation and external dimensions: Nominal diameter, connection type, and connection dimensions, as well as any space or weight limitations.
5. Reliability and service life of the valve: Also consider special requirements for explosion-proof electric actuators, etc.

(When determining parameters, additional factors to consider for control purposes include the operating method, maximum and minimum flow rate requirements, normal flow pressure drop, shutoff pressure drop, and maximum and minimum inlet pressure.)

By following these criteria and steps, and understanding the internal structures of various types of valves, you can make an informed decision when choosing the most suitable valve for your piping system.