Considerations for Selecting Common Valves

Gate Valves, Ball Valves, and Globe Valves: These valves are generally not recommended for regulation purposes due to their structural characteristics. However, they are commonly used for regulation in industrial design. Since the sealing elements of these valves are continuously subjected to throttling, impurities in the oil can erode the seals, causing leakage or improper closure. Furthermore, operators may force the valve to close when the sealing surface is damaged, resulting in over-opening or over-closing issues.

Improper Valve Installation: When using media containing impurities, the lack of a filter or mesh in front of the valve allows contaminants to enter the valve, leading to seal damage or sediment accumulation at the bottom of the valve, causing poor sealing and leakage.

Considerations from a Process Perspective:

Corrosive Media: For media that are corrosive but have low temperature and pressure, non-metallic valves should be preferred. For higher temperatures and pressures, lined valves are a better option to save on expensive metals. When selecting non-metallic valves, economic feasibility should also be taken into account. For viscous media, valves with low flow resistance, such as direct-flow globe valves, gate valves, ball valves, or plug valves, should be selected to reduce energy consumption.

Special Media: When handling media like oxygen or ammonia, specialized valves for oxygen or ammonia should be used.

Bidirectional Flow Lines: Valves with directional restrictions should not be used for pipelines with bidirectional flow. For example, in refinery pipelines where heavy oil may solidify, a steam blow-back process is needed to clean the pipeline. In this case, globe valves are unsuitable, as backflow can erode the globe valve’s sealing surface, affecting performance. A gate valve is a better choice for this application.

Crystallizing or Precipitating Media: For media that crystallize or contain precipitates, globe and gate valves should be avoided due to the risk of damage to their sealing surfaces. Ball or plug valves are more suitable in these conditions, and flat gate valves or jacketed valves are also options.

Gate Valve Selection: For gate valves, rising stem single gate valves and non-rising stem double gate valves are more suitable for corrosive media. Single gate valves are better for viscous media. Wedge-type double gate valves offer better resistance to high temperatures and prevent deformation of the sealing surface compared to wedge-type single gate valves. They are more resilient to temperature-induced sticking problems, especially compared to rigid single gate valves.

Material Selection for Water and Steam Pipelines: For water and steam pipelines, cast iron valves are commonly used. However, in outdoor steam pipelines, condensation may freeze during steam shutdown, damaging the valves. In cold climates, valves should be made from cast steel, low-temperature steel, or be adequately insulated.

Hazardous Media: For highly toxic or harmful media, valves with bellows seals should be used to prevent leakage from the packing.

Common Valve Types: Gate valves, globe valves, and ball valves are the most commonly used types. Selection should be made based on comprehensive considerations:

Gate Valves: They have good flow capacity and low energy consumption for the conveyed medium but require more installation space.

Globe Valves: They have a simple structure and are easy to maintain but cause more flow resistance.

Ball Valves: These offer low flow resistance and quick operation, but their temperature limitations must be considered. In pipelines conveying petroleum products or highly viscous media, gate valves are often preferred due to their superior flow capacity. Globe valves are widely used in water and steam pipelines because of their low pressure drop. Ball valves can be used when conditions permit, offering flexibility.

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