阀门的结构和采用材料多种多样。为了确保效率最高，成本最合理，系统使用寿命最长，阀门的正确选型非常重要。
　　Valves are produced in a variety of design types and materials. Proper selection is important to ensure the most efficient, cost effective and long lasting system.

• 启动 / 阻止流体流动
  Starting / Stopping the flow
• 防止流体倒流
  Preventing reversal of the flow

• 调节(平衡)流体
  Regulating (balancing) the flow
• 释放流体压力
  Relieving the pressure of the flow

• 一件式结构没有潜在泄漏的通道，但是要求采用缩径端口的球体；因此，具有明显的压降。
  One-piece has no potential body leak path, but requires use of reduced port ball; thus, significant pressure drop.
• 两件式结构是建筑领域最常采用的形式。具有最好的性价比。也可以提供不缩径，全流道或标准流道的球体。
  Two-piece end entry is most common in building services. Best price value. Available full- or standard-port balls.
• 三件式结构成本最高，但是易于拆卸，并进行在线维修。可提供全流道或普通流道的球体。
  Three-piece is more costly, but is easier to disassemble and offers in-line repairability. Available in full- or standard-port balls.

• 不缩径，全流道球阀提供的压降安全取决于管道的长度，甚至比闸阀还要好一些。
  Full-Port ball valves provide pressure drop equal to equivalent length of pipe, and even slightly better than gate valves.
• 标准(普通)流道球阀的流道直径小于管道的公称通径，但是与截止阀相比，仍然具有好的多的流动效率。
  Standard (conventional) port balls are up to one pipe size smaller than nominal pipe size, but still have significantly better flow than globe valves.
• 缩径流道球阀与单管流量相比，具有更大的限制，建议不要用于建筑领域管道，但可以用在危险材料的传输系统中。
  Reduced port ball valves have more than one pipe size flow restriction and are not recommended in building services piping, but rather for process piping in hazardous material transfer.

应用所应考虑的事项：
Service Considerations:

1. 压力
   Pressure
2. 温度
   Temperature
3. 流体介质类型
   Type of fluid
   • 液体
     Liquid
   • 气体；即蒸汽或空气
     Gas; i.e., steam or air
   • 肮脏或研磨(侵蚀)性流体介质
     Dirty or abrasive (erosive)
   • 腐蚀性流体介质
     Corrosive
4. 流体
   Flow
   • 开启-关闭或节流
     On-off or throttling
   • 需要防止回流
     Need to prevent back-flow
   • 关心压降
     Concern for pressure drop
   • 流速
     Velocity
5. 操作条件
   Operating Conditions
   • 冷凝
     Condensation
   • 工作频率
     Frequency of operation
   • 可接近性
     Accessibility
   • 可用的通径 / 空间
     Size / Space available
   • 手动或自动控制
     Manual or Automated control
   • 需要无气泡关闭
     Need for bubble tight shutoff