制冷设备中使用的膨胀装置主要基于两种设计:毛细管或节流孔。毛细管通常用于家用电器，不需要对系统进行复杂的控制。然而，在大型制冷设备中，制冷剂质量流量和压力水平必须保持在可接受的工作极限内。为了实现这些控制，已经开发了许多阀门配置。这些阀门的操作基于锋利的- 边缘孔，其喉部区域可以改变，以控制工厂的运行引用:ASHRAE交易，第79卷，第1部分，伊利诺伊州芝加哥

Expansion devices employed in refrigeration plants are based on two main designs: the capillary tube, or the orifice. The capillary tube is usually used in domestic appliances, where sophisticated control of the system is not required. However, in large refrigeration plants both the refrigerant mass flow rate and pressure levels have to be maintained to within acceptable working limits. Numerous valve configurations have been developed to accomplish these controls. The operation of these valves is based on a sharp-edged orifice whose throat area can be varied to control the operation of the plant