Chapter 3 - Control Valves and Dampers

Abstract

This chapter explains how control valves and control dampers devices work and how they are selected and sized. Control valves and control dampers are the two primary means to control the flow of water and air in heating, ventilation, and air conditioning (HVAC) systems. The control valve is possibly the most important component of a fluid distribution system because it regulates the flow of fluid to the process under control. In HVAC systems, control valves are primarily used to control the flow of chilled water, hot water, and condenser water, the subject of this section. Control of other fluids including steam, refrigerants, gasses, and oil are similar in many aspects but are not specifically addressed here because they have specific requirements for design including issues of safety and material compatibility. Control valves can be either two-way which act as a variable resistance to flow or three-way. With the two-way configuration, flow through the circulation system is variable. In the three-way configurations, flow remains relatively constant through the loop, which includes the pump and varies in the loop containing the coil. Dampers are to air as valves are to water: a means of controlling airflow. Many of the design and selection principles are the same for both. Like valves, dampers must be carefully selected and sized to ensure stable and accurate control.