THREE-WAY VALVES MIXING VALVE DIVERTING VALVE NC C NC C NO NO Three-way valves are usually available as mixing or diverting. Mixing valves have two inputs and one output. Diverting valves have one input and two outputs. Usually there is a flow through the common port of three-way valves; however, rarely one type of three-way valve allows flow from the common port and only through either the normally open port or the normally closed port and sometimes no flow at all through the valve. The direction of flow must be correct. The spring ranges can vary from valve to valve creating different throttling ranges. The effective throttling range on valves can be adjusted if a pilot positioner (positive positioning relay) is installed on the valve. FACE & BYPASS AND WING COIL DAMPER ARRANGEMENTS ACTUATOR ACTUATOR WING FACE & COIL BYPASS DAMPER COIL DAMPER COIL BYPASS Wing coil and face & bypass damper arrangements are often used when the upstream air temperatures may fall below the freezing point The control circuit should allow the heating coil full flow before exposing the coil to air flow via the dampers. The wing coil damper arrangement allows the sections of the heating coil to be completely enclosed when no heat is required. Most often the heating coil has full flow when the outside air is below freezing. Proper safety circuits normally are installed on these systems. TWO-WAY VALVES NO NC Two-way valves are either normally open (NO) or normally closed (NC). The spring ranges can vary from valve to valve creating different throttling ranges. The effective throttling range on valves can be adjusted if a pilot positioner (positive positioning relay) is installed on the valve. The direction of flow must be correct. AUTOMATIC DAMPERS OPPOSED BLADE PARALLEL BLADE Automatic dampers are used to isolate the building systems when fans are off and blend fresh air with building return air when the fans are running. Opposed blade dampers achieve more linear flow respecting percentage open to percentage of maximum air flow than parallel blade dampers. Parallel blade dampers, if installed properly, tend to achieve better mixing of fresh air and return air than opposed blade dampers. 2.17
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