Dampers - Honeywell AUTOMATIC CONTROL Engineering Manual

PNEUMATIC CONTROL FUNDAMENTALS
BRANCH
F1
LINE
F2
INLET
F3
FLOW
NORMALLY OPEN VALVE
Fig. 29. Double-Seated Valve.
Figure 30 shows three-way globe valve assemblies. The
mixing valve has two inlets and a common outlet. The diverting
valve has a common inlet and two outlets.
BRANCH
F1
LINE
F2
INLET
FLOW
INLET FLOW
MIXING VALVE, NORMALLY CLOSED TO
STRAIGHT-THROUGH FLOW
BRANCH
F1
LINE
F2
INLET
FLOW
OUTLET FLOW
DIVERTING VALVE, NORMALLY OPEN TO
STRAIGHT-THROUGH FLOW
Fig. 30. Three-Way Valve Assemblies.
Three-way valves may be piped to be normally open or
normally closed to the heating or cooling load. If a three-way
valve has linear characteristics and the pressure differentials
are equal, constant total flow is maintained through the
common inlet or outlet port.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
OUTLET
FLOW
C2612
OUTLET
FLOW
OUTLET
FLOW
C2615
76
Two- and three-way butterfly valves can be operated by long
stroke pneumatic actuators and appropriate linkage (Fig. 31).
One or two low pressure actuators powered directly by
branchline pressure can operate butterfly valves up to about
12 inches, depending on the differential close-off rating of the
valve. For other applications high pressure pneumatic cylin-
ders can be used to provide the force required by the valve. A
pneumatic positioner provides an appropriate high pressure
signal to the cylinder based on a 3 to 15 psi input signal.
Fig. 31. Butterfly Valve Assembly.
For a more detailed discussion of valves, see the Valve
Selection And Sizing section.

DAMPERS

Dampers control the flow of air in air-handling systems. The
most common type of damper, a multiblade louver damper,
can have parallel or opposed blades (Fig. 32).
PARALLEL
BLADES
Fig. 32. Parallel- and Opposed-Blade Dampers.
M10403
OPPOSED
BLADES
C2604