Dampers - Honeywell AUTOMATIC CONTROL SI Edition 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
LINE
INLET
FLOW
INLET FLOW
MIXING VALVE, NORMALLY CLOSED TO
STRAIGHT-THROUGH FLOW
BRANCH
LINE
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.
OUTLET
FLOW
C2612
F1
F2
OUTLET
FLOW
F1
F2
OUTLET
FLOW
C2615
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
300 millimeters, depending on the differential close-off rating
of the valve. For other applications high pressure pneumatic
cylinders can be used to provide the force required by the valve.
A pneumatic positioner provides an appropriate high pres-
sure signal to the cylinder based on a 20 to 100 kPa 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.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
76
M10403
OPPOSED
BLADES
C2604