Capacity Relay; Reversing Relay; Positive-Positioning Relay; Averaging Relay - Honeywell Pneumatic Controls Engineering Manual

Capacity Relay

The capacity relay is a direct-acting relay that isolates an input
and repeats the input pressure with a higher capacity output.
Figure 42 shows a capacity relay enabling a single bleed type
thermostat to operate multiple damper actuators quickly by
increasing the output capacity of the thermostat.
BLEED-TYPE
THERMOSTAT
DAMPER
ACTUATOR
M
M
Fig. 42. Typical Capacity Relay Application.

Reversing Relay

The reversing relay is a modulating relay with an output that
decreases at a one-to-one ratio as the input signal increases.
Figure 43 shows a reversing relay application. A falling
temperature at the direct-acting thermostat causes the
branchline pressure to decrease. The reversing relay branch
pressure increases and opens the normally closed heating
valve.
DA ROOM
THERMOSTAT
M B
M
M
Fig. 43. Reversing Relay Application.
P E EXH
M B
CAPACITY
DAMPER
RELAY
ACTUATOR
DAMPER
ACTUATOR
C2365
M B
E
P
EXH
REVERSING
RELAY
N.C. HEATING
VALVE
C2354

Positive-Positioning Relay

The positive-positioning relay (Fig. 44) mounts directly on a
valve or damper actuator. The relay positions the valve or
damper precisely according to the branchline pressure from a
thermostat or other controller, regardless of the load variations
affecting the valve stem or damper shaft. The relay is typically
used for large actuators for sequencing, or in applications
requiring precise control.
ROOM
THERMOSTAT
M B
P
POSITIVE-
POSITIONING
M
M
RELAY
B
DAMPER
FEEDBACK
ACTUATOR
SPRING
DAMPER
Fig. 44. Positive-Positioning Relay
with Damper and Valve Actuators.
When the relay is connected to an actuator, the feedback spring
produces a force proportional to the actual valve or damper
position. The relay positions the actuator in proportion to the
branchline input. If the connected load attempts to unbalance
the required valve stem position, the relay either exhausts or
applies main pressure to the actuator to correct the condition. If
the valve or damper sticks or the load prevents proper
positioning, the relay can apply the pressure required (up to full
main pressure) or down to zero to correct the condition.
The positive-positioning relay also permits sequenced
operation of multiple control valves or dampers from a single
thermostat or controller. For example, a normally open heating
valve and a normally closed outdoor air damper could be
controlled from a single thermostat piloting relays on two
actuators. Relays typically have a 3, 5, or 10 psi input pressure
span and an adjustable start pressure. As the space
temperature rises into the low end of the thermostat throttling
range, the heating valve positioner starts to close the valve.
Near the midpoint of the throttling range, the heating valve
closes completely and the outdoor damper positioner starts to
open the damper. At the high end of the throttling range, the
damper is completely open.

Averaging Relay

The averaging relay is a direct-acting, three-port relay used in
applications that require the average of two input pressures to
supply a controller input or to operate a controlled device
directly.
70-6925
Relays and Switches
ROOM
THERMOSTAT
M B
P
POSITIVE-
POSITIONING
M
M
RELAY
B
INTERNAL
VALVE
FEEDBACK
ACTUATOR
SPRING
VALVE
C2366
143