Honeywell VP525C, Engineering Manual, Page: 150 / 228

Relays and Switches
142 customer.honeywell.com 70-6925
Figure 38 shows the lockout relay used as a repeater. This
application provides circuit isolation by repeating the pilot signal
with a second air source.
Fig. 38. Lockout Relay as Repeater.
High-Pressure Selector Relay
The high-pressure selector relay is a three-port relay that
transmits the higher of two input signals to the output branch.
The high sensitivity of the relay allows it to be used in sensor
lines with an accuracy of 2 to 3 degrees F.
The application shown in Figure 39 uses pressures from two
zones and a high-pressure selector relay to determine control.
A separate thermostat controls each zone damper. The
thermostat that calls for the most cooling (highest branchline
pressure) controls the cooling valve through the high-pressure
selector relay.
Fig. 39. Typical Application for
High-Pressure Selector Relay.
Low-Pressure Selector Relay
The low-pressure selector relay is a three-port relay that selects
the lower of two input pressure signals and acts as a repeater
for the lower of the two inputs. The relay requires an external
restrictor on the input to the branch port. Figure 40 shows a low-
pressure selector relay controlling the heating coil valve from
the thermostat that calls for the most heat.
Fig. 40. Typical Application for
Low-Pressure Selector Relay.
Load Analyzer Relay
The load analyzer relay is a bleed-type, diaphragm-logic
pressure selector. The relay selects the highest and lowest
branch pressure from multiple inputs to operate final control
elements (Fig. 41). The relay contains multiple diaphragms and
control nozzles. Each input pressure connects to two
diaphragms.
Fig. 41. Load Analyzer Relay in
Multizone Air Unit Application.
In Figure 41, the load analyzer relay selects the lowest pressure
signal from the thermostat in the coldest zone and transmits
that signal to a normally open heating valve. The relay transmits
the highest pressure signal from the thermostat in the warmest
zone to a normally closed cooling valve.
LOCKOUT
RELAY
P1
B
P2 M
M
THERMOSTAT
C2355
TO
ACTUATOR
OUTPUT
EXH
RESTRICTOR
RESTRICTOR
N.C. ZONE
DAMPER
2-7 PSI
DAMPER
ACTUATOR
HIGH-PRESSURE
SELECTOR RELAY
P1
P2
B
DA ZONE
THERMOSTAT
N.C. ZONE
DAMPER
2-7 PSI
DAMPER
ACTUATOR
8-12 PSI N.C.
COOLING COIL
VALVE
M
DA ZONE
THERMOSTAT
M B
C2363
M
M B
N.O. ZONE
DAMPER
8-12 PSI
DAMPER
ACTUATOR
LOW-PRESSURE
SELECTOR RELAY
P1
P2
B
N.O. ZONE
DAMPER
8-12 PSI DAMPER
ACTUATOR
RESTRICTOR
DA ZONE
THERMOSTAT
M B
2-7 PSI N.O.
HEATING COILVALVE
M
DA ZONE
THERMOSTAT
M B
C2364
EXH
M
N.O. ZONE
DAMPER
8-12 PSI
DAMPER
ACTUATOR
LOW-PRESSURE
SELECTOR RELAY
P1
P2
B
N.O. ZONE
DAMPER
8-12 PSI DAMPER
ACTUATOR
RESTRICTOR
DA ZONE
THERMOSTAT
M B
2-7 PSI N.O.
HEATING COILVALVE
M
DA ZONE
THERMOSTAT
M B
C2364
EXH
M