UniControl Cleveland Controls AFS-951 User manual

Cleveland Controls
Division of UniControl Inc.
Model
AFS–951
DESCRIPTION & OPERATION
The Cleveland ControlsAFS-951 Differ-
entialPressureSensing Switchis designed
to provide precise operation and convenient
features for industrial and commercial air
handling applications. The AFS-951 can
monitor positive, negative, or differential
pressure (ow) of air and noncombustible
gases. It is commonly used to monitor
combustion air, furnace pressure, ventilat-
ing blower operation, inatable structure
pressure, fume hood operation, bag house
air ow, dirt accumulation in air lters, and
heat-transfer air ow. The AFS-951 has a
eld–adjustable set point range of 0.05"wc
to 12.0"wc.
COMMON APPLICATIONS
The most common specic application for
the AFS-951 is as a Low Draft (Negative
Pressure) Cutoff Safety Switch for com-
bustion draft control systems.
The general applications of the AFS-951
are:
• Low Positive Pressure Cutoff. (Shut-
down upon insufcient pressure.)
• Low Negative Pressure Cutoff. (Shut-
down upon insufcient draft.)
• Low Differential Pressure Cutoff.
(Shutdown upon insufficient difference
between two samples.)
MOUNTING
The AFS-951 is available in 3 enclosures
designed for surface mounting on any at,
relatively stable surface free of vibration.
To obtain the lowest operating set point
specication, the control must be mounted
with the diaphragm vertical (Fig 1).
The standard enclosure has mounting ang-
es with four 9/32" mounting holes as shown
on page 4. The NEMA-4 rated model has
mounting anges with four 5/16" mounting
holes as shown on page 3. The NEMA-7/
NEMA-9 rated enclosure has two mounting
slots as shown on page 3.
AFS-951-1 in NEMA-4 rated
Enclosure.
AFS-951 in St andard E nclosure,
rated NEMA-1.
AFS-951-2 in NEMA-7 and NEMA-9
rated Enclosure.
Adjustable Set Point Air Pressure Sensing Switch

PIPING
The eld sample line connectors, two 1/4"
- 18 NPT female ttings, labeled H (high)
and L (low), are located on the side of the
enclosure as shown in Figure 1.
For sample lines up to 10 ft., use ¼" OD
tubing or 1/8" pipe.
For sample lines up to 20 ft., use ¼" ID
tubing or 1/4" pipe.
For sample lines up to 60 ft., use ½" ID
tubing or 1/2" pipe.
For sample lines up to 90 ft., use 3/4" ID
tubing or 3/4" pipe.
For sample lines up to 120 ft., use 1"
ID tubing or 1" pipe.For each right angle
bend, add four feet to the computed line
length in order to determine correct pipe or
tubing size.
If either sample line connector is vented
to the atmosphere, attach an elbow to it so
that the open end of the connector points
downward. This will help protect the switch
from contamination.
SAMPLE LINE CONNECTIONS
Positive Pressure only:
Connect sample line to H;
Lremains open to the atmosphere.
Negative Pressure only:
Connect sample line to L:
Hremains open to the atmosphere.
Two Negative Samples:
Connect higher negative sample to L:
Connect lower negative sample to H.
Two Positive Samples:
Connect higher positive sample to H:
Connect lower positive sample to L.
One Negative and One Positive Sample:
Connect positive sample line to H:
Connect negative sample line to L.
ELECTRICAL CONNECTIONS
Three (3) terminals are provided for eld
wiring. Before pressure is applied to the
diaphragm, the switch contacts will be in
the normally closed position as shown in
Figure 2.
To Prove Excessive Air Flow or Pres-
sure:
Connect Terminal 1 to a hot line, Terminal 2
to an alarm circuit (if desired), and Terminal
3 to the control circuit.
To Prove Insufcient Air Flow or Pres-
sure:
Connect Terminal 1 to a hot line, Terminal
2 to the control circuit, and Terminal 3 to an
alarm circuit (if desired).
NOTE: When the switch is wired in this
manner, an alarm circuit will be ener-
gized at start up, and will stay energized
until the set point of the air switch is
satised. To avoid nuisance alarm, a time
delay, equal to the amount of time required
for pressure to activate the air switch, should
be wired in series between Terminal 3 and
the alarm device.
FIELD ADJUSTMENTS
Field adjustments to the operating set point
are made by removing the protective plug
button on the side of the control enclosure
and inserting a standard blade-type screw-
driver, at least 3 inches long*.
The adjustment range is 0.05 ± .02" w.c.
to 12.0" w.c. To adjust the set point, turn
the adjusting screw counterclockwise until
motion has stopped. Next, turn the adjust-
ing screw 4 complete turns in a clockwise
direction to engage the spring.
For the next 10 turns, each full turn
represents approximately 1.2" w.c. At
higher operating pressures, there is a slight
increase in the switching differential. Please
note: To properly calibrate an air pressure
sensing switch, a digital manometer or other
measuring device should be used to conrm
the actual set point.
SPECIFICATIONS
MODELS AFS-951,
AFS-951-1 & AFS-951-2
AIR PRESSURE SENSING
SWITCHES
ELECTRICAL RATING:
300 VA pilot duty at 277 v AC
260 VA pilot duty at 240 v AC
130 VA pilot duty at 120 v AC
15 amp noninductive to 277 vAC.
CONDUIT OPENING:
7/8" diameter opening accepts 1/2"
conduit tting.
ELECTRICAL SWITCH:
Contact Arrangement: SPDT NC.
Single pole, double throw snap-ac-
tion switch. Contacts in a normally
closed position before pressure is
applied.
CONTROL SET POINT / ADJUST-
ABLE OPERATING RANGE:
Field-adjustable, 0.05 ±0.02 to
12.0" w.c.;
(1.3 to 305 mm w.c.; 0 to 0.43 psi)
SWITCH DIFFERENTIAL:
0.02 ± 0.01" w.c. at minimum set
point, to approximately 0.8" w.c.
at maximum set point (0.5 ±.25
mm to approximately 20.3 mm).
MAXIMUM PRESSURE:
1/2 PSI (0.03 bar)
ELECTRICAL CONNECTIONS:
Numbered terminal panel
RECOMMENDED OPERATING
POSITION:
Mount with the diaphragm vertical
to obtain the lowest operating set
point.
OPERATING TEMPERATURE
RANGE:
- 40 TO 180F (- 40 to 82C)
SAMPLE LINE CONNECTORS:
Two 1/4"—18 NPT female t-
tings.
APPROVALS:
UL listed, CE and CSA approved.
*STANDARD ENCLOSURE ONLY.
FIGURE 2: ELECTRICAL CONNECTIONS
PRESSURE CONVERSION
TABLE
1"wc = 0.0361psi
or 0.0736"Hg
1"Hg = 0.491psi
or 13.6" wc
1psi = 27.7"wc
or 2.036"Hg
FIGURE 1

Model AFS-951-1:
14-gauge grey hammertone enameled steel with neoprene gasketed clamped cover hinged on the left side. NEMA 4 rated: provides
protection from dust, dirt, oil, and water.
Shipping Weight: 8 lbs.
Model AFS-951-2:
Cast aluminum alloy, nonmagnetic, non-sparking, and non-rusting. NEMA 7 and NEMA 9 rated. UL approved for Class 1, Group D;
Class II, Groups E, F, G.
Piping: Either pressure inlet, if not connected to a pressure sample, must be piped and vented to a nonhazardous area.
Shipping Weight: 18 lbs.
ENCLOSURE SPECIFICATIONS & DIMENSIONS

Model AFS-951 in Standard NEMA-1 rated housing:
• Flat black epoxy powder coated steel nish.
• Shipping Weight: 5 lbs.
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