Robertshaw 84374 Series User manual

1
GENERAL DESCRIPTION
The patented* No. 84374-Series Pressure Sensor contains
a weather-proof, snap-acting valve operated by pressure
variation around the integral sensing element. Depending
upon model used, it vents or blocks a pneumatic signal
when the setpoint is reached and is available with either
automatic or manual reset. The sensor has adjustable
differential (auto reset versions only) and setpoint,
provision for piped vent operation, and is field reversible.
Setpoint is virtually unaffected by control pressure change
or, in the case of piped vent versions, vent backpressure
change. In the auto reset versions, reset differential can be
changed without shifting setpoint.
For correct operation, control pressure must be provided
thru a .81 mm (.032") diameter or smaller orifice.
*Patent 3,986,524
ORDERING INFORMATION
Specify:
1. Model
2. Control Pressure-If not specified, sensor is set using
207 kPa (30 psi).
3. Setpoint-If not specified, set as minimum.
4. Differential (Automatic Reset models only)-If not
specified, set at standard.
5. Tagging Information
84374-A, C Series 84374-B Series
Vents on Increase Closes Vent on Increase
(Direct-Acting) (Reverse-Acting)
J.I.C. Symbols
Sales Manual Section 335
PRODUCT SPECIFICATION 84374 SERIES
Pressure Sensor
No. 84374-Series
Table 1
Suffix Description Reset
A Direct Acting - Vents on Increase Auto
B Reverse Acting - Closes Vent on Increase Auto
C Direct Acting - Vents on Increase Manual
Table 2
Suffix Setpoint Range - kPa (In. H z0)
1 1.7 - 7.0 (7 - 28)
2 3.5-17.5(14-70)
See Page 2 for SPECIFICATIONS
Form No. P-2356, Rev. B
MODELS AVAILABLE
843714-
Table 1 Table 2

2
Process and Reset Pressure Characteristics:
Model No.
Maximum
Process
Pressure, kPa
(psi)
Standard
Reset
Differential
kPa (psi)
Minimum Process
Pressure Drop to
Manually Reset,
kPa (psi)
84374-Al 172 (25) 5 (0.7)
84372-A2 172 (25) 10 (1.5)
84374-B1 172 (25) 5 (0.7)
84374-B2 172 (25) 10 (1.5)
84374-Cl 172 (25) 2 (.3)
84374-C2 172 (25) 4 (.6)
Reset Differential Range: See graph corresponding to
instrument model numbers.
SPECIFICATIONS
Valve Housing, Housing Plate and Cover: .........Anodized
Aluminum Alloy
Spring Housing: ..................................... 316 Stainless Steel
Springs: ......................................................... Stainless Steel
O-Rings: ...................................Fluorocarbon and Neoprene
Diaphragms and Gasket: ........................Buna-N on Nylon
Control Pressure: .................. 138 to 414 kPa (20 to 60 psi)
Maximum Control Pressure: .................... 172 kPa (25 psi)
Maximum Ambient Temperature: ............71° C. (160° F.)
Repeatability: ............................................ ± 1 % of setpoint
Approximate Shipping Weight: ............ 1.4 Kg. (3.16 lbs.)
Control Medium: .............. Air, Natural Gas, Nitrogen, CO2
Filtration (Minimum): ........................................25 microns
Moisture (Pressure Dew Point): .....8° C. (15° F.) less than
ambient temperature.
Oil Content (Natural Base): ...................................... 5 ppm
Oil Content (Synthetic Base): ................................... 0 ppm
NOTE: These are suggested minimums for control
medium quality. For operation under more
adverse conditions, consult factory.
CAUTION: DO NOT EXCEED MAXIMUM
TEMPERATURE/PRESSURE RATINGS.

3
INSTALLATION
Mounting:
The No. 84374-Series Pressure Sensor may be mounted
in any position, although vertical (upright) is
recommended. It should be securely mounted on the panel
using mounting bracket to prevent excessive vibration.
If the measured variable is a liquid, consideration should
be given to the liquid level. An error in calibration could be
caused by the weight of a body of liquid acting on the
measuring assembly. It may be necessary to adjust
calibration to compensate for the constant weight (See
ADJUSTMENTS).
If the sensor is out of doors or in any way exposed to
water, it should be mounted in a position that will prevent
water entry into the valve or spring housings. Water
trapped in the housing will impair operation and could
freeze during winter months. Vent openings should have
fittings installed turned down. The 1/8"-27 NPT vent
connection can be used for piped vent operation if gas is
used.
If the sensor is used with a liquid process pressure,
entrapped air in tubing connected to the measuring
assembly should be vented. This can be accomplished by
bleeding the connection at the sensing element.
DIMENSIONS - Millimeters (Inches)
Connections:
1. The sensor has three 1/8"-27 NPT connections-one for
control pressure, one for vent pressure and one for case
relief pressure. A 1/4"-18 NPT connection is provided for
the process pressure.
CAUTION: Do not pipe or plug case relief
connection. The vent pressure connection from
the sensor cannot be used as a supply or control
source for any other equipment. Vent
backpressure should be held to as low a level as
possible.
Control port pressure must be provided through a .8 mm
(.032") diameter or smaller orifice using 6 mm (1/4") or 9.5
mm (3/8") O.D. tubing. Using excessive lengths or other
than the specified tubing, is not recommended.
Tubing and fittings used to connect the sensor must be
free of chips, dirt, moisture or other foreign matter.
On fittings, it is recommended that a non-hardening,
"anti-seize" type thread compound be applied to the threads
in moderate amount. The first thread should then be wiped
of excess to avoid compound being deposited inside the
relay. Thread sealing tape is not recommended.
Figure 1
Direct Acting Shown

4
OPERATION (See Figure 2)
NOTE: For descriptive purposes the operation of
the direct acting (automatic reset) sensor shown in
Figure 2 will be explained. The operation of the
reverse acting model is the same although reversed.
It vents on a decrease in high process pressure.
As shown, pressure entering the CONTROL port of the
sensor will flow around the stem and sleeve, through the
bellows head, and out the VENT port. The bellows head is
at the limit of its downward travel that is restricted by the
reset/ differential adjustment screw. By limiting the
downward travel of the bellows head, this adjustment screw
defines how low the process pressure must drop before
causing the sensor to reset and stop venting. (See
Adjustments - Differential).
A decrease in the Process Pressure will cause the stem to
travel downward as the force exerted downward on the
stem by the range spring overrides the force exerted upward
by the Process Pressure. The sleeve will travel downward
with the stem until it seats on the O-ring in the bellows
head.
When the sleeve seats on the O-ring, it will block the
control pressure flowing around the stem and stop the
venting of the sensor. The control pressure will then build
around the outside of the bellows and cause the bellows to
compress. As the bellows compresses, the bellows head will
move upward carrying the sleeve with it until the tubular
portion of the bellows head contacts the upper diaphragm
seat.
When the bellows head seats, upward travel will be
stopped and the sensor reset. The sensor will remain in this
position unless the Process Pressure increases enough to
overcome the force exerted by the range spring.
As the Process Pressure increases, the stem will be forced
upward against the range spring until travel is sufficient to
lift the sleeve off the O-ring in the bellows head. When the
sleeve lifts off the O-ring, the pressure inside the bellows
will equalize with the pressure on the outside of the
bellows.
When the pressure on the inside is equal to the pressure
on the outside, the bellows will attempt to recover to its
free length carrying the bellows head downward until
stopped by the reset/ adjustment screw. The sensor will
again be in the venting configuration as shown.
On Manual Reset models, the automatic reset/differential
adjustment screw will be replaced with a spring loaded
plunger as shown in the inset. The reset plunger will allow
the bellows to extend downward to a point the sleeve
cannot reach regardless of how much the Process Pressure
drops. For this reason, the plunger must be depressed
(while pressure is supplied to the CONTROL port) to raise
the bellows head enough to allow the sleeve to contact the
bellows head O-ring. With this accomplished, the sensor
will reset as previously described.
NOTE: Depressing the plunger without a CONTROL
PRESSURE present will NOT reset the sensor.
Figure 2
84374-A1 Shown
(Inlet port rotated 90° from true position)

5
MAINTENANCE - See Figure 4
WARNING: USE CARE WHEN DISASSEMBLING,
SPRING FORCES PRESENT.
Caution: Do not subject O-rings, gasket, or
diaphragms to cleaning fluid, acetone, or any
halogenated hydrocarbons such as degrease
liquids, etc. Clean only with a soft, dry cloth.
Metal parts can be cleaned with a suitable solvent,
then dried thoroughly before reassembly.
Pressure Assembly
Remove the three screws (detail 35) holding the sensor to
its mounting bracket (detail 34). Remove the sensor.
Remove the remaining seven screws (detail 37) securing the
housing together. Remove the lower housing plate (detail
38) and then the exposed diaphragm, (detail 43). Remove
the retaining screw (detail 39) and the diaphragm shoe
(detail 42). Remove the four screws (detail 41) securing the
upper housing and remove the upper housing (detail 33).
The O-ring (detail 32) should come off with the housing. If
not, remove it. Replace the defective parts and reassemble*
in reverse sequence.
Bushing
To replace the bushing O-ring (detail 24) remove the
bushing (detail 25) and replace the defective O-ring.
Reassemble* and replace in valve housing (detail 15).
Recalibrate if sensor is an automatic reset model.
Spring Housing Assembly
Remove the cap screw (detail 1) and washer (detail 2) and
turn the adjustment screw (detail 5) counterclockwise to
bring the range spring (detail 6) to its free length. Remove
the four screws (detail 11) securing the spring housing
(detail 3) and remove the housing. Remove the range spring,
spring seat locking screw and spring seat (detail 4).
Reassemble* in reverse sequence.
Valve Housing Assembly
Remove the pressure assembly, spring housing assembly
and bushing as described above. Proceed as described under
applicable instructions for either the direct-acting or
reverse-acting sensor.
DIRECT-ACTING
Remove the four screws (detail 31) securing the flange
that was under the pressure assembly. Remove tile flange
(detail 30). Prevent the spring seat (detail 9) from rotating
and remove the exposed diaphragm clamp. Remove the
exposed diaphragm (detail 14). Pull the stem (detail 21)
from the valve housing by removing it as an assembly with
the remaining flange (detail 13). (The spring seat will
remain intact).
Prevent the spring seat from rotating and remove the
locking screw (detail 8). Prevent the stem from rotating and
remove the spring seat. Remove the flange from the stem
assembly. Proceed with the instructions under "DIRECT
AND REVERSE ACTING."
REVERSE-ACTING
Remove the four screws (detail 31) securing the flange
that was under the pressure assembly. Remove the flange
(detail 30).
Prevent the spring seat (detail 9) from rotating and
remove the locking screw (detail 8). Prevent the exposed
diaphragm clamp (detail 10) from rotating and remove the
spring seat. Remove the remaining flange (detail 13).
Still holding the same diaphragm clamp, remove the newly
exposed clamp and diaphragm. Pull the stem (detail 21)
from the valve housing with the remaining diaphragm and
clamp intact. Proceed with the instructions under "DIRECT
AND REVERSE ACTING."
DIRECT AND REVERSE ACTING
Remove the remaining diaphragm and clamp. Remove the
retaining ring (detail 16) while compressing and holding the
spring (detail 19) on the stem. Remove the spring and sleeve
(detail 23) to expose the O-ring (detail 20) for replacement.
Reassemble* the stem assembly in reverse sequence.
To replace the O-ring (detail 18) in the valve housing,
remove the retaining ring (detail 17) and the O-ring directly
beneath it. Insert the new O-ring and replace the retaining
ring.
To replace the O-ring (detail 22) located in the bellows
head, remove the O-ring with a knife or some other sharp
pointed instrument. Carefully remove any residue where the
O-ring was removed and clean the seating area with a
suitable solvent. Dry thoroughly and place a few drops of
liquid Viton (Pelmar Laboratories PLV-2000 or equivalent)
on the seating area. Clean and place the new O-ring on the
seating area. Allow bond to cure for one or more hours.
With all O-rings, diaphragms, gaskets and defective parts
replaced, reassemble* as follows: (refer to Figure 3).
NOTE: For Direct-Acting models hold valve housing as
in Figure 3; for Reverse-Acting models invert housing.
Be certain that all parts are clean and free of foreign
matter. On automatic reset models, turn the differential
adjustment screw counterclockwise several turns. Replace
the stem, diaphragms and diaphragm clamps.* Hand tighten
the clamps and then while holding each clamp with a
wrench, tighten 1/4 turn more.
Replace both flanges and secure with at least two screws
(placed diagonally from each other). On the flange where the
pressure assembly mounts, replace all four screws* (securing
the flange) and snug all screws down.
Replace the spring seat and its locking screw. DO NOT
TIGHTEN YET. Turn the differential adjustment screw
clockwise until it becomes difficult to turn; DO NOT
TIGHTEN. On manual reset models, depress the reset
plunger. Then apply an approximate one pound force at "P"
(See Fig. 3) and turn the spring seat to obtain dimension "A."
Tighten the locking screw* snug and turn the differential
adjustment screw counterclockwise 3/4 turn.
Remove the two screws securing the flange under the
spring seat and replace the spring and spring tower assembly.
Then replace all four screws* to secure the flange and spring
tower.
Reassemble the remainder in reverse sequence and
recalibrate.
*NOTE - The following should be fitted using Loctite
Sealant "H," or equivalent, applied before reassembly:
Spring Seat Screw (detail 8), Diaphragm Clamps,
Spring Housing Screws (detail 11), Bushing, Flange
Screws (detail 31), Housing Plate Screws (detail 41),
Diaphragm Shoe Screw (detail 39) and Cover Screws
(details 35 and 37).

6
FIELD REVERSAL
To change the sensor from direct to reverse acting or vice
versa, disassemble down to valve housing assembly.
Remove the locking screw (detail 8) and spring seat (detail
9). With a long allen wrench, remove the set screw (detail
33) from inside the stem.
Remove the flanges. Invert the valve housing assembly
and re-install the set screw all the way to the end of the
stem. Replace the flanges and secure with screws.
Reassemble the pressure assembly to the valve housing. DO
NOT replace the spring seat or screw at this time. Apply a 5
psi process pressure to the HP process port. Apply a 30 psi
pressure to the control port. Insert the allen wrench at point
"P." Apply approximately a one pound downward force on
the allen wrench and slowly turn the set screw clockwise
until the sensor vents the control pressure on direct-acting
models. Then turn one-half turn further. On reverse acting
models, first turn the set screw clockwise until the venting
stops and then turn counterclockwise until the sensor vents
once more. Then turn one-half turn further. Apply Loctite to
set screw.
Complete the re-assembly per previous instructions and
recalibrate the sensor.
ADJUSTMENTS
Setpoint
1. Remove cap screw.
2. Apply operating control pressure to inlet port through
a .8 mm (.032") diameter or smaller orifice. Control
pressure and orifice size must be the same as that used
during normal operation.
3. Apply process pressure at desired setpoint to the
process port.
4. Insert a 1/8" hex wrench into the adjustment screw
and turn screw counterclockwise (clockwise for
reverse-acting units) until the valve snaps open and
sensor vents. If the valve is already open, turn the
screw clockwise (counterclockwise for reverse-acting
units) until the valve closes, then reverse direction and
turn screw until valve snaps open and vents.
5. Check operation and trim as necessary.
6. Replace the cap screw.
Differential (Applicable to Auto Reset versions only)
CAUTION: Sensor will not vent if differential
adjustment screw is turned clockwise to its
maximum insertion into the valve housing. Do not
set differential below minimum recommended value
as shown in graphs.
1. Apply operating control pressure to inlet port through
a .8 mm (.032") diameter or smaller orifice. Control
pressure and orifice size must be the same as that used
during normal operation.
2. Cycle measured pressure at the process port and
adjust the differential adjustment screw until desired
differential is obtained. Differential is increased by
turning the screw counterclockwise.
Figure 3
Reverse Acting
Direct Acting
Table 3
Model No. Dim. "A," mm (In.) Dim. "B," mm (In.)
84374-A, C 1.65 (.065) 2.79 (.110)
84374-B .51 (.020) 2.0 (.078)

7
Figure 4
84374-A1 Shown
TABULATION
Model No. Det. 6 Det. 7 Det. 25
84374-Al 33980-H1 33970-B61 33964-A2
84374-A2 33980-G1 33970-B62 33964-A2
84374-B1 33980-H1 33970-B63 33964-A2
84374-B2 33980-G1 33970-B64 33964-A2
84374-C1 33980-H1 33970-B65 33964-B2
84374-C2 33980-G1 33970-B66 33964-B2
Det.
No.
No.
Req'd Description Prod. Part No.
1 1 Cap Screw 33718-G0509
2 1 Washer 24425-A1
3 1 Spring Housing 84366-A1
4 1 Spring Seat 24557-B1
5 1 Adjustment Screw 24558-A2
6 1 Range Spring See Tab.
7 1 Name Plate See Tab.
8 1 Screw 33713-G1109
9 1 Spring Seat 33968-A2
10 2 Diaphragm Clamp 33969-Al
11 4 Screw 33713-G1309
*12 1 Gasket 33971-A1
13 1 Flange 33966-Bl
*14 2 Diaphragm 33972-Al
15 1 Valve Housing 84364-A1
*16 1 Retaining Ring 36605-Q9
*17 1 Retaining Ring (Incl. in Det. 15) 36605-B2
*18 1 O-Ring (Incl. in Det. 15) 36240-V0016
19 1 Spring 33975-Al
*20 1 O-Ring 36240-V0010
21 1 Stem 33973-A2
*22 1 O-Ring (Incl. in Det. 15) 36243-V0012
23 1 Sleeve 33974-A2
*24 1 O-Ring 36240-V0007
25 1 Bushing See Tab.
26 1 Differential Adjustment Screw 33963-A1
27 1 Reset Plunger 33962-A2
28 1 Set Screw Not Used
29 1 Spring 33965-A1
30 1 Flange 33966-B2
31 4 Screw 33713-K1309
*†32 1 O-Ring 36240-C0030
33 1 Diaphragm Housing 83898-B1
34 1 Bracket 33603-Cl
35 3 Screw 33713-G1309
36 10 Nut 36603-A22
37 7 Screw 33713-G1109
38 1 Diaphragm Housing 83897-B1
39 1 Screw Not Used
40 1 Sleeve 33990-A1
41 4 Screw 33713-G1309
42 1 Diaphragm Shoe 27462-B1
†43 1 Diaphragm 30873-Al
NOTE: For kit containing all O-Rings, gaskets, diaphragms and retaining
rings to service one valve body, order Repair Kit No. 82665-G1. Kit
contains details marked *
For kit containing large O-Ring and diaphragm to service one Pressure
Assembly, order Repair Kit No. 82665-M1. This kit contains details
marked †.
PARTS LIST

8
U.S.A. and CANADA
Robertshaw Industrial Products Division
1602 Mustang Drive
Maryville, Tennessee 37801
Phone: [phone] Fax: [phone]
http://www.robertshawindustrial.com
Exports
Invensys Appliance Controls
1701 Byrd Avenue
P.O. Box 26544
Richmond, Virginia 23261-6544
Phone: [phone] Fax: [phone]
Q
-4024
(
4/03
)
Printed in U.S.A.