Product Data

1
L404A,B PRESSURETROL® CONTROLLERS
MERCUR
Y
SWITCH
DIFF.
MAIN
PSI
12
10
8
6
4
2
.1
.3
.5
.7
.8
.6
.4
.2
0
.5
1
20
10
30
40
50
3.5
3
2.5
2
1.5
0
DIAPHRAGM
ASSEMBLY
LEVELING
INDICATOR
POINTER
INDEX
MARK
MANUAL
RESET
LEVER
MAIN SCALE
ADJUSTING
SCREW
ADJUSTING
SCREW
SCALEPLATES
D
IFFERENTIAL
S
ETTING
I
NDICATOR
MAIN SCALE
SETTING
INDICATOR
ADJUSTABLE DIFFERENTIAL ON THE L404A,B WITH A 5 TO
150 PSI (0.34 TO 10.3 kg/cm
2
[34 TO 134 kPa] OPERATING RANGE.
M19538
1
DIFFERENTIAL
Fig. 7. Setting a Pressuretrol® Controller.
Checkout
After the controller has is installed, wired, and set, test it with
the system in operation. First allow the system to stabilize.
Then observe the operation of the controller while raising and
lowering its setpoint. Pressure should increase when the
setpoint is raised and decrease when the set point is lowered.
Also check the make and break points of the controller. If they
do not agree with a separate, accurately calibrated pressure
gauge, a slight adjustment of the scaleplate(s) may be
necessary.
Use accurate pressure testing equipment when checking out
the controller. Do not rely on inexpensive gauges. The
controllers are carefully calibrated at the factory.
Boiler Installation
If the controller is being used on a boiler installation, test it as
follows:
1. Note the boiler pressure by checking the boiler pressure
gauge. (To perform this test properly, the boiler should
have a pressure reading near the middle of the
controller‘s main scale range.)
2. Turn the main scale adjusting screw (Fig. 7) until the
main scale setting indicator on the controller
corresponds to the boiler pressure gauge reading.
3. The L404A should break the control circuit(s)
automatically when the boiler pressure gauge reading
equals or slightly exceeds the controller setting.
4. The L404B should make the circuit under the same
circumstances.
5. If the controller is operating properly, turn the main scale
adjusting screw (Fig. 7) until the main scale setting
indicator is at the desired set point.
If a Controller Seems to Operate Improperly
If the controller is suspected of operating improperly, it may be
further checked as follows (Fig. 8):
1. Disconnect all power to the controller, loosen the cover
screw, and remove the cover.
2. Disconnect the wires from the controller.
3. Connect an ohmmeter between the switch terminals.
4. Lower the set point of the controller (simulating a
pressure increase) through a range greater than the
differential. The switch should either make or break,
depending on the model of the controller. (An L404A
should break, an L404B should make.) If it makes, the
ohmmeter reads zero; if it breaks, the ohmmeter reads
infinity.
5. Raise the set point of the controller (simulating a
pressure decrease) through a range greater than the
differential. The switch should break or make, just the
opposite of its action in step 4.
6. An approximation of the differential can be made by
observing the change in set point required for a
resistance change from zero to infinity.
7. If the controller operates improperly, replace it.
8. When the controller is operating properly, reconnect the
wires to the terminal block, replace the cover and
tighten the cover screw, and reconnect the power.
CAUTION
Equipment Damage Hazard.
Improper operation can damage the equipment.
Do not put the system into service until you have
satisfactorily completed all applicable tests described
in this Checkout section, in the Checkout section of
the applicable instructions for the flame safeguard
control, and any others required by the burner and
boiler manufacturers.
7 95C-10187B–1