3570 Series
7
D The maximum pressure rating of the actuator,
from the appropriate actuator instruction manual.
D The maximum allowable valve plug stem load for
the specific valve body assembly being used. Contact
your Fisher sales representative or sales office for
valve plug stem load information, if required.
D For diaphragm actuators, refer to the actuator
instruction manual for the recommended supply pres-
sure and use the larger value of the range listed.
The recommended supply pressure for use with piston
actuators is the highest available supply pressure be-
tween 50 psig (3.4 bar) and the maximum limit deter-
mined by the actuator and positioner specifications.
Selecting the highest pressure within the limits will mini-
mize load error and will maximize stroking speed and
thrust. For the lowest supply pressure that will assure
satisfactory performance, the factors of valve plug unbal-
ance force, valve plug seating force, and frictional force
must be considered in the following relationship:
Supply
pressure, = 98
bar
(Valve
unbalance,
kg)
+
+
(Seating
force,
kg)
(Frictional
force,
kg)
+ 0.7 bar
(Area of the actuator piston,
in square mm)
[
]
or
Supply
pressure, =
psig
(Valve
unbalance,
pounds)
+
+
(Seating
force,
pounds)
(Frictional
force,
pounds)
+ 10 psig
(Area of the actuator piston,
in square inches)
[
]
Consult your Fisher sales office or sales representa-
tive for the appropriate values for specific actuators,
valves, and service conditions. The 10 psig (0.7 bar) is
added to the equation to account for an approximate
10 psi (0.7 bar) differential pressure loss in the posi-
tioner. For spring-return piston actuators, the pressure
required to compress the actuator spring completely
must also be considered.
Cylinder Connections
1. The connection marked CYLINDER (see figure 2) is
connected at the factory to the lower part of the cylinder
(bottom) or to the lower diaphragm casing if the
positioner is used with a pneumatic diaphragm actuator.
2. The cylinder top connection is a pressure passage
located in the bottom of the positioner base (key 1,
figure 10). On Type 3570 and 3570C positioners, an
O-ring (key 33, figure 10) is used between the bottom
of the positioner and the top of the actuator. On Type
3570P, 3570PC, 3571, 3576, and 3577 positioners, a
mounting bracket (key 55, figure 13) is required. This
mounting bracket connects to the bottom of the base.
An O-ring (key 33, figure 10) is placed between the
base and mounting bracket. This mounting bracket
provides a 1/4-inch NPT connection for the positioner
output. This connection is made at the factory if the
positioner is ordered mounted to the actuator or if the
mounting bracket is installed.
Instrument Connection
The connection marked INSTRUMENT (see figure 2)
connects to the output signal connection of the control
device. The positioner operates only on a pneumatic
input signal; the input signal range is marked on the
nameplate (key 23, figure 10). The maximum allow-
able input signal for positioners with standard or op-
tional bellows is in table 1 (bellows pressure rating).
The instrument connection is made at the factory
when a complete control valve assembly with a valve-
mounted control device is ordered. Otherwise, make
field connections to the positioner from an appropriate
control device. Refer to table 1 and the nameplate for
input signal pressure ranges.
Operating Information
Initial Adjustments
Normally, no adjustments are necessary upon initial
installation. The positioner is set at the factory for the
travel, input signal range, and action specified in the
order. Adjustment is necessary when operating
conditions are changed, when the unit has been
dismantled and reassembled, or when the control
valve travel does not correspond to the desired input
signal range. If the operating conditions have not
changed but the positioner requires adjustment, refer
to the adjustment procedures in this section. If the
operating conditions have changed, first, refer to the
signal range code descriptions, then, refer to the
adjustment procedures.
Signal Range Codes
The range spring and the bias spring are matched to a
specific input signal range and length of travel. Also,
the spring retainer length is matched to the application
on the Type 3570, 3570C, 3572, and 3573 positioners.
Refer to figure 3 for location of parts.
The signal range codes in table 4 are based on the
following applications:
D Codes for valve travels up to and including
2 inches (50 mm) are used for actuators that have a
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