Cashco 9540L P/P - Manual (Page 2)

IOM-9540L 2
A force balance is created on the flapper lever (38)
when the force generated by the input diaphragm (50)
balances with the counter-force produced on the range
spring (41). This ensures that the actuator/valve stem
position is always proportional to the input signal.
Dynamic matching of the actuator (sensitivity, stability)
is factory set by means of the throttle screw (42) and
the damping throttles (44). The stroke range and zero
are set by means of the stroke factor thumbscrew (40)
and the zero thumbscrew (39). The changeover plate
(15) is used to set either an increasing or decreasing
output pressure for an increasing input signal, i.e.
direct or reverse acting.
The normal factory set position of the bypass switch (3)
is “EIN” (ON) (pointer at 6 o'clock), and the positioner
will be operational. If the positioner bypass switch (3)
is set to the “AUS” (OFF) position (pointer at 9 o’clock),
the input signal SIG is supplied direct to the actuator;
i.e. the positioner has no effect. Operation in the “AUS”
(OFF) position is only practical for control valves where
the positioner action is “Direct” and the actuator bench
range is approximately equal to the 3-15 psig “SIG”.
Use of bench ranges with upper limits greater than 15
psig will cause the control valve to not be able to fully
stroke when bypassed.
III. MOUNTING TO SPRING DIAPHRAGM
ACTUATORS
A. The following text applies to field mounting of a
positioner.
B. Determining Mounting Side:
1. The action/failure position on the control valve
unit must be known “Air-to-Open, Fail Closed”
(ATO-FC); or “Air-to-Close, Fail Open” (ATC-
FO). The mounting side is selected from Table
1 considering:
a.) Valve action/failure position
b.) Stem travel direction with increasing “SIG”
c.) Positioner action - Direct or Reverse
(Choose either steps 2a. -to- 3a.; or choose
steps 2b. -to- 3b.)
2a. On actuator yokes with a cast-on rib located
on one of the legs that support the lower
diaphragm housing, see representative cross-
section Figure 3A. Rotate the actuator until
the rib with its mounting taps is located on the
side (right or left) as indicated in Table 1.
(Includes 987’s, 964’s and 2” 2266’s, 520 &
521 TFE’s with Models 55D, 55R, 115D and
115R actuators).
2b. The actuator yokes without a cast-on rib will
have four mounting holes on one of the yoke’s
legs. (See representative cross-section Fig-
ure 3B.) Rotate the actuator until the leg with
the four holes is on the side (right or left) as
indicated Table 1. (Includes 520 & 521 TFE’s
with Model 30 actuator.)
3a. On yokes with a rib, attach the positioner’s
mounting bracket (12) in accordance with the
dimensions of Figure 4 to the actuator
yoke. Use the center hole of the mounting
bracket (12) for attachment using the rib
mounting bracket (12) will give the proper
dimensions. (Figure 4 is shown as right-hand;
if left-hand is required, then dimensions are
mirror-imaged.)
3b. On yokes without a rib, attach the positioner’s
mounting bracket (12) in accordance with the
dimensions of Figure 4 to the actuator yoke.
Use two yoke mounting screws and nuts
(10B) and the two holes closest to the frontal
position when properly rotated. (Figure 4 is
shown as right-hand; if left-hand is required,
then dimensions are mirror imaged.)
SECTION III
Figure 2: Single-acting positioner functional diagram.
Travel
LOAD
SIG
IAS
3
44
53
42
39
40
41
51
52
15
19
55
On
N U
50
38
13