Cashco 9540L P/P - Manual

I. DESCRIPTION AND SCOPE
Model 9540L is a single acting, compact, force bal-
ance, pneumatic positioner used on linear travel (slid-
ing stem) control valves. This positioner is utilized to
linearize the relationship between valve stem position
and the system’s control signal. This design is only
suitable for nominal 3-15 psig input signals, or split
range variations thereof.
Each unit comes complete with a set of built-in gages
within the internals; the cover includes a clear see-thru
panel to monitor gages. Gages monitor input “SIG”
and output “LOAD”.
The Model 9540L P/P positioner may be utilized with
the following current Cashco product models:
987 964 520 TFE SCV-30
988 2266 (2” size) 521 TFE
989 2296 SCV-S
IAS - Instrument Air Supply
PC - Pressure Controller
PCV - Pressure Control Valve
ATO-FC - Air-to-Open, Fail Close
ATC-FO - Air-to-Close, Fail Open
P/P - Pneumatic Input/Pneumatic Output
DIR - Direct Acting
REV - Reverse Acting
SIG - Controller Output Signal
V - Vent
CW - Clockwise rotation
CCW - Counter-clockwise rotation
II. METHOD OF OPERATION (See Figure 2)
The positioner operates with the force balance
principle: the input signal “SIG” (3-15 psig) acts on the
input diaphragm (50).The stroke of the input dia-
phragm is transferred to the flapper lever (38). The
resulting movement of the flapper varies the dynamic
pressure at the nozzle (51). This pressure acts on the
amplifier (53) and the change in output pressure
causes a movement of the actuator/valve stem.
This movement is back fed from the actuator/valve
stem (55) by the feedback lever (13) of the positioner,
and transferred to the stroke factor lever (19). The
stroke factor lever (19) is connected to the flapper
lever (38) by means of a range spring (41).
INSTALLATION, OPERATION & MAINTENANCE MANUAL (IOM) IOM-9540L
06-99
MODEL 9540L
P/P - PNEUMATIC POSITIONER FOR LINEAR VALVES
SECTION I
SECTION II
Figure 1: Typical Pressure Reducing Pneumatic Control
Loop - PCV with P/P Positioner
PCV
5-13 psig
3-15 psig
LOAD
DIR.
P1 = 500 psig ATO-FC
IAS
P/P
SIG
PROCESS
P2 = 100 psig
15-3 psig
IAS
20 psig REV.
PC