Cashco 764T Temperature Controller - Manual (Page 7)

IOM-764T 7
NOTE: Many temperature control system loops
have sizeable time constants; i.e. fl ywheel effect.
Make ad just ments in small increments and wait
for the results to stabilize.
If the control valve and 764T becomes unstable,
leave the setpoint adjustment as is and increase
PB adjustment by rotating needle valve (3) ap-
prox i mate ly 1/8 revolution CCW. Wait for results
to sta bi lize.
Continue Articles 13. and 14. slowly until the control
valve bypass valve is fully closed, and the 764T
controller is regulating fl ow.
It is recommended that an "upset" be imposed
onto the system, and observe the capability of the
controller to stabilize the upset. If instability re sults,
PB should be increased in 1/8 CCW rev o lu tions
until stability is within the 764T's capability.
By observing the output SIG of the 764T as in-
dicated on instrument gage (11), and manually
varying control valve bypass fl ow upwards and
downwards, the setpoint can be confi rmed as ap-
proximately the point where output SIG pres sure
is at 9 psig (0.62 Barg).
Increase or decrease 764T setpoint to drive the
control valve closed. Remember the ∆T change
adjusted.
Open the block valves isolating the control valve.
Begin to manually close the control valve bypass
valve while simultaneously changing the 764T
setpoint back towards the desired setpoint prior to
Article 11, this sec tion. Attempt to simultaneously
change the setpoint and further close the bypass
in pro por tion al increments; i.e. close the bypass
about 10% while changing the setpoint by about
10% of the ∆T change of Article 11.
12.
13.
14.
15.
16.
SECTION V
11.
10.
1.
2.
3.
4.
5.
MAINTENANCE
General:
Refer to Figure 10 for cutaway view of 764T
tem per a ture controller and Figure 6 for cut-
away view of the high temperature thermal
bulb with extension post (Opt. -63).
Maintenance procedures hereinafter are
based on re mov al of the controller with the
thermal bulb (12) as a unit from the thermal
well (17) or piping system.
When removing the tubing to/from the con-
trol ler, tag the tube utilized with either Port
"A" or "B".
There is no maintenance performable to the
ther mal well (17) for the controller. If the
thermal well (17) is corroded, a liquid pres-
sure test may be performed at the following
maximum pressure levels:
SST Thermal Well —9,300 psig (641 Barg)
Brass Thermal Well —1,500 psig (103
Barg)
There is no maintenance performable to the
thermal bulb (12) portion of the controller. If
V.
A.
the thermal bulb (12) is corroded, a liquid pres-
sure test may be performed at the fol low ing
maximum pressure levels to assure pres sure
integrity.
SST Thermal Bulb — 9,300 psig (641 Barg)
Brass Thermal Bulb—1,500 psig (103 Barg)
Lightly grease all O-rings upon replacement
with lithium grease; cloth wipe all excess
grease.
Place thermal bulb (12) into a vise and grip on
the hex surfaces of the thermal bulb assembly
(12). Orient the pneumatic section upwards.
Remove output pressure gage (11) and test
cal i bra tion. If gage (11) is off ±2 psi (±0.14
Bar), replace gage (11).
Using channel lock pliers or similar tool,
loos en knurled lock nut (16) by rotating CCW
(viewed from front). Back lock nut (16) away
from thermal bulb (12) until it is stopped by
contact with the sensor housing (1). Keep
track of the number of rev o lu tions loos ened
for lock nut (16) in table below:
1.
2.
6.
7.
Pneumatic Circuit Overhaul: B.