LowFlow 8000 Series Control Valve - Manual (Page 4)

(32).
Reverse Acting Actuator: ATO (Air to Open)
1. Remove actuator from body (refer to Section 2). Re-
move the actuator case bolts (20) and nuts (45) that
hold the upper case (17A) to the lower case (16A),
and remove the upper actuator case. Remove
springs (32), hex bolt (20), diaphragm plate (18),
diaphragm washer (19), and thread seals (13).
2. Check actuator stem o-ring (14), remove actuator
stems (22), unscrew the gland nut (44) from the
gland (43) and remove the o-ring.
3. Clean all parts with an approved, non-residue form-
ing solvent. Remove encrusted material with fine
emery paper or very mild aluminum cloth. Inspect all
parts for excessive wear and/or damage. Replace
any worn or damaged parts.
Reassembly of Actuator
After all parts have been thoroughly cleaned and inspect-
ed, reassemble the actuator.
1. Greasing the o-ring, insert the actuator stem (2) through
the gland (43). Thread on, and tighten gland nut (44).
Direct Acting Actuator ATC (Air-to-Close)
2. Place springs (32) on lower actuator case (16A).
Place diaphragm plate (18) on springs, making sure
springs are nested on the punched bosses. Install
the diaphragm (12) with the holes lined up with the
bolt holes in the lower actuator case. Place the dia-
phragm washer (19) on diaphragm (12). Install the
thread seal (13) on the hex bolt (20) and thread hex
bolt into the actuator stem (22) and tighten.
Reverse Acting Actuator: ATO (Air-to-Open)
2. Install thread seal (13), diaphragm washer (19), dia-
phragm (12) and diaphragm plate (18), and tighten
down the hex bolt (2). Place the springs (32) on dia-
phragm plate (18) so that the springs are nested in
the punched bosses.
3. Place upper actuator case (17A) on diaphragm (12),
lining up with the bolt holes.
4. Replace four bolts (20) and nuts (45) 90° apart and
tighten fingertight. Replace the remainder of the
bolts and nuts and tighten evenly alternating across
the actuator case.
5. Thread the stem adapter (46) into the actuator stem
(22), and reinstall the actuator onto the body assem-
bly. (Refer to Section 3: Valve Reassembly (points
6-10).
6. Adjust spring load. Refer to Section 4: Actuator
Spring Pre-Load Adjustment.
Reversing Action
CHANGING THE VALVE ACTION FROM DIRECT TO RE-
VERSE ACTING OR FROM REVERSE TO DIRECT ACT-
ING.
-4-
the actuator pressure reaches 3 psig.
If movement starts before 3 psig, increase the preload;
if movement starts at a pressure higher than 3 psig, de-
crease the preload.
Reverse Acting Actuator ATO (Air-to-Open)
1. In an ATO actuator, the valve plug is closed by the
actuator spring force which operates against the
stem thrust created by the inlet pressure pushing
up on the plug and stem. If the spring preload ad-
justment is made without pressure in the valve body,
additional preload may be needed to overcome the
effects of this thrust when the control valve is placed
in service. The amount of additional preload will be
dependent on the size of the seat orifice and the inlet
pressure. For the smallest trims and low pressures,
it will be negligible. For the largest trim it could be
significant. The catalog lists the maximum pressure
that the valve is capable of shutting off against with a
3 psig preload. If higher pressures are needed, then
a positioner should be used.
2. Spring preload is adjusted by threading the stem
adapter (46) into the actuator stem (22). Keep the
actuator stem from turning with a wrench and turn
the stem adapter. Threading the stem adapter into
the actuator stem decrease preload when the valve
stem starts to open when the actuator pressures
reaches 3 psig.
3. Slowly increase the air pressure up to 3 psig while
observing the stem for movement. Correct spring
preload is when the valve stem starts to open when
the actuator pressure reaches 3 psig.
4. If movement starts before 3 psig, increase the pre-
load; if movement starts at a pressure higher than 3
psig, decrease the preload.
5. After the preload is set , lock the travel scale indica-
tor nuts (46) against the actuator stem. The valve
travel scale indicator (24) may require adjustment
relative to the indicator (37).
Section 5: Actuator Maintenance
Disassembly and Inspection of Actuator
1. Close inlet and outlet stop valves. Operate system
on bypass, if necessary.
2. Shutoff operating medium and relieve pressure from
diaphragm by disconnecting tubing at diaphragm
case.
Direct Acting Actuator ATC (Air-to-Close)
1. Disconnect the actuator stem (22) from the stem
adapter (46) by loosening the two adapter stem
nuts (47), moving them down the stem adapter and
locking the two nuts together. With appropriate tools
holding the adapter stem nuts and the flats of the
stem adapter, thread the stem adapter out of the
actuator stem. Grip actuator stem and remove hex
bolt (20), thread seal (13), diaphragm washer (19),
diaphragm (12), diaphragm plate (18) and springs