Leslie Controls CONTROL VALVES SINGLE PORTED DOS - Manual (Page 8)

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3. Place new gasket (50) in recess in valve
body.
4.
Follow with seat ring/insert (51), with valve
plug seating face toward bonnet end of
body.
5.
Position seat retaining guide (48) on seat
ring/insert.
Adjusting Actuator Spring
Preload (Starting Pressure)
1.
Connect controlled air line to diaphragm
case connection at “A”.
2.
Supply 3 psig air pressure to actuator
diaphragm.
3.
Compress actuator spring until travel
indicator begins to move when air pressure
is raised above 3 psig.
TO COMPRESS ACTUATOR SPRING
SCREW SPRING ADJUSTOR UPWARD
NOTE: Alternately add compression and check
starting pressure slightly above 3 psig until
correct adjustment is attained. After each check,
return air pressure to 3 psig.
Single Ported Unbalanced
Control Valves (DL, DOS Types)
Control Valves with Direct Acting Actuators
Actuator spring preload adjustment can be made
either with or without pressure in valve body.
Once correct compression is made no further
adjustment is necessary.
Single Ported Control Valves
(DDL, DDOS Types)
With Reverse Acting Actuators
Spring Closing Types
In a single ported unbalanced control valve
(reverse acting actuator), the valve plug is closed
against upward fluid thrust by actuator spring
force. Total compression placed on actuator
spring must be sufficient to provide the 3 psig
preload plug force required to close the valve.
If preload adjustment is made with no pressure in
valve body, when the control valve is placed in
operation, additional compression must be
placed on the actuator spring to provide valve
closure force. With proper adjustment valve will
close tightly and will not begin to open until the
3 psig operation pressure is exceeded.
NOTE A: A control valve which has been
adjusted to provide 3 psig starting pressure plug
valve closure force (with pressure in body) will
have a considerably higher start-pressure than 3
psig, when tested at 0 body pressure.
NOTE B: Air pressure quoted are relative.
Actual pressures required in operation may vary
with pressure drop conditions existing and/or
actuator springs used.
Adjusted Control Valve for Rated
Travel
(Indicator scale shows rated travel of a valve)
Single Ported Unbalanced (DL,
DOS Types)
With Direct Acting Actuators
With valve plug and actuator stem threads
engaged as described in “REASSEMBLY”,
supply 20 psig operating pressure to actuator
diaphragm. Observe travel obtained as shown by
travel indicator and indicator scale. Readjust as
follows:
Overtravel - If travel is too great, loosen stem
locknut and turn valve plug stem out of actuator
stem the amount necessary to obtain correct
travel.
Undertravel - If travel is too short, loosen stem
locknut and turn valve plug stem further into
actuator stem the amount necessary to obtain
correct travel.
Positive Compression Force
When correct travel has been obtained reduce
operating pressure sufficiently to move valve