6. If the actuator is equipped with an
MCV-3 Manual Control Valve), place
the left MCV-3 handle in the manual
position. If the actuator is not
equipped with an MCV-3, use the
block valve (1/4 “ ball valve) installed
between the positioner output and
the actuator. Once the actuator has
reached its desired position (based
on the mid-signal applied to the in-
strument port – Step 5), place the
block valve in the closed position.
7. Final Sensitivity Drum Adjustment
Turn the Sensitivity Adjustment to set
the Cylinder Top and Cylinder Bottom
at the proper Cylinder Balance Pres-
sure (P
c
) - See Equation 1 and 2 below.
Turn Sensitivity Adjustment to the right
(decreasing numbers on the scale) to
increase the Cylinder Top/Cylinder Bot-
tom Pressures. Turn Sensitivity Adjust-
ment to the left (increasing numbers on
the scale) to decrease the Cylinder Top/
Cylinder Bottom Pressures.
The correct Cylinder Balance Pressure
(P
c
) is found using the Cylinder Balance
Pressure equations:
HPP-4 Discharge to PRESSURE SYS-
TEM (NO Volume Boosters)
P
c
= P
d
+ [0.4*(P
s
- P
d
)] (Equation 1a)
HPP-4 Discharge to Atmosphere (NO
Volume Boosters)
P
c
= 0.4*P
s
(Equation 1.b)
Deadband Setting
1. Turn the deadband adjustment drum
in the direction of decreasing the
numbers until the drum can no
longer turn. Then turn the adjust-
ment drum
one full turn in the oppo-
site direction (use the numbers on
the drum as a guide).
2. If not already attached, wind 3-4
coils of the range spring
onto the re-
tainer.
3. If not already adjusted, set the bias
adjustment screw in the middle of
its travel range.
4. Apply power gas to the HPP-4 posi-
tioner
5. Set the instrument signal pressure
at the midpoint of its range (e.g.. 9
psig for a 3-15 psig range, 18 psig
for a 6-30 psig range). Allow the ac-
tuator to stroke the valve to an inter-
mediate position and the gauge
pressures to balance. (if the valve
does not stroke, insure that the po-
sitioner is communicating with the
actuator cylinder. If equipped with
an MCV-3, make sure the MCV-3
left handle is in automatic.
Signal Line from Control-
HPP-4
8
September 1999
HPP-4 Positioner
Adjustment Procedures
