Badger Meter Research Control Valve - Manual (Page 12)

the upward force exerted by the range spring is balanced
by the downward force of the zero adjustment spring. In
balance condition, positioner vents to atmosphere.
When control-instrument pressure increases, the
diaphragm assembly will move upward closing the
exhaust port and opening the pilot valve allowing supply
air to pass directly to the actuator diaphragm. The supply
air will drive the actuator downward. As the actuator
moves down, the range spring relaxes until its force
decreases enough to offset the increase in control-
instrument pressure, allowing the pilot valve to close
and exhaust to open. On air-to-close valves with
positioners, the supply pressure should be sufficient
for function, but never excessive. For function the
positioner supply pressure needs to be a minimum of 3
PSIG above instrument signal. Excessive supply
pressure can result in damage to trims when the
innervalve touches the seat and the signal continues
down. The positioner sees this as resistance and reacts,
causing the full supply pressure to be applied to the
main diaphragm in the actuator.
Bottom Loading, Air-to-Open
Air pressure from control instrument is inserted between
the dual upper diaphragms and the center diaphragm.
Because of the difference in the two diaphragm areas,
the resultant force is exerted in a downward direction.
In balance condition, the pneumatic force on the
diaphragm, plus the downward force exerted by the zero
adjustment spring, is balanced by the upward force of
the range spring. In balance condition, positioner vents
to atmosphere.
When control-instrument pressure increases, the
diaphragm assembly will move downward allowing the
spool valve to close the exhaust port and allow the
supply air to pass through interior porting to the bottom
side of the diaphragm or piston in the actuator. The
supply air will drive the actuator upward. As the actuator
moves up, the range spring will compress until its force
increases enough to offset the increase in control-
instrument pressure causing the spool valve to move,
shutting off supply air to the actuator and opening
exhaust.
Adjusting Zero
For ATC valves with type TLDA or Moore 73N12F
positioners, zero adjustment is made with 15 psi
instrument air (for 12 psi span) to the positioner, turning
zero adjustment screw until valve seats at 15 psi. For
ATO valves with type BLRA or Moore 73B positioners,
zero adjustment is made with 3 psi instrument air to the
positioner, turning zero adjustment screw until valve
seats at 3 psi. Full travel within tolerances governed by
the range spring should occur on ATO or ATC valves
using the standard 3-15, 3-9, 9-15, etc. instrument signal.
NOTE: Factory zero adjustments are made on Research
Control Valves with positioners, using 90 PSIG air
pressure piped to the upstream valve port, connecting
a Tygon or rubber tubing to the downstream port and
immersing the end in a water filled container to detect
any leakage across the seat during zero adjustment.
Servicing
Badger’s valve positioners must be isolated from the
system before service or removal can be accomplished.
(Recommended procedure is to move complete valve
with positioner to instrument repair bench where
necessary tools and manual set air regulators are
available.)
To clean pilot or spool valve, remove brass hex head
sealing screw under top cap and with small sharp nose
pliers, tweezers or other device, remove and clean pilot
or spool valve and replace. On air-to-close TLDA and
Moore 73N positioners, the pilot is a one piece unit that
seldom fails due to dirty air or material such as Teflon
tape getting into the pilot and causing malfunction. On
air-to-open BLRA and Moore 73B positioners, the
functional clearances around the spool valve is very
close and more likely to fail due to dirty air or Teflon
tape. Clearance is a function of bleed and must be close
as possible, but large enough to function. To replace
the diaphragm assembly, it is necessary to unscrew
the six screws holding the positioner to the adaptor and
remove the positioner assemble. Invert positioner and
remove the two assembly screws in the bottom ring.
When assembling the positioner diaphragm assembly
to the main housing, make sure to align index grooves.
Positioners must be correctly assembled in order to
function. Individual sub-assemblies such as the
diaphragm assembly should be replaced as one unit.
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