Aventics AA-1, Service Information

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ADJUSTMENT
It is important to utilize the full travel of the positioner and to
match the end travels of the control lever and the operator rod.
The operator rod is adjustable in length from 1” to 5 ½ “ (25.4 to
139.7 mm), which alters the end travel from
7
/
8
” to 2 ¼ “ (22.2 to
57.2 mm). For decreased rod end travel, loosen the jam nut
and screw the operator rod toward the lever arm. Tighten the
jam nut to secure this position. Rod end travel can be
increased by unscrewing the operator rod and then tightening
the jam nut.
If the end travel of the governor control arm exceeds the
maximum adjustment of the operating lever, the normal
procedure is to drill a hole in the control arm at the point which
has a travel range of two inches (50.8 mm). Fasten the
connecting link to the new hole and re-adjust the end travel of
the control arm and operating lever to match.
As assembled, the adjustable elements of the positioner are
matched to provide zero lever travel with indicated preload
pressure (usually 10 psi or 0.7 bar), and maximum lever travel
with rated top pressure (usually 60 psi or 4.1 bar).
The push rod and follower (ref. 5, pg. 4) travel is factory set to
correspond to rated top pressure. If the top pressure of the
control valve is greater or less than that of the positioner, the
travel of the control valve handle can be made to match the
travel of the operating lever by using the push rod and follower
adjusting screw (ref. 9, pg. 4).
Two or more positioners can be matched to provide the same
movement for a given change in air pressure. They can also be
deliberately mismatched to provide different rod end travel to
compensate for inequalities in operating characteristics of the
controlled device. If necessary to adjust for incorrect initial
pressure, remove or add shims (ref. 7, pg. 4) as needed, or
reset the preload on the control valve.
REPAIR AND CONVERSION
In late 1969 improvements were made starting with a stronger,
lighter weight push rod and follower assembly (ref. 5, pg. 4) and
utilization of the smaller adjusting screw (ref. 9, pg. 4) from the
A-2-H Actuator Positioner. (To accommodate the smaller
adjusting screw, the main body (ref. 8, pg. 4) was modified.) To
further simplify the various models a standard lever arm was
designed along with the accompanying bearings, bolt and
washers. Finally, the stop cylinder on the AB-1 model was
replaced by a readily available unit using TaskMaster
®
Cylinder
components.
When replacement of the main diaphragm body (old style) (ref.
8, pg. 4) is required, it is recommended that a main operator
portion be purchased assembled. (Order part number
R431005447 Old P/N P -060272-00000) and refer to page 4 for
parts included.) New and old push rod and follower assemblies
(ref 5, pg. 4) are completely interchangeable. The new and old
vernier follower (ref. 20, pg. 6) will function with the new or old
lever arm, the old stop cylinder will function with the new lever
arm provided the old connecting link (ref. 18, pg. 7) is used, and
the new stop cylinder will function with the new or old lever arm.
Fulcrum pins with grease fittings located at one end are no
longer available, if replacement ever becomes necessary it is
recommended that lever arm conversion kit, part number
R431006221 (Old P/N P -063382-00000) or P/N P -063383-
00000 be purchased.
In AB models, rubber parts in the stop cylinder should be
lubricated with Dow Corning No. 55 Pneumatic Grease.
Reassemble the positioner using the exploded and assembly
views as references. No special tools are required. To
maintain the same preload on the spring (ref. 6, pg. 4), shims
(7A, B & C) must be included. Apply No. 107 Lubriplate, or its
equivalent, to all grease fittings.
OPERATION
The positioner has a usual pressure range of 10-60 psi (0.7 to
4.1 bar) within a temperature range of -40°F to 165°F (-40°C to
74°C). Pressure is supplied by a pressure control valve such as
the AVENTICS CONTROLAIR
®
, Type “M” Plus™ Pressure
Control or Flexair
®
Valves. The pressure imposed on the
diaphragm (ref. 4, pg. 4) is proportional to the handle travel of
the control valve. The movement of the positioner operating rod
is also proportional to this movement. Finally, the position of
the controlled device is proportional to the handle travel of the
control valve.
When supply pressure is reduced, the force of the spring (ref. 6,
pg. 4) against the push rod and follower assembly (ref. 5, pg. 4)
returns the operating rod to its new position corresponding to
the value of air pressure remaining. Supply pressure of 10 psi
(0.7 bar) usually provides idle position with 60 psi (4.1 bar)
usually providing full travel or full fuel position.
AA-1
The AA-1 Actuator Positioner, which is larger and more
powerful than the A-2-H, is the basic configuration from which
the AB-1 and BA-1 are constructed. The AA type actuators
have a nominal stoke of 2” (50.8 mm) with a power rating of
1125 in-lb-degrees (127.1 Nm) or a work rating of 10 lbs (4.54
kg) through 2” (50.8 mm).
BA-1
The BA-1 Actuator Positioner is similar to the AA-1 but has a
vernier feature added by the inclusion of an additional
diaphragm. This diaphragm is controlled by a separate valve to
provide an adjustment to a maximum of +/- 10% of full travel on
the rod end. Normal air pressure on the vernier diaphragm is
35 psi (2.4 bar), being varied between zero and 65 psi (4.5 bar)
to increase or decrease the index position.
AB-1
The AB-1 Actuator Positioner is also similar to the AA-1 except
that a separately controlled stop cylinder has been added.
When air is admitted to the stop cylinder, the operating lever
arm is moved 2” (50.8 mm) in the opposite direction. If pressure
is present on the main diaphragm, the operating rod will move
to idle position and if pressure is vented from the main
diaphragm, the arm moves to the stop position.