This invention relates generally to fluid flow control devices and
in particular to rotary valve actuators for fluid flow valves.
Background Of The Invention
A variety of fluid flow control valves and corresponding valve actuators
are utilized for on/off control or throttling the flow of fluid, such as in a
gas or oil pipeline system, or in other process fluid systems. The fluid flow control
valves are typically sliding stem control valves or rotary action control valves
and are operated by a valve actuator such as a pneumatic piston or diaphragm actuator
responding to the output of a valve positioner or valve controller instrument
for accurate throttling control of the valve.
In the case of rotary action control valves, these units typically
employ a flow control member in the form of a rotatable ball, rotatable ball segment,
or a rotatable butterfly element. The rotation of the flow control element opens
and closes the valve gate or plug.
Valve actuators for controlling such rotary action control valves
typically employ a movable diaphragm connected to a rod at the diaphragm center,
see for example US-A-4 261 546. Moving the diaphragm displaces the rod linearly
and thus requires a linear to rotary action translation. A rotational link arm
has one end fixed to the valve rotary shaft and the other link arm end is coupled
to the diaphragm rod. Linear movement of the diaphragm rod moves the link arm
and thereby actuates a rotational movement in the valve shaft which is ultimately
connected to the rotatable flow control element in the fluid control valve.
Such presently available rotary valve actuators employ many components,
several of which require time consuming and expensive machining during manufacture.
A manufacturer and users of rotary valve actuators therefore must inventory a large
number of parts, and also must inventory an increasing number of expensive, machined
spare parts for repair and replacement.
It is desired therefore to reduce the number of parts as well as
to reduce the number of time consuming and expensive machined parts in a rotary
valve actuator so as to thereby reduce manufacturing costs and inventory requirements
both for the manufacturer and the user. In addition, it is further desired to
provide a rotary valve actuator of reduced size and weight, and one having the
capability of actuating a variety of rotary valves to reduce the number of rotary
valve actuators required.
Summary Of The Invention
In accordance with the present invention, there is provided a rotary
valve actuator as defined in claim 1. Prefered embodiments of the invention are
defined in the dependent claims. A preferred rotary valve actuator of the present
invention includes a sliding cylinder or canister operated by a pressurized bladder,
enabling a rolling diaphragm bladder action to linearly move the sliding canister.
A cylindrical shaped lever is attached by a flexible canister/lever linkage to
the sliding canister on one side of the lever. The linear motion of the sliding
canister and the resulting pulling tension of the canister/lever linkage is converted
into a rotary motion of the lever about its cylindrical axis.
Opposed to the sliding canister and on the other side of the rotatable
lever there is provided a return spring which is attached to the lever with a
flexible spring/lever linkage. The spring is precompressed to a predetermined load
so the pulling tension of the spring/lever linkage tends to rotate the lever in
the direction of the spring, and at the same time pull an unoperated sliding canister
towards the lever and against an adjustable, canister bottom travel stop.
When the pneumatic pressure is introduced into the bladder, the pressure
will force the sliding canister away from the lever and thereby rotate the lever
in the direction of the sliding canister. The top travel of the sliding canister
is restricted by an adjustable, canister top travel stop that is aligned with
a stop pawl extending from the lever. As the lever rotates, it comes into contact
with the stop. As the sliding canister rotates the lever, this causes the spring
to compress and resist the pull from the sliding canister. When the pressure is
released from the bladder, the spring pulls the sliding canister back down against
the canister bottom travel stop.
The respective linkage between the lever and the sliding canister
on one side, and between the lever and the spring on the other side of the lever
can be flexible or rigid in nature. Flexible linkage can be formed for instance
of chain material, cables, etc. Rigid linkages can be formed of linked bars, rack
and pinion members, etc. When using flexible linkage, the lever arm length is
always the same distance from the center of the lever arm through its 90° rotation.
In contrast, with rigid linkage, the lever arm length is reduced by 30° at the
end of the lever arm travel. Also, the flexible linkage produces constant torque
through the 90° rotation of the lever and is desired over rigid linkage which
produces variable torque throughout the lever rotation.
A significant advantage is provided by the mounting of the rotating
lever intermediate the sliding canister on one side and the return spring on the
other side of the lever in a "pull-pull", constant tension configuration. With
the spring being mounted separately from the sliding canister, this enables the
lever arm to be shorter for the spring as compared to the lever arm for the sliding
canister. A shorter lever arm reduces the spring travel and in turn reduces the
spring height, making the actuator profile smaller, the actuator weight lighter,
and the actuator construction less costly.
The pull-pull, constant tension valve actuator configuration of the
present invention continually takes any lost motion out of the linkage connecting
the sliding canister cylinder, rotating lever, and return spring. In contrast,
in normal linkage configurations in actuators, continuous cycling of the movable
actuator components causes wear and eventually an undesired lost motion condition
is exhibited. In the present invention the pull-pull, constant tension feature
between the sliding canister and the spring with the intermediate rotating lever
not only eliminates the lost motion problem of prior actuators, but also eliminates
the need for precision mated parts, since all mating parts are kept in tension.
In a preferred embodiment of the present invention, the sliding canister
and spring are spaced 180° apart, in-line and resisting each other through the
connecting linkage. The tension forces transmitted through the linkage of the sliding
canister to the lever and from the lever to the spring linkage minimizes the load
on the lever bearings and thereby minimizes bearing wear. Also, with the linkage
in tension, the actuator housing is placed in compression, and the housing material
in compression is more desirable than in tension. Also, with the housing material
parts in compression only a minimum number of fasteners are required for reliably
maintaining the housing parts assembled.
A return spring, spring end caps and spring linkage is preassembled
to form a spring cartridge. The spring cartridge can then be mounted in the housing
as a unitary unit. This insures that the spring linkage is not damaged when preloading
the spring and insures good linkage alignment with the lever and also reduces
user safety issues during assembly of the actuator components.
The linkage between the lever and the sliding canister is connected
at the side wall of the sliding canister thereby simplifying the over all assembly.
This connection reduces the number of parts required to carry the pulling load
to the rotatable lever thereby reducing actuator size, weight and cost.
A valve positioner or a valve controller instrument is mountable
directly onto the actuator. The use of a sliding canister enables the ease of
providing manifolding air passageways from the bladder unit to the direct mounted
valve positioner, which eliminates the need for exterior tubing interconnecting
the positioner and actuator units.
In an alternative embodiment of the pull-pull, constant tension rotary
valve actuator of the present invention, the return spring is mounted 90° to the
center line of the sliding canister, with the same rotatable lever as in the prior
mentioned in-line actuator embodiment. This alternative 90° embodiment of the
pull-pull actuator of the present invention provides a more compact profile configuration
than the in-line embodiment, and may be preferred for use with certain valve situations.
The same pressure actuated bladder, sliding canister, rotating lever, and spring
cartridge are utilized as in the in-line embodiment. Also, the same advantages
of the in-line rotary actuator embodiment are obtained by this alternative 90°
rotary actuator embodiment, except that because the spring is positioned 90° to
the center line of the sliding canister, this tends to create a diagonal load
on the lever bearings, which diagonal bearing load is not present in the in-line
Brief Description Of The Drawings
The invention may be best understood by reference to the following
description taken in conjunction with the accompanying drawings, in which like
reference numerals identify like elements in the several figures and in which:
- Figure 1 is an elevational view, partly sectional, illustrating a rotary valve
actuator constructed in accordance with the principles of the present invention,
and with a canister cover at one end fragmented and a spring cartridge cover at
the other end removed for convenience of illustration;
- Figure 2 is a right side elevational view, partly sectional, of Figure 1 illustrating
the rotary valve actuator with a direct mounted valve positioner and a spring
cartridge cover assembled in position;
- Figure 3 is a left side elevational view, partly sectional, of Figure 1 illustrating
the rotary valve actuator with the spring cartridge cover removed;
- Figure 4 is a partly sectional view taken generally along section lines 4-4
of Figure 3, illustrating the rotary valve actuator operating a rotary shaft for
actuating a fluid control valve;
- Figure 5 is a perspective view illustrating a rotatable cylindrical lever utilized
in the rotary valve actuator of Figure 1;
- Figure 6 is a plan view illustrating a bladder used in the rotary valve actuator
of the present invention;
- Figure 7 is a sectional view taken along section lines 7-7 of Figure 6;
- Figure 8 is a sectional elevational view, partly fragmented, illustrating an
alternative embodiment of a rotary valve actuator according to the present invention
wherein the sliding canister and return spring are located 90° relative to each
- Figure 9 is a sectional elevational view taken along section lines 9-9 of Figure
Referring now to the drawings, there is illustrated a rotary valve
actuator for fluid control valves, wherein the actuator includes linear to rotary
transformation in which tension is always maintained in the linkage between opposing
actuating elements by enabling the actuating elements to pull against each other
in a pull-pull, constant tension configuration. In particular, Figures 1-7 illustrate
a rotary valve actuator wherein the pull-pull actuating elements are in an in-line
configuration. Figures 8 and 9 illustrate a rotary valve actuator wherein the pull-pull
actuating elements are in a right-angle configuration.
With reference to Figures 1-7, there is illustrated a rotary valve
actuator 10 which includes a slidably movable canister 12, an opposite spring
cartridge 14 and an intermediately coupled rotatable lever 16, such that the linkage
coupling mechanism is always in pull-pull tension. That is, when the canister
12 is being moved in a linear manner oppositely away from the lever 16 in a pulling
linkage manner, the opposite spring cartridge 14 is resisting this pulling action
of the canister and is itself exerting a pulling force on the respective linkage
coupling. Therefore, there is provided a unique "pull-pull" rotary valve actuator
10 which keeps the coupling or respective linkage always in tension.
The rotatable lever 16 is formed of a hollow hard metal such as steel,
cylindrically shaped with opposite flange ends 18, 20 and an intermediate middle
portion 22 as shown in Figure 5. The lever 16 is rotatably mounted within a lower
housing 24 and is supported on suitable bearings 25 (see Figure 1) such that the
lever middle portion 22 is supported on bearing support columns 26 in the frame
24. A pair of support columns 28 similar to columns 26 are also provided in an
upper housing 30. As can be seen from Figure 3, mounting of the lower housing 24
to the upper housing 30 captures the lever 16 between opposing support columns
26, 28 so as to rotatably mount the lever 16 within the rotary valve actuator 10.
Instead of support columns, other lever support structure can be provided, such
as cast-in wall sections in the housing.
Respective canister linkage mounts 32, 34 project from the respective
link flanges 18, 20 for mounting respective chain linkages 36, 38 to the canister
12 (see Figure 1). A boss 40 projects from the lever middle section 22 for mounting
chain linkage 42 to the spring cartridge 14.
The canister 12 includes a top portion 44 and depending side portions
46. A respective canister/chain connector 48 is mounted to respective opposite
canister sides 46 at one connector end and at the other connector end to a respective
chain linkage 36, 38.
With reference to Figure 3, it can be seen that one end of the chain
42 is connected to the lever boss 40. The other end of chain 42 is mounted to a
spring connector 50 which extends from a spring rod 52 within the spring cartridge
14. The spring cartridge 14 also includes opposite end plates 54 and a spring 56
mounted between the end plates 54. As can be seen in Figure 3, spring rod 52 extends
through a suitable aperture in the upper end plate 54 and is mounted by a split
rod connector 57 at the grooved rod end to the lower end plate 54. The upper end
of the spring cartridge 14 is nested within a spring cavity 58 provided within
the housing 24.
A sealed, expandable bladder unit 60 is provided between canister
12 and an upstanding dome section 62 of the frame 30. The bladder 60 preferably
is a sealed, preformed bladder unit formed of two pieces joined by heat sealing.
Referring to Figures 3 and 6, it can be seen that the bladder 60
has an oval shape with an internal surface 64 which fits snugly around the dome
shaped projection 62 in the initial deflated bladder condition. As shown in Figures
1 and 3, the bladder 60 is mounted on the dome 62 such that the inside bladder
surface 64 at the bladder sides is immediately adjacent the dome 62 exterior sides,
and with a bladder bottom surface 66 immediately adjacent the dome top surface
of the dome 62. A bladder top surface 68 also lies immediately adjacent the canister
top 44. Therefore, the expandable bladder 60 is trapped between the stationary
housing dome 62 and the slidably movable canister 12.
The bladder may be formed of polyurethane with a cloth backing layer.
For lower temperature usage the cloth backing layer is not required. The cloth
backing layer, if used, surrounds the entire bladder and serves to reinforce the
bladder material for use at high operating temperatures. At extreme upper temperatures,
a thermopolyester plastic material such as Riteflex may be used for the bladder,
with or without a cloth reinforcing layer.
The bladder is preferably preformed in the natural state to the smallest
chamber size between the canister 12 and the top of dome wall 62. A bladder annular
perimeter portion 63 is formed as a convolution of the bladder bottom surface 66.
A cloth reinforcing layer can be placed on the exterior surfaces of the bladder
by insertion during injection mold forming of the bladder. Alternatively, after
injection molding of the bladder, the cloth can be applied thereto by suitable
pressure and temperature conditions. A urethane layer can be used on a bias cut
cloth prior to heat bonding to the bladder at a temperature of about 330°F (166°C)
at 50 psi (345 Kpa) for about 1-1/2 hours. Instead of applying a cloth layer on
the entire bladder exterior, the cloth may be applied only to the annular perimeter
The cloth reinforced, preformed bladder is then baked in an oven
to stress relieve the material. It has been found that such stress relieving of
the bladder in an oven can be accomplished at about 250°F (121°C) for about 24
To keep the bladder in place during actuator operation, upon assembly
into the actuator, bonding adhesive beads may be applied above and below the bladder
two-piece joint at the canister 12. Similarly the bladder can be bonded with a
suitable adhesive to the top of the dome wall 62.
The bladder enables a rolling diaphragm action at the bladder perimeter
portion 63 instead of an undesired balloon-type action during expansion of the
bladder. As the valve actuator is operated by coupling fluid into the bladder chamber
the bladder perimeter portion 63 in contact with the stationary dome side wall,
merely rolls off of engagement with the stationary member while simultaneously
increasingly engaging the side wall of the movable canister.
Thus, the bladder perimeter portion 63 is expanding in going from
an initial unpressurized position to a pressurized position with the bladder perimeter
portion merely moving from the inside diameter of the bladder to the outside diameter
of the bladder in a rolling fashion placing the bladder material under tension.
This significantly reduces bladder wear, increases the bladder life and enables
repeated actuator operation over extended operating cycles and wide temperature
and pressure ranges.
A bladder inlet tube 70 is inserted within a passageway 72 in housing
30 which passageway 72 leads to a connecting passageway 74 having an opening 76
at the bottom of frame 30 as seen in Figure 3. The inlet tube includes a shoulder
71 for mounting an O-ring (not shown) to seal the bladder inlet within the passageway
Passageway opening 76 communicates with an instrument 78, such as
a pneumatic positioner (see Figure 2) so that initiating pressurized expansion
and contraction of the expandable bladder 60 is under control of the instrument
78 in a known manner. It is understood that the positioner 78 has been removed
from Figure 3 for convenience in illustrating other components of the rotary valve
actuator 10. A plug 80 is inserted into the end of the passageway 72 during normal
operations and may be removed from the passageway to gain access to the fluid passageway
With reference to Figure 4, there is illustrated the rotary valve
actuator 10 with a mounting bracket 82 which may be used to mount the valve actuator
10 to a fluid control valve 84, as schematically illustrated in Figure 4. A valve
shaft 86 includes a splined end so as to be rotatably driven by the rotating lever
16 with very little if any lost motion between the rotating lever 16 and the valve
shaft 86. Providing this lost motion connection is a splined sleeve 88 (see Figure
3) having interior splines 90 matching the splines on the end of shaft 86. The
sleeve 88 has an outer diameter adapted to the lever bore 92, and further includes
a flat section 94. A shaft mounting projection 95 having an internal threaded
bore extends from the lever middle section 22 (see Figure 5). The lever is rotated
so the projection 95 is placed opposite an access hole 96 provided in the lower
housing 24 as shown in Figure 3. The sleeve 88 is inserted into the lever bore
92 and the flat section 94 is positioned opposite the access hole 96 in the lower
frame 24. A threaded set screw 98 known as a "dog point set screw" includes a corresponding
flat end for locking engagement with the flat section 94 of the sleeve 88.
With the valve shaft and sleeve positioned within lever bore 92 such
that the sleeve flat section 94 is aligned with the threaded bore hole provided
through the mounting projection 95 and into the interior of the lever 16 at the
bore 92, the set screw 98 threadably engages the bore. The threaded set screw
98 is mounted into the projection 95 until the set screw flat faces lockingly engages
the flat section 94 of the sleeve 88 to thereby secure the splined sleeve 88,
and the splined end of shaft 86. This ensures that the valve shaft 86 will rotatably
move with the lever 16 with very little, if any, lost motion between the shaft
and lever. The sleeve 88 may be split to provide a secure connection to the shaft
Respective adjustable stops are provided for the movement of the
spring as well as the sliding canister. With reference to Figure 3, there is illustrated
a canister top position adjustable stop 100 which includes a threaded stop rod
102 threadably engaged within housing 24 and which can be locked into position
by a locking nut 104. A pawl 106 extends from the mounting projection 95 so as
to rotate with the position of lever 16. As can be seen in the notations provided
on Figure 3, linear upward movement of the canister 12 during expansion of the
bladder 60 rotates the lever 16 in a clockwise direction, which is indicated by
the reference arrow and notation "C". In Figure 3 there is also provided a notation
indicating the direction of rotation of the lever 16 under pulling action of the
spring 56, which reference arrow notation is marked "S". Accordingly, as the canister
12 moves linearly upwardly in response to the expanding bladder, the pawl 106
rotates clockwise until engaging the end of the stop rod 102. Stop 100 therefore
sets the uppermost or top position of the canister 12. The stop position may of
course be adjusted by unlocking nut 104 and threadably adjusting rod 102 until
the desired uppermost canister position is reached.
Referring to Figure 2, a respective canister bottom position-adjustable
stop 108 provided on opposite canister sides includes a threaded stop bolt 110
which is threadably engaged into the housing 30 and can be locked into position
using a locking nut 112. The spring 56 tends to pull the canister 12 downwardly
in Figure 2, which rotates lever 16 in the illustrated clockwise direction "S"
until the bottom end 114 of the canister engages the threaded stop bolt 110. The
stops 108 therefore sets the lowermost or bottom position of the canister 12.
The position of the adjustable stop 108 can readily be changed by unlocking nut
112 and threadably adjusting the position of stop bolt 110.
A canister cover 116 is provided for completely covering the canister
46, chain connector 48, and adjustable stops 108. The cover 116 may be suitably
detachably mounted to the top of the housing 30. Similarly, a spring cartridge
cover 118 may be suitably detachably mounted to the lower housing 24 to cover
the spring cartridge 14.
With reference to Figure 2, there is illustrated a feedback linkage
120 interconnecting the positioner 78 to the rotatable lever 16. A feedback arm
122 is connected such as by screws to the lever flange 20 so as to rotate with
the lever 16. A bent linkage 124 is pivotably connected at one end to the feedback
arm 122 and with the other bent linkage end passing through a slot in the housing
24 to pivotably engage a straight link arm 126, which in turn is connected to
a rotating shaft 128 in the positioner 78. It is to be understood that the valve
positioning instrument 78 can be a digital valve controller, such as a communicating,
microprocessor-based current to pneumatic instrument. In addition to the normal
function of converting a input current signal to a pneumatic output pressure,
the digital valve controller, using a communications protocol, can provide easy
access to information critical to process operation. Thus, one can gain information
from the principle component of the process, i.e. the fluid control valve 84,
using a compatible communicating device at the control valve or at a field junction
box, or by using a personal computer or operator counsel within a control room.
Alternatively, the instrument can be an analog device or a pneumatic positioner.
As can be seen in Figure 2, the feedback linkage 120 has one end
mounted to the rotating shaft 128 on a positioner 78 and another end mounted via
the feedback arm 122 to the actuator rotating lever 16. Because the lever 16 is
interconnected with the rotating valve shaft 86, the position of the valve shaft
is sensed by the positioner 78 through the feedback linkage 120.
Assembly of the components of the pull-pull rotary valve actuator
10 illustrated in Figures 1-7 is readily provided in the following manner. Initially,
the bladder 60 is snugly mounted atop the dome 62 on the upper housing member
30. The spring cartridge 14 is inserted into the spring cavity 58 on the lower
housing 24. The spring cartridge 14 is then mounted to the lever using appropriate
nuts and bolts fasteners to interconnect the spring chain linkage 42 to the spring
connector 50 at one end and to the lever boss 40 at the other end. The two canister
chain links 36, 38 are then connected to the respective lever linkage mounts 32,
34 at one end and to the respective chain connectors 48 at the other end.
The lever 16 may now be emplaced onto the support columns 26 with
suitable bearings. Next, upper housing 30 is mounted onto the lower housing 24
and the housings are secured together. The canister chain links 36, 38 are then
connected to the respective canister sides using respective canister connectors
48 and suitable fasteners. The positioner 78 is then mounted to the housing 30
and the feedback linkage 120 is interconnected between the lever 16 and the positioner.
Thereafter, the covers 116, 118 can be mounted and the mounting bracket 82 as well,
The initial positioning of the canister and spring with respect to
the adjustable stops is accomplished as follows. Initially, the spring 56 in the
spring cartridge 14 is precompressed to a predetermined load, and the spring cartridge
is inserted into the housing and connected to the lever as described. Then the
spring 56 is preloaded with the linkage so the spring block 53 on the spring rod
52 is moved off of the top end plate 54 as shown in Figure 3. Next the bladder
is pressurized to move the canister up sufficiently so the two adjustable stops
108 can be mounted to the housing 30. Both travel stops 110 are then adjusted
so that the sliding canister 12 bottoms evenly against the stops before reaching
the end of its travel in the downward direction and so there is still tension
maintained in the linkage (see Figure 3). This sets the canister bottom position.
Note in Figures 2 and 3 that as the spring 56 pulls on the linkage
42 it will rotate the lever 16 in the reference direction "S" and at the same time
pull the sliding canister 12 downward against the adjustable travel stops 110.
Also, Figure 2 and 3 show the reference direction "C" as the upwardly moving canister
12 pulls on linkage 36, 38 and at the same time compresses the spring.
When air pressure is supplied through openings 76, passageways 74,
72 and into the bladder 70, the pressure will expand the bladder 60 and force
the sliding canister 12 in a linear upward movement which correspondingly rotates
the lever 16 in the clockwise direction "C" as shown in Figure 3. The adjustable
stop 100 is adjusted to restrict the uppermost travel of the sliding canister 12
and ensure that the desired control valve position is reached.
Several advantages are afforded by the pull-pull rotary valve actuator
10 as shown in Figures 1-7. The linear upward movement of canister 12 under the
pressure of the expanding bladder 60 rotates the lever 16 and causes the spring
56 to compress and resist the pull from the sliding canister. This pull-pull action
maintains the chain linkages 36, 38, 42 in substantially constant tension i.e.,
with about only a 3% variance in torque. As the pressure is released from the
bladder 60, the spring 56 pulls the sliding canister 12 back towards the adjustable
stops 110. This pull-pull configuration in the actuator continually takes any
lost motion out of the connecting linkage due to wear caused by cycling, and further
eliminates the need for precision mated parts, since all mating parts are kept
in tension. Also, because the spring 57 is mounted separately from the sliding
canister 12, this allows the lever arm for the spring (in Figure 5 measured radially
from the centerline of lever 16 to the connection point on boss 40) to be shorter
for the spring than the lever arm for the sliding canister (as measure in Figure
5 radially from the centerline of the lever 16 to the connection point on linkage
mounts 32, 34). A shorter lever arm reduces the spring travel and in return reduces
the spring height, making the actuator smaller, lighter, and less costly. Furthermore,
it may be noted that since the spring and canister are substantially in-line at
180° opposite positions with respect to the lever, and with the connecting linkage
to the lever in a pull-pull maintained tension condition, the amount of bearing
forces exerted on the support columns 26, 28 and the associated bearings during
driving rotation of the lever 16 is significantly reduced. Using flexible linkage
chains 36, 38, 42 provides the lever arm (either the spring lever or the canister
lever arm) to always be the same respective distance from the center of the lever
through the 90° rotation of the lever. Thus, the flexible linkage produces constant
torque through the 90° rotation of the lever and is therefore desired over rigid
linkage which produces a variable torque over the rotatable position of the lever.
Referring now to Figures 8 and 9, there is illustrated an alternative
embodiment of a right angle rotary valve actuator 130 which includes operating
components of the sliding canister, bladder, spring cartridge, and lever identical
to the same components with respect to the previously described in-line rotary
valve actuator 10 of Figures 1-7. As can be seen from Figure 8, rather than the
in-line configuration of prior described rotary valve actuator 10, the rotary
valve actuator 130 provides the return spring cartridge 14 configured 90° to the
center line of the sliding cartridge 12. This tends to reduce the size, number
of parts and corresponding cost of the actuator. However, because the spring cartridge
14 is angularly positioned with respect to the center line of the sliding canister
12, (rather than in-line positioning in actuator 10) this creates a diagonal load
on the bearings of the rotating lever 16 of the actuator 130.
It must be recognized, however, that the rotary valve actuator 130
also provides pull-pull tension of the linkages 36, 38, 42 between the canister
12, lever 16 and spring cartridge 14, thus maintaining the linkage in constant
tension. Therefore, the many significant advantages afforded by the pull-pull,
in-line rotary valve actuator 10 are also accomplished by the pull-pull, 90° rotary
valve actuator 130.
The foregoing detailed description has been given for clearness of
understanding only, and no unnecessary limitations should be understood therefrom,
as modifications will be obvious to those skilled in the art.