An improved push-pull cable assembly (10) is provided with means for automatically compensating for changes in the cable's effective length, thus requiring a minimum of adjustment over an extended period. To this end, the cable's actuating rod (124) may be provided with a spring-loaded backlash compensating coupling (30) operatively connecting the actuating rod with an operating lever (106) on the controlled mechanism. A helical compression spring (198) is provided at the end of the push-pull cable assembly such that the spring exerts a compressive force in the longitudinal direction of the actuating rod between a spring retainer (196) and a clevis fitting (122) pivotally connected to the controlled mechanism's operating lever. The clevis fitting is slidably mounted with respect to the actuating rod such that the spring will tend to displace it from a compressed position (210) closer to the spring to an extended position (216) further away. The positions of both ends of the spring are adjusted with respect to the actuating rod such that the spring's compressive force will exceed the force required to operate the valve and also any backlash will be fully taken up and a continuing force applied to the lever when a handle (116) at the other end of the cable is fully pushed in.

TECHNICAL FIELD 
The present invention relates generally to mechanisms for transferring 
motive forces from a remote location and more particularly to an improved 
push-pull cable for remotely operating a valve or other similar mechanism. 
BACKGROUND ART 
Push-pull cable assemblies are well known in the prior art. They are 
conventionally used to control the operation of valves and other 
mechanisms from a conveniently located position remotely located from the 
actual mechanism being operated. For example, when designing a pressurized 
potable water supply for installation in large commercial passenger 
aircraft, it is desirable to keep the total length of the individual fluid 
conduits as short as possible in order to minimize weight. Furthermore, 
the shorter the fluid conduit, the less energy is required to pump the 
fluid through the system. Additionally, the probability of leaks occurring 
somewhere in the system will be diminished to the extent that the system 
can be reduced in size and capacity. As a result of such considerations, 
the several valves which are commonly required in such systems to seal off 
the portions of the system from one another or from the external 
environment are preferably located in the immediate vicinity of the fluid 
reservoirs and other plumbing subsystems with which they are functionally 
associated, rather than having their location determined solely by ease of 
access during normal operation and maintenance. Thus, it is desirable that 
it be possible to operate a control valve from a remote location by means 
of a simple, convenient and reliable mechanism for transferring motive 
forces. For such purposes, push-pull cable assemblies are commercially 
available having an operating handle at one end and an actuating rod at 
the other end connected by a flexible cable contained within a closely 
fitting sheath. Such as assembly can transmit both tensile and compressive 
forces from one end to the other. Because such a cable is designed to 
transmit compressive as well as tensile forces, it does not require the 
use of any return spring that would increase the force required to pull 
the cable to its retracted position and which would probably require the 
use of a brake or detent to prevent the cable from inadvertently returning 
to its unretracted position, thereby further increasing the operating 
force required. Since many valves and other mechanisms employ a conical or 
spherical member that must be rotated through an angle (typically 
90.degree.) from one position (e.g., "off") to another position (e.g., 
"on"), prior art push-pull cable assemblies have been provided with a 
swivel fitting at the actuating end which permits a swiveling movement of 
the actuating rod at the end of the cable so that the cable's outer sheath 
and its associated mountings are not subjected to bending moments as a 
lever arm operatively connected to the valve's rotating member moves in an 
arc about the valve's rotational axis and so that the end of the cable 
will always be able to exert its pushing and pulling motive forces in a 
straight line and thus will not become bent or kinked. 
Typically, a push-pull cable such as described above will be so oriented 
with respect to the lever arm on the valve such that the "normal" (i.e., 
when the aircraft is airborne) position of the operating handle on the 
other end of the cable will be fully pushed-in (or "retracted") and its 
"alternative" (i.e., its condition during a refilling or draining 
operation) position will be with the handle pulled-out (or "extended"). 
Accordingly, to prevent the push-pull cable from being accidentally 
extended from its normal position to its alternative position, a keeper 
assembly may be operatively associated with the control handle for 
maintaining the handle in its retracted position, thereby insuring that it 
will not be moved to a partially extended position by gravity, vibration 
or other environmental forces. 
With respect to such prior art push-pull cables, it will be appreciated 
that a certain amount of backlash is associated with their operation, 
since the fit between the outer surface of the flexible cable and the 
inner surface of the sheath must be sufficiently loose to prevent any 
binding even if the sheath is bent and accordingly, when the cable is 
pushed in, the inner walls of the sheath will tend to force the inner 
cable into a somewhat spiraled or undulating condition having an effective 
length shorter then the effective length of the pulled-out cable by an 
amount known as "backlash". Furthermore, as a result of normal use, the 
diametrical clearance between the cable and sheath will gradually 
increase, with the result that a worn push-pull cable will have even more 
backlash than a new push-pull cable. 
When such a push-pull cable is being utilized to control a valve or other 
similar mechanism provided with a mechanical stop to define the valve's 
normal position, it will be appreciated that the effective length of the 
pushed-in cable must be precisely adjusted. When the cable's operating 
handle is fully retracted and held in place by the keeper assembly, the 
cable's actuating rod should press against the valve's lever arm so as to 
hold positively the valve against its stop, while taking up all the 
backlash between the cable and its sheath; however, there must not be any 
excessive forces that could distort the valve or its lever or which could 
subject the cable assembly and its mountings to excessive stresses. The 
known prior art cable assemblies accordingly provided a backlash 
adjustment (in the form of an adjustable threaded rod and locknut) which 
determines the effective overall length of the cable from its handle up to 
the point at which the cable pushes against the valve's lever arm. 
It will be appreciated that such a prior art cable assembly was difficult 
to adjust since the backlash in the cable had to be determined by trial 
and error techniques, with one mechanic operating the handle and a second 
mechanic trying different positions of the threaded rod and locknut. If 
the adjustment were made too long, the various components would be 
overstressed and the weakest member would frequently be broken (for 
instance, the telescoping actuating rod at the end of the cable assembly). 
If the adjustment were made too short, the valve would be free to move 
away from its normal position, causing the aircraft's water supply to 
function erratically. 
Accordingly, it is a primary objective of the present invention to provide 
an improved push-pull cable that may be readily adjusted to hold a valve 
or other similar mechanism in a predetermined normal position against a 
fixed stop when an operating handle at the other end of the cable is held 
in its normal pushed-in position by a keeper assembly. 
It is a related objective to provide an improved push-pull cable that 
automatically compensates for changes in the cable's effective length 
caused by backlash, wear, etc. 
It is yet another related objective to provide an improved push-pull cable 
having a spring operatively connecting the cable and the mechanism being 
operated to provide automatic compensation for backlash in the cable 
without requiring excessive operational forces or stresses. 
It is an overall objective of the present invention to provide an improved 
push-pull cable assembly that will positively hold the controlled 
mechanism in a normal position, that will automatically take up for wear 
and backlash in the cable, that will prevent accidental overloading of the 
mechanism, that will remain in adjustment for an extended period of time, 
and that will be simple and can be adjusted accurately when such 
adjustment is required. 
DISCLOSURE OF THE INVENTION 
In accordance with the teachings of the present invention, a push-pull 
cable assembly having a handle at one end and an actuating rod at the 
other end is provided with means for automatically compensating for 
changes in the cable's effective length, thus requiring a minimum of 
adjustment over an extended period even when it is necessary that the 
cable be capable of positively holding the controlled mechanism at a 
predetermined "normal" position against a fixed stop. To this end, the 
cable's actuating rod may be provided with a spring-loaded backlash 
compensating coupling operatively connecting the actuating rod with an 
operating lever or other similar control means on the controlled 
mechanism. 
In accordance with the presently preferred embodiment of the invention, 
such a spring-loaded backlash compensating coupling comprises a helical 
compression spring mounted about the actuating rod at the end of the 
push-pull cable assembly such that the spring exerts a compressive force 
in the longitudinal direction of the actuating rod between a spring cup or 
other retaining means attached to the actuating rod and a clevis fitting 
or other suitable connecting means pivotally connected to the control 
means of the mechanism being operated. The clevis fitting is slidably 
mounted to the actuating rod such that the spring will tend to displace 
the clevis fitting in the longitudinal direction of the rod from a 
compressed position closer to said spring cup to an extended position 
established by a clevis stop at the far end of the rod. 
For ease of installation and maintenance, the actuating rod is preferably 
also provided with means for adjusting the portions of both the spring cup 
and of the clevis stop with respect to the actuating rod. 
In normal use, the spring-loaded coupling is adjusted such that when the 
cable's handle is pushed fully home, the compression spring is partially 
compressed and the clevis fitting is at an intermediate position between 
its extended position and its compressed position, whereby providing a 
resultant over-travel clearance between the clevis fitting and the clevis 
stop. The lever or other control means of the controlled device is thus 
subjected to a continuing compressive force exerted by the compression 
spring which holds the device in its "normal" position as determined by a 
control stop provided as an integral part of the device. As soon as the 
handle is released from its fully pushed-in position, the compression 
spring is free to extend to its fully extended position by an amount 
determined by the over-travel clearance. As the dimensional clearance 
between the inner cable and the outer sheath increases with a resulting 
increase in the cable's backlash, the over-travel clearance between the 
clevis and the clevis stop decreases, until it becomes again necessary to 
re-adjust the mechanism after prolonged use.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings and in particular to FIGS. 1 and 2 thereof, 
it will be seen that the preferred embodiment of the push-pull cable 
constructed in accordance with the present invention (10) is generally 
similar to the prior art push-pull cable (20), with the notable exception 
that a spring-loaded backlash compensating coupling (30) has replaced the 
simple disconnect fitting (40) of the prior art. 
More specifically, both the prior art cable assembly (20) of FIG. 1 and the 
improved cable assembly (10) of FIG. 2 utilize a flexible cable (102) 
retained inside an outer sheath (104). Furthermore, the cable assembly is 
utilized to rotate a lever arm (106) about an operational axis (108) of a 
valve assembly, of which only the packing gland (110) is visible in the 
Drawings. The lever arm (106) is welded to or otherwise forms an integral 
part of the operating shaft (112) of the valve; an emergency operating 
handle (114) is also provided whereby the valve may be operated directly 
without resorting to a push-pull handle (116) that is at the other end of 
the push-pull cable (see FIG. 4). It will be seen that the valve operating 
lever arm (106) is provided with a bore (118) (see FIG. 5) parallel to the 
lever's rotational axis (108). A retaining pin (120) passing through this 
bore thus may pivotally connect the arm (106) with a fitting in the form 
of a clevis (122) at the upper end of the push-pull cable assembly (10). 
An actuating rod (124) telescopes within an extension (126) of the outer 
sheath (104) secured thereby by means of a swivel fitting (128) which 
accommodates the to and fro movement of the actuating rod (124) as the end 
of the lever arm (106) rotates in an arc about its rotational axis (108). 
It will be noted that in both the prior art cable assembly (20) of FIG. 1 
and the improved cable assembly (10) of FIG. 2, the actuating rod (124) is 
terminated at its upper end by an end fitting (130) through which passes a 
pinch bolt (132) which secures the upper end of flexible cable (102) to 
the actuating rod (124). However, the portion of the respective cable 
assemblies between the cable pinch bolt (132) and the clevis (122) are 
quite different from each other. 
Referring specifically to the prior art configuration illustrated in FIG. 
1, it will be seen the quick disconnect fitting (40) comprises a collet 
(134) for gripping an appropriately shaped extension (136) of the end 
fitting (130) and may be readily released therefrom by proper manipulation 
of a knurled sleeve (138). Extending above the sleeve (138) is a threaded 
rod (140) which may be adjusted in length relative to a downwardly 
descending internally threaded boss (142) depending from the clevis 
fitting (122). Once properly adjusted, these threaded parts are held in 
place relative to each other by means of a locknut (144). 
Referring now specifically to the improved cable assembly of FIG. 2, it may 
be seen that the corresponding structure is a spring-loaded backlash 
compensating coupling (30) that is secured to a threaded extension (146) 
of the end fitting (130) and which is connected at its upper end to the 
clevis fitting (122) by a spring-loaded arrangement that will be described 
in more detail hereinafter with particular references to FIGS. 5 and 6. 
Referring now to FIGS. 3 and 4, which it will be recalled are respectively 
an isometric partially cutaway view and an elevational side view of the 
fittings provided at either end of the push-pull cable outer sheath (104), 
it will be noted that the outer sheath (104) is rigidly mounted to a 
strengthening rib (148) of the aircraft in the vicinity of the swivel 
fitting (128) by means of a nut (150). Furthermore, a number of supporting 
clamps (152) also mounted to various structural members of the aircraft 
are provided along the length of the outer sheath (104) at appropriate 
intervals from the upper swivel fitting (134) to the lower handle (116). 
An intermediate coupling (154) is also provided to facilitate mounting and 
adjusting of the relatively rigid conduit forming the sheath (104), 
thereby enabling it to be adjusted and installed in conveniently sized 
sections. 
The lower end of the outer sheath (104) is rigidly mounted to the rear of a 
maintenance panel (156) and partially protrudes therethrough as handle 
shaft bushing (158). The handle shaft (159) is of the same external 
dimensions as the flexible cable (102) and thus is free to slide into and 
out of the outer sheath (104) and the outer sheath handle bushing portion 
(158). The handle (116) is held in its fully pushed-in position by a 
keeper assembly (160) which, as best seen in FIG. 4, comprises a channel 
member (162) and a latch member (164). The channel member (162) is pivoted 
at one end to a supporting post (166) and at the other end is hingedly 
connected to the aforementioned latch member (164). The latch (164) 
co-acts with a pin (168) mounted to the same supporting structure that 
holds the post (166) but separated therefrom by a distance approximately 
equal to the length of the channel member (162). It will be seen that the 
latch member (164) is provided wih a camming surface (170) and a detent 
surface (172) such that, as the latching member (164) is pressed upward, 
the camming portion (170) co-acts with the pin (168) to force the channel 
member (162) to push up on the handle (116) until the detent surface (172) 
catches on the pin (168) and the latch, the channel and the handle are 
then all held in their normal or fully pushed-in position. A resilient 
rubber pad (176) may be provided between the lower surface (174) of the 
handle and the upper surface (178) of the channel member to protect the 
handle from scuffing and to provide a certain resiliency to the latching 
action between the handle and its keeper. However, when a properly 
adjusted spring-loaded backlash compensating coupling (30) is provided in 
accordance with the present invention, the resilient pad (176) could be 
omitted and the push-pull cable assembly (10) would still function 
properly. 
Referring now to FIGS. 5 and 6, which will be recalled are enlarged 
cross-sectional views of the spring-loaded backlash compensating coupling 
(30) and other related fittings utilized in the embodiment of FIGS. 2, 3 
and 4, it should be noted that FIG. 5 shows the coupling in its 
"intermediate" position when the operating handle (116) at the other end 
of the push-pull cable (102) is secured in its fully pushed-in position by 
the keeper assembly (160) (as best seen in FIG. 4) and the coupling is 
exerting an upwards compressive force against the clevis fitting (122) and 
clevis pin (120) at its upper end and at its lower end is exerting a 
downwards compressive force against the actuating rod (124) through the 
end fitting (130). 
Referring specifically to FIG. 5, it will be seen that the threaded rod 
(180) effectively functions as an upper extension to the actuating rod 
(124) since it is rigidly secured thereto by means of a flange nut (182) 
that secures a flange (184) at the lower end of the threaded rod (180) 
against the upper surface (186) of the end fitting threaded portion (146) 
provided at the upper end of the actuating rod (124). A locknut assembly 
(190) comprising an internally threaded bushing (192) and a lower locknut 
(194) is provided towards the lower end of the threaded rod (180) to 
adjust the position of a spring retaining cup (196) relative to the 
longitudinal dimension of the threaded rod (180). A compression spring 
(198) is retained inside the spring retaining cup (196) and is aligned 
co-axially with respect to the longitudinal axis of the threaded rod (180) 
such that its lower end presses downwardly via the base (200) of the 
spring retaining cup (196) and the locknut assembly (190) to act on the 
threaded rod (180) and thence via the flange (184) and the upper surface 
(186) of the threaded portion (146) to exert a downward compressive force 
onto the actuating rod (124) and the rest of the cable assembly (10). 
The upper end (202) of the compression spring (198) presses against a lower 
horizontal surface (204) of the clevis fitting (122) and accordingly tends 
to press the clevis fitting together with the lever arm (106) pivotally 
mounted thereto in an upward direction until a horizontal inner surface 
(206) of the clevis fitting (122) comes into contact with a second 
adjustable locknut arrangement (208). 
Since the valve being controlled by the push-pull cable (20) is provided 
with an internal stop at its "normal" (for example, closed) position, it 
is possible to adjust the lower locknut assembly (190) and the upper 
locknut arrangement (208) relative to the threaded rod (180) such that 
when the operating handle (116) is in its fully pushed-in position and the 
valve operating lever (106) is at the upper limits of the arc through 
which it rotates, the compression spring (198) will not be fully 
compressed, but will rather assume an intermediate position wherein a 
measurable gap (210) will be visible between the lower surface (204) of 
the clevis (122) and the upper edge (212) of the spring retaining cup 
(196) when the keeper assembly (160) is in its latched position. In one 
exemplary embodiment, it has been found convenient to make this gap 
approximately 0.12 inches (3.0 millimeters). This clearance may be 
conveniently achieved by latching the handle (116) in its fully pushed-in 
position by means of the keeper assembly latch member (164) and then 
rotating the adjustable bushing (192) until the proper clearance has been 
established, whereupon the lower locknut (194) may be tightened against 
the bushing (192) to prevent the assembly from coming out of adjustment 
due to vibration, etc. The clearance provided by this adjustment 
establishes the proper pre-load on the compression spring (198) when the 
valve is in its normal position and the push-pull cable handle (116) is 
held in its fully pushed-in position by the keeper assembly (160). 
Accordingly, this initial pre-load force will serve both to retaining the 
valve in its normal position and to retain the push-pull cable handle 
(116) against the keeper channel member (162) and pre-load the detent 
portion (172) of the latch against its latch pin (168). A cushioning 
effect is also provided between the push-pull cable assembly (10) and the 
valve, even if the handle (116) is subject to extreme forces. 
The upper locknut (208) is adjusted to provide an over-travel clearance 
(214) that effectively determines how much backlash wear can be 
accommodated in the cable assembly (10) before re-adjustment becomes 
necessary. However, it is preferable not to provide excessive over-travel 
clearance (214) upon initial assembly since this will result in additional 
lost motion. 
FIG. 6 shows the components of FIG. 5 in their fully "extended" position 
which they will assume after the handle (116) has been released from its 
fully pushed-in position by unlatching the keeper assembly (160). It will 
be noted that upper locknut (208) now is in contact with the clevis' 
internal surface (206), thus a downward force on the threaded rod (180) 
will be exerted via the locknut (208). A corresponding downward force on 
the clevis (122) then is transferred to the valve lever arm (106) through 
the pivoting action of the clevis pin (120). It will be noted in 
particular that once the compression spring (198) is in its fully extended 
(216) position (limited only by the position of the over-travel locknut 
(208) relative to the threaded rod (180)), compressive forces from the 
handle (116) are transmitted directly to the clevis (122) and vice versa 
via the compression spring (198). It should be noted that, even when it is 
in its extended position, as shown in FIG. 6, the compression spring (198) 
is still pre-loaded so as to exert a compressive force greater than the 
actuating forces required to operate the valve mechanism and thus 
functions to effect a relatively solid connection between the valve 
mechanism and the operating handle (116), even when only compressive 
forces are involved. Conversely, tensile forces from the operating handle 
(116) to the clevis (122) are transmitted directly by the over-travel 
locknut (208). In either case, no additional operating or frictional 
forces are involved, compared to a solid mechanical connection between the 
clevis (122) and the actuating rod (124). 
FIG. 7, it will be recalled, is a cross-section view of a second embodiment 
of a spring-loaded backlash compensating coupling (30) for a push-pull 
cable (10). Referring now specifically to this Figure, in which components 
or elements similar to but somewhat modified from their counterparts in 
the above-described presently preferred embodiment have been identified 
with the same reference numerals but followed by the "prime" symbol ("'"), 
it will be noted that the clevis (122') is also provided with an 
internally threaded adjusting bushing (192') held at the appropriate 
position on the threaded rod (180). However, the compression spring (198) 
exerts its compressive force not on the spring cup (200) as shown in FIGS. 
5 and 6, but rather upon an annular recess (218) provided in a horizontal 
surface (220) of the bushing (192'). Furthermore, the modified clevis 
fitting (122') has an elongated downwardly depending bushing portion (222) 
which functions both as a gauge for adjusting the position of the bushing 
(192') and to maintain the compression spring (198) in its proper 
concentric position about the threaded rod (180). Thus, in this embodiment 
it will be seen that the functions of the internally threaded sleeve 
bushing (192') and of the clevis (122') have been somewhat modified so 
that a separate spring retaining cup (196) as shown in FIG. 5 is no longer 
required. 
In the case of this alternative embodiment, the normal pre-load force 
exerted by the compression spring (198) against the lever arm (106) can be 
adjusted by reference to the measurable gap (210') between the lower end 
(221) of the bushing portion or boss (222) extending down from the clevis 
(122') and the upper surface (220) of the modified bushing (192') when the 
handle (116) is held in it fully pushed-in position by the keeper assembly 
(160) and the compression spring (198) is thereby compressed and exerting 
force against the lever arm (106) to hold the valve in its normal 
position. 
It is apparent that there has been provided with this invention a novel 
Spring-Loaded Push-Pull Cable Assembly which fully satisfies the objects, 
means and advantages as set forth hereinbefore. While the invention has 
been described in combination with specific embodiments thereof, it is 
evident that many alternatives, modifications and variations will be 
apparent to those skilled in the art in light of the foregoing 
description. Accordingly, it is intended to embrace all such alternatives, 
modifications and variations as fall within the spirit and broad scope of 
the appended claims.