Backlash, which is apparent as lost motion under light push-pull input forces, is caused by the core member of the cable assembly moving from the inside to the outside of the bends in the cable with the change in direction of movement. It is a function of the clearance between the core and liner, the input force, and the total number of degrees of bend in the cable. See Figure 1.
These figures are for input forces just sufficient to move the core. Lost motion, the sum of backlash plus core and conduit elongation (stretch and compression) will increase as cable length, degrees of bend, and loads are increased. The use of larger cable sizes for a given load will decrease the elongation portion of lost motion.
Teleflex cables, with standard lubricant, will operate at sustained temperatures from -40°F (-40°C) to +210°F (99°C). For operation at temperatures up to a maximum of +300°F (150°C) consult the Teleflex Engineering Department
Efficiency, or the relationship between the required input force for a given output load is primarily determined by bends in the cable calculated by using the following formula:
The Teleflex cable has a recommended minimum bend radius of 5" (125mm). This simply means that installations of 5" bend radius or greater will render optimum cable life. Installations requiring less than 5" can easily be achieved but may shorten the cable's life.
Other variables affecting cable life include: output loads, cable length, and total degrees of cable bend in the installation. The sum effect of higher bend radii lower loads, shorter lengths and fewer degrees of total bend will all contribute to longer cable life.
Cable bend radii should always be as generous as possible for maximum cable life and efficiency. The following are the minimum bend radii recommended. The life specified for the smaller bend radii reflects the fatigue life of the core. See Figure 3.
All Teleflex cables have patented Dynamic Rod Seals. Their one-piece design was tested up to pressures of 50 psi after 1.3 million cycles. The seals are made from a proprietary thermoplastic composite impregnated with lifetime lubricant to minimise operating friction and reduce breakaway force by at least 30%. That translates into improved efficiency with reduced operator effort when Teleflex cables are used.
There are two sources of lubrication in Teleflex cables, the lubricants impregnated in the core cover and the specialty lubricants applied to the core's exterior during manufacturing. The combination of these lubricants creates a low-friction environment that provides superior efficiency over the entire life of the cable, outlasting other cable designs.
Recommended load ratings reflect the best balance between load and life characteristics. Cable operating life can be extended by utilising less than the maximum recommended load rating.
Infrequent, or momentary loads, may exceed recommended load ratings considerably without causing failure. This will however, shorten cable operating life.
Measure the force required to operate the object to be controlled (valve, throttle, PTO, etc.)
For the best efficiency and longest operating life, install the cable so that it encounters the heaviest load in the "pull" mode of operation as shown in Figure 4.
The cable travel required to move a lever of a given length through a given number of degrees can be computed as follows (See Figure 5):
Travel = 2 (sin0)(lever length)
The output motion of the workend of the cable is essentially the same as the input motion. For example, a 3” pushing movement at the input end will result in a 3” pushing movement (less backlash) at the output end. If a differential between input/output and/or direction of movement is desired, it must be accommodated in the design of the lever and attaching point at the workend. See Figure 6.
Control & Work End
Where cable ends are to be connected to objects requiring linear movement only (such as valve spools, etc.) Maximum life and efficiency can be achieved by accurately aligning in both planes, the cable hubs with the objects to be controlled. See Figure 7.
Where cable ends are to be connected to levers, etc., the connection point will describe an arc as the cable moves through its travel. Standard cables with rod and sleeve type end fittings have a built-in swivel to accommodate this deflection.
For best operating life and efficiency, keep this deflection to a minimum. This can be accomplished by locating the cable centre line as shown in Figure 8.
Cable Path Although cables are flexible motion transfer devices, the best performance and life can be attained by keeping the number of bends to a minimum. Where bends are required allow as generous a radius as is practical.
Protection Teleflex cables are sealed and resist abrasion and contamination. They should however be protected against pinching, shearing and crushing and the effects of excess heat. The operating ends should be shielded against direct spray and excessive dust.
