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                                                                 570 Valdry Court, Suite C-4 • Brentwood, CA 94513

         82 and the second eyelet 84 increases in proportion to the   been eliminated. Instead, the main hoist wire rope 23 loops
         applied tension. This elongation in proportion to the applied   back over the sheave assembly 36, and from the sheave as-
         tension tends to keep the tension in the main hoist wire rope   sembly 36, the dead-end of the main hoist wire rope is at-
         23 more constant when heave loads are applied. The overall   tached to the first eyelet of the elastomeric load compensator
         effect of the elastomeric load compensator 80 is to provide   80. The different ways of using the first kind of elastomeric
         passive heave compensation by reducing the crane stiffness   load compensator as shown in figures 15, 16, and 17 all have
         from the main hook 34 through the pedestal structure.  the device in line with a single part of main hoist wire rope
           Figure 16 shows a more permanent mounting of the elas-  23. This is in contrast to a load compensator that would be
         tomeric load compensator 80 to the boom 22. A bracket 91 is   inserted between the hook  34 and a payload. The in-line
         welded or bolted to the underside of the boom 22, and the sec-  mounting as shown in figures 15, 16, and 17 are more conve-
         ond eyelet 84 of the elastomeric load compensator is pinned to   nient for customers, and is more challenging to implement
         the bracket 91. An idler sheave 92 is secured to the underside   with a conventional load compensator such as one using a
         of the boom 22 at the original attachment location of the dead   gas cylinder. The in-line mounting does not leave a device
         end 32 of the main hoist wire rope 23. The main hoist wire   hanging in the way of the people trying to rig the load to the
         rope 23 is strung over the idler sheave 92, and again the dead   crane hook. The in-line mounting does not limit the hook
         end 32 of the main hoist wire rope 23 is attached to the first   drop height of the crane. In-line mounting is more challeng-
         eyelet 82 of the elastomeric load compensator 80.    ing for non-elastomeric devices because in-line mounting re-
           The  assembly  in  figure  16  has  a  number  of  advantages   quires  much  more  flexibility  than  hook  mounting  because
         over the configuration in figure 15. In figure 16, the elasto-  the in-line mounting has more mechanical advantage since
         meric load compensator 80 is mounted at a smaller radius   it acts on fewer parts of line. Due to the mechanical advan-
         from the pedestal axis so that maximum static load of the   tage, less required force is put on the load compensator, but
         crane is reduced less by the weight of the elastomeric load   the load compensator provides more travel or displacement.
         compensator 80. In figure 16, the length of the elastomeric   Gas cylinders do not deal well with large displacements be-
         load compensator 80 does not reduce the appropriate mini-  cause their force versus displacement response is not linear.
         mum distance of the hook 34 from the jib 37. In addition,   This is due to the fact that adiabatic but non-reversible gas
         the amount of space between the first mounting eyelet 82   cylinder expansion/compression follows a polytropic pressure
         and the sheave 92 provides a visual indication to persons   vs. volume curve: P V =P V , where V=Area*Length. Thus
                                                                              1  1  2  2
         near the crane of available capacity of the elastomeric load   P =P (V /V ) =P (L /L ) , where L  is actually L +displacement.
                                                               2  1  1  2  1  1  2      2         1
         compensator for absorbing heave loads.               The exponent n is a number somewhere between 1.1 and 2.
           Figure 17 shows an alternative way of using the first kind   Therefore this results in a non-linear force response. In com-
         of elastomeric load compensator  80 mounted under  the   parison, the elastomer response for elongation is much more
         boom  22.  In  this  example,  the  sheave  92  of  figure  16  has                   continued on next page
                                                               Wire Rope News & Sling Technology   August 2017  65
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