The term “yield load” refers to the maximum resisting force of the support and is determined by a preset yield valve in the leg of the powered support. The yield valve generally releases the fluid from the support leg circuit at a constant pressure and in such a manner to insure that, even during yield, the fine control of convergence is still achieved. In Australia the setting load of the supports is 80% of the yield load.
Support capacities in Australia vary and are dependent upon geological and geoenvironmental factors. In general the support capacities can be between 650 tonnes to over 1100 tonnes. For example, Baal Bone mine, located near Lithgow NSW, uses a 630 tonne yield load 4 leg chock shiled support for a depth of cover up to 240 metres. Another example is Crinium mine, located near Lilyvale QLD, uses a 950 tonne yield 2 leg support for a depth of cover of 130 metres.by