9-1 Introduction

Modern longwall mining employs self-advancing hydraulic powered supports [1] (which will simply be called powered supports in this book) at the face area. The supports not only hold up the roof, push the face chain conveyor��AFC��, and advance themselves, but also provide a safe environment [2] for all associated mining activities. Therefore their successful selection and application are the prerequi

site for successful longwall mining. Furthermore, due to the large number of units required, the capital invested for the powered supports usually accounts for more than half of the initial capital for a longwall face. Therefore both from technical and economic points of view, the powered supports are very important piece of equipment in a longwall face.

9-2 Classification of Powered Support

The application of modern powered supports can be traced back to the early 1950s. Since then, following their adoption in every part of the world, there have been countless models designed and manufactured in various countries. But unfortunately there still is no uniform system of classification.In this section a simplified classification is used. Since a powered support consists of four major components (i.e., canopy, caving shield, hydraulic legs or props, and base plate), the ways by which they are interrelated are used for classification. In this respect, two factors are most important: (1) presence or absence of a caving shield [3]��if a caving shield is included, the support is a ��shield��type, otherwise it is a frame or a chock; (2) number and type of arranging the hydraulic legs [4]��since support capacity is generally proportional to the number of hydraulic legs, it is important to specify the number of hydraulic legs that a support has. Furthermore the way the hydraulic legs are installed is important; for example, a vertical installation between the base and the canopy has the highest efficiency of application whereas an inclined installation between the base and the caving shield has the least efficiency in supporting the roof.

Based on this concept, there are four types of powered supports, those are, frame [5], chock [6], shield [7], and chock shield [8], in order of evolution of their development. However, it must be noted that the trend of their development in each type is such that it becomes less distinguishable in terms of application.

A. Frame

The frame support is an extension of the single hydraul

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