When props, bars or cogs have to be withdrawn it is prohibited by law to withdraw them by hammering. Suitable safety prop-withdrawer like the Sylvester prop-withdrawer has to be used.
It is an advantage to fix the chain C on the prop P G in such a manner before withdrawal that when the chain is pulled and is getting tightened, the prop receives n slight twist — an action which loosens the prop in its position.(Fig. 9.13).
In the depillaring areas, a long chain is often required in place of the chain C. To avoid such long length, a flexible wire rope with steel core (e.g. 15 mm dia. Coal cutting machine haulage rope) having capels at both the ends may be used in conjunction with the usual 6 m long chain.
Where the roof is high, a suitable anchor prop may not always be available for operation of prop withdrawer. In such case a piece of rail is fixed in a half metre deep hole in the floor. It serves the purpose of anchor prop. Alternatively, a strong bar fixed in the coal pillar may be used to serve the object. Care should be taken to see that the anchor prop or other props which provide safety to the timber men operating the prop withdrawer should not be dislodged by the prop under withdrawal when it is released.
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