and cleaning mechanism 12 are in the upper position with the head 16 retracted into the guide sleeve 18 the cylinder body 8 of the jack 2 is maintained in the extended position through the action of the locking means v which is then in the locked position from this position a barrel 6 can be inserted into the chamber 1 the crushing table 3 is then lowered by means of the jack 2 until it comes into contact with the barrel 6 to block it on the base 7 to this end the lower side of the plate 3 is fitted with spines 65 66 which dig slightly into the upper wall of the barrel 6 the next stage consists in lowering the mechanism 12 to the lower position by means of the jack 26 so as to successively bore the upper side then the lower side of the barrel 6 until the head 16 penetrates the opening 19 in view of the relatively large diameter of the head 16 in the region of some ten centimeters the edges of the perforations performed in the barrel 6 have downwardly curved lips those of the lower bore engaging partially into the opening 19 furthermore metal barrels usually have vertical rims 61 to 64 perforation by pressure applied from below thus forms a funnel in the lower side of the barrel 6 once the mechanism 12 has reached the lower position the next stage which concerns the cleaning of the barrel 6 consists.