GB870514A - Improvements in or relating to hydraulic pit props - Google Patents

Abstract

870,514. Mine roof supports. BECORIT GRUBENAUSBAU G.m.b. H. June 27, 1957 [June 28, 1956], No. 20355/57. Class 20(2) A hydraulic pit prop comprising two telescopic cylinders 1, 2 is extended by a twostage pump 5, 10, Fig. 1, operated by an electric vibratory motor to transfer fluid from a storage chamber 2a into a pressure chamber 1a. The motor comprises an electromagnet 17 and armatures 18, 18a secured to a carrier 20 by a spring 19 which engage respectively the head 11 of a high pressure piston 10 and a bearing 13 of a low pressure piston 5, a compression spring 12 acting between these parts. Operation of the motor reciprocates the pistons 5, 10 extending the prop by the action of the compressive piston 5 until the prop engages the roof overcoming the spring 9 loading a valve 8 to set the prop under the action of the high pressure piston 10. The vibratory motor is then cut out by a relay controlled by the fluid pressure. Fluid enters the low pressure stage through a bore 23a and the high pressure stage through a bore 21. It passes from the pump to the pressure chamber 1a through a flared bore 6 which acts as a non-return valve during the operation of the pump. An additional valve (Fig. 4, not shown) assists in filling the low pressure pump. The prop is released by first connecting the motor to a D.C. supply to open the high pressure piston 10 allowing fluid to escape through bores (not shown) to the storage chamber 2a. A release valve comprising a closure member 26a movable within a sleeve 29 is then operated by means of an electromagnet 28 which is energized to attract an armature 27 connected to the member 26a which is thus lifted from its seating. The electric motor may be operated by an A.C. or chopped D.C. supply, In another embodiment, Fig. 5, an open ended cylinder 38 passes through the head 3a of the inner cylinder 2. The pistons 5, 10 are situated within a block at the base of the pressure chamber 1a, the pressure therein serving to retain flanges 39 on the lower end of the cylinder 38 sealed against a seating on the base. To release the prop, the high pressure piston 10 is first opened. When the pressures in the chambers la and 2a are substantially equal, operation of an electromagnet. 28 causes an armature 44 to raise the cylinder 38 by acting on a bar 45. The armatures 18, 18a are discs.