Hydraulic pit prop valve system - includes safety valve at top of upper section to oppose sudden pressure from above

摘要

The hydraulic pit prop with a lower tube (2) which slides inside an upper portion (1) has a piston (3) between them. It has a shallow inverted cup-shaped cap (12) on the upper portion, located immediately above a stop valve (9) designed to oppose sudden pressure applied to the cap (12). This stop valve has a funnel-shaped seating (9) which is blocked by ball shaped or tapered spring loaded plug (7). This communicates with the pressure chamber (10) underneath. The cross section of this chamber (10) is equal to that of the discharge opening at the bottom of the lower tube (2).