Telescopic hydraulic props

Claim 1

A HYDRAULIC PROP COMPRISING AN OUTER CYLINDER CLOSED AT ITS UPPER END, A HYDRAULIC CYLINDER CLOSED AT ITS LOWER END AND EXTENDING SLIDABLY INTO THE OUTER CYLINDER, A PISTON MOUNTED IN SLIDABLE SEALING ENGAGEMENT WITH THE HYDRAULIC CYLINDER TO ENCLOSE THEREWITH A PRESSURE CHAMBER, THE UPPER PORTION OF THE PISTON EXTENDING ABOVE THE HYDRAULIC CYLINDER HAVING A SEALING RING MOUNTED THEREIN TO ENGAGE THE BORE OF THE OUTER CYLINDER AND SEAL THE LOWER END OF A RESERVOIR FOR LIQUID IN THE UPPER PART OF THE OUTER CYLINDER, AN APERTURED VALVE ELEMENT IN THE UPPER PART OF THE PISTON INCLUDING PASSAGE MEANS EXTENDING THROUGH THE PISTON TO AFFORD LIQUID COMMUNICATION BETWEEN THE RESERVOIR AND THE PRESSURE CHAMBER, A VALVE SEATING FIXED IN THE OUTER CYLINDER AT THE LOWER END OF THE RESERVOIR IN POSITION TO ENTER INTO CO-OPERATIVE ENGAGEMENT WITH SAID APERTURED VALVE ELEMENT WHEREBY TO SEAL THE PRESSURE CHAMBER FROM THE RESERVOIR, AND A LOSTMOTION CONNECTION BETWEEN SAID OUTER CYLINDER AND SAID PISTON PROVIDING LIMITS OF RELATIVE AXIAL MOVEMENT WITHIN WHICH SAID SEATING AND APERTURED VALVE ELEMENT ARE RELATIVELY MOVABLE INTO AND OUT OF SEALING ENGAGEMENT.