Gas spring including hydraulic locking means

Claim 1

In a hydraulically lockable gas spring for continuous height adjustment of an object, in particular of drawing-tables, including hydrauylic locking means comprising a liquid-filled cylinder, a piston rod sealingly guided for movement inward and outward of said cylinder, a piston carried by said piston rod within said cylinder, said piston rod being connected to said object, the cavity of said cylinder being connected to a second liquid chamber via an externally controlled locking valve, and said second liquid chamber being subjected to the pressure of a pressurized gas contained in a gas chamber, the improvement comprising: piston rod drop preventing means associated with said piston rod, comprising a liquid connection line between said cylinder cavity and said second liquid chamber, and pressure responsive valve means responsive to an excess of a predetermined pressure differential between said cylinder cavity and said second liquid chamber for controlling liquid flow through said connection line so as to prevent the sudden dropping of said piston rod, said pressure responsive valve means comprising a piston valve acted upon on one side by the pressure of the cylinder cavity and upon the other side by the pressure of the second fluid chamber, a biassing spring acting on said piston valve in opposition to the pressure within said cylinder cavity, and a valve disc connected to said piston valve to close said connecting line in the presence of said excess pressure differential.