Remote operation– Thrust direct on a frame – None rising extension systems.
Non rising stems rotate through a gunmetal nut in the penstock door. The screwed portion of the stem at the bottom is probably immersed in the water, effluent etc.
Used where thrust reaction is accommodated at the top of the frame.
Are connected to the penstock door and work through a revolving bronze nut located in the operating gear. The screw thread at the top of the stem is generally not immersed and is readily accessible for lubrication.
Open top frame
Used where thrust reaction is accommodated at a point other than the top of the frame.