Pullings Pistons

In the early days of the hydraulic elevator era very low water pressures were typical, sometimes as little as 25 to 30 pounds per square inch.With gravity tanks on six or seven story roofs - about the limit to which most American cities could lift water - large diameter cylinders and piping were necessary to keep hydraulic losses small. Slow car speeds and poor efficiency were the consequence. When pumping directly into the cylinder, or later when a system of pressure tanks was employed, 100 psi was common and smaller cylinders, piping and valves possible. Increasing loads and speeds in the multi-story commercial building systems required ever-higher pressures until 200 psi was commonly used. These pressures required heavier equipment so the space occupied by elevator machines was not materially reduced. The introduction of pressures up to 1000 psi eventually led to the development of the pull machine.The push machines had both the standing and drive sheaves on the same side of the cylinder whereas with the pull machine all sheaves were on the same side. The building were growing ever-taller and one thought was to stand the cylinder on end, alongside the hoistway, where it could be easily extended. The basements of the higher rise buildings were becoming a conglomeration of cylinders and piping. The pushing and pulling water hydraulic machines ruled the industry for a number of decades. Even when the electric drum machine was refined the greatest contention in the industry's history was between those still favoring the water hydraulic and others eager to welcome the electric powered elevator.