The original construction of most hydraulic cylinders before 1970 consisted of a single bottom design. This design was more susceptible to rust because of its cylindrical design and welded flat bottom. This area in particular allowed for a concentration of underground currents (electrolysis) to damage the weld more rapidly than other areas of the cylinder. A cylinder’s life span can increase or decrease significantly given soil acidity levels and water table condition for any particular geographical area. Although most buried cylinders are covered in a protective coating, it is possible that the cylinder's protective coating may have been damaged during the installation which can effectively further reduce the life of the cylinder. Since we are unable to inspect the condition of a buried cylinder, it is difficult if not impossible to accurately assess the life of a single bottom cylinder.
Catastrophic failures of single bottom cylinders have occurred with little to no warning, in some cases causing severe injury and fatalities. For these reasons, where single bottom cylinders are a concern, we recommend immediate replacement of the cylinders. In addition, it is important that your service provider have an oil monitoring program in place to help proactively reduce the exposure to this type of a failure.
More recently with the introduction of double bulkheads, PVC protection and flex-liners, hydraulic elevators have taken necessary steps towards a much safer future. The advantage of a double bulkhead design versus single is in the construction of the cylinder’s bottom plate. The double bulkhead is similar in design to that of the old design, but has the added security of an additional encapsulated reservoir head located at the very bottom of the cylinder. The inner head of the cylinder, located within the reservoir, contains a slow leak port. Should the first or primary bulk head fail, this port is designed to allow the car to descend at a controlled rate. This alone, does not completely resolve the potential of a failure due to possible uncontrollable and/or incidental installation damage to the side wall, as previously described. For this reason, most cylinders installed today are encapsulated with additional protection of either PVC or a flex-liner. PVC also allows the ability to monitor any potential oil loss between the cylinder and PVC buried beneath the ground.
A piston gripper monitors the speed at which the piston is traveling under normal conditions and clamps down on the piston bringing the elevator to a controlled stop in the event of an over speed. A piston gripper is not designed to eliminate the potential of a failure but reduce the impact of an occurrence. If you are concerned about the type of hydraulic cylinder present in your building please feel free to contact our sales department for additional information.
City of Chicago code now mandates that by 2013 all elevators with single bottom cylinders be replaced completely and/or retro fit with the installation of a piston gripper.
For equipment outside of the Chicago City Limits, the State of Illinois is currently only requiring this change for equipment that "(1) is already undergoing a (permit-required) alteration, (2) has failed, or (3) failing to replace the equipment jeopardizes the public safety and welfare as determined by the Local Administrator or the (Elevator Safety Review) Board." While across the board enforcement has been officially delayed, we know that single bottom cylinders pose some level of potential risk to public safety. We recomend that owners of this type of equipment make the necessary modifications before a catastrophic failure; while you still have control over costs, timelines and Liability issues.
For equipment in Indiana the grace period had already passed. If you need these modifications performed, we recommend you act immediately.
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