White Papers

Over the past several years, newspaper stories have drawn attention to various incidents involving the catastrophic failure of in-ground hydraulic elevator cylinders installed prior to 1971 in the United States.  Subsequently, various elevator manufacturers raised concerns regarding the continued use of these original equipment hydraulic cylinders and have recommended replacement with a new double-bottom cylinder within a PVC (polyvinyl chloride) casing.

The old, single-bottom cylinder design features a bottom plate welded to the cylinder.  The weld is subject to in-ground corrosive action or electrolysis.  Failure of the cylinder – a sudden escape of pressurized hydraulic oil – could cause the elevator to descend out of control, posing the risk of serious bodily harm to passengers and potential environmental contamination of ground or water.  Revisions to the code (see Figures 2 and 3) that supersede this design, are not retroactive and many single-bottom cylinders are still in service today.

Gauging the life expectancy of an in-ground hydraulic cylinder is not an exact science because of varying influences such as the method of installation and the surrounding soil conditions.  In some installations, hydraulic cylinders have been known to begin to leak after just a few years of service.  In others, they last well beyond thirty years.

It is difficult to argue against the extra measure of safety derived from a double-bottom cylinder within a PVC casing.  But, in judging the urgency for replacement of any existing cylinder, keep in mind:

• Replacement is not required under current codes; codes vary by State
• Catastrophic cylinder failure is a rare occurrence, typically preceded by a period of unexplained hydraulic fluid loss

Instances where it is not possible to add a PVC liner, consideration to change hydraulic fluid to a biodegradable fluid is recommended. 

As part of the preventive maintenance routine for any hydraulic elevator, your service contractor should include regular (monthly) monitoring of the hydraulic fluid and immediate repair of above-ground leaks.  If the hydraulic fluid level is found to be low, fluid should never be added unless the cause can be found.  Prudent management would dictate the elevator be shutdown immediately in the event of unexplained hydraulic fluid loss.  In addition, static pressure testing and testing of the pressure relief valve should be performed on an annual basis.

Cylinder replacement, as proposed by various manufacturers, clearly represents the ultimate approach to leak prevention but regular monitoring and period testing of the existing cylinder is a viable alternative to such an undertaking.

Related Staff

M. Wade Smith President and CEO