Lerch Bates Inc. Building Insight

Global Leaders in Technical Consulting for the Building Industry

Hydraulic Jack Leaks

Has your elevator maintenance contractor told you that you have a leak in a hydraulic jack and that it must be replaced?  Have they told you that it will cost you anywhere from $25,000, (on the low end), to over $100,000?  Have they told you that this price is not firm and if they encounter unexpected underground condition the cost could go significantly higher?  Have they told you that this added cost is on an hourly, time and material basis, and that the rate is over $350/hour?

The cost to replace a below ground hydraulic jack is huge!  And leaks are always unexpected.  So unless these kinds of dollars don’t mean much to you, you may want to make sure that the leak is REAL!   If the jack moves a foot or more, and there is no visible signs of the displaced oil, chances are you have a leaker.  But if the movement is several inches or less, more testing is still a lot cheaper than that complete jack replacement job.

Elevator codes require no-load hydraulic jack tests annually and full-load tests every five years.  But it is impossible to know for sure what is going on under the surface, so there is no way to be sure if there is a leak.  An elevator may pass the testing one day, and start leaking the next.

Prior to 1972, in ground hydraulic jacks were made with flat, single bottoms.  The stationary part of the jack, the part that is burried in the ground and subject to corrosion and electrolysis, is the cylinder.  Early cylinders were nothing more than standard pipe with a welded cap at the bottom.  Starting in 1972, the elevator code required that cylinders have a safety bulkhead, commonly referred to as a double bottom.  The double bottom jack provides protection against catastrophic failure from the whole bottom of the jack giving way, typically at the welded cap, due to deterioration of the weld and the pressure in the hydraulic system.  But a double bottom doesn’t protect against the effects of electrolysis along the entire length of the burried jack.  Most leaks these days occur somewhere along the length of the jack where is has been exposed to water or other unknown and unpredictible below ground conditions.

In California, Code requires that an elevator be shut down if there is any unexplained loss of hydraulic oil.  But there are many possible explainations for a loss of oil.  Oil can leak through the various valves in the system and back into the tank.  The volume of oil decreases as the temperature of the jack decreases.  Over the years small amounts of oil can leak around the jack head and into the ground. Drip cans and buckets often fill up and overflow, or the drain lines may clog, causing the oil to leak around the top of the jack down to the pit floor.   Most jacks over 20 ft. in length are made from multiple sections.  The piston, the moving part of the jack that is attached to the bottom of the elevator car, is a machined piece of hollow pipe and multiple sections are threaded together.  A rubber ‘O’ ring seals the joint.  If that ‘O’ ring fails, the oil can even leak into the jack itself.

The surface area of an elevator tank is large enough that, even on smaller tanks, a single gallon of oil, more or less, is unnoticable.  So if the oil leaks back through the valve and into the tank, there is no way of knowing for sure.

We recently encountered a 15 inch diameter jack that the elevator company claimed was leaking.  They tested the elevator with a full load of almost 20,000 lbs. and in one hour the elevator dropped less than one half inch.  This they claimed was a leaker.  But this owner was not about to authorize spending over $100,000 on this evidence.  So we did another test.  The oil in the ground was allowed to cool to ground temperature to eliminate thermal effects.  Next, the elevator was loaded to full capacity.  Then the oil line in the pit was disconnected as the cylinder so there was no chance of any oil leaking back into the tank or anywhere along the oil line.  The location of the car was marked, and the elevator was left for over 24 hours.

Low and behold, the elevator did not move.  No leak!  This test cost the owner less than $5,000.  Pretty good savings compared to replacing a jack that might not even be leaking.

There are 50 year old single bottom jacks installed in areas with high ground water that continue to work without leaking.  And there are jacks less than five years old, installed with protective tape coating and installed within sealed PVC liners, that leak.  There are many variables in the installation process that can render the PVC and other protections ineffective.

A leaking jack is a serious and costly problem, not to mention that the EPA frowns on hydraulic oil contaminating the ground.  This is not a problem to be taken lightly.  But considering the costs, it is best to make double sure that the leak is genuine and not imagined.

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