This note is a follow-up to our continuing saga of the "leaking" hydraulic piston. Based on empirical evidence that the piston lost 40 gallons of hydraulic fluid (later recovered in an adjacent sump with no apparent path)we assumed the piston cylinder was leaking. We pulled the piston and removed the cylinder, then filled the cylinder with oil, capped it and with a hand pump, pumped it up to 300# pressure. The next day the pressure was up to 400#! We redid the test with a new gauge and again the pressure went up overnight. This certainly looked like the piston was not leaking but the maintenance company was at a loss to explain the rise in pressure. Any ideas??

Also, how did we lose 40 gallons of oil? Inspection and testing of the gasket at the piston/housing junction and the piping to the piston showed no signs of leaks. Again, no theories from the maintenance company (ThyssenKrupp), or from Otis (the original installer) for that matter who also reviewed the cylinder inspection at various stages. We're not making this up!-- again any ideas.

Based on the foregoing pressure tests ThyssenKrupp has elected to replace the cylinder and put the car back into service. We will also be installing Union-gard in the pvc cylinder/piston void for protection against future water infiltration and resultant corrosion. Comments appreciated. Thanks.

-- Mike Johnson (design@cummings.com), June 20, 2002

Answers

hydraulic piston

Mr. Johnson, Using the same pressure test, re-assemble the jack. 1) Restrain the ram from extending. 2) Tilt the assemly so all the air rises against the packing. 3) Fill with oil and bleed off the air. 4) Pressurize the the jack assembly. 5) Tilt the assemly so all the oil presses against the packing. 6) Place something under the head of the piston to gather oil. 7) Take pressure readings as before one atthe beging and one the next day.

By your disciption, the first test only tested the casing. I would like to know what Thyssen hand pumped into the casing? Air or oil? If it was air, the mix of fumes could have expanded in side the casing.

Good luck and thank you for continuing keeping us posted on your progress.

Jon

-- Jon (jkh824@aol.com), June 21, 2002.

Oil Loss

One possibillity for your oil loss could be from the packing seal. If the elevator had at any time set on the buffer springs and the internal pressure in the jack was lowered, the packing may have relaxed and allowed the oil to siphon back from the tank into the pit. If this happened during an evening with a power outage and the power was restored, elevator came back on before morning then nobody ever knew it was down.Oil ran into the adjacent sump and no one is the wiser. This is a very dangerous situation as we had this happen. Almost all the oil came out of the pump unit leaving just enough for the pump to stay lubricated and fill the cylinder with air. The elevator made it all the way to the fourth floor on air.It came back down with almost a free fall and blew the lid right off the tank. A good reason to have safeties on ALL elevators. This was a dry pump unit with the tank directly above the pump so the oil could trickle into the impeller, I doubt it could happen to a submursible unit.

-- Jerry Rexer (jjrexer@uplink.net), June 21, 2002.

cylinder

I'm not an engineer, but assuming the cylinder was filled with oil and not air - seems to me that temperature is the only variable. Was this test performed in a temperature controlled environment? both metal and oil have a significant rate of expansion as temperature increases- just a guess.

-- turner (tuscfr@aol.com), June 25, 2002.