Hi guys, have a head scratcher. I'm over in the Uk after working in the American market for ten years and one of the first jobs I get is from a service guy who rings me to tell me he is at a large store working on a goods passenger that he attended for an entrapment. When he got there he said he proceeded to the machine room and as he walked in he heard a whoosh and the lid of the tank tried to lift off. He ran back Down stairs and the cab that was about ten foot up was now in the pit and the people had extracated themselves and walked away. He put up barriers and went back upstairs. Looked in the tank and most of the oil was gone .

This is where I get involved. The next day I arrive on site and hang two Yale pulls to pull the cab up. I duly do so expecting to see a hose ruptured ( we use mixture of 2" flex hose as main feed then into a rupture valve before teeing off in rigid to each cylinder in the Uk) but apart from the oil being in the pit nothing leaps out at me.

It is a schindler with twin upside down pistons. Essentially a 330 but the hydraulics are by GMV the only difference being they use chains to sync the stages not ropes. After propping the cab and while still tackled I jumped underneath. There is no splatter on the recently white washed walls, all pipework and hoses seem intact all joint seem tight, all packing is in place and not excessive oil on the pistons.

I cleaned all the oil out put new oil in the tank and lifted it expecting once pressurised for the problem to become obvious. It takes some pressure and...holds it. I go to the ground floor take a look ..no leaks. Take a measurement cill to cill. Go get a coffee return and check ...not moved a fraction. I check the static pressure and its 20 bar. I decide next to test the releif valve which I do and kicks in at 53 bar. I take the lift up to the top floor put it up on stop rings and continue until the pressure releif kicks in. I then turn it off and carry on hacking up the pressure using the built in hand pump ( common on hydros in the Uk) until.it reaches 78 bar. The nanometer only ties to 100 bar and this is neatly 4 times the working empty car pressure ... gotta show up the problem right? Nope. I leave it 30 minutes does not drop one bar. I let it down to get back to normal pressure and visually inspect underneath. Spotless. Packing, pipes, hoses all ok. I'm going back Monday to do a rupture valve test and put 12000 ILB of weight in there ( 55 person lift) . If both of those successful then I'm putting it back in service.
However I am still completely confused as. To what caused the loss of oil. Especially if the service guy is to be beleived ( which I'm not sure he is) that ot was a 'catostrophic' failure.

Any one got any theories? I thought maybe a packing shifted and when depressurised it shifted back again? Grasping at straws tho.

Thanks in advance.

It seems to me the question is did the system really loose any oil? Do you think that there was enough oil to reach the top floor when you got there? Maybe there wasn’t as much oil in the tank as he thought. I’ve seen some strange things but oil has to go somewhere.
A down high speed run with the baffle out of place would try to lift the tank lid.

Hey IDWT ,
The oil was In the pit . It's a well sealed pit with no sump and I had to have it sucked out by oil removal specialists. When I arrived there was only enough oil to cover the pump left in the tank with the lift Sat on the buffers . Its only a two floor job with about twenty foot of rise but I had to put nearly 400 litres ( 100 us gallons ? ) of oil back in . Only removes about 80 gallons from the pit but the one next to it ( it's one of a pair ) has low oil level so I think they had some issues before and never replaced fully .

I considered a slow leak but the guys who work in the store say they used it the night before and it was fine , not noisy coming in to top floor etc...

What really throws me is the walls are whitewashed and I expected to see splatter of some description on the walls indicating which side went but nothing . It's almost as if someone has just scooped the oil out of the tank carried it downstairs and poured it in the pit . Surely if a seal blew it would have made some mess , even if they are inverted pistons ? The oil wouldn't spray straight down ?

Here's the other thing that doesn't ring true. The service guy says when he got there it was about mid shaft (10 ft ) up . He went to the machine room to hand lower , that's when it , in his terms 'dropped ' . But when he went back downstairs the trapped passengers had removed themselves and left the scene . Now , if you had been stuck in a lift for an hour and then it 'dropped surely you would hang around to complain , even ring a lawyer etc.. these people were never heard from again .

My only other theory was a slow leak the night before it only had just enough to make top floor , I know they always park and lock it top floor overnight and through the night the leak got worse . The first run of the morning people got in and a mixture of the remaining oil and some air was enough to let them take off .

These are ten year old schindler controllers , you would have thought they had low oil protection ?

Nothing about this job makes sense . It's part of a large national contract that we have just taken on , I'm two weeks into a new job new company the contract is fully comp . I'm getting pressure from the store to reinstate the unit as it's there busiest time of the year . I have dug my heels in and said I won't until I can either seen the cause of the leak or conducted every safety test possible . Have done a 200 % static test , will do a full load test on Monday and test the rupture under full load ..if that all passes, and I'm sure it will as full load won't be 200% of empty car static , then I'm going to have to turn it back on and file this under the ' what the hell ' category .

Oh I missed that. You got me... What if you sit it on props and leave it without pressure for a while? The seals may need pressure to hold but for that to explain it the car would have had to hang itself up somehow.

Wondered that myself..pressurised it dropped it back on props , left it , repressurised it ....nothing . Not a drop.

It's one that has you questioning everything you know about hydraulics ! If it passes a 200% test , weight test and rupture valve test that is no different to a commissioning test here in the UK. I will put it back in service but it will bug the heck out of me for some time that I couldn't point at something and say ' that's it ' .

Good one

Just an update, did a rupture valve test and now have a leak from one set of pistons . Is this the original problem ? Don't know , bit at least it's something we can point to.

If the car hung up, like maybe the pistons racked, and there was a down call perhaps the seal on one of the pistons relaxed. if that were the case you should have seen oil on the outer portion of the Jack. if the head of the the jacks are higher than the tank, then the low pressure switch should have tripped. Is there any heavy equipment near there that uses hydraulic oil? A theft is a possibility. How does the Oil recovery system in the pit work, is it a pump, or just 2 buckets?

Hi John jay, tanks higher than piston heads so no low pressure. In the Uk we don't really use buckets. There are two large drip trays that the piston sit in. I'm working on the theory of a a relaxed seal on one side. Maybe out of plumb? I have a 3rd party hydro specialist doing a repack on Monday. I found out that this is the 3rd re pack in 4 years and the second in 12 months. Something is not right