Posted By: pieman
inverted piston puzzler - 12/09/17 09:03 AM
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.
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.