Hydraulic lift design

[Piotr]

I need some help with designing a hydraulic lift built in concrete driveway to lift my truck (semi, but just a tractor) about 2.5 to 3 feet. It will have 4 hydraulic cylinders all connected together. I used to be metallurgical engineer (17 years ago), so I think I can communicate well on the technical level. I am willing to compensate some $$ for practical design and component selection. It does not have to be full fledged project with blueprints and specifications, but something little more than a sketch. I drive a truck now (7 years) and I would like to inspect it and do some repairs when necessary. But I do hate laying on my back and try to squeeze in tight places getting immensely dirty in the process (been there done that). I will provide more details if I get some responses.

[JAlberts]

Obviously, the simplest arrangement is one with the cylinders set into four wells. With two cylinders at each end of a wheel rail for each side of the truck.

The only problem is that there is an inherent problem with this arrangement that will have to be addressed and that is insuring all four cylinders will lift together to keep the two rails lift together and level as they lift. Simply putting a common pressure on the four corner cylinders will not insure this will happen. Unless your truck loading is exactly the same on each cylinder during the lifting is that the cylinder(s) with the lowest loading will try to lift to a full extension height before the next higher loaded cylinder(s) will even start to lift; and, I am sure you can appreciate the problems this creates.

I observed this problem many year ago in a set of hydraulically operated parallel control valves; but, unfortunately I did not have the opportunity to see how it might have been addressed. Just be sure this issue is addressed in whatever lift design you are offered.

[Piotr]

Thank you for your comments. Yes, I do intend to use four cylinders each in its own well. And yes, I have exactly the same concern that you have mentioned. It will have to lift equally. I think that I do have to tie all four cylinders in as one rigid component. And then I could use removable supports under the axle and/or frame so I can lower the lift and have more space under the truck. I want to have it all planned and possibly put together before I do the driveway.