Seeking low thermal expansion

[bobneumann]

I always thought that both sides of the piston in a double action hydraulic cylinder were filled with fluid? Or supposed to be at least. Is it just volume of the piston rod on the in the retract side of the cylinders adds up to a significant amount?

Correct, the volume of the piston rod. In my case 4 piston rods @1.25" OD, times 18" length. Adds up to 88 cubic inches, about 1.5 quarts. Since my reservoir is something around 6 quarts, including the designed in headroom for heat expansion, adding an extra 1.5 quarts of oil is pushing my luck. I might get away with it, time will tell. But if there is a smarter/better oil type or spec, I wanted to be sure to choose that one.

From everything I'm reading, it's going to be a wash. I'll either squeak by or not, but the oil type is apparently irrelevant.

At least now I know.

 

[bobneumann]

While it would work, it would be more complicated, less reliable because of additional places for leaks, and weigh more and cost more than simply adding a larger or second reservoir. Heck you could add a simple tap (or two, maybe also one above the fluid level to maintain the same air pressure above the fluid) onto the side of the existing reservoir to connect to the side of an additional one. Or just T or Y fit on the existing lies(s) of the reservoir to enable the additional. Reservoirs are low pressure or even atmospheric ( + a little hydraulic fluid head pressure and or feed retract pressure or suction ). It is not like they have to be built to withstand the maximum pump output pressure.

I think you could MacGyver something up with a piece of pipe of decent ID, or some other containment. The vibration from what it is mounted to is probably of more concern than anything the fluid will throw at it.

I agree. If I do have to expand, I'm thinking a sealed cap on my current reservoier with siphon tube to the bottom of the adjacent "standby" reservoir, something along the lines of a radiator expansion tank. But I think the 1/4" tube used for coolant isn't going to do well trying to push/pull meaningful flow of 15w40 through it. But if you make it too huge, the siphon/suction won't hold. I'm guessing about 5/8" id. What do you think?

 

[JimPghPA]

Mount the add on at the same height as the existing and close to it. Tap onto the line that feeds it, and connect the additional line from the tap to the add-on.