We have problems with lubrication oil returning by gravity from the bearing houses to the tank, especially when the bearing houses are cold (after start-up). Oil is then pumped out of the labyrinth into the paper machine. We want to increase the return line capacity to be able to always get the oil back into the tank.
1. Does anyone know how to calculate the oil return line dimensions? Oil viscosity at 15 degrees C (59 F) is 1200 Cst.

Thanks,

Hans

Hansvo,
If you enlarge your oil return lines from the bearing housing(s) are you enlarging the discharge port on the bearing also? That would be the location of restriction you are dealing with.
Can you state if this is in the press section bearings or the dryer section bearings? This would make a difference regarding a solution to your issue.

Hansvo The problem of return of the oil from the bearing housing will not be corectedby an increase in pipe size unless you have some means of increasing the outlett sizing from the housing. A common rule for return line sizing is double the size of the inlett or pressure line. You should have a heating system in the reservoir to bring the oil up operating temperature before start up. If you introduce oil of a higher viscocity into these bearings you run a high risk of bearing damage from skiding and other related problems that shorten the life of thes units.

Jim, main problem I refer to are the press section bearings. As it is we have 2x NW25 mm (1") return lines (hoses) per bearing, both have a quick connector which do restict the return line open area. I am searching for quick connectors that have a larger open area, however that are not to big and/or heavy for the operator to handle.
I am thinking of enlarging the 2x NW25 into 1x NW50 (hose plus discharge port)which will increase the open area by 100%.

Saltron, the feed line is only NW15 (0,5") and we do have a heating system, however to not risk bearing damage we do not like to reduce the oil flow at start up. Because we do not have a circulation possibility, other than through the bearings, the oil cooles down in the cold lines and bearing houses during start/up giving the return problems.

Hans

What is the purpose of the quick connects? Would open hydraulic quick connections (no poppets) or valves work in this application? Could a heat trace be used to warm the lines before a start-up?
You really shouldn't have to re-engineer the whole system to solve a transient problem.

It is possible that increasing return line size would help without enlarging the bearing outlet by reducing line resistance if that is what is causing the problem.

You might also look at the other end of the system and find a way to reduce the oil supply rate temporarily while the system is warming up like a temperature regulated shunt back to the sump that would automaticly close as the system warms up.

Good luck

The quick connections (including valves) in the oil return lines are needed, because these lines need to be removed by the operators when the paper machine felts are exchanged. These endless felts are brought in the machine from the side, crossing all oil feed and return lines.

Thanks for the reply.

Hans

Hansvo,

If this is for press section brg's, can you interlock the recirculation valve with the press section to limit flow until desired temp's & machine speed are reached? If this system has a heat exchanger, do you isolate this during downtime?
Is a heating element installed in the sump?
I realize that the piping temp's are generating some of the issues. Have you checked for orifices in the piping?