Need help position of HYD fliter

[planeperson]

Wise ones,

I have a HINOMOTO E202 which is basically a MF 1020. The Service Manual for a MF 1020 shows a HYD filter between the sump and the pump. If my E202 has one, I can't find it. I have pulled the returne line from the sump to the pump and I can't even find a screen.

I am looking for a filer or screen because I suspect the fluid return path is blocked some place. The symptoms being that with the fluid level at the correct level, the lift works fine just after start up. However, within a half hour the lift will no longer hold position . If I shut down and let the rig sit for about an hour and restart I can rise the lift and lock it in a raised position using the lowering speed control.

Any suggestions or comments welcome.
John

 

[MHarryE]

Generally a company doesn't put a filter on the suction side because in cold temps when the oil is very viscous, filter restriction can cause the pump to cavitate which can cause multiple problems, all of them bad. Instead a strainer is often used (having a screen with something like 100 mesh screen - 100 wires per inch) and finer finer filtration comes in the pressure or return. If you are looking at a schematic, the symbol for a strainer or filter are the same. On a hydro the charge oil is usually filtered before entering the closed circuit because piston pumps and motors need really clean oil to live.

Since your problem comes after the oil is warm I would look elsewhere in the circuit. Is something worn so that when the oil warms up and thins out it won't work right? Is it possible some seal or other rubber like material becomes floppy when it warms up and flops down to a place where it can block oil flow? These are just a couple things I can quickly think of.

 

[planeperson]

Harry,

Thanks much for the response. I will see what I can find.

John

 

[planeperson]

All,

Issue was a clogged screen in the return path. The screen is located in the differential case just inboard of were the return line meets the case. In fact the flange that is a part of the return line holds the screen in place. Removed, cleaned and replaced screen, installed new gear oil and bled system and I am back in business.

Lessons learned:

1. A filter and screen are dipicted the same on a hydraulic schematic.

2. It may be good pratrices to clean hydraulic screens at every oil change or two.

John