Bleeding system

A Bruce · Sep 16, 2020

Hi,
I have a new to me Jinma HW 03 backhoe, the Jinma hydraulic pump doesn't work on my Kubota L295 so I changed to a 6 gpm Prince style PTO pump. Unit was working flawlessly for a couple of hours each day . On the second day it shot oil out the breather cap. I assumed maybe over full. On the third day it did the same thing and lost power. I did some research figured maybe my return line was too restrictive, so I changed it to a full 1 inch line with sweeping bends and 1 1 inch 90 at the pump.
The system now has no power and the cylinders jump and bounce like they have air in them. The oil is Shell 32 and while it was all foamy I drained it let it sit over night and its almost clear.
With no manual and no experience, I have no idea if its air or what a bleed procedure would be? Any advice would be most appreciated.
thanks

Tx Jim · Sep 17, 2020

Replacing return line shouldn't create any problems requiring any bleeding. Due to oil being foamy I suggest you check suction line(inlet) side of hyd pump for air leaks.

rScotty · Sep 17, 2020

I agree. It shouldn't require any specific bleeding procedure, but make sure that the vent to atmosphere on your return oil storage is clean and open. That will enable the system to purge itself of air. If it were me I'd check the vent, put the the oil back in and run it slowly while adding oil and moving the controls.

Again as Jim says, most foamy hydraulic oil problems are due to an air leak in the suction side of the system. Specifically look at the suction line that transfers oil from the reservoir or sump up to the hydraulic pump. If you have a hydraulic filter, it will almost always be a suction hydraulic filter and technically it will also be somewhere in this line. Look closely at the line and fittings and any hydraulic filter mounting. You won't see a leak; on the suction side of the pump it's air getting in rather than oil getting out.

The fact that you could drain the oil, let it sit, and it was clear after overnight are all good. Oil can also foam if it has water in it, (detergent action) but you can always tell if water is involved because the water turns the oil into a milky fluid more like chocolate milk rather than a clear oil. If you have the oil out and sitting in jars, Decant it carefully and if clear you can reuse it. Letting oil sit like that is an excellent way not only to get the air out, but it also lets microscopic particles settle to the bottom and be left behind.

There were some tests years ago that showed that letting used oil sit absolutely still for 30 days was equivalent to a 1 micron filtration. That's better than most high end commercial filters. Of course sitting doesn't address additive depletion or acidity.
rScotty

WranglerX · Sep 17, 2020

Go to go with the others that say its a air leak on suction side... Air in pump gears cause cavitation and can not draw oil and build pressure...

Dale

A Bruce · Sep 20, 2020

A Bruce said:
Hi,
I have a new to me Jinma HW 03 backhoe, the Jinma hydraulic pump doesn't work on my Kubota L295 so I changed to a 6 gpm Prince style PTO pump. Unit was working flawlessly for a couple of hours each day . On the second day it shot oil out the breather cap. I assumed maybe over full. On the third day it did the same thing and lost power. I did some research figured maybe my return line was too restrictive, so I changed it to a full 1 inch line with sweeping bends and 1 1 inch 90 at the pump.
The system now has no power and the cylinders jump and bounce like they have air in them. The oil is Shell 32 and while it was all foamy I drained it let it sit over night and its almost clear.
With no manual and no experience, I have no idea if its air or what a bleed procedure would be? Any advice would be most appreciated.
thanks

Thank you all for responding, I found the issue. The dipstick is incorrect. If you set the level at the mark on the dipstick the screen on the return line inside the tank is only covered by 1/8 inch of fluid. And out of level, any extra oil moving in the system, or down the least amount and it grabs air. I spent hours going around the new fittings I had installed looking for leaks, all sealed now with high tech loctire, and it turns out to be so simple. I Over filled the tank a half inch and everything works fine. This winter a new larger tank with standard pipe threads and a suction screen well below the fluid level. But for now it works like a champ and we will get the work we need to done.
Thanks again, for your assistance,
Bruce

WranglerX · Sep 21, 2020

A Bruce said:
Thank you all for responding, I found the issue. The dipstick is incorrect. If you set the level at the mark on the dipstick the screen on the return line inside the tank is only covered by 1/8 inch of fluid. And out of level, any extra oil moving in the system, or down the least amount and it grabs air. I spent hours going around the new fittings I had installed looking for leaks, all sealed now with high tech loctire, and it turns out to be so simple. I Over filled the tank a half inch and everything works fine. This winter a new larger tank with standard pipe threads and a suction screen well below the fluid level. But for now it works like a champ and we will get the work we need to done.
Thanks again, for your assistance,
Bruce

Just remark dipstick..... On my log splitter is says oil should be 1 to 1.5 inches below top of tank.... DUH.... There is no manufactured in dip stick.... I just use convenient twig....

Tank can probably not be to full if oil is not being forced out breather or filler cap....

Dale