My loader screams at me!

[mikegt4]

I have a1951 Oliver OC3 crawler that has been equipped with a White 1010 loader probably since the 1970's. It's a light duty loader that was commonly found on Iseki tractors imported and re-badged by White. It had been operating well for 20+ years of my ownership, recently it has become reluctant to lower down. If I move the handle to the float position it lowers normally. When I try to power it down from any height the engine bogs and the inline pressure control valve emits a loud shrill as if fluid is rushing through it bypassing the control valves and returning to the reservoir. The engine will actually die trying to over come the load on the hydraulic pump, it's as if both sides of the lift cylinders are fully pressurized at the same time. My first inclination is to remove the lift/lower spool and clean it and it's bore in case there is something clogging any passageways.

Attached is a somewhat crude diagram of the hydraulic system. Any suggestions would be welcome before I start taking things apart.

 

[K5lwq]

I would start by disconnecting the return to tank line and put in a bucket. Then try to raise the loader a little and note how well the return is flowing. Then lower and look for the same results. If no flow lowering the the valve definitely has a problem with that spool.

Another test would be to swap the lines on the valve for the lift and see if it has the same issue trying to lift now. Of course the controls will be backwards so keep that in mind.

 

[oldnslo]

Since raises fine and lowers in float I do not suspect a restriction in the tank line or valve problem but I could certainly be wrong. Are there any quick disconnects in the lines to the loader. On a crawler I doubt it but trying to eliminate possibilities.

Does it fail if you try to feather it down under power?

not a common occurrence but I have had hoses where inner tube separated from outer steel wire reinforcement and would restrict flow at higher oil velocity in one direction

 

[K5lwq]

Since raises fine and lowers in float I do not suspect a restriction in the tank line or valve problem but I could certainly be wrong. Are there any quick disconnects in the lines to the loader. On a crawler I doubt it but trying to eliminate possibilities.

Does it fail if you try to feather it down under power?

not a common occurrence but I have had hoses where inner tube separated from outer steel wire reinforcement and would restrict flow at higher oil velocity in one direction

I thought the same thing at first. However, the fact it does lower in float leads me to believe the problem is with the valve. The oil travels through the same hose and in the same direction when in float or lowering. But I think it would travel through different passage ways in the valve for float vs lowering.

Could a load check fail and cause this symptom?

 

[oldnslo]

K5
you may have a point on float vs power down. During float pressure galley is not connected to cylinder both cylinder ports are just common to tank.

load check should be common for both lower and raise.

since loader does not lower restrictions has to be in return from cylinder blind end and not pressure to rod end. Trying to think of what could fail in the valve that would cause this. Since float works it does not point towards a spool travel issue caused by crud build up in can covering the detent - centering spring assembly. If that is the cause I would suspect it would still power down if spool is feathered to lower slowly

Mikegt
when lowering can you observe both hoses going to lift cylinder, do they both stiffen and swell like under pressure?

 

[mikegt4]

After starting it up today (these 4 cyl. flathead Hercules engines sure start easy) I started to cycle the hydraulics and look at some of the areas suggested and after just a cycle or two everything began working like it was suppose to. Apparently whatever was clogged or stuck has self repaired. I cycled up/down repeatably just in case I was dreaming, not dreaming, everything is back to normal.

I don't use this machine very often, sometimes it goes for many months without even starting so that was probably what led to this problem. I also have an Oliver OC46 loader so the OC3 w/loader is somewhat redundant. I have a blade setup for it which it originally would have had when new in 1951, and will at some point return it to dozer status. Thanks to all for your suggestions and interest.

BTW, this is how my OC3 was configured when delivered new.