Any hydraulic experts- slight issue with tractor/loader

[Tom D]

Sounds like the pressure relief valve to me, the rams on the lift will be a wider bore and so will lift more at a lower pressure. The thinner rams on the bucket will be far more susceptible to low pressure. If its the valve block leaking then you would expect the bucket to relax over time even when not in use. If its the pressure relief valve it will only happen under load. You will have two pressure relief valves, one on the tractor itself and one on the loader valve block. they can sometimes stick slightly open if a bit of dirt gets in, even a half millimetre gap could cause a pressure drop. I'd remove the valve and check carefully.

[Breezeblock]

Sounds like the pressure relief valve to me, the rams on the lift will be a wider bore and so will lift more at a lower pressure. The thinner rams on the bucket will be far more susceptible to low pressure. If its the valve block leaking then you would expect the bucket to relax over time even when not in use. If its the pressure relief valve it will only happen under load. You will have two pressure relief valves, one on the tractor itself and one on the loader valve block. they can sometimes stick slightly open if a bit of dirt gets in, even a half millimetre gap could cause a pressure drop. I'd remove the valve and check carefully.

 

on these open centre valves there is usually only 1 relief valve and once the spool is in the hold position the relief valve doesn't have any influence on the ram if its creeping it in the hold position it can only be internal leakage thru the ram seals or across the landings of the spool

[Tom D]

I meant the one on the valve block and the one on the tractor itself. I know that on my loader the valve will blow off if you dig too hard into a heap, allowing the bucket to fold back...

[Breezeblock]

I meant the one on the valve block and the one on the tractor itself. I know that on my loader the valve will blow off if you dig too hard into a heap, allowing the bucket to fold back...

 

it doesn't matter which relief valve once the spool is in the hold position the relief valve is irrelevant it will only lift the relief valve when either spool is moved and the lowest valve dictates the max pressure

[Tom D]

I don't believe thats the case, certainly on my crane if you lift a heavy load close in and then boom out the relief valve will allow the main boom ram to lower as the pressure rises.. Maybe some systems are piped differently......

[Breezeblock]

I don't believe thats the case, certainly on my crane if you lift a heavy load close in and then boom out the relief valve will allow the main boom ram to lower as the pressure rises.. Maybe some systems are piped differently......

 

theres loads of different systems cranes are a different matter altogether they have oddball stuff like proportional relief valves and various line relief valves tractors are usually a basic system with not much to go tits up

[Matthew Storrs]

I don't believe thats the case, certainly on my crane if you lift a heavy load close in and then boom out the relief valve will allow the main boom ram to lower as the pressure rises.. Maybe some systems are piped differently......

 

Yes, this is what happens with my digger too- but the trouble i am experiancing with the loader is that if i drive the bucket into a big pile of soil i can't seem to even curl the bucket up to get a full load- if i really put the revs up it starts to move very slowly but soon drops again once i lower the revs again.

 

Thanks for your help everyone- all valid points.