Backhoe JW-03 Backhoe Problems

[Rich Waugh]

Nope, the JW03 hoe doesn't have individual PRVs on each cylinder or valve port - just one PRV for the whole control valve. Yes, you should pull it out and clean it. How does the hoe work if you increase the rpm to say, 1800 rpm?

 

[cv63usafsfs]

I haven't yet run it that high, but ill test it when I get out there. Where is the PRV located?

 

[wdchyd]

Thats what I was kind of thinking and would explain why just that one function doesnt work but may randomly work when the fluid is cooler. What do you guys think?

If only one function is giving you trouble, I'd be changing around hoses to rule-out control valve issue with that one circuit......if the problem doesn't change then check out PRV and/or pump delivery issues....

Sometimes if the circuit you are having trouble with requires the most pressure to do a function then if you have pump problems that one circuit would drop when actuated if the pump can't deliver enough pressure.....

A flow test would determine pump troubles...... Kubota Flow/Load Meter Test - Tractor Videos - Kubota, John Deere, New Holland and More

Pumps that are weak will sometimes fail once they heat up......

IE: if your failed circuit needs 800 psi to function minimally......during a cold start the pump may deliver say 900 psi (and the boom would lift up), after the pump warms up and can only deliver say 700 psi, then the boom would drop when you actuate the control valve......

Maybe I'm not explaining it properly but sometimes pump problems can effect only one circuit if it is the highest pressure needed.......

 

[RonMar]

I don't know the specific type, just that its a PTO pump and not a power beyond from the JD. I usually run it around 10,000 - 12,000 RPM, slightly above idle.

That may be an issue right there. PTO pumps only deliver rated output at rated RPM, in this case 540 RPM on the PTO shaft. To get 540 on the PTO shaft, you need to have the engine RPM up near the PTO rateing mark on the tach. In the case of a diesel tractor, that mark is probably 2300-2400 RPM.

in theory, the pump should be able to deliver full pressure at reduced flow at a lower RPM, but in reality, it dosn't always work like that, as at lower RPM, the speed of the internal pump impellar can allow for more backflow/cavitation...

The input check valve should not allow any reverse flow back toward the pump though, and if the pump is not able to make enough pressure to lift the boom, at the most it should just stay in one place, and not go down. It going down when commanded up still points to fluid leaking by the relief valve.

A quick check to try would be to run the tractor engine up to rated PTO RPM on the tach, and see how the BH performs...

Do you know what fluid is in the BH? If it is still the chinese stuff, I would highly reccomend getting rid of it, flushing the system with kerosene and putting in AW-32 hydraulic fluid. The folks I got my BH from said the only real problems they ever had with these hoes were caused by crap in the oil interfering with spool and relief valve function.

 

[cv63usafsfs]

After I get out of work tomorrow I am going to run a few tests including switching the lines, hopefully that will atleast narrow it down. As for the RPM problem, I have had the hoe since november and have always run it at idle, why has it only become a problem this week? The last owner flushed the lines numerous times and refilled the system with the expensive JD brand fluid right before I got it.

 

[Bob Rooks]

...in theory, the pump should be able to deliver full pressure at reduced flow at a lower RPM, but in reality, it dosn't always work like that, as at lower RPM, the speed of the internal pump impellar can allow for more backflow/cavitation...

Oops.
The pumps are gear type (no impeller) and positive displacement. No back flow at all while running and negligible when stopped, unless it is totally trashed. Gear type pumps will always deliver rated pressure no matter what the r/m, subject to horsepower and relief valve limitations. Only liters per revolution (l/r) or gallons per minute (gpm) will be affected by speed.
Cavitation usually does not occur on the pressure side, this is mostly associated with suction side restrictions.

 

[wdchyd]

The input check valve should not allow any reverse flow back toward the pump though, and if the pump is not able to make enough pressure to lift the boom, at the most it should just stay in one place, and not go down. It going down when commanded up still points to fluid leaking by the relief valve.

??....Input check valve..??....is this something new to tractor hydraulics.....

A check valve can be added anywhere but ......"Input check valve"..??

Post #7 you said this unit has no load check valves also......

I am not familiar with this exact unit so I'm just guessing according to the OP's observations......if there is no "input check valve" and load check valve, and if there is a bad pump (or relief valve), it can drop under load in the right circumstances when it heats up......

 

[RonMar]

??....Input check valve..??....is this something new to tractor hydraulics.....

A check valve can be added anywhere but ......"Input check valve"..??

Post #7 you said this unit has no load check valves also......

I am not familiar with this exact unit so I'm just guessing according to the OP's observations......if there is no "input check valve" and load check valve, and if there is a bad pump (or relief valve), it can drop under load in the right circumstances when it heats up......

The BH valve block on the JW-03 does NOT have any individual load check valves on the individual spool circuits. because of this Some multiple commands do not work well together, and you pretty much can only use the boom up command by itself, as the pressure on that cylinder will overpower any of the other circuits. The valve block does have a single large check valve(spring and ball type) at the input. The fluid comes in from the pump, thru this checkball, passes by the relief valve inlet and feeds on to the main pressure gallery of the valve. That is why I think the problem is most likley a relief valve issue...

Bob, you are correct, gears not impellar, but I have seen pumps fail to deliver full pressure at reduced RPM... Not enough total fluid flow thru the pump to create full displacement or overcome wear leakage inside the pump?

 

[wdchyd]

The valve block does have a single large check valve(spring and ball type) at the input.

Is this typical cuz it's Chinese..??....never seen this before.....

 

[RonMar]

Is this typical cuz it's Chinese..??....never seen this before.....

Don't know if it is typical, but it is a pretty basic chinese valve.