3PT squeals on partial raising

[MoreCowbell]

Here is something that has always bugged me about my Kubota BX2350. When there is any kind of weight attached to my 3PT, it squeals when I try to slowly raise it by partially raising the lever. It sounds like the relief valve making the noise. The issue exists regardless of HST temperature.

When I fully pull the lever up, it works fine. It raises the attachment vigorously with no squealing.

I assume that this is due to nuances in the way the spool valve is switching oil flow as it transitions between the neutral and raise positions. The FEL works fine with this type of usage so I am wondering why the 3PT acts like this. Is this just poor spool valve design?

If anything, I would have expected it to be the opposite. My understanding of this machine is that the 3PT is the last of the line in the hydraulic circuit and, unlike the FEL valves, does not have to handle power-beyond flow. It would seem to be a simpler design and and easier one to get right.

Thanks.

 

[MoreCowbell]

Responding to my own post. Even though the 3PT is the last in line in the hydraulic circuit, I suppose it still does need to handle the flow of oil through the valve even though no other valves are beyond it.

Still though, I think this is a design issue of the spool valve. However, I have little hydraulic knowledge other than what I read here and there.

 

[J_J]

You can determine if the screech is from the relief valve by using a gage in the system. If it is relieving, it will read relief pressure.

It should only relieve when the load exceeds the lifting capacity.

If you put 100 lbs on the 3pt, the relief should not go off until you raise it all the way.

 

[uglyboywith11fingers]

my BX24 3pt also makes that noise, only when lifting slowly, so it's not just your machine. I mostly use the 3pt just for my snow blower, so it's really not much of an issue.

Pete

 

[oldnslo]

This is normal on the BX. Since this is an open center machine all the flow must go somewhere. When feathering the control to lift slowly, the excess flow is going across the relief valve.

 

[J_J]

Can one of you put a gage in the hyd system and verify that you have relief pressure on the gage when slowly lifting.

Just curious.

 

[MoreCowbell]

Thanks for the quick replies everyone. J J, I'd sure like to get that pressure reading. However, I don't have a gauge for this so I would need to pick one up first.

I found 80195 5000 Psi Pressure Gauge at AgriSupply. It is pretty inexpensive. Is this what I would need? Any other suggestions on what to get - flexible extension hose maybe?

Thanks again.

 

[J_J]

A hyd gage test set like this should only cost about $30.

The gage should run about $10 to $15, plus the 1/4 in QD set, short hose , and a tee.

 

[Baby Grand]

Interesting ... our B5100 seems to screech/squeal like a pig when lifting anything, even if it's just the lift arms with nothing attached. I had been thinking cavitation, which I would want to nip in the bud before it caused any damage. Maybe this is normal?

 

[MoreCowbell]

J J, thanks for the tip. I'll get a hold of a gauge. I will just need to figure out where to tap into my hydraulic system. I guess that is not really a general hydraulics question since that would be specific to each machine.

I have quick disconnects for my FEL, but since everything else still works without the FEL attached, it seems like those connections are not in the power beyond circuit, but maybe behind some kind of priority valve. I'll take a look and see where I can tap in.

Baby Grand, if your relief valve is kicking in when raising the 3PT without a load, that does sound like something is wrong. Here's a question: if you loosen the dial that controls the 3PT lowering speed does that help? If so, maybe the 1-way check valve that runs parallel to the dial valve is stuck and the raise flow is being forced past the dial valve.