Bh77 hydraulic pressure relief issue

[Cessnadriver]

I have an issue with the bh77 on my lx2610. When digging against something hard say a stump or something, the curling of the bucket overcomes the dipper hydraulic cylinder and it gives way and gets pushed out. The dealer checked it all over and tested pressures etc. They said there's nothing they can do as both the curl and dipper cylinder share the same relief valve. It just seems odd and quite frustrating to operate. It's still under warranty but the dealer said they can't keep diagnosing or I may be on the hook for paying shop rate if they come up empty handed.

 

[fried1765]

I have an issue with the bh77 on my lx2610. When digging against something hard say a stump or something, the curling of the bucket overcomes the dipper hydraulic cylinder and it gives way and gets pushed out. The dealer checked it all over and tested pressures etc. They said there's nothing they can do as both the curl and dipper cylinder share the same relief valve. It just seems odd and quite frustrating to operate. It's still under warranty but the dealer said they can't keep diagnosing or I may be on the hook for paying shop rate if they come up empty handed.

Dealer probably knows that you have an airplane, and figures you can afford tractor repairs.

 

[beckmurph]

I have an issue with the bh77 on my lx2610. When digging against something hard say a stump or something, the curling of the bucket overcomes the dipper hydraulic cylinder and it gives way and gets pushed out. The dealer checked it all over and tested pressures etc. They said there's nothing they can do as both the curl and dipper cylinder share the same relief valve. It just seems odd and quite frustrating to operate. It's still under warranty but the dealer said they can't keep diagnosing or I may be on the hook for paying shop rate if they come up empty handed.

I think mine does the same thing.
It doesn’t act like this just digging dirt.
But, when you are working on stumps and roots the dipper stick is over powered by the bucket curl.

 

[BAP]

I have an issue with the bh77 on my lx2610. When digging against something hard say a stump or something, the curling of the bucket overcomes the dipper hydraulic cylinder and it gives way and gets pushed out. The dealer checked it all over and tested pressures etc. They said there's nothing they can do as both the curl and dipper cylinder share the same relief valve. It just seems odd and quite frustrating to operate. It's still under warranty but the dealer said they can't keep diagnosing or I may be on the hook for paying shop rate if they come up empty handed.

Sounds like maybe the dealer doesn’t know what they are doing. If they share the same relief valve, then the curl would not be able to overcome the dipper, because if the relief was bad, it would dump pressure to both cylinders. It sounds more likely the dipper cylinder internal seals are leaking by or the control valve for that cylinder.

 

[PoTreeBoy]

There is a free WorkShop Manual download for the BH77 available at KubotaBooks.

The hydraulic diagram shows these overload reliefs on the dipper circuit. If one is opening too early, it would cause the problem. The setting could be measured by installing a pressure gauge on the line to each end of the dipper cylinder. A quick perusal of the WSM didn't reveal the setting, but I'd expect 2000-2500 psi.

 

[TheOldHokie]

I have an issue with the bh77 on my lx2610. When digging against something hard say a stump or something, the curling of the bucket overcomes the dipper hydraulic cylinder and it gives way and gets pushed out. The dealer checked it all over and tested pressures etc. They said there's nothing they can do as both the curl and dipper cylinder share the same relief valve. It just seems odd and quite frustrating to operate. It's still under warranty but the dealer said they can't keep diagnosing or I may be on the hook for paying shop rate if they come up empty handed.

I believe the behavior is the result af activating the port relief(s) on the dipper stick valve.

Those reliefs are not "shared" with the bucket but they are there for a reason. They prevent overpressuring the cylinder by the combined forces and shock loads generated by the bucket and boom.

You can monitor the opening pressure by installing a pressure test tee in each of the two hoses going to the dipper stick cylinder. I dont know what the cracking pressure should be but typically its a few hundred PSI greater than max pump pressure. Those relief cartridges are known to fail and they are quite pricey.....

Dan

 

[Cessnadriver]

Sounds like maybe the dealer doesn’t know what they are doing. If they share the same relief valve, then the curl would not be able to overcome the dipper, because if the relief was bad, it would dump pressure to both cylinders. It sounds more likely the dipper cylinder internal seals are leaking by or the control valve for that cylinder.

I would agree with that. Especially since you can hear a bit of hydraulic a bit of hydraulic squealing in the control pedestal when it happens

 

[TheOldHokie]

I would agree with that. Especially since you can hear a bit of hydraulic a bit of hydraulic squealing in the control pedestal when it happens

PoTreeBoy showed you the circuit.schematic with the dipper stick port reliefs circled. The squealing is likely on of those reliefs operating due to the cylinder pressure generated by the bucket digging forces.

Thats how it is supposed to work. The only question is what the actual pressure is when the relief opens and if its too low. Ask the dealer if they have tested the port reliefs on the dipper stick and if sobwhat the cracking pressures are. If you want to do it yourself the pressure gauge, a hose, and two test tees with caps should set you back about $100. Way cheaper than dealer rates.

Here are the port relief specifications from the WSM

Dipperstick port A2: 2990 - 3060 PSI
Dipperstick port B2: 2640 - 2700 PSI

if you need new relief cartridges they are $500 each.....

Dan

 

[Cessnadriver]

PoTreeBoy showed you the circuit.schematic with the dipper stick port reliefs circled. The squealing is likely on of those reliefs operating due to the cylinder pressure generated by the bucket digging forces.

Thats how it is supposed to work. The only question is what the actual pressure is when the relief opens and if its too low. Ask the dealer if they have tested the port reliefs on the dipper stick and if sobwhat the cracking pressures are. If you want to do it yourself the pressure gauge, a hose, and two test tees with caps should set you back about $100. Way cheaper than dealer rates.

Here are the port relief specifications from the WSM

Dipperstick port A2: 2990 - 3060 PSI
Dipperstick port B2: 2640 - 2700 PSI

if you need new relief cartridges they are $500 each.....

View attachment 140136

Dan

Thanks! I just looked myself and found those pages. Just trying to figure out which relief valve it would be a2 or b2.

 

[PoTreeBoy]

Thanks! I just looked myself and found those pages. Just trying to figure out which relief valve it would be a2 or b2.

The Ax ports are on the stem end (top, I think). The Bx ports are on the end away from the stem.

I was a little off on my pressure guesstimate.

 

[PoTreeBoy]

The troubleshooting section of the WSM mentions "Dust in overload relief valve" as a cause of weak cylinder, and "Flush hydraulic line" as a solution. If, after testing, you determine a relief is opening too soon, you could remove, disassemble and clean, and replace it. If it still opens too soon, the relief pressure can be adjusted to spec.

Or, especially if under warranty, have the dealer do it.