Bending cylinder ram

[Bobjones]

Working with a BH76 back hoe and we keep bending the Dipperstick cylinder ram. We did move the controls to match Excavator track hoe rather than rubber hoe. We moved the relief valves to follow the coresponding cylinder but keep bending rams. Any ideas ???
Regards, Bobjones

 

[Billdog350]

Bobjones, what are you doing when the rams bend? I had a customer that used to use his backhoe to remove trees on a nursery. The helpers would dig around the stump with the BH and then hook the tree to the BH and drive away! They were breaking pins, bolts, rams, etc. The BH pressure reliefs do NOT work when your levers are centered. If you're moving the machine under its own power through the wheels and the BH is being pulled by something, you're likely to destroy the cylinder.

If you're just digging and keep bending the ram, you totally have me stumped. The Pressure reliefs are supposed to operate LONG before you destroy your ram.

 

[Bobjones]

The releif being non effective when control are centered makes alot of sence.
The way we have it changed to Track Hoe type controls means that when operating the bucket cylinder when dipperstick is neutral puts alot of stress on the extended dipperstick cylinder ram. Maybe another relief should be permently attached to the dipperstick bleeding relieved pressure to the tank side or return on the hoe hydraulics?
Thanks, Bobjones

 

[Billdog350]

I think changing around your hydraulic configuration is what is screwing you up. When you said "moved the controls" do you mean you moved around hydraulic lines? If you swapped them around, it sounds like you have something wrong in there. The newer Kubota excavators have a lever you can flip to go between JD controls and Kubota (and others) controls. however most backhoes don't have that feature so you likely are defeating some detent or creating a situation where the return isn't right.

 

[cerlawson]

Is there any chance the cylinder pin connection is worn on one side, dirty or partly frozen? Any twist on the cylinder support will reflect itself in early failure of the weakest part in the system while under compression. Is there any unusual pull on hoses? That's my structural engineer side viewing this. You don't want any eccentricity in the force lines from pin to pin.

 

[Bobjones]

re: Moved the lines. Yes I moved the hydraulic lines on valve body but also moved the relief valves to the corresponding cylinder. I think that defeating the relief valve when levers are in neutral is more than likely the problem. When your guy was driving the tractor ahead to pull out stumps proves that point. When dipperstick is in neutral and the bucket is operated to fill it must put allot of stress on the extended dipperstick cylinder ram.

Regards, Bobjones

 

[Bobjones]

Bobjones, what are you doing when the rams bend? I had a customer that used to use his backhoe to remove trees on a nursery. The helpers would dig around the stump with the BH and then hook the tree to the BH and drive away! They were breaking pins, bolts, rams, etc. The BH pressure reliefs do NOT work when your levers are centered. If you're moving the machine under its own power through the wheels and the BH is being pulled by something, you're likely to destroy the cylinder.

If you're just digging and keep bending the ram, you totally have me stumped. The Pressure reliefs are supposed to operate LONG before you destroy your ram.

When you said "The BH pressure reliefs do NOT work when your levers are centered." I checked the Hydraulic diagram and the reliefs are "Line Reliefs" so they would release pressure even in center possition.

 

[Billdog350]

They're only line reliefs when you move your spools/levers. I'm 100% sure on this. If you put your BH in any position and attach a chain to it and try to pull something without using the BH levers, the reliefs will NEVER operate. This is a FACT. The hydraulic cylinder is the weak point and that will bend since your lines cannot relieve pressure.

Ask any of the knowledgeable guys here on the board, same goes for loader valves. If you put your front loader at a set height and then overload your bucket, it will stay there, or even pick the back of your tractor up. However as soon as you try to lift your loader, it will DROP down since you're activating the pressure reliefs once you move the lever.