Bent Cylinder

[Wayne_Freeman]

My Kubota L3400 has an older 4690 backhoe that has done quite well until today when I bent the boom cylinder rod. I was digging some riprap around my spillway mouth and had the bucket four feet below the ground surface when I realized the boom could not come back up and the cylinder was visibly bent. The new cylinder is on order but I would like to figure out what I did to cause this failure. Searching this site I have found where dipper and crowd cylinders have bent when digging close in to the tractor but nothing concerning the boom cylinder. Does anyone have any information to share?

 

[Wayne_Freeman]

Attached is a picture of my bent boom cylinder. I took it to Savannah Ga. yesterday to a repair shop and found out pretty quick the repair was as much or more than a new one. Cost is $300 plus shipping from Messicks. Wonder if there is a cheaper generic somewhere? I have dug a ton of stumps with no problems. This time I was digging 4 feet below ground level and obviously did something wrong?

 

[rbargeron]

Can't be sure from the picture, but I'll bet somebody could straighten it. The key is to use rubber or leather at all contact points to protect the rod when pushing on it. You may not get it perfectly straight but it's surprising how much "wiggle" will pass through the end seal without leaking, as long as the rod is not scratched.

A machine shop may tend to price the job based on perfection and low liability. But if you take it in the back door of a place that repairs farm equipment and ask them to attempt to "improve it" you might be pleasantly surprised at how good they get it and how little it costs.

The dipper rod on my old Wayne-Roy got bent once. After shade-tree "straightening" it was pretty good but still had a visible whoop in it. Worked fine for years, didn't leak a drop, never bent it again.

 

[wushaw]

Cylinders are more likely to bend when they are fully extended. You can check your pressure relief to make sure it is working.
I have bent a cylinder also shortly after I purchased my BH75 and the BH75 was not my first backhoe.
I am just a little more carefull now.

 

[leonz]

Attached is a picture of my bent boom cylinder. I took it to Savannah Ga. yesterday to a repair shop and found out pretty quick the repair was as much or more than a new one. Cost is $300 plus shipping from Messicks. Wonder if there is a cheaper generic somewhere? I have dug a ton of stumps with no problems. This time I was digging 4 feet below ground level and obviously did something wrong?

Ah yes, Bent Cylinder Itus;

No the cylinder is not salvageable as the stuffing box and barrel will have been egg shaped by the damage done!!!!!!!!!!!!!!!


The reason it happened is that the cylinder was fully extended and could not retract as the oil port was blocked and when crowding the bucket with the boiom the hydraulic cylinder did not have adquate support/strength in the piston area which is at the base of the cylinder rod.

In many applications the the piston is under heavy side loading stress and a "Stop Tube" is inserted between the piston and the stuffing box of the hydraulic cylinder.

The engineering rule of thumb is one inch of stop tube length for every foot of fully extended cylinder rod length.

Meaning if the cylinder at its fully extened length is three feet long fully extended it needs a stop tube three inches long inserted between the piston and packing gland to reduce its actual working length to 33 inches of travel to eliminate the problem. Why the builders of these machines do not do this is an unknown to me. It is most likely a case of I have an application and ordering the cylinders sized to match the application-bad idea from an operating standpoint.



You can buy or order cylinders everywhere, but its an opportunity cost thing. It is a case of what are you willing to give up to get something else and how quickly do you want it.

To simply solve your problem requires a reduction of system pressure to the backhoe or the installation of two needle valves to control the speed and pressure of the cylinder in travel.

Its up to you; ordering a cylinder from Mr. Messick will get it and it will be done etc. If you do that i would buy two needle valves and the fittings to go with them along with resetting the main valve on the valve body to a lower pressure.

Odering cylinder requires removal of the paint from the barrel and looking for the ID tag and removing the paint from it very carefully to obtain the cylinder part number.

If you have gone that far- ask the order desk to have a stop tube installed in the cylinder (one inch for each foot of useable cylinder rod length-including the partial measurement of less than any one foot distance- so if you have a fourty inch stroke you need a four inch stop tube.

Reducing the system relief valve pressure is the easiest method of the three after replacing the cylinder.

My two cents as a hydraulic system rebuilder.

leon

 

[Wayne_Freeman]

Thanks Leon! Your description of the cause fits what I was doing at the time of failure. Main boom cylinder fully extended and crowd cylinder in use. I am going to relay a copy of your post over to Messicks and request the additional fittings.

 

[leonz]

Greetings and salutations Wayne,

I am glad we found out what happened, Neil may have to have a stop tube machined for the new cylinder rod unless he buys one-which ever is less time consuming.

As far as the needle valves go you should shorten both hoses coming to the cylinder to properly fit the needle valves if you buy them or replace them with new ones-which is what I would do out of general principle simply due to hose stress from pressure surges

The set up should be like this:

Two ninety degree pipe to pipe steel hydraulic elbows-one for the barrel end and one for the rod end of the cylinder.

Two way needle valve(hand adjusted)

Restricted flow in BOTH directions only!! as other wise the same problem will occur.

The needle valve should have good flow marking settings on the valve to equalise oil flow for the rod end and barrel end, no jerking, spongy operation or lag time that way.

That way you can just work at a slow pace and not have any worries period.

The probelm with working a back hoe in any case is not knowing what is down there unless you are the one who knows where it is and what it is.

The cylinder barrel mount is the only way as the valve body itself does not have the area to plumb the needle valves at the spool for the circuit :^(

The needle valves with Female Pipe Thread on both ends are standard as a rule Parker Hydraulics has them too.

Two straight JIC to Pipe thread steel hydraulic fittings (depends entirely on the barrel port pipe thread size) most likely a half inch but Neil should have everything on hand or he can obtain it quickly for you. These fittings are screwed into the open end of the needle valves to mate with the female hose swivels.

Wayne please take note:

I would not reuse the old hose unless you can obtain the exact same fittings for the hose manufacture as they are all different and mixing fittings hose can and will create deadly consequences.

Please be sure to fill cylinder prior to installation of the fittings- that said; two JIC fitting caps will hold the oil in the cylinder-buuuuut be sure to attach the barrel end hose first on the cylinder be sure the boom is on the ground with the lower boom fully extended and on the ground and the rod fully retracted and cylinder full of oil then install rod end pin and pin retainer. Have fun etc.

If the rod end pin or barrel pin s are bent they will not go willingly back in- roll them on a flat surface and if they hesitate; well you know you need two new ones. :^(


leon

questions lzaharis@lightlink.com

 

[Stradbash]

"Please be sure to fill cylinder prior to installation of the fittings- "

Leonz,

Could you expand a bit on this point? Is it a necessary step or just one of those things that is good practice? If it's not done, is the air hard on the pump?

Thanks!
(from someone who puts oil in his filters before putting them on)

 

[leonz]

"Please be sure to fill cylinder prior to installation of the fittings- "

Leonz,

Could you expand a bit on this point? Is it a necessary step or just one of those things that is good practice? If it's not done, is the air hard on the pump?

Thanks!
(from someone who put oil in his filters before putting them on)

Sure,

A starved pump is bad whether it is hydraulic oil, motor oil or water. As the fliud is a lubricant in the case of hydraulic oil and motor oil and a method of delivering useable energy in a hydraulic circuit.


1. the idea is to have the full volume of oil in the cylinder prior to operating the circuit.

2. no air bubbles in the return oil, eliminating the slug of air entering the valve spool and the return to tank oil line. no oil foaming from an air slug.

3. no cavitation air bubbles entering the hydraulic system, no air bubbles entering the pump delivering the oil to the "open center" hydraulic system which can cause damage as the pump will have oil and not be starved due to the slug of air-which will cause the gears to grind.

4. no spongy operation/no cylinder jerking(uncontrollable travel) of the boom cylinder due to the compression of the air during the operation of the cylinder to remove air bubbles or while digging in the cylinder as there is no air.


I hope I did not bore you to death :^0.

And yes adding motor oil to the filter is the proper way to do things- eliminates oil starvation, air bubbles in the oil galleries, foaming etc.

I only like foam in my beer