BL4690 Bent cylinders

[leonz]

For what is worth, ordering a shorter cylinder with a stop tube and new base weldment for the new barrel will cost you less money in the long run and will eliminate the rod bending issue- thats the mistake they made with this backhoe design.

If this cylinder position had been thought out they would have specd for a cylinder with a rod diameter that should have been a 1/4 inch smaller in diameter than the cylinder barrel to begin with and bending would not have been and issue in the first place.

I can provide you with the contacts to do this purchasing if you would like them.

leonz

 

[_RaT_]

Leon, what is a stop tube?

For what is worth, ordering a shorter cylinder with a stop tube and new base weldment for the new barrel will cost you less money in the long run and will eliminate the rod bending issue- thats the mistake they made with this backhoe design.

If this cylinder position had been thought out they would have specd for a cylinder with a rod diameter that should have been a 1/4 inch smaller in diameter than the cylinder barrel to begin with and bending would not have been and issue in the first place.

I can provide you with the contacts to do this purchasing if you would like them.

leonz

 

[rScotty]

Yes, I have no confidence in this backhoe, will be looking to replace it with a good WOODS hoe.

Is that the only problem? I had a similar problem with an old JD loader and simply took the old cylinder plus some measurements to my local ag cylinder rebuild and fab shop. They made me up a cylinder that fit right on and didn't bend. Cost about half what the dealer wanted for a new cylinder too.
rScotty.

 

[leonz]

Leon, what is a stop tube?

A stop tube is a slug of brass that has a bore slightly larger than the cylinder rods diameter 1/32 inch and 1/32 smaller than the inside diameter of the cylinder barrel.


The stop tube is designed size is measured to equal 1 inch of length for every foot of cylinder rod and the remaining inch for the remaining length less than 12 inches.

The stop tube creates a huge piston in a sence creating a huge bearing surface and virtually eliminates any chance of the rod bending in use unless it is impacted and bent by an object that could hit the rod like a boulder.

The loss of cylinder stroke is only the length in inches of the stop tube but any atttached implement will have its range in arc or total stroke affected by the bucket lip edge arc or a ram plates extended length on a log splitter.

Bronze is used to prevent damage to the cylinder barrel, rod, piston packins and the hydraulic system valves as it is much softer metal.


I believe I uploaded a scanned picture of a drawing of a stop tube here if let me know if you can not find it and I will upload it again or I just may do it anyway again.


(the reason the cylinder rods are not larger in diameter in relation to the cylinder is that it costs more to make a cylinder with a larger rod diameter so its not done by the small back hoe makers).

 

[_RaT_]

Thanks Leon, I think I have it down in my head. Your saying you are basically limiting the designed travel of the piston of the rod side of the cylinder if I understand it correctly. The length then of the stop tube can be something you determine by cutting it to length prior to installing it? Do I have it right?

 

[leonz]

Yes that is correct.

The best material is bronze and there will be no issues with metal steel shavings doing any damage.

The Standard rule of thumb for the engineered length of an internal stop tube is:

one inch of internal stop tube for every foot of original fully extended cylinder stroke plus

the measurement of the cylinder eye length from rod end to the outer edge of the rod eye;

so if you have a cylinder that has a fully extended length rod of 29 inches plus a the rod eye being 3 inches in width it is thirty two inches-

1 inch of stop tube for the first foot
1 inch of stop tube for the second foot
1 inch inch of stop tube for the 5 inches remaining and the three inch rod eye width

totaling three inches of bronze stop tube (preferrably bronze to avoid cylinder rod damage from wear as the bronze will not damage the chrome plating of the rod.

 

[dfkrug]

All 4 of the bends have been straight in-line and down as shown in initial post.

If you want to restrict the extend of your dipper cylinder, you can weld
on or add to the stop pad on your boom/dipper, instead of putting stop
collars inside your cylinder. Not all hoes have these pads, but the 4690A
has one (photo), and they are common on FEL booms. You can experiment
with bolted on steel plates until you get the stroke the way you want it.

I collect data on hoe attachments, and it is interesting how the different
designers approach the dipper digging force issue. The length of the
dipper moment arm varies widely for the 7.5' class of hoe, from a tiny
8.5" for the JD 448, to a huge 13.5" for the BushHog BH750. A longer
arm gives you higher dipper dig forces at the cost of having a longer
cylinder stroke.

I do not know the dipper moment arm length for the 4690....do you want
to measure it and post? It is the spacing of the upper cyl pivot to the dipper
pivot.

 

[dfkrug]

I do not know the dipper moment arm length for the 4690....do you want
to measure it and post? It is the spacing of the upper cyl pivot to the dipper
pivot.

I forgot you posted a photo.

It looks like your arm is about 13", if your pins are 1". I would add to your
stop pads to limit the cyl stroke.

 

[leonz]

Back hoe problems continued:


An even better method is to plumb in flow control needle valves on the barrel end of the dipper boom and bucket cylinders and simply have a slow moving pair of functions to avoid the problem entirely by restricting available flow to the cylinders in question.

This allows full flow upon extension and restricted flow on the retraction of the cylinder (digging portion)

The problem is still the lack of 6 required relief valves in the valve body for the upper and lower booms and the bucket functions.





leon

 

[wdchyd]

I'd be willing to bet a beer that if you tee'd in a pressure guage at the base end of the Dipper/crowd cyl you'd have an overpressure condition in that cyl while digging/curling bucket cyl only while dipper/crowd was extended out and stationary ......

Of course this rod doesn't bend retracted in because the column strength is greater when collapsed and less when your hyd rod is extended......adding "Stop Tubes" only covers up the real problem......Too Much pressure on the base end of the cyl.....

This is called an induced load from external forces......(getting pushed in from leverage by the bucket curl cyl.......

The BH should have a larger (bore/rod) dipper/crowd cyl to carry this load or a WPR to relieve the overpressure........

I've seen this on small backhoes before.........I've done this test with other units with the same problem.....

Ummmmm.....This beer tastes soooo gooood.....:drink:

 

[dfkrug]

An even better method is to plumb in flow control needle valves on the barrel end of the dipper boom and bucket cylinders and simply have a slow moving pair of functions to avoid the problem entirely by restricting available flow to the cylinders in question.

This allows full flow upon extension and restricted flow on the retraction of the cylinder (digging portion)

But, Leon, even if you cut down the flow with restrictors, you will still
exert the same hyd pressure, and therefore have the same force at the
business end of the bucket. All you get is slower action on the dipper.

The problem is still the lack of 6 required relief valves in the valve body for the upper and lower booms and the bucket functions.

The work port relief valves on the hoe valve (if the 4690 has them) will be
set higher than the system RV, however. Not lower. So, additional RVs are
not going to help, unless you replace the existing shock valve (if any)
on the dipper extend cyl work port with a RV that is lower than system
pressure.

It would be much easier to restrict the dipper motion, IMO.

 

[wdchyd]

Dfkrug,

You're right about "Restrictors"......No Good!!!!:thumbsup:

I'll back away from Leonz's advice...:thumbdown:

 

[hawkeye08]

I didn't follow the restrictors either. In my simple mind, it just plain looks like too much force being exerted on that link (the bent cylinder). I suspect it could be solved several ways, the quickest is probably a stronger cylinder (larger diameter rod) or changing the force being applied to the cylinder by changing the design (moving the pin location so less force is applied back to the cylinder that bends when used in the manner that causes the problem). Putting extra relief in where appropriate might eliminate the damage, but would most likely reduce the usefulness of the BH.

Good information to know, if I can just remember it if I ever get a BH for my tractor.

 

[leonz]

But, Leon, even if you cut down the flow with restrictors, you will still
exert the same hyd pressure, and therefore have the same force at the
business end of the bucket. All you get is slower action on the dipper.



The work port relief valves on the hoe valve (if the 4690 has them) will be
set higher than the system RV, however. Not lower. So, additional RVs are
not going to help, unless you replace the existing shock valve (if any)
on the dipper extend cyl work port with a RV that is lower than system
pressure.

It would be much easier to restrict the dipper motion, IMO.

Controlling flow +motion =no broken cylinders and only allows movement at one speed=limited force over square area as the system is protected with one relief valve.


FWIW you can physically peel the rod eye like a potato skin or rip the rod eye off a cylinder rod with an unrestricted flow and enough fluid power.

 

[wdchyd]

I didn't follow the restrictors either. In my simple mind, it just plain looks like too much force being exerted on that link (the bent cylinder). I suspect it could be solved several ways, the quickest is probably a stronger cylinder (larger diameter rod) or changing the force being applied to the cylinder by changing the design (moving the pin location so less force is applied back to the cylinder that bends when used in the manner that causes the problem). Putting extra relief in where appropriate might eliminate the damage, but would most likely reduce the usefulness of the BH.

Good information to know, if I can just remember it if I ever get a BH for my tractor.

Have you ever noticed the largest cyl on an Excavator is the dipper/crowd???

It's all force and levers......

 

[hawkeye08]

Have you ever noticed the largest cyl on an Excavator is the dipper/crowd???

It's all force and levers......

agreed:thumbsup:

 

[dfkrug]

Too much force, but only too much when the rod is fully extended. It
is not too much when the rod is not so far out of the cylinder. That is
an extremely long cylinder, and the rod is only maybe 1.125"?

 

[hawkeye08]

Too much force, but only too much when the rod is fully extended. It
is not too much when the rod is not so far out of the cylinder. That is
an extremely long cylinder, and the rod is only maybe 1.125"?

so,

Stronger rod,
Shorter stroke (limit stroke for that cylinder, either with cylinder stop or boom stop),
or less force.

Really seems like a design problem more than an operator problem. The video really showed it was not operator abuse (at least not the normal sense of abuse).

Edit: someone find the right part number of the stronger cylinder with the right fittings and make it a sticky.

Ok, if I bend the cylinder and it is not covered by warranty, why wouldn't just get one that is stronger? It sure seems that if I pay $300 for a new one, but a new stronger one is $400, then I buy the $400 and be done with it.

 

[leonz]

Mag and kubotaboy


If you would be so kind as to provide me with the dimensions of the cylinder
including

1. cylinder barrel diameter
2. rod diameter
3. rod eye inside diameter
4. rod eye weldment width
5. cylinder rod stroke

a. a replacement cylinder with a stop tube will and a 2 way needle valve be less costly than a replacement cylinder with a larger rod diameter.

b. the retraction speed with a larger diameter rod will have a faster retract speed with or with out resistance (please keep this in mind with your decision)

I will forward many names and contacts of reputable hydraulic cylinders for your use and the part numbers for them with and without stop tubes if you would like them.

I would ask that you make a small contribution to your local SPCA animal shelter or adopt a pet if you like in return.

leon:thumbsup:

 

[hawkeye08]

If you would be so kind as to provide me with the dimensions of the cylinder
including

1. cylinder barrel diameter
2. rod diameter
3. rod eye inside diameter
4. rod eye weldment width
5. cylinder rod stroke

a. a replacement cylinder with a stop tube will and a 2 way needle valve be less costly than a replacement cylinder with a larger rod diameter.

b. the retraction speed with a larger diameter will have a faster retract speed with or with out resistance (please keep this in mind with your decision)

I will forward many names and contacts of reputable hydraulic cylinders for your use and the part numbers for them with and without stop tubes if you would like them.

I would ask that you make a small contribution to your local SPCA animal shelter or adopt a pet if you like in return.

leon:thumbsup:

Not sure who are asking for this information, but it is posted right after my post so perhaps me?

I don't have a backhoe and have no information to send you. Please make a donation to the local food bank for my response. thx.:thumbsup: