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: