Backhoe Mystery

[vintovka]

Have a newly aquired B7800 with a Woods 7500 BH on it. They work great together and have no problems moving on flat to low slopes. On two occaisions the BH has extended itself half way out, by itself. Both times the locks were on, pto off and was climbing a 20% hill. The unexpected half extension of the BH made it near impossible to keep front wheels on ground going uphill. Couldn't figure WTH was going on till i looked behind me. Do I need to chain the BH in the folded position or am i doing something dumber than normal?

 

[KennyV]

If you are saying that it is leaking down... that is something you can expect.
Is there not a pin that cages it for transport when not in use? KennyV

 

[J_J]

You said the locks were on. How did the boom move. I have a locking bar on my backhoe, and I don't think the boom could overcome that. Now, if your boom was not locked and your valves are leaking, then they could perhaps extend. or seek neutral, or your cylinder is leaking internally, and seeking to balance the pressure on both sides of the piston.

Just noticed the PTO was off, so no pressure, but the boom will try and balance itself, and that would be hanging vertically not tucked in. If you are saying that the boom is trying to extend itself, with no pressure, then the above reason is all I can think of.


A boom not tucked in will change the balance, and going up hill will change it even more.

 

[leonz]

Have a newly aquired B7800 with a Woods 7500 BH on it. They work great together and have no problems moving on flat to low slopes. On two occasions the BH has extended itself half way out, by itself. Both times the locks were on, pto off and was climbing a 20% hill. The unexpected half extension of the BH made it near impossible to keep front wheels on ground going uphill. Couldn't figure WTH was going on till i looked behind me. Do I need to chain the BH in the folded position or am i doing something dumber than normal?

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my assumption is that the "bucket" is not the issue BUUUUUT-


The actual issue is simply gravity and bypass of fluids in the circuit.


If the valve spool is worn(as it is a used unit with unknown hours) "a valve spool will wear with use no matter the valve".

The weight of the dipper boom and bucket will be enough to force oil to bypass the spool seals with no issues period seeking gravity to stop it
and this will occur going up hill.

As the dipper boom is dragged the bucket will eventually drag enough to pull the bucket open with oil bypassing the spools.

"If the piston packings were shot you would not be able to use the dipper boom or the bucket" in any case.

Short of locking the upper boom and chaining the dipper boom and bucket in place every time you go up hill there is s simpler way to solve this issue.



The Woods backhoe own needs:


6 2-way needle valves mounted at the 6 valve ports for the upper boom, dipper boom, and bucket to stop thisin its tracks.


you need to install or have these installed at the valve body for the three cylinders that control the upper boom, dipper boom and bucket to stop the oil bypassing problem entirely.

It is entirely possible to install them on the cylinders BUUUUT the risk of damaging the 2 way needle valves is always present due to debris or falling materials while excavating.

How to do it:

needed
1 grease pencil

12 paper tags with wire ties
-------------------------------------------------------------------------
More tags will be needed if you have to remove all the hoses to reach these

hoses-If this is the case simpy label the valve spools accordingly
1,2 3,4,5,6

facing the hoses exiting the valve body:



1. out rigger left
a port
b port

2. out rigger right
a port
b port



3. swing cylinder
a port
b port

4. main boom cylinder
a port
b port


5. dipper cylinder
a port
b port


6. bucket cylinder
a port
b port
--------------------------------------------------------------------------



parts list continued


6 2-way needle valves sized for the oil ports of the valve body
female female pipe thread sized for the oil ports
liquid pipe thread sealer-NOT teflon TAPE!!!!!!!!!!!!!!!!!!!!!!

6 long male to male properly sized hydraulic fittings to plumb into the valve body.


DO NOT SUBSTITUTE PIPE NIPPLES AS THEY WILL EXPLODE FROM THE OIL PRESSURE



You will reuse the 6 male- male fittings in the valve body installing them in the 6 needle valves prior to installing the needle valves on the straight pipe to pipe extension fittings.





The upper boom, dipper boom and bucket must be fully extended and lowered to the ground with all pressure released after the PTO and engine are shut of.

You need a lot of oil absorbing sheets and several small pails to reclaim the oil from the hoses when you break them to install the 2 way needle valves.

before you do anything you must label the ports of the back hoe for the three functions this way:

The upper port of all three spools must be labeled A port in the hand drawn sketch.

The lower port of all three spools must be labeled B port in the hand drawn sketch.


The upper boom valve must be labeled as number 1 valve in the drawing
The dipper boom must be labeled as number 2 valve in the drawing
The bucket valve must be labeled as number 3 valve in the drawing


The upper ports for the 1,2, and no. 3 valves are labeled the A ports
The lower ports for the 1,2, and no. 3 valves are labeled the B ports
in the drawing.

The upper hose for the upper boom valve must be tagged 1A
The lower hose for the upper boom valve must be tagged 1B


The upper hose for the dipper boom must be tagged 2A
The lower hose for the dipper boom must be tagged 2B

The upper hose of the bucket valve must be tagged 3A
The lower hose of the bucket valve must be tagged 3b


only use a tiny amount of thread sealer when assembling the new fittings in the valve body and assembling the needle valves to the straight fittings
and the 6 fittings you removed from the valve body and installed in the needle valves.

after installing the six needle valves in the valve body with the fittings from the valve body installed in the needle valves simply follow the drawing inventory and the labeled hoses to properly install them to the correct valve.


- no more than a single thread full of liquid pipe sealer is needed!

DO NOT use the pipe dope on the female hose fitting in any circumstance as they are a close tolerance fit .



after all the hoses and needle valves are installed start the tractor and PTO for the back hoe and just let it idle- the leaks if any will quickly show them selves.

add oil back to the hydraulic reservoir to be sure it is full and then cycle the individual valves to ensure the system is correctly assembled as the 6 needle valves will reduce the oil in the tank by amount of oil they require to be filled.

the six needle valves will guarrantee that the cylinders will not leak unless they are broven to be badwhich is not likely as you would have problems controlling the booms and bucket.


using the 4 needle valves for the dipper boom and bucket will allow you to control the speed and force of the two circuits to prevent damaging these cylinders by excess mechanical advantage as the cylinders do not have relief valves.

leonZ

 

[vintovka]

Thanks for replies. Going to really watch it from now on to see what is happening and "park" it correctly so all pressure is relived before climbing hill. A friend suggested that gravity and shocks are "bumping" the levers while climbing may cause the dipper to move out. May call woods and ask as well. The shift in center of gravity is pretty severe when it happens and could be hazardous. Hope other similar users pay close attention.

 

[shaley]

So is the Boom locking pin in place while all this occurs? That pin needs to be in place anytime hills are involved. If you end up traveling across the hill and a hose ruptures the boom/dipper will swing quickley and cause a roll-over.

 

[leonz]

Thanks for replies. Going to really watch it from now on to see what is happening and "park" it correctly so all pressure is relived before climbing hill. A friend suggested that gravity and shocks are "bumping" the levers while climbing may cause the dipper to move out. May call woods and ask as well. The shift in center of gravity is pretty severe when it happens and could be hazardous. Hope other similar users pay close attention.

NO NO NO NO NO NO NO!

This backhoe mosty likely does not have check valves otherwise it would have either a two way check valve block welded/ mounted on either one or both ports of the cylinder or at the it would have a two way check valve mounted at the valve body for each function.

If it had position control valves the cylinders would not drift while under way during the climb-as the oil would be prevented from moving or bypassing within the barrel unless the packings were so bad the booms would drop after the levers were returned to center.



The valve bank has either: one relief valve at the pressure side of the valve body with a relief cartridge installed to bypass back to tank with a separate line or a relief cartridge installed in each spool section-which is not likely in this case.


If you have to climb this incline simply do it in reverse to stop the issue if you are not able to repair the backhoes hydraulic system.

As I mentioned previously the valve spools, spool seals, centering springs each valve section wear out and this is what your problem is with about ninety nine percent certainty-unless the cylinders has O rings for piston packings which is possible

that is why most if not all back hoes have a lever to lock the upper boom in place as the low priced hydraulic componenents on a small back hoe of any size do not justify the cost of a high quality control valve.

And as most backhoes do not have stop tubes in the cylinders the cylinder barrels eventually become egg shaped allowing oil to bypass until they fail due to rupturing the barrel.


cylnder drift for any hydraulic system is always an issue unless it uses 2 way check valves or 2 way needle valves to control the speed of the function and or lock it in one position for transit or level control.



about shock loads;

Your friend is mistaken in this regard, if the springs in the spools were bad and lost tension you would have poor to no control of the functions period.

If the boom has/had locking mechanism with a lever that simply folds over to hold the upper boom in place it may be damaged or gone.


The attachment builders build these things to sell to a specific market with eyes on total cost and net profitablity for each unit sold only.