BF900 hydraulic issue

[reckless]

I removed my loader to make it easier to replace some fuel lines. Upon reattach bucket will not curl. Joystick seems to operate properly. Removed lines at bottom of cylinders, plenty of flow there. Still no curl. Removed lines at top of cylinders, bucket curls, spewing out fluid. Reattach lines, nothing. Can hear pump working. Seems like the system is working against itself, concerned the loader valve is screwed, not releasing the dump function to allow rollback. How could this happen? Any fix not to replace control? HELP!

 

[Russell King]

one or more disconnect points are not properly connected.

on the cylinder that you know is working, follow the hose back to the valve and verify that the connection to the valve is connected properly or just disconnect it and firmly reconnect it.

You may have to replace the disconnect if it is damaged and won’t connect properly…

 

[North Idaho Wolfman]

Loader valves very very very rarely just go bad!
Sounds more like you have a couple lines connected wrong.
Also if they are quick disconnects disconnect and reconnect them.
One not opening fully will cause issues.

 

[TheOldHokie]

Diagnostics are pretty definitive - curls when you disconnect rod end hose. Pretty clear the exhaust circuit from bucket cylinders is obstructed. I would guess that coupler or tank return between valve and tractor is not properly connected.

 

[reckless]

Loader valves very very very rarely just go bad!
Sounds more like you have a couple lines connected wrong.
Also if they are quick disconnects disconnect and reconnect them.
One not opening fully will cause issues.

I get what you are saying, but....I did not disconnect any lines from loader to bucket, only the quick disconnects from tractor to valve. The way they are designed with male/female ends it is not possible to connect them wrong. I did disconnect and reconnect them, they seem tight, but I will do again.
And thanks.

 

[TheOldHokie]

I get what you are saying, but....I did not disconnect any lines from loader to bucket, only the quick disconnects from tractor to valve.

The tank return line would be the suspect. If reconnecting does not resolve the problem remove the coupler from the tank return hose, stick the hose in a bucket, and run your curl test again.

Dan

 

[reckless]

The tank return line would be the suspect. If reconnecting does not resolve the problem remove the coupler from the tank return hose, stick the hose in a bucket, and run your curl test again.

Dan

OK, will do, but why in the world would only one function be affected?

 

[TheOldHokie]

OK, will do, but why in the world would only one function be affected?

Thats an excellent question. The answer would be because only one function uses it. I dont know the specifics of the loader valve on your BF900 so I am guessing based on Kubota design practice. I do know that more modern Kubota loader valves:

1. Put lift cylinders in series with power beyond - i.e. does not use tank return.
2. Uses regen for fast extend on bucket dump - i.e does not use tank return
3. Has standard control on curl - i.e routes exhaust oil to tank return

Run the return hose test and we will see how well my guesser is working this morning

Dan

 

[rbargeron]

To help control the bucket while curling down, kubota's FEL valve pressurizes both ends of the curl cylinders at the same time - the rod reduces the area of one end so the big end makes more thrust, extending the rod.

I'd suggest interchanging the 2 curl hoses at the loader boom couplings or at the control valve. With hoses swapped it should work as intended. (only one side has a check valve preventing backflow)

BTW I learned about this when using my loader valve to control the chute rotator cylinder on a front snowblower. To turn the chute LEFT, push the lever Right - which took some getting used to back then - and still does

 

[TheOldHokie]

To help control the bucket while curling down, kubota's valve pressurizes both ends of the cylinder at the same time - the rod reduces the area of one end so the big end makes more thrust, extending the rod.

I'd suggest interchanging the 2 curl hoses at the loader boom couplings or at the control valve. With hoses swapped it should work as intended. (only one side has a check valve preventing backflow)

I dont think so.

The purpose of a regenerative spool is to increase actuator (extend) speed.

If you swap hoses the cylinders will only extend..

There are no check valves.

Dan

 

[rbargeron]

I think the check valve function is built into the spool (its load checks) - valve doesn't have a regenerative spool, if I'm reading the diagram right.

 

[TheOldHokie]

I think the check valve function is built into the spool (its load checks) - valve doesn't have a regenerative spool.

Yes a load check is part of the valve - one per spool and it works in both extend and retract operations.

If the spool is not regenerative I would have to reconsider my fault analysis. Bottom line is the cylinder will retract with the hose disconnected so something downstream of that pount in the circuit is blocking flow

Dan

 

[rbargeron]

I'd suggest interchanging the 2 curl hoses at the loader boom couplings or at the control valve. With hoses swapped it should work as intended.

The upper left diagram in the above attachment shows only one hose is open to the tank on reverse flow - connected the right way the cylinder can move, even with pressure to both sides.

As always, prompt cheerful refund if theory is bogus - Take care, Dick B.

 

[TheOldHokie]

I'd suggest interchanging the 2 curl hoses at the loader boom couplings or at the control valve. With hoses swapped it should work as intended.

The upper left diagram in the above attachment shows only one hose is open to the tank on reverse flow - connected the right way the cylinder can move, even with pressure to both sides.

As always, prompt cheerful refund if theory is bogus - Take care, Dick B.

On my phone but I dont see anything connected to tank. Per description exhaust oil flow is going to PB and from there to 3pt.

Edit; got the bigger image.

In the schematic it looks like one of the valves may have a regen position. Post the WSM page showing curl operation.

Dan

 

[PoTreeBoy]

I think the check valve function is built into the spool (its load checks) - valve doesn't have a regenerative spool, if I'm reading the diagram right.

View attachment 105871

Your diagram does show regen. When the bucket valve is in the right position, the A2 and B2 ports are both connected to the P port and the T port is blocked. This gives fast extension of the bucket cylinder.

 

[TheOldHokie]

Your diagram does show regen. When the bucket valve is in the right position, the A2 and B2 ports are both connected to the P port and the T port is blocked. This gives fast extension of the bucket cylinder.

That also means that if he had the lines reversed at the valve he would not have curl and the cylinder would extend when the spool is shifted either direction. Thats not how he described the problem but.....

Dan

 

[rbargeron]

Your diagram does show regen. When the bucket valve is in the right position, the A2 and B2 ports are both connected to the P port and the T port is blocked. This gives fast extension of the bucket cylinder.

Ok, I'll back out of the room now.......besides my scanner just winked out.

 

[reckless]

OK, will do, but why in the world would only one function be affected?

Thats an excellent question. The answer would be because only one function uses it. I dont know the specifics of the loader valve on your BF900 so I am guessing based on Kubota design practice. I do know that more modern Kubota loader valves:

1. Put lift cylinders in series with power beyond - i.e. does not use tank return.
2. Uses regen for fast extend on bucket dump - i.e does not use tank return
3. Has standard control on curl - i.e routes exhaust oil to tank return

Run the return hose test and we will see how well my guesser is working this morning

Dan

Whoo-hoo, its working! Disconnected dump line at valve, obviously no obstruction there. Disconnected tank return line. Get flow when curl function, but very little from any other. Nonetheless, reconnected lines and everything works! Whoo-again! THANKS!

 

[TheOldHokie]

Whoo-hoo, its working! Disconnected dump line at valve, obviously no obstruction there. Disconnected tank return line. Get flow when curl function, but very little from any other. Nonetheless, reconnected lines and everything works! Whoo-again! THANKS!

You are welcome.

What you are seeing on the tank return line is typical of Kubota loader valves. The only loader function that uses tank return is curl so you should only see flow when that function is active.

Sounds like that tank return coupler was the culprit.

Dan